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Old 08-10-2016, 06:13 PM   #31
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Originally Posted by TheReaper! View Post
With what you wrote below the poor gas mileage , is it possible that you have a fuel injector leaking ? TheReaper!
While it is certainly possible, there'* no evidence to support the idea. There is no fuel smell coming from the engine compartment while the engine is running, nor after. Same for fuel lines (I originally considered there could be a leak, or air getting into the line somewhere. They look and smell good.)

After spending hours talking to you guys, Googling about what could possibly cause the symptoms, considering the intermittent nature of the problem, and that it seems to start well after the system would have gone closed-loop... I'm inclined to believe that this is all being caused by one (or more) of the following electrical components:
  • Fuel pump/sender (This is most likely the cause in my mind, it'* just a very weird presentation of symptoms. Usually, they just die and it'* a bunch of wasted money and effort to replace it if it'* not gonna solve the problem.)
  • ICM/coils (Could be. Replaced them with Delco, still misfires but presents with a new partial stall condition in the middle.)
  • Bad Plugs/Wires (This is actually possible, they did pass the visual check. Definitely spark coming out of them when the engine is cool enough to pull them.)
  • Clogged/Overheating/Leaking Injector (Possible, but engine runs great when not acting up, and feels like it'* missing on more than one cylinder at times. Also, no fuel after-smell that would usually point to a leak.)
  • PCM (Not firing all injectors every cycle after a while on closed-loop? Maybe. Odds aren't great.)
  • Crank Position Sensor (Odds are low, engine starts up every time and doesn't usually stall.)
  • Camshaft Position Sensor (Ditto.)
  • Throttle Position Sensor (Ditto.)
  • O2 Sensor (Ditto.)
That'* a lot of possible failure points, and some of those parts aren't cheap or easy to swap. At this point I'd rather wait for the diag results than spend more time and money when it may not solve the problem. If the Tech I scanner doesn't immediately pick up any sensor problems, I'm betting they'll get a hit on the fuel rail test.
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Old 08-15-2016, 11:55 AM   #32
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Okay... I don't know the answer, but Buick was able to narrow it down a little. The fuel pump is good, I was really relieved to hear that.

It'* definitely an electrical problem and it'* definitely heat-related. The diag tech thinks it'* probably either the ICM, ICM harness connector plug, or ECM.

The crank position sensor might be the cause, but the possibility is very remote and it'd be presenting symptoms in a very strange way. The tech tried tapping on the CPS and the CPS harness plug with a long screwdriver and it didn't seem to affect the engine at all.

He did say that the shielding on the ignition wires where it runs behind the alternator could be the problem (the magnetism could be causing interference.)

All the other sensors apparently checked out.

Apparently the bottom of the ICM is supposed to be greased with dielectric and mine is dry. I'm going to try that first because it'* a $3 fix if that'* the problem.

Next, I'll check the ICM plug and see if there'* a pin that looks larger or smaller than the others. Then it'* new plugs/ignition wires. Finally, I'll start throwing parts at it; ICM/coils first, ECM second. I'll let you guys know if I find it.
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Old 08-15-2016, 09:20 PM   #33
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It'* heat sink compound that helps remove heat not dielectric grease. The same stuff computer techs use on the cpu'* heat sink fan.
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Old 08-16-2016, 05:33 AM   #34
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It'* heat sink compound that helps remove heat not dielectric grease. The same stuff computer techs use on the cpu'* heat sink fan.
Yeah. The service manual does call for dielectric grease, but according to Google the entry is wrong. Where exactly does the compound need to go on the bottom of the ICM for it to be effective? I am guessing only the area in the middle on the one end where the control unit is?

I do IT and computer repair for a living but unfortunately I don't have any Arctic Silver laying around, so I guess I'll head to AutoZone and pick up a tube of their thermal compound when they open in a few hours.
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Old 08-16-2016, 08:45 AM   #35
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there is a web site called troubleshoot my vehicle .com ___ he has a very good way to test to see if the ICM is good or bad, it is a step by step procedure with pictures, my buick died, it would crank but not fire, I printed out the info from the web site and followed the steps closely and found that the ICM was bad, got a new one from NAPA for 240.00, put it on and it fired right up, in the procedure you will also test the coils to see if they are bad or good, hope this helps you out
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Old 08-16-2016, 08:54 AM   #36
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there is a web site called troubleshoot my vehicle .com ___ he has a very good way to test to see if the ICM is good or bad, it is a step by step procedure with pictures, my buick died, it would crank but not fire, I printed out the info from the web site and followed the steps closely and found that the ICM was bad, got a new one from NAPA for 240.00, put it on and it fired right up, in the procedure you will also test the coils to see if they are bad or good, hope this helps you out
Thanks, I'll check that out! However, if not overheating (which will be solved with thermal compound) the ICM and coils otherwise seem to be working fine. We'll see, I guess.

By the way, $240 is WAY more than I'd pay for an ICM. RockAuto has them starting at $66 for the pre-1993 Magnavox unit, and $75 for the 1993-1995 Delco unit.
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Old 08-16-2016, 12:48 PM   #37
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Okay, I've applied thermal paste to the ICM and it'* mounting plate. Hopefully that will solve the problem. I'll let you guys know if it comes back!
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Old 09-28-2016, 12:45 AM   #38
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Thermal Paste! That must be the ugly stuff slowly dripping out of my coil pack. SineDeviance, did the thermal past help relieve the symptoms?


P.*. this is my first post, my LeSabre is having some similar issues to what is described in the thread here.
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Old 09-28-2016, 01:00 AM   #39
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Thermal Paste! That must be the ugly stuff slowly dripping out of my coil pack.
Very doubtful. Thermal paste is generally a high-viscosity substance that couldn't possibly drip. As it ages (over many heat cycles) it will usually harden, not soften. It'* the same exact stuff that is used between processors and heat sinks in computers.

If your car is using the original 'grey box' Magnavox ignition pack, the drip is more likely to be the gel-like packing that is inside. With my original unit I noticed that the underside (where the ICM would be located) was filled with a gel-like substance.

Presumably, this is to protect the components inside from moisture, heat and vibration. A Jeep Wrangler I used to own had the ECU module encased in a very similar gel-like substance.

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SineDeviance, did the thermal past help relieve the symptoms?
I think so. I haven't been driving the car much since applying it so I'm not certain. However, I do believe it'* very safe to assume that running the ICM 'dry' would cause it to eventually overheat, at which point it could easily be responsible for a random misfire.
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Old 09-28-2016, 01:02 AM   #40
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Forgot to mention ... thermal paste is usually white or grey/silver in color and is fairly easy to identify. If what you are seeing is a reddish-brown color, it'* the gel-like substance I was talking about in the previous reply.
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