Now that you’re convinced that converting to EFI is right for you, the legwork begins.
This Tech Tip is From the Full Book, EFI CONVERSIONS: HOW TO SWAP YOUR CARB FOR ELECTRONIC FUEL INJECTION . For a comprehensive guide on this entire subject you can visit this link:
SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://musclecardiy.com/muscle-car-tech-tips/carburetor-to-fuel-injection-choosing-the-right-efi-system/
Converting to EFI isn’t quite as simple as purchasing a system, unpacking it, and bolting it on. Furthermore, no system that I’m aware of is designed to work in all applications. Fortunately, the process of narrowing the field of available products to determine which system or systems are best suited to your needs is a pretty easy one. This chapter provides all the information you need to easily choose a system for your vehicle as well as any additional parts to ensure your installation goes smoothly and gives you years of reliable service.
I’m one of those guys who prefers to do a job once and then enjoy the fruits of my labor. And that means I install it right the first time so I can drive and enjoy my vehicles versus spending a bunch of time troubleshooting an installation that wasn’t done correctly on the front end.
Before you can choose which system is right for your application, it’s vital to consider the following: parts combination compatibility, fuel system requirements, ignition system requirements, and electrical system requirements.
Parts Combination Compatibility
Most aftermarket EFI kits are designed for naturally aspirated engines making less than 650 hp. The size of the injectors included in the kit (typically four), the airflow capability of the throttle body itself, the fuel pressure, fuel pump, etc. determine how much horsepower the engine can produce. These kits represent 90 percent of the market. That being said, some products are compatible with much-higher horsepower, naturally aspirated combinations as well as those kits that are fully compatible with power adders.
650+ HP Applications
If your naturally aspirated combination makes in excess of 650 flywheel horsepower, you should be looking at an MPFI system, a TBI system that allows you to run dual throttle bodies, or a stack system. At the time of this writing, both FAST and Holley offer TBI systems that allow you to run a slave throttle body.
In addition, FAST offers a TBI system that uses a single throttle body with eight injectors that is capable of 1,200 hp.
If you’re using or intend to use a power adder (nitrous oxide, superchargers, or turbochargers), you should shop for an EFI system that was designed from the ground up to be compatible with your power adder of choice. For example, the Holley HP-EFI and Dominator EFI systems are designed to work with all power adders and have lots of features that are readily accessible in the tuning software. Either platform is ideal for nitrous or water/methanol users, and both have four stages of progressive control available.
I’ve used a Holley HP-EFI system with my 6-71 blown big-block Chevy for three years now and I couldn’t be happier (see Chapter 4 for more details).
One of the limitations of speed-density EFI systems is that they typically require a good vacuum signal at idle, such as 10 inches of manifold volume or more. Some manufacturers specify camshaft profile limitations (e.g., duration at .050 inch must be less than 250 degrees). If your camshaft profile falls outside of their recommendations, you should pick up the phone and contact their tech support department for recommendations before proceeding. Don’t be shocked if they recommend a different camshaft profile.
Fuel System Requirements
Each of the following should be considered in an effort to ensure your fuel system works efficiently and reliably.
If you didn’t already know, EFI systems operate at a much higher fuel pressure than do carburetors. A typical carbureted system requires between 5 and 7 psi of fuel pressure. EFI systems require a higher operating fuel pressure (typically from 20 to 80 psi). This necessitates the installation of an EFI-style electric fuel pump, which can be installed in the tank or externally. If your vehicle is still equipped with the stock fuel line, it may also be necessary to upgrade it to meet the fuel demands of the system. Keep in mind, some systems are not compatible with hard lines.
Equally important are filters for the fuel system: one before the pump itself (pre-filter) and a much finer one before the injectors (post-filter). Some systems include one or both filters; others rely on you to supply them.
Many aftermarket EFI systems also require a return line to the tank, which requires that the tank also have a vent. Don’t let the installation of a return line discourage you from considering a particular system. Most factory tanks have a vent, but its size may be a limiting factor. Some EFI systems, such as the MSD Atomic system, can be installed with or without a return line. However, MSD encourages the use of a return line (see page 76 for installation details). It is imperative with a returnless-style system that the fuel pump be located in the tank to keep it from overheating.
