Bad ECM question...
Thread Starter
Safety Car
Joined: Dec 2004
Posts: 4,088
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From: Poop land
Bad ECM question...
Is it possible that a bad ECM can intermittently stall the car in the transition from cold open loop to closed loop and off idle acceleration? Each time the car stalls from part throttle, normal acceleration I just unplug the ECM fuse and I am able to start the car normally again and drive for a cumulative 100 miles again without it stalling out randomly. Why are there no ECM failure codes when this happens????
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
Sure, but I'd be more inclined to think that one of the elements it needs to run is lacking - Air (MAF) - Fuel (filter, pump or injectors) - Spark - (Faulty HEI ground, Pickup Coil or Module). I would want to rule all these out first and I'd start by logging some data to see if there were any clues, such as whether it was running Rich or Lean. I'd also check my wiring very closely - wriggling the MAF and HEI harnesses to see if it would duplicate anything. I'd probably move on to taking apart my HEI (if only because some guru at Car Craft said this was the most likely cause of all the TPI misgivings) and verify the pick up coil produced a small a/c voltage; have the Module checked at a Discounter or a Dealer and look at the Reluctor under the shaft to make sure it didn't have any cracks. I know that intermittents are tough - they rarely set off a code of any type and my own experience is that they are allmost wiring. Yours of course may be different.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
PS - a couple of other things you might try - aim a hair dryer at the ECM. A cracked solder joint will sometimes show up when you apply some heat and duplicate the intermittent. Look for a sharp electrical surge when a solenoid or relay is activated. Ground the fan relay while monitoring voltage. Is there a significant drop? Ditto the a/c compressor and blower motor. Finally, monitor the ECT signal and make sure it rises steadily as the engine warms up and doesn't suddenly rise or fall. A sudden rise in temp would lean it out - a sudden fall would richen it up. Either condition might be enough to stall it if there was a significant rise or fall in this sensors output.
Thread Starter
Safety Car
Joined: Dec 2004
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From: Poop land
Thanks SunCr, I'll definately try that. Well, ya know, it baffles me about how these intermittents happen. Like I'd say, these things only happen when the car is warming up. Last time they happened, I was using that same ECM, one that came with the car when I traded up for it. Problem seems to happen when in the transition from open to close loop. Sometimes, this problem seems to happen in either mode. If its an ignition issue, then the problem probably would still be there even if I reset the ECM....
I'll have to scan more, because this problem goes away completely, then suddenly comes back in a few days, to about 3 months. Weird....
I'll have to scan more, because this problem goes away completely, then suddenly comes back in a few days, to about 3 months. Weird....
Thread Starter
Safety Car
Joined: Dec 2004
Posts: 4,088
Likes: 0
From: Poop land
Originally Posted by SunCr
PS - a couple of other things you might try - aim a hair dryer at the ECM. A cracked solder joint will sometimes show up when you apply some heat and duplicate the intermittent. Look for a sharp electrical surge when a solenoid or relay is activated. Ground the fan relay while monitoring voltage. Is there a significant drop? Ditto the a/c compressor and blower motor. Finally, monitor the ECT signal and make sure it rises steadily as the engine warms up and doesn't suddenly rise or fall. A sudden rise in temp would lean it out - a sudden fall would richen it up. Either condition might be enough to stall it if there was a significant rise or fall in this sensors output.
Well, if the CTS signal does that, wouldn't it throw codes also??
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Nope, had a friend chase an intermittent for a year-tured out to be the CTS, his explanation was the problem corrected before the ECM could set a code.I do believe there are several components-especially faulty wiring that can cause an intermittent without throwing a code.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Nope, had a friend chase an intermittent for a year-tured out to be the CTS, his explanation was the problem corrected before the ECM could set a code.I do believe there are several components-especially faulty wiring that can cause an intermittent without throwing a code.
Sorry for the DUPE-work computer
Sorry for the DUPE-work computer
Burning Brakes
Joined: Oct 2005
Posts: 798
Likes: 116
From: OAKLEY CA
Originally Posted by kopbet89c4
Is it possible that a bad ECM can intermittently stall the car in the transition from cold open loop to closed loop and off idle acceleration? Each time the car stalls from part throttle, normal acceleration I just unplug the ECM fuse and I am able to start the car normally again and drive for a cumulative 100 miles again without it stalling out randomly. Why are there no ECM failure codes when this happens????
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
Most codes require that the condition be present for a couple of seconds which is eons in the computer world. A nano second short in a power supply, signal or ground will kill it, but not set a code. I learned this the hard way when I crimped - instead of soldering - the MAP signal on a Gran Prix I used to own. Took 3 dealers to find my stupid mistake. In any event, the last time I replaced the ECM on the Vette, the ECT was toggling between 230 and 250 (or thereabouts), hot and cold. The sensor and wiring were fine. ECT codes are for when the signal is open (about -32 degrees) or shorted to ground (300 degrees). Nothing in between. I'd still poke around the distributor on yours - lose the reference and it's like turning off the key because the ECM won't pulse the injectors without it.
Race Director
Joined: Oct 2001
Posts: 19,653
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From: Melbourne Florida
Cruise-In IV Veteran
I can only tell you this...my car went into "limp home mode" about a mile from my house...got it back to home and it died for good..turns out it was the ECM and it never threw a code...
Thread Starter
Safety Car
Joined: Dec 2004
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From: Poop land
So far, I'm using a spare ECM I got from Ebay the day I got my SuperRam. I got my memcal and just slapped it on since the ECMs are the same, 7165 MAF computers for an 86-89 TPI. Hasn't stalled yet. And hopefully never will, unless I turn off the key...
At the moment, I'm about to either, A. throw away this old ECM, or B. Burn baby burn!!!
At the moment, I'm about to either, A. throw away this old ECM, or B. Burn baby burn!!!