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Old 05-14-2006, 08:58 PM   #1
jabbott
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'92 Lesabre starting and PCM issues

I've been having a starting problem with my '92 Buick Lesabre recently... The car has 99,200 miles on it. 3.8L V6 EFI. It will start but then hesitates and dies after a few seconds. I'm able to keep it running if I keep the throttle pushed in a little, but if I let off for more than a few seconds, the engine just dies. When I keep the throttle in I can hold it at 2,000 RPM but the engine occasionally hiccups, drops a few hundred RPM real quick, then goes back up to 2,000 RPM. Sometimes it stays at 2,000 RPM even when I let off the throttle. The car ran completely fine up until this problem, and this is the first time I've had any trouble at all in four years. I've checked the fuel pressure and air intake and both seem to be fine. Battery seems fine, so does the starter. I also changed the fuel filter and spark plugs with no change in behavior. Spark plug wire resistances are well within spec. This problem has not gone away since it started about three weeks ago.

The check engine light is on (for the first time ever) and blinking very erratically... I purchased an AutoXray 5000 scan tool and hooked it up recently. It said that the PCM was reporting the Throttle Position Sensor was reading high. After getting that diagnostic code, I used the AutoXray's monitor function that reports all of the sensor values over time. It said that the coolant temperature sensor and manifold temperature sensor were anywhere from -80 degrees F to 270 degrees F (they never matched either), were random with no pattern, and that the throttle position sensor was going from 0 to 5 volts, again random with no pattern. It also said my battery voltage was anywhere between 0 and 25 volts, and that my brake was depressed sometimes, or not depressed other times, and that the AC was alternating between on and off. It also said both of my Quad Driver units were on "high", but they should have been reading "low" according to the tech manual. Most of the other sensor readings (such as fuel/air mixture) were OK.

None of this makes a whole lot of sense, as I checked the coolant temperature sensor itself on the engine with a multimeter and it was accurate to within 2 degrees... I checked the battery voltage at the terminals and it is fine as well. I've disconnected and reconnected the battery wires, but didn't see a change in behavior. I never had the AC on or the brake depressed either.

I can hear relays clicking under the hood, sometimes very rapidly (much more clicking than normal). The radiator fans now come on when the key is turned on with the engine off, which never used to happen. I've seen other posts which have indicated that this is a sign of a bad PCM (aka ECM, ECC). The faulty sensor readings also make me wonder if this is the case, or maybe if there is a bad ground (or both).

The other issue I noticed when I got it to run for a few minutes was that one of the refrigerant lines became white and frozen over, even though I wasn't running the AC. There was a cylindrical tank with two lines running into/out of it (close to the windshield on the passenger side) that was also frozen over. The top line that ran into the tank was frozen. I'm not an AC expert so I don't know if this is normal or not. It's the first time I've seen either of those freeze over like that.

I've read another post which said that the blower motor can often draw too much current and kill the PCM. Do you believe that could be what has happened to my vehicle? What other things do you think might be causing the problem? I know that I need to check the PCM and other ground connections, but I'm not sure where they all are (I see the one on the engine but that's the only one I see). Any other ideas or suggestions? Should I get a new PCM? If so, does the '92 PCM need to have the EPROM transferred/flashed or can I just install any aftermarket PCM (Cardone, Borg Warner, Standard Motor, Superchips) out of the box? Or is the OEM PCM the only way to go?

Thanks a bunch for any help you can provide. I want to get this problem fixed!

Jon Abbott
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Old 05-14-2006, 09:19 PM   #2
vwhobo
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I have seen those exact symptoms plenty of times before. The correct procedure is to test each sensor seperately which you have mostly done, and if they check good, replace the ECM with a known good unit. It always causes a headache, no matter how many you've seen do this, but it always fixes the problem.

Yes, the eprom needs to be swapped out, but that's a s simple as removing a couple of screws on the cover.
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Old 05-20-2006, 07:14 PM   #3
jabbott
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Problem fixed!

Quote:
Originally Posted by vwhobo
I have seen those exact symptoms plenty of times before. The correct procedure is to test each sensor seperately which you have mostly done, and if they check good, replace the ECM with a known good unit. It always causes a headache, no matter how many you've seen do this, but it always fixes the problem.

Yes, the eprom needs to be swapped out, but that's a s simple as removing a couple of screws on the cover.

I finally fixed the problem! It was a bad ECM/PCM after all. I checked all the sensors and grounds at the PCM connector (and at the sensors), and everything checked out fine. I ordered a salvage PCM from eBay, dropped it in, and the car runs perfectly, just like it did before! I was grinning from ear to ear while driving it.

Thanks again for the help, I really appreciate it!
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