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Thread: 95 gmc Tbi to MPFI conversion

  1. #1
    Fuel Injected!
    Join Date
    Apr 2014
    Posts
    23

    95 gmc Tbi to MPFI conversion

    Have a 1995 gmc 2500 7.4 liter with a 16197427 PCM, a 4.1:1 full floater rear end and a well built 4l80e. I recently redid the bottom end with flattop pistons at 30/1000's over, remachined for a roller cam/lifter/rockers, comp cams xtreme 264 (mild), edelbrock 60499 performer high compression heads. The intake has been replaced with the edelbrock MPFI and the 19lb/hr injectors replaced with the 36 lb/hr injectors ( 29 lb/hr may be a better selection and I am hoping this gets commented by the knowledges members on one way or another... To big or not to big? Detrimental or not detrimental?)

    This is week I purchased the moates APU1 and the G1 adapter and a pair of 512k chips too.

    i have been working with a chip tuner by exchanging TTS datamaster live drive files via internet to get the data analyzed, corrections made and a chip burned and snail mailed to the house, it takes about a week per iteration.

    i have made the current sense resistors modification as suggested except I used 20 ga for the resistor jumpers because 16 ga as suggested will not fit in the circuit land hole. I also made the jumper connections to the memcal as suggested. The resistors replaced by jumpers were 0.1 ohms resistance, so I don't think there is much additional current driving capacity derived from this modification but I am going on the blind faith of the contributors that have told me it was necessary to drive the total 4 ohm load on each injector driver (16 ohms divided by quantity 4).

    The the resistor jumpers allow more current and prevent the injector from going into peak hold mode and will allow the saturated driving of the high impedance 36 lb/hr injectors. And the memcal modification is to-enable the PFI mode versus the TBI mode, essentially changing the injector firing to once per revolution vs. every other revolution per injector of the TBI injectors

    hope I got that right .

    I have have beefed up the grounds and signal return lines from all sensors to the PCM. I have the roller rocker adjusted to zero lash (for now) and am watching vacuum about 16 lbs and pulsing a few pounds. The spark plugs are at 40/1000 and are RC12YC champions.

    Now we are on the 7th iteration of chip revisions and we are getting better each revision, BUT the popping through the exhaust is significant and is messing up the TTS datamaster data cuts I am running that the chip updating is based on..

    i am interested in any 7427 programming files that are close to this set up and would be a good point to start from. I am also interested in learning how to use the new equipment ordered from moates (APU1) to both: make data swapping and chip burning easier and faster with the tuner person I am working with and to run real time emulation without blowing things up...

    the the tuner person I am working with is not familiar with the mods accomplished above and if I can better understand the mods and software switches and flags that need to be changed in the software I can better explain it to him and we can advance this whole rebuild

    thanks for reading and any replies in advance

    john

  2. #2
    Fuel Injected!
    Join Date
    Feb 2013
    Location
    Euless, TX
    Posts
    1,608
    Quote Originally Posted by 95GMC_sierra View Post
    Have a 1995 gmc 2500 7.4 liter with a 16197427 PCM, a 4.1:1 full floater rear end and a well built 4l80e. I recently redid the bottom end with flattop pistons at 30/1000's over, remachined for a roller cam/lifter/rockers, comp cams xtreme 264 (mild), edelbrock 60499 performer high compression heads. The intake has been replaced with the edelbrock MPFI and the 19lb/hr injectors replaced with the 36 lb/hr injectors ( 29 lb/hr may be a better selection and I am hoping this gets commented by the knowledges members on one way or another... To big or not to big? Detrimental or not detrimental?)

    This is week I purchased the moates APU1 and the G1 adapter and a pair of 512k chips too.

    i have been working with a chip tuner by exchanging TTS datamaster live drive files via internet to get the data analyzed, corrections made and a chip burned and snail mailed to the house, it takes about a week per iteration.

    i have made the current sense resistors modification as suggested except I used 20 ga for the resistor jumpers because 16 ga as suggested will not fit in the circuit land hole. I also made the jumper connections to the memcal as suggested. The resistors replaced by jumpers were 0.1 ohms resistance, so I don't think there is much additional current driving capacity derived from this modification but I am going on the blind faith of the contributors that have told me it was necessary to drive the total 4 ohm load on each injector driver (16 ohms divided by quantity 4).

    The the resistor jumpers allow more current and prevent the injector from going into peak hold mode and will allow the saturated driving of the high impedance 36 lb/hr injectors. And the memcal modification is to-enable the PFI mode versus the TBI mode, essentially changing the injector firing to once per revolution vs. every other revolution per injector of the TBI injectors

    hope I got that right .

    I have have beefed up the grounds and signal return lines from all sensors to the PCM. I have the roller rocker adjusted to zero lash (for now) and am watching vacuum about 16 lbs and pulsing a few pounds. The spark plugs are at 40/1000 and are RC12YC champions.

    Now we are on the 7th iteration of chip revisions and we are getting better each revision, BUT the popping through the exhaust is significant and is messing up the TTS datamaster data cuts I am running that the chip updating is based on..

    i am interested in any 7427 programming files that are close to this set up and would be a good point to start from. I am also interested in learning how to use the new equipment ordered from moates (APU1) to both: make data swapping and chip burning easier and faster with the tuner person I am working with and to run real time emulation without blowing things up...

    the the tuner person I am working with is not familiar with the mods accomplished above and if I can better understand the mods and software switches and flags that need to be changed in the software I can better explain it to him and we can advance this whole rebuild

    thanks for reading and any replies in advance

    john
    John,

    The stuff I have still is all 305/350 TPI and GM Vortec 350 intake. However I will do some searching to see if I can find a .BIN or a guys contact info on Thirdgen.org. He had a port fuel injected HT502 and a 4L80E in his motorhome running on the 7427.

  3. #3
    Fuel Injected!
    Join Date
    Apr 2014
    Posts
    23
    Thank you fast355

  4. #4
    Electronic Ignition!
    Join Date
    Feb 2014
    Location
    Klein Texas
    Age
    57
    Posts
    16
    Any reason you haven't preloaded your lifters? Sorry I can't help you on the electronic questions. I'm just learning myself.

  5. #5
    Fuel Injected!
    Join Date
    Apr 2014
    Posts
    23
    Hello big dave. The lifters are at zero lash to insure the vacuum wiggling is not valve bypass, I'm going to put a half turn more in them this weekend... When I first started it up the vacuum gauge was all over the place and an old school guy like me immediately thought the valves were to tight...

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