Notes & Comments on Swamp's High-Voltage High-Frequency Injector Driver Modules.
This modification was developed more as a repair technique than as a performance modification, although it has given some very noticeable gains on most trucks. Stock trucks show the most gains, highly modified ones the least.
Any gains are also very dependant on what condition the original IDM
is in: If the original IDM
is already modified, and the pulse gap is shorter than .36-.38 milliseconds, little to no gains will be seen. If the original IDM
is a stock EDU-100A model (used in 1994-1995.5 PSD's), the greatest gains will be seen. (Every EDU-100A I have seen was a weak, sick puppy.) Trucks with higher mileages on their injectors will also see more gains.
The only way to tell whether a truck will benefit from the HV-HF mod is to view the injector voltage waveforms on an oscilloscope. If the pulse gap is longer than .40 ms, if there is a double gap, or a ragged and uneven hold-pulse, then this mod can help.
The HF mod is not nearly as simple as the HV mod; whereas the latter involves replacing a single resistor with another one of a fixed, known value, the HF mod is more of a balancing act akin to changing the rate at which a playground see-saw pivots: the weight of the kids, how far they sit from the center, and how hard they push, all have an effect. The characteristics of the injector waveforms dictate which component(s) need to be changed or replaced, and since no two units respond identically, I often have to solder and desolder components multiple times to get satisfactory results.
It takes a minimum of 1-1/2 hours from the time I crack the IDM
case open until I can seal it back on. After opening the case, I hook it up to my test bench / engine simulator which consists of a complete engine wiring harness modified with two PCM
connectors (one for 1994-1997 PCM's and the other for 1999-2003 units), an IDM
connector, 8 injectors and a cam trigger wheel with a CPS
mounted to a variable speed motor which allows testing up to 6000 RPM. A control box allows simulating any sensor input to the PCM--EOT, EBP
, MAT, BARO
, etc and a custom circuit provides an ICP
"feedback" signal to the PCM
proportional to the IPR
duty cycle. A cutout box allows disabling any injector, and a breakout box allows instant access to any signal into or out of the PCM
, and the wiring harness also has the ODB-II plug for connecting a diagnostic scan tool, so I can monitor the PCM
Data Stream, etc, and also run Injector Buzz Tests.
After I get it up and running, I scope the waveforms on all 8 injectors. Then I start making notes on a form: customer data, IDM
model & serial number, PCB revision number, and a dozen or so voltage, frequency and duty-cycle readings. The voltage and frequency readings are re-recorded after any change is made. Once I deem the waveforms to be satisfactory, I do what I call a "Heat Stress-Test". A stock IDM
draws 10-12 amps at full load, a HV one 12-14 and a HV-HF 18-20 amps, causing a substantial increase in temperature. For this test I put a thermocouple probe into the heat sink for the low-side switching transistors (the hottest components), wrap the IDM
in a heavy bath towel, and run it at 2 ms of injector pulse width and 3,000 RPM, recording the temperature at 5 minute intervals while monitoring the injector waveforms. If the unit is still running normally after 25-30 minutes, I call it good.
If it fails, usually evidenced by injectors dropping out and not firing, but sometimes a complete shut-down with it recovering after it cools, or occasionally something something going up in smoke, then I fix the problem and then repeat the test until it passes.
The 2 ms / 3000 RPM is based on an engine running WFO under a sustained, heavy load mile after mile, and the engine will probably melt down before the IDM
overheats. However, I currently do not want people who do heavy towing to order the HV-HF IDM's; we still need to do more testing in this area.
All IDM's that we sell will now have both the Hi-Voltage and the Hi-Frequency mods done to them. Price is $275.00 with a $200 core charge if we don't get your old IDM
back, and it includes return shipping to send your core back. (We don't want your $$$, we just want our cores back. :) )
Warranty is one year.
If anyone has an extra IDM
, we will mod one of them in trade for the other one. If you have non-working IDM's, 2-3 of them will get your good one modded.