Driving me nuts, please help!!

[Pontiac GT]

i have a 2002 Pontiac Grand Am GT (with Ram Air) 3400 series motor. A few months ago I had a head gasket job done on it but now it skips and runs rough on idle and I can't even get it inspected because it's throwing the cylinder 3 misfire code. We have replaced the cylinder 3 injector, all new plugs and wires. The coil pack was tested and that's also fine. We've run 2 separate compression tests and both were great. We have also checked the intake harness and all is well there too. Multiple mechanics have looked at and we've followed their recommendations with no luck. I absolutely LOVE my car and I've been told I'm putting money into a dead horse and to just get rid of it but I've put SO much money in it I can't walk away from it. Please help!! All ideas and thoughts are greatly appreciated!! Also, since the head gasket job it's eating through gas like you wouldn't believe. I MIGHT get like 12 miles to a gallon. Absolutely RIDICULOUS

[Tech II]

Couple of questions....

Was it misfiring before the headgasket job?

Did the misfiring happen as soon as you got the car back after the headgasket job was done? If yes, then it's up to the garage that did the work, to make the repair right....

Local garage, chain, or Dealership do the work?

Do you know how the coil was checked? These coils fire two cylinders...3 is paired with 6....was coil output checked with a spark tester, on 3 AND 6?

So compression is ok....new wires and plugs.....new injector on #3.....is the injector firing? Has to be checked with a noid light for a pulse from the computer....

If spark is ok to 3 and 6...if compression is ok on 3 and 6.....if you have injector pulse on #3, and the injector is ok, then the only thing I can think of is a lean misfire on #3......and the only way that can happen is improper installation technique on the lower intake gaskets, when the head job was done.......

I hope you are not driving this vehicle......when you have a misfire, this creates a lean condition, because the oxygen in the cylinder is not burned....this oxygen then goes into the exhaust, and is detected by the O2 sensor, which tells the computer you have a lean condition....this causes the computer to run the car rich, which is a reason for your gas mileage dropping.....Is your Check Engine light flashing? Especially on acceleration/Load? If yes, you are dumping unburned fuel into the cat, which will cause it to heat up even more, thus damaging the cat, and causing you replace it, for big bucks....

[Pontiac GT]

First, thanks so much for responding!! Lol. It was back in November that I blew the head gasket but it sat until the beginning of March before the work was done because I had to save up the money. I truly honestly believe it didn't have the misfire problem Before the head job because my check engine light wasn't on like it is now. But it may have been? Before the head gasket went though it WASN'T eating gas like it does now. It's a local garage that did the work and they have been looking at it since trying to figure it out. The check engine light has been on since the car was started after it got fixed. I'm not driving it because it has no inspection sticker and of course won't pass until the problem is fixed. I just texted the mechanic if the injector itself was firing (after reading your post) and I just received a text back from him saying "No it's not. The wire is dead shorted (he just found it an hour ago) and he's going to run a temp 1 from the computer to see if it's the wire or computer" What are your thoughts and/or opinion on that?

[Tech II]

He should have found that out before he replaced the injector in the first place.....

I doubt that it is dead shorted....if it was it would fill that #3 cylinder up with fuel(because the injector would be grounded and wide open), and would have failed a fuel pressure check.......chances are it is open, on the control side.....either an open wire to the PCM, or the PCM is bad(which I doubt).....

[Pontiac GT]

This is all so confusing and frustrating... What is a dead short to begin with?? I don't even know if he ever did a fuel pressure test, just a compression test. Unless that's the same thing? And you're thinking it's an open wire to the PCM?

[Pontiac GT]

Any and all opinions are welcomed at this point

[Crvett69]

dead short means the 2 wires are shorted together (unlikely) or one is shorted to ground, chances are either one of the wires was pinched between the parts was put back together or a plug has a dirty connection or one broke inside the harness. compression test makes sure the cylinder has enough compression to fire, the issue is the fuel injector is not squirting fuel into the cylinder to fire or or its putting in to much and and drowning the spark out. the new wire he is running should work unless the pcm itself is bad

[Pontiac GT]

Crvette69- I took a screenshot of your reply and TechII's reply and I'll be sending them to my mechanic, lol. I haven't heard anything from him since he said he was going to run a temp wire to test it. I'm so overly frustrated. I've had this car for 5 yrs and besides the windows not working the head job and now this are the only big problems I've had with it. If it didn't look as good as it does it would be easier to walk away from it but it's a VERY attractive car and when running top notch it's a great car all around. I'm still open for other options and opinions from u and anybody else incase this doesn't work. Fingers crossed!!

[Pontiac GT]

Here's a little something else to throw in there that I forgot about, maybe it's related? My fuse for my horn and trunk relay constantly blow. I just stopped replacing them bc it got SO annoying. And about a year ago my horn went off in the middle of the night, like someone was just holding the horn down. Steady. Car lights were flashing like someone had set off the alarm but my doors were still locked, no one around and like I said, steady horn. Not the panic alarm. I had to start the car, put it in reverse for a few feet and back into drive for a few feet before the horn would stop. Sounds crazy right?? Maybe it's all a huge related electrical thing since ppl are saying PCM?? Any advise or opinions?

[Tech II]

I doubt it....the horn circuit would have nothing to do with the injector circuit....

As for the horn, only two things ground that relay.....the horn switch circuit, and the BCM...and only the BCM circuit would set the alarm off....

[xeroinfinity]

i'd bet the injector wire(s) are broken inside the loom and tape. due to the high heat the wire casings get brittle and break easy if care isnt taken. and their prob was nothing wrong with the injector they replaced.

Misfires are very common, which i blame on the recirculating fuel system clogging them.
Using fuel injector cleaner every month or two does help keep them down to a minimum.
They changed the fuel system in 03 models

also on the horn, try replacing the horn relay.