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Thread: Need to Learn Tuning 101 Quick!

  1. #1
    Carb and Points!
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    Need to Learn Tuning 101 Quick!

    Hi,
    I am new to the Tuning DIY world and have decided to leap in with both feet! I have purchased the Moates AUD1 kit and GX2/EX multi-program stacker for my 1614299 ECU.

    A bit of history: 1992 GMC K1500 P/U with highly modified 383 SBC (was original 5.7L, stroked); Edelbrock alum heads, small chamber; 8.1:1 C/R; Whipple supercharger with 454 TBI, 75# injectors. Dave Darge of Powertrain Electronics originally tuned it by burning an EPROM and the truck was turn key for years, passing smog in Cali every 2 years like clockwork. Somewhere as it aged, it would not pass smog and I let it sit. Preparing to move to Prescott, AZ where there is no smog requirements, I went through the setup to get it running again.

    Things I found and fixed: One or both fuel injectors were dumping fuel erratically; I rebuilt the TB and replaced the injectors and had it bench tested and verified; I had the supercharger rebuilt, seals and bearings, rotors timed; I replaced the distributor with the GM Performance OE model; Replaced plugs, wires, O2 sensor, MAP sensor, TPS sensor. Compression test, fuel pressure, etc. all good.

    This setup uses the factory fuel pressure regulator up to zero manifold pressure and an auxiliary multi-stage fuel pressure regulator takes over in a linear fashion as boost pressure increased... sent that to Dave Darge and had him install a new diaphragm kit and set it up again (not complicated, various spring tensions can be swapped to change the response to boost pressure).

    The problem: After all this work, the engine fired up cold fine and idled down smoothly while I went through the ignition timing procedure (zero degrees with Electronic advance wire disconnected). Test drive was as it always had run right up until getting into positive/boost and power dropped off 20-30%... just no power at WOT.

    I have pulled my hair out trying to find any reason why this turd wouldn't run as it used to and what I may have done wrong or overlooked in my cleanup work. I looked for vacuum leaks, none idles at -15psi (supercharger turning). I looked for fuel pressure curve as boost increased by attaching a fuel pressure gauge to my windshield and going for a drive; sent a video of that to Dave Darge and he said it was fine! Ramps up to over 40psi at 5.5psi boost. JUST PISSING ME OFF!

    Further problem: NO ONE will help me with an old school OBD1 highly modified forced induction engine running TBI!!! Enter the Moates group.. I am no obsessed with learning and understanding the tuning process and able to make tuning adjustments independent of the Dyno shops.

    I think I have an option to share data logged info and BIN files with Dave Darge as he is not fully retired yet but he is a long way away to deal with him personally! HELP!!

    I am at the stage where i have 'read' the Powertrain d2732a chip into my Autoprom, stored it as a BIN file, Burned it to one of my new 27SF512 chips at the top address in the stack for multi-tunes. I am now soldering in the G2X adapter onto my ECU board and (fingers crossed) I don't screw that up, I will be installing the ECU back into the truck and attempting to start it with the "Original" PowerTrain tuning BIN.

    Can any of you recommend a proper XDF file for my 16146299 ECU... I am assuming I will find NO BIN files close to my setup. Do I need an ADX or ADS file or does the XDF file accomplish everything TunerPro RT requires?

    Thanks in advance for any and all help!!
    Mark

  2. #2
    Carb and Points!
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    -- forgot to mention, this truck has a 700r4 trans and the $99 XDF seems to reference a 4L60E electronic trans?? Want to find the correct XDF for my ECU?!

  3. #3
    Fuel Injected!
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    Hello,
    As you and Dave and I know, unless something mechanically changed in the engine, there is no reason to alter the eprom. I am assuming this is a 3 port regulator? The fuel pressure in your application should ramp up from ~13psi stock to ~25psi at WOT at your boost level.

    Based on experience I suspect your "new" injectors. I have seen many replacement tbi injectors work fine at stock fuel pressure and fail horribly under higher pressure(stick closed) The fact that your fuel pressure is 40psi kinda tells us that you have no fuel flow unless there is a problem with the regulator(doubtful).