In addition, you really shouldn’t expect to supply fuel to your brand-new EFI system from a 40-year-old tank that is full of sediment and rust. Also, realize that such a tank was designed for a low-pressure carbureted fuel system, not a high-pressure fuel injected system. If you elect to use the stock fuel tank, you’re going to have to remove it to add the provisions for the return line so this is the perfect time to flush it out. If you are running a stock-style tank, you have a few options. You can flush it and add provisions for a vent and return line, or you can install one of the readily available in-tank fuel pump kits.
Additionally, a return-style system requires the use of a return-style regulator. Many companies offer them. The main difference between a return-style and a traditional regulator is that a return-style regulator is designed to install at the end of the fuel system and is the point of origin for the return line.
Another option is to replace the tank altogether with one that has been specifically designed for an EFI system. If you elect to go that route, several companies offer fuel tank kits that have a fuel pump, filter, and sending unit located within the tank and all the provisions to easily install it.
Removing the stock fuel tank and replacing it with an EFI-specific tank is really not as expensive as you may think, and it offers several benefits:
- You start with an absolutely fresh tank with zero rust or sediment
- The internal fuel pump is cooled by the fuel it is submerged in
- The pickup has been located in such a way that it won’t be uncovered during hard acceleration or cornering, as is possible with a stock pickup
Keep in mind that fuel injection systems don’t have a fuel reservoir, such as the bowls of a carburetor, in which fuel is stored. Aside from the relatively small amount of fuel in the fuel lines and the fuel rails, no fuel is stored other than in the fuel tank. If you spend time autocrossing, road racing, or in high-g cornering situations, you absolutely should consider a fuel tank specifically designed for EFI as fuel slosh can uncover the pickup in a stock tank.
If you elect to use the stock tank, you should consider keeping it more than half full at all times to prevent fuel starvation from the pickup being uncovered. Edelbrock has an ingenious solution that allows you to retain the stock fuel tank. Their Universal EFI Sump Fuel Kit is designed to work in conjunction with your stock tank to provide predictable performance with an EFI system of up to 60 psi in fuel pressure.
The type of fuel you intend to run influences the type of fuel lines, pump, and regulator you should run. For example, if you’re presently running E85 in your carbureted setup, you know that this fuel is caustic and corrosive to traditional fuel system components. I recommend that you determine this early in the process so you can narrow down your choices.
If your E85 combination produces in excess of 450 hp, some kits may not be compatible simply because of the additional fuel volume requirements of E85 as compared to traditional gasoline. In some cases, the fuel requirements are beyond the capability of the included fuel injectors. In other cases, the components themselves may not be designed to work reliably with E85 (see Chapter 6 for more details).
All components of a fuel delivery system should be chosen to complement one another: feed line, delivery line, return line, regulator, filters, etc. Some kits include some of these components; others include none. Because fuel system components can be one of the biggest expenses in an EFI conversion, it’s best to understand the exact requirements of a particular system before selecting it for your application.
Fortunately, I’ve got some fuel system gurus at my fingertips and they’ve proven to be an incredibly valuable resource. The more time I spend designing and building fuel systems the more I find hints and tricks for getting the job done correctly (and avoiding problems). When designing a fuel system for your vehicle, your goals should be performance, reliability, and safety.
The fuel system should be designed so that it is capable of supplying all the fuel your engine requires. Choosing the correct fuel pump is the easy part, as most companies provide compatible maximum horsepower levels. Once you choose the pump, it’s also easy to select the pre-filter, post-filter, and regulator to go with the pump because most manufacturers recommend components that are compatible with a particular pump.
The difficult part is deciding what size and type of fuel lines to use with all the new parts. If you’re installing a throttle-body-style EFI system, the system’s manufacturer typically specifies a given diameter of fuel line to supply the throttle body, but not much more. And, depending on who you ask, you may get varying answers. In my experience, I have found the following to be true:
Fuel Line Size to Throttle Body: Use what the manufacturer of the throttle body specifies. This should be in agreement with the manufacturer of the fuel pump. (Keep in mind that the post-filter is in-line here.)
Fuel Line Size from Throttle Body to Regulator: Use what the throttle body manufacturer specifies. This should be in agreement with the manufacturer of the regulator. Use a minimum of -6 line for returns.
