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Elusive Misfire

Hello everyone,

I have a 1995 Pontiac Grand Am SE, four speed auto, 2.3L "Quad Four" engine.

The other day the SES light came on, and would go off, and return again. Later, it simply stayed on until I shut off the car and started it back up. I had the codes read, and it says: "engine misfire detected, cylinder

4, dejected"

Drivability is fine, but it is an audiable misfire otherwise. The ONLY time the misfire is picked up by the ECM is after it is at full operating temperature, and I've come to a stop or or very slow, and started to accelerate again. It will not pick up the misfire while cruising, or when cold.

One by one, I've replaced the spark plugs (twice), spark plug "boots", coil pack housing (old and new are white), and both coil packs.

Now I'm stumped, and exhausted and tired of spending money.

I am a bit confused as to what else might cause a misfire on that particular cylinder. Other than the fuel injector itself. My gut tells me that's not it, but of course I'm no mechanic. And I'm not completely sure how the ignition module works. Looks like it simply sends voltage to both coils when asked to by the ECM.

Any help is very much appreciated!!

Tony

Reply to
Tony
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Did the #4 plug look different than the others? Did they look like there was a lean, rich, or 'blow-by' condition?

I'm not either-- but I don't understand why you don't think it could be the injector. [or the o-ring that makes the seal there]. If you can see it while running, get the engine good & hot & inspect the #4 cylinder to see if there is some discoloration where it meets the intake. If not, then take some water in a misting bottle and spray the base of the injector & see if the engine speed changes.

If they are easy enough to get to, I might try replacing o-rings. If they are like my Taurus & yo need to remove the intake manifold to see one bank, then I'd just replace them all with a matched set.

I spent a crap-load of money on my 95 Taurus this summer before I just said "screw it", removed the intake manifold & replaced all 6 of the injectors. Best $250 I ever spent on that beast.

Jim

Reply to
Jim Elbrecht

Hey, thanks a lot for the tips! I'll have to try the water mist to see. I could spray it, but inspection otherwise would be a bit difficult.

I did inspect all the spark plugs. Sorry I didn't post that in my original. The spark plug for that cylinder only had one odd condition. The insulation on the end it fires had a dark red/orange streak on it. Covering about a third of it around, and all the way up and down. Those spark plugs where pretty new. And I replaced those, and misfire condition continues.

Tony

Reply to
Tony

Water mist did nothing.

I set up an appt. with my mechanic on Friday. He will hook up a scope machine and do a leak down test.

I'll post the findings when I know.

Tony

Reply to
Tony

Okay, I feel like a moron, and I'm going to admit that right here in this group.

Now, a misfire may have been taking place, but the mechanics scanner didn't read that from the ECM.

The cheap-o-scanner they had at the local parts store MAY have given me a bogus code somehow. But that's beyond the point.

Turns out there was a short in the wiring for the IAT senor. (Intake Air Temperature) It was reading -58 degrees all the time!! So the engine was getting an absolute flood of extra fuel. Which could have caused a misfire along with excessive timing if the ECM responded so.

All in all though, I made out pretty cheap, and all is good.

Thought I would post the answer to anyone who was curious.

Tony

Reply to
Tony

Thanks for posting the solution. Always nice when someone takes the time to let the rest of know what the problem was!

PS. Hope you changed your oil, with all that extra gas your oil would be contaminated.

Dave in Columbus

Reply to
noone

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