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MPFI ICM vs. 3100 ICM The same? *Update 7/5*


Dirty Rockstar

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Hey guys.. The Cutty died on me today.. WOnt start.. WHen it did start, it would idel real real rough and the second I hit the gas, it would kill..

 

..SO, I have it narrowed down to a few possibilities:

 

1)Bad coil(s) or ICM

2)Fuel Pump or Injector

3)EGR- THe EGR was the ONLY thing I knew of that was wrong with the car, and even that allowed me to drive it every day..

 

..If it is the ICM, I have a spare one from a 3.1 MPFI sittin at the car right now.. My query is, will it work just the same? I dont have any info available, and cash is too tight to get a new one right now.. If anyone knows, or has some possible remedies other than what I suspect, or inside info, let me know.. Thanks!

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got a fuel pressure gage? or better yet can you hear the pump run when you turn the key on?

 

I doubt its the egr because that fucker doesn't work on my sister's 94 either and that runs fine.

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I can hear the damn pump start up, but what it feels like is there is no gas getting to the motor.. (Reminds me of when my mother would run her car out o gas and attempt to start it.. THe pump's usual noiuse changed tones a little as well, so Im thinkin it could be that.. Plugged filter? Who knows.. Gonna try workin on it hopefully tomorrow..

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fuel filter is such cheep insurance, i don't know why more people don't replace them yearly, i replaced mine about a year ago (due again come to think of it) and the car ran so much better it was insane.

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Before my fuel pump died, I noticed a few things (in retrospect, of course) that could tip someone off if it was going to die. First, after the car sat for a day or more, when I would start it, it would chug for the first few seconds, then run fine. Second, was fuel mileage got a little worse. Third, the pump's sound before startup was that of one trying to suck the last bit of fuel from an empty tank. Fourth, turning the battery, thus priming the pump, would give a gurgling sound from the fuel rail. Car still ran though, just one day it wouldnt.

 

As for your problem, I think a coil or ICM is the culprit. Most of these fuel pumps, from what I've heard, when the die, they die all at once. Car runs one day, won't the next.

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Steve I'm certain they're different. I don't believe it would work. The FI is totally different in that '94+ are SFI, and pre '94 are MPFI. The ICM is programmed to run a totally different type of FI, so I don't think it would work unless it was possible to reprogram it for SFI. I don't even have a clue how you'd go about doing that. Also, IIRC '94+ do not have a ICM, but they have a PCM. Remember '94-'95 have that stupid onboard flashed memory with OBD 1.5...it's not a chip like other years.

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I just remembered something else that might help you Steve. Shawn posted this for me when I had my #4 fuel injector go out a few weeks ago. It didn't solve my problem, but it might help you find yours.

 

If you have an inductive timing light, you can check the plug wires going to each cylinder when it's running bad. If you see 2 bad plugs going to the same coil, it's a bad coil. If the problem is now permanent, you should be able to tell by pulling the plugs and seeing if any are moist looking. 2 moist plugs on the same coil = bad coil. One moist plug most likely = bad injector.

 

My 1st instinct when I first read your description is it's a bad coil. A single bad injector doesn't have symptoms that severe.

 

 

Start the car and let it run. If it's intermittent, you'll have to drive the car or run it till the problem shows up.

When the problem shows up, connect the timing light to each plug wire one at a time and watch the strobe. If it's a good coil, the timing light will flash rapidly for plug wires connected to good coils, and flash intermittently or not at all for bad coils.

 

I have an inductive timing light because it's a very handy tool for diagnosing bad coils without actually having to disassemble anything.

 

 

This should help you find out if you have a bad coil & which one it is. Hope this helps

 

 

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Steve I'm certain they're different. I don't believe it would work. The FI is totally different in that '94+ are SFI, and pre '94 are MPFI. The ICM is programmed to run a totally different type of FI, so I don't think it would work unless it was possible to reprogram it for SFI. I don't even have a clue how you'd go about doing that. Also, IIRC '94+ do not have a ICM, but they have a PCM. Remember '94-'95 have that stupid onboard flashed memory with OBD 1.5...it's not a chip like other years.

icm???? ignition control module? they all have ICMs.