Fuel Line Size from Regulator to Tank: Use what the manufacturer of the throttle body specifies. This should be the same size as the size of the fuel line from the throttle body to the regulator. Use a minimum of -6 line for returns.
Size of Line from Tank to Pump: Use one size up from the size of the fuel line to throttle body. Keep in mind that the pre-filter is in-line here.
Size of Line for Vent: Use the same size as that of the return line. For example, if you install a throttle-body EFI system that calls for -6 feed line to the throttle body, the line specifications are as follows:
The type of line you use is a function of the fuel you run as well as personal preference. Push-lock line is probably the most common choice for fuel systems because it’s inexpensive and easy to install. That being said, if you choose a push-lock line that does not have a non-collapsible design with a tough core, it absolutely cannot be used for the inlet of a high-volume pump. High-volume fuel pumps are in many cases capable of creating a high vacuum on the inlet. This can collapse any line that does not have a non-collapsible design, creating a restriction and possible pump failure.
Mount the fuel pump in a location where it can run cool. Heat is a fuel pump’s worst enemy and you want your electric fuel pump to live a long and healthy life. If you choose to locate the pump externally, choose a location that has good airflow and is preferably not within close proximity to the exhaust.
Or, you can do what the OEMs do, which is to locate the pump in the tank. The obvious advantage to this is submerging the pump in the fuel keeps it cooler than locating it externally. If you elect to locate the pump in the tank, it (and the wiring to it) should be designed specifically for an in-tank application. As with any vehicle with an in-tank electric fuel pump, you should avoid running the gas below 1/4 tank so that the pump is always submerged in the fuel, especially in the summer.
Ask any engine builder where you should install an external electric fuel pump, and they will tell you the same thing: locate the pump rearward of the fuel tank and below the lowest point of the tank. This is because electric fuel pumps are better pushers than pullers. By locating the pump below the lowest point of the tank, gravity feeds fuel to the pump, no matter the level in the tank. Locating the pump rearward of the tank ensures that the pump is never starved of fuel during hard acceleration, which is also sound thinking. In many cases, however, this is simply undesirable as it places the pump well below the rear bumper of the vehicle and in plain sight.
Regardless of whether or not you locate an external pump rearward of the tank, it absolutely needs to be mounted as low as possible with respect to the fuel tank. It goes without saying that you can’t locate it in such a fashion that it or the fuel lines can be damaged from debris on the road. In some cases, you can find a place along (or even within) the frame rail to locate the pump that keeps it protected and places it below the lowest point of the fuel tank. If you are simply unable to locate the pump below the lowest point of the fuel tank, you need to keep the level of fuel in the tank above the inlet of the pump or you risk damaging the pump.
Pickup for External Pumps
Any competent engine builder will also tell you to use a sump to supply an external electric fuel pump. Again, this is not always possible and you may choose to rely on a pickup within the tank. This is fine, as the principle of a siphon allows fuel to remain in the fuel line all the way to the pump, once it has been filled by the pump during the initial power up of the pump, that is. If you elect to run a pickup, keeping the level of the fuel in the tank above the inlet of the pump is that much more critical.
Placement of the return line within the tank is often overlooked. I’m talking about where the fuel is returned within the fuel tank and whether that’s above or below the level of the fuel within the tank. Any fuel system with a return line returns all unused fuel to the tank. It is preferable to return the fuel below the fuel level in the tank and not above it. If fuel is returned above the level of the fuel within the tank, this can cause aeration (the addition of air to the fuel) which can cause the pump to cavitate.
High-Horsepower Fuel Pumps
So, you’ve got a nasty combination that makes serious horsepower. This means that you’re also running a high-flow electric or mechanical fuel pump. As you convert to EFI, you may need to replace that fuel pump with a high-flow electric fuel pump capable of much higher operating pressure. Big electric fuel pumps require big current, so it’s critical to wire it per the manufacturer’s explicit instructions and even more important that your charging system can adequately power it. If you’re also converting to a return-style system at the same time, you’ve got a new concern: heating the fuel.
