Aftermarket EFI Tech 101:

An aftermarket fuel injection system, when in the hands of an informed user is an extremely powerful tool. Our experience has shown that over 99% of the problems encountered by aftermarket EFI users are not the fault of the system at all. Before you pick up the phone to call the tech line, please make sure that you have read and followed every one of these tips! Even though the engineers have gone to great lengths to produce a robust, reliable, user friendly ECU, failing to completely follow each and every one of these steps is a certain recipe for headache & disaster! If you are having problems, or are doing an installation and don't want to have problems, print this page and read it until you have tried, or remember every tip on this page!

Garbage in = Garbage out!

Though modern aftermarket ECU's utilize complex control strategies, it only takes one false input to produce erratic , unreliable operation. A common problem we have seen in crank trigger equipped vehicles is the failure to use a shielded crank trigger harness, and/or the failure to keep the crank trigger lead away from high load (current) wiring. With the many electrical components found under your hood, there are many opportunities for "noise" to induce a false input pulse which may cause the ECU to issue an ignition signal out of sync, resulting in misfiring, backfiring, or even worse, detonation. Other common culprits are improperly secured MAP sensor lines, damaged sensor wiring, or in rare cases, a faulty sensor. Extreme vibration or high manifold temperatures (250+ F) can damage the inlet air temperature sensor. The DFI main dashboard screen is an excellent tool for verifying the proper operation of all sensors. Typically when a sensor fails, it will output a value at one extreme of the sensor's output range (0 volts or 5 volts). If a sensor does fail in such a manner, modern aftermarket ECU's will detect the error and store a corresponding code in system memory. Stored ACCEL DFI error codes can be checked from the main dashboard. Another useful tool is the ECM Status & diagnostics option, found on the diagnostics pulldown menu, where you can confirm the proper operation of your crank and cam sensors (the cam sensor is only required for full sequential operation of an aftermarket EFI system).

Modern aftermarket ECU's are engine management systems, and are not capable of performing miracles (though some users might beg to differ!).

The Gen VII, BigStuff3 and XFI are all very capable units. They are capable of accommodating many variables, but will only work well if you provide them with a proper "supporting cast". You must utilize a fuel system that is capable of consistently providing sufficient fuel pressure under all operating conditions. A modern aftermarket EFI system can be tuned to accomodate a marginal fuel system, but doing so is asking for trouble. A system configured to operate in closed loop will provide a margin of safety against degradation of components (an aging fuel pump, a plugged fuel fuel filter, etc) but should only be relied upon until you are able to perform the necessary maintenance. One telltale sign of an undersized or underperforming fuel system is the need to use VE table values (at or near peak RPM) in excess of 1.10. With a fuel system in proper working order, values in the VE table will rarely exceed 1.10. Not only is fuel pressure critical, your ignition system is equally important. Though an underperforming ignition system may not produce the same catastrophic results as a weak fuel system, no ECU can make an "undersparked" engine perfom to it's full potential. No engine will run well unless all of your ignition components are in good condition. If you have an engine that does not cleanly pull to full rpm, check the condition of your ignition components (check plugwires with an Ohm meter, visually inspect the distributor cap and rotor for corrosion, carbon tracks, etc.). If you question the performance of your coil or ignition amplifier box, they are best verified by replacing them with known good components. Another "band-aid" fix for an undersized ignition system is to decrease the spark plug gap, in some cases spark plug gaps as small as 0.020" may be necessary for clean operation at full rpm.

When wiring your vehicle, you should apply the same practices as you would with a high powered car stereo system.

Just as poorly terminated, undersized wiring will cause a high powered car stereo system to operate improperly, it will do the same to your fuel, ignition and engine management systems. Each component requires positive and negative power cables large enough to deliver the maximum required current without excessive voltage drop. Running dedicated positive and negative leads to each component is the best way to minimize voltage drop and "noise" that may prevent components from operating at their peak. For the modern aftermarket EFI system, MTP recommends a minimum of a 10ga power and ground leads wired direct from the vehicle's battery. When wiring fuel pumps and ignition systems, consult the manufacturer for wire size recommendations. A general rule of thumb is to use a wire one size larger than that of the factory leads connected to the device in question. An excellent resource for premium grade wiring supplies is your local car stereo installer.

Rotor phase and crank/cam reference angles must be properly configured for proper operation of an aftermarket ECU.

Rotor phase is an often overlooked factor. In order to prevent crossfire it is important to "phase" the rotor, which is nothing more than ensuring that the rotor is in line with the terminal on the distributor cap during ignition (spark). Though not all distributors will permit independent rotor phasing, most applications will permit the distributor to be rotated to provide proper rotor phasing. If the crank sensor is in the distributor, turning the distributor will require a change in the "Crank Index Offset/Crank reference angle" value (found in the Engine Configuration/Operational parameters screen). The most foolproof way to confirm proper rotor phase is to drill a hole in the top of the distributor cap between the number one terminal and the coil terminal. When the engine is running and a timing light is connected to the number 1 spark plug wire, the timing light can be used to observe the position of the rotor during ignition. Even more important than proper rotor phase is the "Crank index offset" also referred as the crank reference angle. This is the crankshaft position that the engine is at when the ECU receives the pulse from the crank sensor. In order to properly control ignition, the value stored in the system Configuration screen must coincide with the actual value at which the ECU is receiving the signal. Ths proper reference angle is confirmed by enabling "Forced Timing" from the main dashboard and checking the timing with a timing light. If the value observed with the timing light is lower than the forced value, the "Crank Index Offset" value should be decreased by the amount of the difference. If the observed value is higher, the "Crank Index Offset" value should be increased by the amount of the error.

Crank trigger know-how

One of the greatest culprits we have observed on racing engines using a crank trigger is the failure to set the crank sensor polarity correctly. When using a "flying magnet" type crank trigger, you typically connect the purple wire to the negative terminal (black wire, terminal B) on the DFI Universal ignition harness, (FAST XFI and BS3 systems utilize the opposite configuration and require the green lead to be connected to the ECU negative input). However,it is possible for the sensor wiring to be internally reversed. A system with improper sensor polarity is generally insensitive to changes in commanded timing values. If a sensor is carefully visually aligned at the proper reference angle (The "Crank Index Offset" value specified in the Gen VII DFI Engine Configuration screen) and the polarity is correct, the spark timing value indicated in the software dashboard will agree with that observed with a timing light. In order to keep values from fluctuating while checking with a timing light, it is best to enable "Forced Timing" when software allows you to do so. A sensor with incorrect polarity will typically result in an observed value (as seen with the timing light) that is 6-8 degrees different than the commanded value. Another item to consider when using a crank trigger is the sensor to wheel air gap (MTP recommends 0.070-0.080").

Tech article archive: Various FSC (Fastest Street Car) Magazine Articles penned by MTP's own Chris Spies!

Click here to download a pdf of the recent Fastest Street Car Magazine article on the Gen VII DFI

Click here to download the recent Fastest Street Car Magazine article on Camshaft design for power adder applications

Click here to download the Fastest Street Car Magazine article on E85 and a writeup on MSD's APS alternators.

Click here to download the Fastest Street Car Magazine article regarding turbo header design & construction.

Click here to download the Fastest Street Car Magazine article regarding Intake Manifold theory & selection.

Click here to download the Fastest Street Car Magazine article regarding the latest turbo components and systems (Note: most are available from MTP!).

Click here to download the Fastest Street Car Magazine article regarding the shortblock build for our twin turbo Fairmont.

Click here to download a Super Chevy EFI/Blower install feature performed by MTP owner (then ProCharger engineer) Chris Spies.