Really bad misfire

[99pewterv6]

Got a P0300 (random misfire) code the other day while driving on the highway and can't figure out the problem, maybe someone here can help.
I also have gotten a P0303(cylinder 3 misfire) code a few times during this as well.
I have changed all plugs, coils, check all wires, tested the ICM, replaced the injector on the #3 cylinder, recently changed fuel filter, cleaned MAF, crank sensor is fairly new as well.
I idles really rough with rough acceleration as well.
What else can I check or should I take it somewhere to figure out the problem?
I'm still driving it to and from school/work but its sucking gas pretty fast.

[Firebirdkid96]

Re: Really bad misfire

If it's a random misfire, have you checked all the injectors? Perhaps a vacuum leak, but that doesn't explain your misfire...

[techsan23]

Re: Really bad misfire

i would test the coil on that cylinder again just to be sure.

[99pewterv6]

Re: Really bad misfire

all coils are brand new, I have swapped out the injector on #3 but still had problems.
I was suggested to test the MAF by unplugging it and starting the car and driving and if drivability comes back that the MAF is bad. Anyone know anything about the maf test?

[Firebirdkid96]

Re: Really bad misfire

Basically the the computer monitors the MAF and if the correct air flow isn't recorded, then it doesn't run. If the MAF is unplugged then there is no info for the computer and the computer is forced into speed density mode where you don't need MAF data to run the car.

[99pewterv6]

Re: Really bad misfire

well I unplugged the MAF erased all codes. Started the car and went a little ways then got the reduced engine power light and the car would barely go anywhere(ie: no throttle response). Got P1514 (Airflow to TP Sensor Correlation High) and P0102 (MAF low freq)codes. Plugged it back in and now its just back to the same old really bad misfire.

[unvmyrs]

Re: Really bad misfire

do you have any coolant in your cylinders maybe? does the misfire go away at all when warmed up?

[Firebirdkid96]

Re: Really bad misfire

compression test time?

[v6mOtOrhEAdftOp]

Re: Really bad misfire

take the icm and replace it. Mine bench tested fine also, but under load, it would malfunction. I replaced it and it was fine

[99pewterv6]

Re: Really bad misfire

We've narrowed it down to being a bad PCV valve letting oil in the intake or a lower intake gasket problem.
Would get the p0300 (random misfire)code as well as the p0303 (cylinder 3 misfire), checked the #3 plug and it was covered in oil as well as oil on the MAP sensor.
Car is not burning coolant or anything. And misfire does not go away at all.

[jnxV6]

Re: Really bad misfire

We've narrowed it down to being a bad PCV valve letting oil in the intake or a lower intake gasket problem.
Would get the p0300 (random misfire)code as well as the p0303 (cylinder 3 misfire), checked the #3 plug and it was covered in oil as well as oil on the MAP sensor.
Car is not burning coolant or anything. And misfire does not go away at all.

Well I would replace the PCV valve as that is the cheapest part and then see what happens. If it doesn't fit it, it didn't cost that much and you know that is not the problem.

[99pewterv6]

Re: Really bad misfire

Update:
After installing a new PCV valve, ICM, all new coils and checking sensors. I started to get a #3 misfire and I heard some clacking so took off the valve cover and the exhaust valve on the #3 would stay the same when rotating the engine and the rocker arm had tons of play in it. I figured collapsed lifter so we dig in to the lifter and it looks fine. So now it has to be on the valves.
So We got the head off and the exhaust valves on #1 and #3 are stuck open and I looks like the valve guides were coming out at the bottom causing the valves to bend. Both valves hit the piston as well. Pistons just have a scar so they should be ok, but IDK?
I'm ruling out bad install on the valve components since i've put about 4k miles on these and recently have had and overheating problem.
So I think what has cause this mess is the head getting too hot and the valve sticking to the valve seat causing the valve to get bent.
I guess im going to send that head back to abbott to see if it can be fixed. Just odd that only the #1 and #3 messed up.

[bigbrian442]

Re: Really bad misfire

I would send them both back, so the guides can be checked in the other head as well. I wouldn't rule anything out yet. Sounds like the valve guides were too tight.

[99pewterv6]

Re: Really bad misfire

If they were too tight wouldn't they fail sooner than 4000 miles?

[bigbrian442]

Re: Really bad misfire

They could have started to along time before the 4000 miles get there. Most shops put a small disk on heads and engines they rebuild that the center falls out of if it is over heated. Let the guy that did the heads decide what happened.