 

the ecm/pcm on the 3.1 is different and won't even plug in the place of a 3100s pcm and programming would be different.

 

 

 

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Yea, I wasn't sure if the ICM activity were controlled in the PCM. Thanks for the info. Either way, the ICM's wouldn't be compatible because of the different FI method. Correct?

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The ICM sits underneath the coil packs. You can run a SFI on MPFI with no problems. In fact, atleast the 94-96's that are SFI are only part-time SFI, most of the time they do in fact run on MPFI.

 

And, the ICM should be interchangeable from the 2.8's, 3.1's, 3x00's(not the 3800 though). But, from what I understand, the 2000+ 3x00's ICM and coil packs have a better spark curve. I have no evidence of this though.

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Yea, I wasn't sure if the ICM activity were controlled in the PCM. Thanks for the info. Either way, the ICM's wouldn't be compatible because of the different FI method. Correct?

 

Yeah, like slick said an SFI setup will only be SFI until 3000 rpms, then it reverts to MPFI. Plus, that is all controlled by the ECM, not the ICM, its for spark.

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Yea, I wasn't sure if the ICM activity were controlled in the PCM. Thanks for the info. Either way, the ICM's wouldn't be compatible because of the different FI method. Correct?

 

Yeah, like slick said an SFI setup will only be SFI until 3000 rpms, then it reverts to MPFI. Plus, that is all controlled by the ECM, not the ICM, its for spark.

 

You learn something new every day. Thanks! :D

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Thanks for all the replies guys..

 

..I spent a couple hours down at the car today, and think I have something:

 

2 of the coils (The 2 on the pass. side of the engine) A)Would NOT let the plug wires off their electrode towers.. And there was a "crusty" type of oxidation, and an orange-ish film on the coil and tower.. B) I swapped the 2 worst looking packs with 2 spares I had, and I got the car to run at idle.. It ran really rough, but I got it to run, and I managed to move it about 50 feet up the driveway before it cut out..

 

..I think I am on the right track here.. I am guessing it is the ICM itself, but I could swap the MPFI ones I had there, becasue the bolts mounting the pack on both of them had been rounded off (By prev. owners I imagine..) so I couldnt get it off.. BUt I looked, and the ICM connections were all identical.. So I imagine it would all swap..

 

..Now, I am goin back down hopefully tomorrow w/ 3 new coils and a new ICM to try curing this problem.. I will go the injector route if this doesn't work.. I will also be changing the fuel filter as well since I think it needs to be done.. I have 6 injectors from my MPFI 3.1 that was in the Lumina (The black Euro I titalled) and 6 from my LQ1 I am building.. The injectors are from a 96, and I dont recall the pund rating on them.. Thanks again for all the help guys!

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Well, it's not a huge deal on the 94 SFIs.. THe coils/ICM are located right at the top of the engine, directly behind the plenum.. BUt the MPFI, being down there just kinda pisses ya off.. But I won't be able to get to work on the car today.. I freakin work until 11 PM tonight.. ANd I wont have the parts here until 7, 4 hrs. after I start.. Ah well..

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When I buy my Vert from Jay, I am gonna prolly drop the 3100/3400 top end onto the MPFI in there so the coils already have a nice mount up ontop of the plenum:

 

ND620186.jpg

 

I got my work schedule confused, so Ima try and get down there tomorrow.. (Sat.) and swap that ICM out.. I think I might need new wires and plugs, but thats gonna need to wait because I have to pay off the Lumis coil overs save to pay off the Olds, and buy a turbo :willynilly: So that'll prolly be next check

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Swapped the ICM and the coils.. Still no start :sad:

 

Replaced the fuel filter today as well.. I am going to try the pump next.. If that still doesnt cure my problem, what's next? Injectors are all that i havent done yet..

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