Most of the big high-volume electric fuel pumps on the market (including those for carbureted applications) are really more suited for short-term operation at the drag strip than they are for long-term operation on the street. When you use such a fuel pump in a return-style fuel system for a street application, you’re moving a great deal of fuel to the front of the vehicle and fuel that’s not burned is returned to the tank. As the fuel is circulated it is also heated. Operating a high-volume pump for long periods of time isn’t the best idea as it can result in pump failure. Managing the pump speed based on fuel demand is a far better idea, but how? Pulse width modulation (PWM). That’s how.
PWM allows the pump speed to vary based on the actual fuel demands of the engine. A PWM fuel pump controller manages the pump speed by varying the duty cycle in the same way that the ECU manages the output of a fuel injector. This is typically done by tracking engine RPM. A few companies offer PWM solutions for high-volume electric fuel pumps, including Fuelab, Weldon, and Aeromotive. (See Chapter 4 for details on installing an Aeromotive Fuel Pump Speed Controller, a PWM controller compatible with any electric fuel pump.)
Fuelab offers high-volume fuel pumps with built-in PWM control. In fact, these can be interfaced directly with their mating electronic regulator so that fuel pressure can be managed in real time based on actual fuel requirements.
One of the benefits of installing such a controller (or pump with a built-in controller) is that the pump noise is greatly reduced. Anyone who has ever used an electric fuel pump knows full well that they’re super noisy. I don’t know about you, but I’d rather listen to the blower whine and exhaust tone at the stoplight than the annoying buzz from the fuel pump.
In my time at cruises and car shows, I’ve heard plenty of stories about high-volume fuel pump failures. I’m convinced that 99 percent of these failures are a function of incorrect installation. If your installation requires a high-volume EFI pump, you’re well advised not to cut corners in its installation. Otherwise, when it fails, you know exactly who to blame.
Consider that an electronic fuel pump can move a lot of fuel. What would happen if you were to become involved in an accident and the fuel system became compromised? Obviously, turning the ignition off would be your first move, which would instantly disable the fuel pump. But sometimes our brains don’t work like that in such a situation. Holley recommends the use of a simple pressure shutoff switch (PN 12-810) that can automatically disable the fuel pump if fuel pressure drops to below 5 psi. It can be wired to disconnect the trigger lead between the ECU and fuel pump relay or controller.
OEMs often use an inertia switch that disconnects power to the fuel pump in the event of a sudden impact. They’re readily available and one could easily be wired to work with an aftermarket fuel system.
My dad taught me as a kid that any job worth doing is a job worth doing correctly. The fuel system is the heart of an EFI system so you mustn’t take any shortcuts. If you do, you will certainly have problems and you risk damaging the fuel pump and possibly your engine. Why take that chance?
Ignition System Requirements
As discussed in Chapter 1, some aftermarket EFI systems also offer the ability to manage the engine timing (engine management). In my opinion, this is absolutely the way to go. The MSD Atomic system and other more expensive systems offer this feature. Managing fuel delivery and engine timing separately is an antiquated idea, albeit a more affordable one. Managing fuel delivery and engine timing simultaneously and electronically provides so much more tuning potential, which allows you to more easily achieve better drivability and performance.
Regardless of which path you choose, it’s vital to understand the manufacturer’s recommendation for lighting the fire in the cylinders. Some kits allow you to utilize some or all of your existing ignition components. Other kits require that you upgrade some or all of them. Even others, such as the Edelbrock Pro-Flo EFI kits, include a distributor as part of the equation. However, most kits require that you supply these components separately.
If you elect to go with a system that provides engine management, however, you need to eliminate all outside influences on timing, such as centrifugal advance, vacuum advance, boost retard, nitrous retard, dash-mounted timing controls, etc. The ECU electronically manages the timing automatically based on all of these variables. If your distributor has centrifugal or vacuum advance, it may be as simple as locking these out. Also, if you’re like most performance enthusiasts who use a stand-alone capacitive discharge (CD) ignition box for a hotter spark, you absolutely want to ensure that you select a kit that allows you to retain it.
In addition, this may be an excellent time to consider the triggering of the ignition system itself, either independently or via the ECU. Most common is the traditional method of allowing the distributor to manage this. However, it would be remiss of me not to mention that this is the time to consider a crank trigger. Several companies offer complete kits that are compatible with most EFI systems.
