1999 Grand am misfire...

[ChrisReigly]

1999 pontiac grand am 4-cyl.

One day an oil leak sprung, ran out of oil, overheated, and drove home. This is when it started misfiring.
Gasket between the timing chain housing and engine was put in backwards. Fixed that and replaced several other gaskets.

Started misfiring on one cylinder and I've tried damn near everything.

Has a high compression of 230 on three and 210 on one.

Was spewing way too much gass out of one cylindar, switched out its computer for it's old one and stopped the gas spewing, but not the misfiring.

Checked and partially replaced the entire ignition system as well as the cam positioning sensor. No problems there, which leads me to beleive the fuel system.

All four fuel injectors are working fine (switched em up too-same cylinder is misfiring), couldn't find a vacume leak (hard to check for those, could be wrong), and the fuel filter is offering no resistance. Ok.

Tested the wire leads to the injectors, also fine. Even replaced one whos wire looked in bad shape. Retimed the timing chain for grinns too, no change.


I'm at a loss of what the problem could be. The other cylinders are running normal. Idling it misfires, reving up it's fine, at the top of the rev it misfires. Weird.

Any ideas or suggestion?

[xeroinfinity]

Welcome to AF.

What exactly did you replace in the ignition system ?

Did you test the ohms readings on the injectors , if so what was the readings ??

[ChrisReigly]

Thanks for helping

Replaced the spark plugs, coils, wire harnes, distributor cap thingy, and had the little computer in there tested. All were good.

Don't recall the exact ohm readings, but from a bolt to the coil something like .5 ohms. Not even sure about that though, I'll re-test asap for ya.
Which tests would you like done? And how exctly?

[J-Ri]

The injector resistance should be measured between the terminals on the connector.

If it ran without oil for long enough to overheat, and then you drove it home, I would be looking for a mechanical problem. I would look at the camshafts and valves. Did you do a leakdown test too, or just compression?

[xeroinfinity]

The ohms reading on your 2.4 injectors.......
1.95 -2.3ohm w/EGR and 11.4-12.6 ohm without an EGR

Your fuel pressure should be around 41-47psi w/EGR and 52-58 W/O EGR

[ChrisReigly]

Been raining a lot here so I havn't had a chance to really get at my engine, but I'll post the test results as soon as I can.

Just the compression check.

[ChrisReigly]

2.3 ohms on each injector. Pulled them out and started the car, each one gives out a good healthy spray too.

No one in town has a fuel pressure tester so I can't check that.

Also checked the fuel return line, it's clear.
Replaced one of the oxygen sensors, the one on the exhaust manifold.

[98xploder]

ok well... check the o rings on the injectors. spray starting fluid around them and listen to see if the idle changes

[ChrisReigly]

Ran out of time to work on it, so I took the hit in the pride and let the shop fix it. Turned out there was a series of problems, like some broken return wires and the wrong sparkplugs (curse you auto-zone!). Shoulda checked to see if the plugs were compatible myself. Kinda weird that none of my tests or the dealership's tests didn't catch those. Don't remember all of the problems, but for $215 it's running better than ever in one day's worth of work. Thanks for helping me on this, it's good to know someone is willing to do so.

[98xploder]

good to know you got it goin good.