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.

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.

If you jump the resistors with a piece of wire, you can start the engine.

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.

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.

I'm almost positive that there compatible with just a prom change.

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Originally Posted by romac55

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.

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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.

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.

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...:laugh:

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...:laugh:

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.