Running a crank trigger allows you to sidestep any slop in the timing chain and/or cam gear on the distributor. If you’ve fought a timing problem for whatever reason with your carbureted combination, you will fight it with the EFI system as well. Why not eliminate it altogether? The owner of the Olds Cutlass featured in Chapter 6 fought this problem for years. Converting to a crank trigger solved this problem once and for all.
Electrical System Requirements
If electrical isn’t your strength, consider picking up a copy of my other books, Automotive Wiring and Electrical Systems and Automotive Electrical Performance Projects to supplement this discussion. Look at it like this: The electrical system is the only system in the vehicle that can influence the performance of the others. If you have electrical problems that you’ve been “gonna get around to fixing,” get to them before undertaking an EFI upgrade. You will avoid all the heartache associated with choosing to address this “if it becomes an issue.” Trust me; it will.
I read many of the enthusiast automotive magazines, and all too often, readers have written to them when experiencing problems with their aftermarket EFI conversion. In many cases, the tech editor identified problems that were caused by electrical system inadequacies. It’s amazing to me how many perfectly good fuel pumps are burned up by inadequate wiring and excessive voltage drop especially when you consider how clear the included manuals are in regards to their electrical requirements.
If you take nothing else from this chapter, recognize that an EFI system is a major investment. If you starve its components of the current they require to operate optimally, you run the risk of damaging the components themselves or even damaging your engine. At a minimum, you have one heck of a time getting the system to operate properly, let alone getting it to work optimally. Choosing the wrong alternator is the number-one mistake enthusiasts make again and again. If you’re making the conversion to EFI, you may also have to upgrade your alternator and possibly its wiring. You can easily (and definitely should) make this determination with your vehicle while it is in running state with the carburetor. I can’t stress enough how important this is.
Depending on the system you choose, the ECU can require between 10 and 40 amps of current to do its job. In addition, the electric fuel pump can require between 10 and 30 amps of current. On the low side, this is a 20-amp increase in current requirements over a carbureted application with a mechanical fuel pump. Now, let me quantify that further. On the low side, this is a 20-amp increase in the current required of your alternator at idle (800 engine rpm).
Establish Size of Alternator
Here’s the correct way to learn what size alternator you require after the upgrade:
- Determine the maximum amount of current the system requires at 14.4 volts.
- Determine the maximum amount of current the fuel pump requires at 14.4 volts.
- Determine the maximum amount of current the ignition components require at 14.4 volts.
- Determine how much current your existing vehicle accessories require at idle with the engine at operating temperature. (This process is outlined below.)
- Add the above amounts together.
The ECU, fuel pump, and ignition components all require less current at idle than at 6,000 rpm, but that’s okay. By using these worst-case-scenario numbers, you have a bit of a buffer, which prevents your alternator from working at 100 percent of its capacity at idle. The net result is a reduction in heat created by the alternator at idle, so it has a nice long life.
Don’t sweat numbers 1, 2, and 3, because most manufacturers supply this information on their website in the specifications for the kits. For example, MSD specifies that their 6 series ignition boxes require 1 amp per 1,000 rpm. If you are unable to locate these numbers, I recommend that you contact their technical support department.
Determine Accessory Current Requirements
As I mentioned, it is to your advantage to make this determination with the vehicle in its presently running condition, carburetor and all. This provides a baseline to determine whether you need to upgrade your alternator as part of the conversion. To make this determination, you need access to these tools: a digital multimeter (DMM) to measure voltage at the battery (connect its probes directly to the battery terminals) and a second DMM and DC current clamp (or a stand-alone DC current clamp) to measure the output current of the alternator (install the current clamp around all wires connected to the charge stud).
Here is the basic procedure to get the readings:
Record the resting voltage of the battery with the engine not running.
Start the engine and bring the vehicle to operating temperature.
Turn on all of the accessories, including high-beam headlights, A/C, electric cooling fan(s), audio system at a common listening level, etc.
After the engine has reached operating temperature, record the voltage at the battery.
Record the output current of the alternator.
Think of this as a state of health for your charging system as my friend Todd Ramsey refers to it. If you don’t have the above tools at your disposal, a qualified shop can perform this for you. This data is invaluable if you desire to have your new EFI system work as intended.