    The 99 ecu cannot control the trans except for TCC lockup. The xdf must be improperly labeled. I believe GM called them 4L60 when they went to electronically controlled lockup torque convertor instead of 700r4.
    -Carl

  4. #4
    Fuel Injected!
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    Listen to what engine wants, avoid knock and get WBO2. that is true 101 of tuning.

  5. #5
    Fuel Injected!
    Join Date
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    Greg Banish has some great books on tuning. Agreed with above - fix the fueling first, then play with timing, then revise the fuel one more time and you'll be good.

  6. #6
    Administrator
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    Hi Mark,

    I would also suspect the injectors are not delivering sufficient fuel. Whether they are faulty or not they might not be able to operate properly with that much fuel pressure. Oscilliscope curves of the injector opening and closing could help determine whether or not they are the problem.

  7. #7
    Carb and Points!
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    Thank you for the responses!
    The TBI has been apart and investigated ad nauseam. The original injectors were sent to RC Fuel Injection in Torrance, CA where they found one dumping fuel and both poor spray pattern. They were rebuilt and bench certified, returned to me and installed.. I was hopeful this is all that had gone sideways causing it to fail SMOG and lending to poor mileage. It didn't change the way it ran. I then sent the entire TBI to another specialist who found one of the 'rebuilt' injectors reacting intermittently and recommended replacement - I agreed and replaced BOTH injectors with the same GM Delco P/N 75# units.

    The Fuel Pressure Regulation system is somewhat unique. It operates in vacuum/cruise mode off the TBI integral regulator which has been modified to see direct MAP: 12-13psi up to about 22psi. At that point the auxiliary FPR increases pressure linear with positive MAP/Boost pressure between 30 and 40psi (somewhere in that range; needle is fluctuating and hard to read an actual number). According to Dave Darge, this is correct. Picture is the multi-stage regulator.
    Fuel Pressure Regulator04-07-19.jpg

    The truck is running very rich in boost. Mileage is down around 6mpg and used to be better than 10 when pulling a load. I used the truck 'as is' to tow a 5-6k lb loaded trailer when moving from SoCal to Prescott, AZ up the mountain grades. Sucked fuel and left a black smudge around the exhaust outlet rear fender. Like a Diesel :)

    Another 'Expert' suggested I probably have intake gaskets blown and blowing pressure into my crankcase instead of cylinders... I don't buy that; especially on a professionally built SBC. Engine was built and assembled (long block) by Rancho Performance Machine, Temecula, CA - a very competent racing engine machine shop and builder. I can't imagine the intake manifold to head fit using top notch FelPro gaskets would fail with a 5.5lb boost system. I could be wrong... Still pulling my hair out!

    Appreciate all your knowledge and input as I approach learning to look at the fuel mapping and understand what is going on. Should have it running on the new ECU mods later this week. Keep you all posted,
    Mark

  8. #8
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    Mark, the number one way to fail to correct a problem despite investing substantial effort is to fail to test systems while the problem is occurring. You will find that most of the folks here are hands-on, test and fix types. You will be expected to be directly involved and actively participating in the diagnosis. :)

    If the tailpipe is producing black smoke and mileage is down that would appear to indicate a low air:fuel ratio. Set up a laptop with an OBD1 cable and Tunerpro. Drive your truck and record data. The datalogs will store a picture of the engine operating conditions as seen by the computer. Once you have several runs recorded you can familiarize yourself with the data. You may see issues in the sensor readings that can help narrow the search. If you upload some of the logs to this post you may find folks willing to help you learn to read the data.

    As a "throw it out there" suggestion, consider there were three different injectors used with the 7.4L TBI engine over the years. The 94-95 7.4 engines received an injector that delivered approximately 74 lbs/hr fuel at double the pressure used for the '92 engines. If you are using earlier injectors with a calibration designed for later injectors they would likely deliver too much fuel, especially at high manifold pressure. The calibration will contain a value that represents a ratio between engine displacement and injector flow. This could be used to attempt to determine which injectors were originally used.

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