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Old 03-22-2009, 10:05 AM
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Make: Pontiac
Model: Grand Am
Engine: 2.4TC
2000 Grand Am SE 2.4 Misfire

Hello all!

Picked myself up a 2000 Grand Am SE, 2.4 w/AT w/~200k on it.
Initially it had a cylinder 3 misfire reported, along with a random misfire. I pulled it apart and found cylinder 3's spark plug inner electrode gone. Put it back together thinking clearly I'd found the issue, but alas I had not.

It shakes on idle (but idles consistently without stalling). When put in gear, it chugs and rpm drops to around 500. Occasionally stalls. Very sluggish acceleration, w/ blinking SES light (misfire). Still logs the random misfire, no longer cylinder specific.

Have swapped entire IDI assembly with a known good assembly. New plugs gapped at 60 initially, then dropped to 50. Looking at doing fuel tests, but no fuel port, so have to find the adapater hoses (anyone know if autozone/checkers will lend these??). Visual inspection shows a leak at/near the power steering pump (fluid is low and pump is noisy on turns). The wiring harness(es)near there (which appear to be the fuel injector and IDI wiring) are covered in sludge/oil/dirt. Also plan on doing a compression (wet/dry) test later on.

Any advice appreciated. A listing of all engine grounds would also be nice, as I have had similar problems on Honda's from bad grounds.

Thanks!
Jon
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Old 03-22-2009, 10:52 AM
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Engine: LL0 stick
I believe the only engine grounds are at the front of the block near the bell housing bolts, and where the negative battery cable attaches to a bell housing bolt. Does the tach jump around erratically? If your crank sensor is becoming problematic, you could get random cylinder misfires. That might also explain the burnt spark plug electrode. Do the spark plugs look like they are burning properly? (not sooty black or ???)

I haven't found anywhere that you can get an adapter to hook a fuel gauge up. Snap-On probably has one, but I didn't care to check because I knew it would be insanely expensive. I cut off a couple quick connect fuel lines and hosed them to the plastic "T" (it has a schrader valve) that came with my gauge for checking (mostly) foreign cars that use clamped rubber hoses. Then you just pop off the quick connects on the pressure line to test it. Just make sure you use the fuel injection clamps, as standard ones will probably blow off the lines. Ignore the wrong clamps that I used in the pic.
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Old 03-22-2009, 11:39 AM
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seem to me you iac motor is acting up too, you should try a throttle service
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Old 03-22-2009, 01:47 PM
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Model: Grand Am
Engine: 2.4TC
Thanks for the tip on the fuel pressure gauge. I'll see about making something up like that if the parts stores don't have anything.

The tach and gauges are a little weird on startup - like they don't want to go to the correct value. Once there they stay decently. I also have the Trac Off light come on. When I push the traction button, nothing happens, BUT if I reset all the codes, I can turn the ETS on and off normally until I shut it off again. Anyway to check the crank sensor without swapping it? I can do a CASE relearn with my scanner, but that is just intended give the computer the ability to detect a misfire, not cause one. The plugs do not look like they are burning properly, and I'm getting the fuel smell out the exhaust. My current leading theory is a stuck open injector (due to sticking or a bad ground), because I also have the tick/tap on throttle. I'm going to pull the injector rail, and clean up the nasty sludgy mess around the injector and IDI wiring harnesseses hopefully today.

Since the idle will track with accessories, I'm going to leave the IAC alone for now until I fix the misfire. I'm assuming the shake has more to do with that than the IAC. If need, I can certainly dissassemble. I'll also run the IAC through full range of motion next time I hook up the scanner.

Thanks for the replies!!

Jon
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Old 03-22-2009, 03:30 PM
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A stuck open/leaky injector should give you a misfire code for the particular cylinder that is affected. You can check resistance on the CPS, but that doesn't mean 100% that it is good. Did you pull the vac line off the fuel pressure regulator to check for leakage and check the MAP hose for cracks?
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Old 03-22-2009, 04:36 PM
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Haven't checked the regulator line while running/pressurized but it's been disconected and nothing has come out. The MAP line "looked" bad, replaced it with no difference, scanner shows what I would expect for a misfire being reported by the MAP (low 40's KPA idle park, low 50's in drive, but fairly steady) The only weird scanner indication was a jumping spark advance, jumped from low 20's advanced to -3 advanced, at random.
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Old 03-22-2009, 05:33 PM
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That may be in indication of something screwy with the knock sensor. Or perhaps the ECU retards the ignition timing when the rpm drops to a certain point as it stumbles?? Do you get anything weird with the rpm reading?
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Old 03-25-2009, 12:54 AM
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replace the map sensor.. 5 out of 10 times the map sensor goes bad when the hose goes bad. if you had a scanner with live data then you could watch it and make sure its working to the correct way. also check for carbon buildup in the intake manifold.
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Old 03-29-2009, 03:13 AM
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Engine: 2.4TC
Okay, finally got some time so here's an update:

Removed the fuel rail. Pressurized the rail several times (turned key to On, listened for pump to prime rail). No leakage observed from any of the injectors. Put some trays underneath and turned it over for a while. A good amount of fuel was collected in each tray, and each had about the same amount. I haven't tried to get the jumpers for a fuel pressure test but I'm not thinking that will be bad/a problem.

Got a compression tester.
Dry test results from passenger side to drivers:
165psi; 155psi; 25psi; 90psi

Wet test results:
165psi; 155psi; 30psi; 150psi

Noting that the spark plug inner electrode was completely gone, I'm thinking of pulling the head to check for valve damage. I may ahead and pull the whole thing for a rebuild, as the compression numbers seem a bit low to me in the first place (although all steady). May also run the wet test again in the morning, the 3rd cylinder may just be badly washed out from running without the spark plug firing (PO drove several hours with car missing badly).

Comments/suggestions appreciated/welcome!

ps MAP sensor is good, I did watch it real time, and it adjusted as I would expect. The idle was a bit high (see above post), and idle in drive a bit higher, but that is expected with a missing engine. I also blipped the throttle to verify it went to ~100kpa.
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Old 03-29-2009, 08:46 AM
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Your compression test results would point towards a valve problem. I would pull the head and check the valves out. Also check the cylinder walls for scoring. Of the cylinders looks good, I wouldn't bother looking at the rings. Pull the valve out and look at the valves and seats for cylinder #3 and I think you will know what the prblam is.
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