Now, keep in mind that a 12-volt battery is really a 12.6-volt battery because it has six 2.1-volt cells in series (2.1 x 6 = 12.6). As such, it should rest at a minimum of 12.6 volts with the engine not running and it requires a minimum of 13.4 volts when the vehicle is running to allow a charge from the alternator to flow into it.
A 12-volt battery resting below 12.6 volts is not fully charged. And, if during the running measurements (as outlined above), you recorded the voltage to be below 13.4 volts, your existing alternator isn’t big enough for your vehicle in its present state, let alone adding the requirements of an EFI system. I run into this all the time, most commonly because of the addition of electric fans and fuel pumps.
Finally, it’s important to know just how much current your alternator is capable of putting out at idle, defined as 800 engine rpm and 2,400 rpm, and at cruise, defined as 2,000 engine rpm and 6,000 alternator rpm. Your alternator should be fitted with a pulley that allows it to spin at three times the crankshaft speed for these measurements taken at operating temperature to be meaningful. To determine this, you have three choices.
One, ask the manufacturer of the alternator. This is actually the least accurate method as operating temperature is typically not factored in and some companies tend to exaggerate their output ratings by not taking this into account. Some do take that into account; you just have to ask.
Two, remove the alternator from the vehicle and take it to your local alternator shop to have this measured. This is far more accurate but operating temperature may still not be factored in during testing. Loading the alternator for a period of time to get it to an operating temperature approximating that of being in use in your vehicle and then measuring its output is the most accurate way to determine these figures.
Three, have a shop make these measurements with the alternator in the vehicle. This requires a charging system analyzer with a built-in carbon pile load. This is a very accurate way to determine this as operating temperature is factored in, but it’s critical that engine RPM is kept as close to the specified RPM for each measurement as possible during the load testing, and this can be tricky.
If you’d like to learn more about exactly how your charging system really works, I have a great video on my YouTube channel called, “Charging Systems 101: How does your alternator and battery really work?”
Let’s consider the MSD Atomic system as an example. On the manufacturer’s website I found the following in their FAQ section:
Q: How much current is the total system capable of drawing?
A: If both fans are on, the fuel pump is at full capacity, the IAC is moving, the injectors are at their maximum, and the input voltage is around 10V (it can draw as much as 30 amps). Normal operation is approximately 14 to 18 amps.
First, a correctly operating charging system should never be “around 10 volts,” so you can see MSD has engineered this system to work to as low as 10 volts, assuming ahead of time that many enthusiasts’ charging systems are woefully inadequate.
Second, the “both fans are on” reference does not take into account the actual current requirements of the fans themselves, just the drivers for the fan in the ECU. (Refer to “Calculating Alternator Output at Idle,” left.)
If you purchased a 100A alternator, you’re off to a bad start because depending on how it’s designed, it may have far less output at idle than you really need. In addition, how much output does it really make at operating temp? About 15 percent less output at operating temperature is common, so I always recommend a 20-percent buffer.
This may mean that the maximum output rating of the alternator is 150 amps, which is well above the maximum current required. If you take into consideration a 15-percent loss in output at operating temperature, it gives you about 102 amps of maximum output at operating temperature at idle and 128 amps of maximum output at cruise. That’s perfect.
Such an alternator requires a minimum of 4 AWG cable between its output stud and the battery, assuming the battery is under the hood and within 10 feet of the alternator. Cable size increases if the distance between the alternator and battery is greater, such as in vehicles with rear-mounted batteries.
Finally, the size of the charge lead is only half of the equation as the return path of the alternator needs to be similarly upgraded.
Properly Planning an EFI Installation
I was recently sent a referral from local engine builder Beck Racing Engines. Owner Frank Beck had sold a customer a 468 big-block Chevy and a FAST EZ-EFI system. This engine was installed into a gorgeous 1969 COPO Camaro clone. On the dyno, the engine made more than 630 hp. In the vehicle, it ran and performed terribly. So bad, in fact, that the owner was pretty frustrated with it.
