Cylinder missfire question
Thread Starter
Teching In
Joined: Sep 2005
Posts: 23
Likes: 0
From: Richardson, TX
Cylinder missfire question This AM on the way to work, I noticed the car started hesitating while cruising on the highway. Eventually the SES started flashing and eventually stayed on. I pulled the code p0304 which is missfire at cylinder 4.
I recently had LT headers installed so I assumed that I had a loose plug wire or a coil pack problem. I played with the 4th cylinder plug wire and can convince myself that it was loose so I pulled it off and replaced it securely.
On the way home the car ran great as usual, no more hesitating, but the SES light remains on and the code remains.
My questions are these: 1) if a plug wire is off, does the PCM stop sending fuel to that cylinder in order to avoid having fuel end up in the exhaust system (seems like this would be dangerous), or will something else equally damaging occur? 2) should the SES light have come off right away if I did really fix the problem or do I need to reset it?
Thanks in advance
I recently had LT headers installed so I assumed that I had a loose plug wire or a coil pack problem. I played with the 4th cylinder plug wire and can convince myself that it was loose so I pulled it off and replaced it securely.
On the way home the car ran great as usual, no more hesitating, but the SES light remains on and the code remains.
My questions are these: 1) if a plug wire is off, does the PCM stop sending fuel to that cylinder in order to avoid having fuel end up in the exhaust system (seems like this would be dangerous), or will something else equally damaging occur? 2) should the SES light have come off right away if I did really fix the problem or do I need to reset it?
Thanks in advance
Thread Starter
Teching In
Joined: Sep 2005
Posts: 23
Likes: 0
From: Richardson, TX
update on my woes I subsequently kept getting 0300 DTC which is multiple misfires and another error code for the bank 1 sensor 1 "heater circuit". Long story short, V6Bird has been helping me diagnose the issue and had me unplug both O2 sensors (the rear sensors have sims). The car ran beautifully.
I then plugged one sensor in at a time and the hesitating/jerking recurred and if I really got on it, 0300 would come back up. This happened with either sensor being in place. I then bought a new sensor and tried it on one side, same problem.
This all started a couple of weeks after installing brand new coated pacesetter LT headers. After searching this board the only other things I have seen is that perhaps trying a corvette "rear O2 sensor" (which apparently has a built-in heater unit) may do the trick and another theory was that "fumes" from the coated headers are the problem and eventually these will dissipate and I can plug in my O2 sensors in a few months and maybe things will be better.
Anybody else have any other thoughts, experience with the coated headers or anything else to contribute?
Thanks in advance,
I then plugged one sensor in at a time and the hesitating/jerking recurred and if I really got on it, 0300 would come back up. This happened with either sensor being in place. I then bought a new sensor and tried it on one side, same problem.
This all started a couple of weeks after installing brand new coated pacesetter LT headers. After searching this board the only other things I have seen is that perhaps trying a corvette "rear O2 sensor" (which apparently has a built-in heater unit) may do the trick and another theory was that "fumes" from the coated headers are the problem and eventually these will dissipate and I can plug in my O2 sensors in a few months and maybe things will be better.
Anybody else have any other thoughts, experience with the coated headers or anything else to contribute?
Thanks in advance,
TECH Senior Member
Joined: Mar 2004
Posts: 14,620
Likes: 17
From: BFE
Fumes from header coating will only last a couple of runs.
Sounds like bad sensors.
I do not know where you live but you could dissable the sensors via tuning and run an open loop tune.
OR replace sensors.
Sounds like bad sensors.
I do not know where you live but you could dissable the sensors via tuning and run an open loop tune.
OR replace sensors.
Thread Starter
Teching In
Joined: Sep 2005
Posts: 23
Likes: 0
From: Richardson, TX
It looks like one of my wires would keep loosening after the header install. I swapped the wires with MSDs, changed out the spark plugs and everything is running great now. I'm even still using the old O2 sensors.
Hope this helps anyone searching the matter in the future.
Hope this helps anyone searching the matter in the future.
