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Thread: Testing a 7427

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    Fuel Injected! JeepsAndGuns's Avatar
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    Testing a 7427

    Actually a little more to the question than that. I pulled the 7427 from the same truck I got that charcoal canister from to have as a spare. I already have one un modded 7427 as a spare, and I know its good. But I would like to have a spare MPFI modded one, so if something wild happens and the one I am running now fries, I can have a spare ready to go. So I want to mod the one I just picked up, BUT, I want to test it before I spend the time tearing it down and removing the resistors for the MPFI. As far as what actually hooks to the pcm, the injectors are the only diffrence between a tbi harness. So will it harm the un modded pcm to plug it into my harness, install my memcal, and be powered up (but not start the engine)? I figure I can just connect tunerpro and bring up the dash and check and make sure it connects, and I am getting feeds from the sensors. Or will plugging it up with 8 mpfi injectors harm the resistors or other internal parts? If so, could I un hook the injectors and would that cause any errors or problems with testing it?
    I guess you could say I would be using my jeep as a test bench.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

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    8 MPFI injectors (assuming they're high impedance) is roughly 8 amps when commanded on. 2 TBI injectors (assuming ~ 2 ohms each) is 6 amps each, total of 12 amps.

    you shouldn't hurt anything even by running it, but key on, engine off? definitely not a problem.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  3. #3
    Vintage Methane Ejector
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    If you jump the resistors with a piece of wire, you can start the engine.

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    Fuel Injected! JeepsAndGuns's Avatar
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    Thanks, I just wanted to make sure before I hooked it up. I just didnt want to run the risk of hurting a posiably good pcm.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

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    Can you keep us posted on your results ? I'm in a similar spot and can't seem to get straight answers, re ; TBI/CMPFI compatability for the same ECM, 16197427. I jus want to update the one ECM from auto trans to manual , and am thinking I could just swap the manual prom from the TBI ECM for my auto one in CMPFI . They're the same year, 1995 ; I just didn't want to brick a good ECM . Be safe...Bob.

  6. #6
    Vintage Methane Ejector
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    I'm almost positive that there compatible with just a prom change.

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    Super Moderator Six_Shooter's Avatar
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    Quote Originally Posted by romac55 View Post
    Can you keep us posted on your results ? I'm in a similar spot and can't seem to get straight answers, re ; TBI/CMPFI compatability for the same ECM, 16197427. I jus want to update the one ECM from auto trans to manual , and am thinking I could just swap the manual prom from the TBI ECM for my auto one in CMPFI . They're the same year, 1995 ; I just didn't want to brick a good ECM . Be safe...Bob.
    As said in your other thread the PCMs are the same, the MEMCALs are not, and in your situation will only complicate things to use the TBI MEMCAL.
    The man who says something is impossible, is usually interrupted by the man doing it.

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    Jeeps and guns ; keep us updated on this experiment . Thanks for the correction , gentlemen. I'm on the right track now . Hope the Jeep survives . Be safe...Bob.

  9. #9
    RIP EagleMark's Avatar
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    Just stick the memcal in it and give it a shot. If it smokes... well once you let the smoke out they don't work anymore...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

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    Fuel Injected! JeepsAndGuns's Avatar
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    Ive never really had a problem keeping the magic smoke in wires or other devices. Cant think of the last time I let the smoke out of something...
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  11. #11
    Fuel Injected! JeepsAndGuns's Avatar
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    Just to update, I hooked up the un modded 7427, added my memcal and turned it on and hooked up tuner pro. I got the correct flash of the check engine light and tunerpro connected just fine. Got proper and correct readings from all the sensors. So the pcm tested good. I did not start the engine, didnt want to risk harming anything (pcm or engine)
    Took it back inside and did the resistor mod and now have a spare pcm ready to go incase the worst happens.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

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