I was called to see if the electrical system was up to snuff. The owner brought it by, and as he pulled it into the drive, I noted that the headlight on the passenger’s side was not working. He said that he had trouble with his HID headlights and they worked intermittently at best. (This was a hint of things I would soon find.) Then he gave me the scoop on what was in the Camaro: a brand-new American Autowire Classic Update wiring harness, MSD Digital 6AL Pro-Billet distributor, tach adapter (so that he could use the stock tach in the cluster), March drive system (serpentine style), and an Aeromotive fuel system with 11140 Stealth EFI fuel pump (in the tank).
I noticed a few general problems with the underhood electrical wiring, such as poor grounding, lack of proper grounding, and possible undersized charge lead. Considering the poor connections and workmanship in general, I felt it best to perform the “state of health” measurements. The results were not good:
- Resting voltage of the battery with the engine not running: 12.28 volts.
- Voltage at thebatteryat idle,at operating temperature, all accessories on: 12.80 volts.
- Output current of the alternator at idle, at operating temperature, all accessories on: 95 amps.
I explained to the owner that 12.80 volts were well short of the voltage required to keep the battery charged and operate the accessories, hence the low resting voltage of the battery when the engine wasn’t running. He said that he just replaced the battery and couldn’t figure out why his other one wouldn’t stay charged. I also explained to him that 95 amps was too much for the existing charge lead to support, as it was 10 AWG. As the charge lead was too small, I was unable to make a determination as to whether the alternator was up to the task, so that had to wait for later. He took me for a quick ride, which confirmed that the vehicle ran terribly. He left me the keys: time to dig in.
First, I measured the parasitic draw on the battery at 25 mA (milliamperes) with the vehicle and all accessories off, which is well within reason. I typically measure parasitic draw before I start on a project like this, especially because the owner mentioned that the battery had already been replaced.
Frank always says, “The more you look, the more you find,” and that was certainly the case with this Camaro. A quick inspection of the fuel system showed that the regulator was installed in a good location (although it wouldn’t pass tech at the local drag strip because it’s on the firewall), the feed and return lines were of the appropriate size, and the tank was vented. I researched the fuel pump and determined it was adequate to supply the horsepower this combination makes. The ignition system didn’t fare so well because the ignition box was shoved behind the heater ductwork on the interior side of the firewall and nearly impossible to access. It and the tach adapter were mounted with velcro and both had pulled loose. This left the box and tach adapter hanging on by their wiring only, which is absolutely unacceptable in any vehicle, let alone one with 630 hp under the hood.
I was unable to access the ECU for the EFI because it was mounted above the glove compartment and short wired.
Charging System Repairs
On the surface, I had assumed that I’d be making the following repairs and upgrades, mainly to get the charging system performing correctly, as well as address the ignition system shortcomings: upgrade the wiring and return path for the alternator; properly ground the engine, ignition system, and chassis; and relocate the ignition box and correctly mount the tach adapter.
In addition, it was obvious that the headlight and engine harnesses (part of the brand-new American Autowire harness) needed some work (correct routing, terminations, etc.) because there were numerous splices and the work was generally sloppy. But the more I dug in, the more I found. And wow! This Camaro was a mess.
In addition, most of the harness for the EFI system was located between the firewall and the passenger-side cylinder head. The small length of harness inside the vehicle was virtually impossible to unplug from the ECU, even after I had removed the glove compartment. As a result, a large portion of the main EFI harness was relocated to correct this.
After a quick phone call to the owner to let him know approximately how long it would take to make these repairs, I was underway.
Major Repairs Performed
- Remove and relocatethe MSD ignition box, including repairing and re-routing the main harness, replacing the magnetic trigger harness to the distributor (the original was shortened), and repairing and extending the main power and ground leads.
- Relocate a large portion of the main EFI harness, including re-routing the harness to the oxygen sensor (passing it through the floor by the firewall), repairing and extending the harness to the fuel pump relay (this was cut unnecessarily short), and repairing and extending the power and ground leads directly to the battery, as directed in the instructions.
- Correctly wire the fuel pump, which involved installing a correct-size waterproof relay (I only use waterproof relays for underhood applications), running the correct-size wire to the fuel pump (I removed a 14-gauge unprotected wire and installed 10-gauge in split-loom tubing per the manufacturer’s recommendation), and correctly grounding the fuel pump, also with 10-gauge, as this was done prior with 18 AWG (the last two steps included dropping the fuel tank which was full).
- Correctly wire the cooling fans (same as the fuel pump).
- Wire the alternator with the correct-size cable and upgrade its return path.
- Correctly ground the engine,ignition system, and chassis.
- Build new battery cables specification.
- Add an auxiliary fusepanel to facilitate the ECU, ignition box, and fuel pump and fan relays.
- Repair, re-route, and correctly terminate the engine and headlight harnesses.
All but the last repair had a direct impact on the operation of the EFI system and fuel delivery. I kept as much of the electrical harnesses and components hidden from view to the casual onlooker as possible.
- The power and ground leads for the FAST ECU were tied together with the power and ground leads of the MSD Digital 6AL. This alone is a no-no as a CD ignition box is a noisy beast by the nature of its design and purpose. To make matters worse, the power leads were tied to the battery terminal on the starter, and the ground leads shoved under the switch mounting bracket on the block-off panel for the aftermarket A/C on the firewall: a terrible place to ground anything, let alone the ECU.
After the repairs were made, it was time for more measurements:
- Restingvoltageofthebattery with the engine not running: 12.4 volts
- Voltage at the battery at idle, at operating temp, all accessories on: 13.85 to 14.00 volts
- Outputcurrentofthealternator at idle, at operating temp, all accessories on: 63 amps
The Parasitic draw remained unchanged at 25 mA. I put the battery on a charger before re-installing it. After the surface charge is depleted, it rests at only 12.4 volts, which is an indication that it has been compromised already. This battery may have to be replaced in the near future.
Notice the dramatic change in operating voltage with the engine running, with more than enough to charge the battery and operate all accessories. I was surprised to see that the output current of the alternator decreased as much as it did. In this case, I believe this is a direct result of the charge lead being so inadequately sized. The fact is that the alternator is a one-wire design, and it senses voltage off its charge stud. I’d be willing to bet the alternator was at full capacity trying to overcome a problem it would never be able to.
After I made the repairs outlined above, Frank came by and we did an hour or so of idle/off idle/ tip-in learning via the FAST handheld controller. When the owner came by to pick up the car, he and I took it for a drive and it was way different. It broke the tires loose on even the hint of throttle application. The engine also had a sinister tone, which was far more representative of its horsepower.
The Camaro now required a lot of drive time or chassis dyno time so that the ECU could get itself back to where it was on the engine dyno in a controlled environment.
It became apparent that the ECU had been working overtime trying to correct things that didn’t need to be corrected. This was most likely a direct result of the fuel pump wiring, which inhibited it from performing optimally. As I mentioned before, the oxygen sensor also needed to be relocated before any WOT tuning could be done.
The owner left happy, and first thing the following day shipped the ECU back to FAST to have its fuel pump output repaired. Once that is back in, it’ll be time for some tuning on the engine dyno. After that, it’s back to me to get the rest of the wiring harness installed correctly . . . Oh, my goodness . . .
I think it’s worth pointing out that this Camaro exemplifies some of the conversations that tech support departments have with customers every day. The electrical problems I uncovered in this Camaro were serious enough to cause premature failure of the alternator, fuel pump, battery (the first one failed, the second was well on its way), ECU, and possibly even damage the engine. In addition, given how the electric fans were originally wired, engine overheating was a real concern in the hot Phoenix summer.
I found no fault with the FAST system, the MSD components, the Aeromotive components, the March alternator, or even the HID headlights. The only fault was the way these components were installed.
The owner took the Camaro to have it fine-tuned and has been driving and enjoying it for some time. The alternator failed after only a few months of service and had to be replaced. We replaced it with a BILLET-TECH 170-amp unit from Mechman, which is similar to the unit we installed on the 1970 Olds Cutlass in Chapter 6 (see Figure 6.9 on page 101). I still see no reason to blame the alternator itself, as it was improperly installed and in service that way for far too long. This undoubtedly shortened its life.
It is so important to follow the manufacturer’s instructions explicitly. You really should read the included manuals from cover to cover before beginning any installation. The manuals provided by FAST, MSD, and others include comprehensive installation instructions written, in some cases, by the engineers that design the products. If you follow them, you will achieve the performance the product is capable of.
Written by Tony Candela and Posted with Permission of CarTechBooks