I took my car to my friends shop to see if it would pass smog without cats just to save me the hassle dealing with it. Anyways it turns out my car has a random misfire but the check engine light has never gone on. The first time he plugged my car in it was the #4 cylinder then #5 then we turned it off and tried again and then it was # 2, 3 6 and 7. The cars just got lid, filter, longtubes, ory, and catback with 43k miles and its a 2002. I figured if it was a loose wire or bad sparkplug then it would consistently be the same cylinder misfiring. We checked the fuel pressure and it was 55 because we suspected the fuel pump. Is there anything that commonly fails on these cars or any other ideas on what to check?

 

check to see if o2 sensors are reading lean.

 

I am in the same boat dude. Nearly identical problem, just after a header install.

Starting with plugs and wires tomorrow.

My o2's are properly working from what I saw on the tech 2.

 

headers will make o2 sensors run colder because its mounted further downstream and give off false lean conditions the pcm reacts by dumping mass amounts of fuel in and fouling the engine.

 

any way to counteract that?

 

did it set a code at all saying the misfire or were you viewing it on a scanner for misfire count? and if so do you know what kind of scan tool it was?

 

there was no code i am not sure what kind of scan tool it was but ill ask my friend later on tonight. It seems like everyone is correct on the false lean conditions because when he ran my car on the smog dyno it was running really rich. The scanner said something about the oxygen sensor but i assumed at the time it was referring to the ones that are supposed to be behind the cats.

 

Also wondering the same thing.

 

Hmm after talking with my friend about it he said most modern 02s have heaters in them to warm them up so this shouldnt occur. Besides when he scanned my car it didnt say it thought the car was running too lean.

 

same exact boat ...exact...^^^ i used a snapon scanner to watch it miss, it didnt set a code. Does the miss go away after the car is fully up to temp? Cause thats what happens to mine...so I think unless it was coincidence, I have to do another test to confirm.

oh and i also have headers, ory, and cat back.

 

My car has done this since the day I got it. I've changed everything you can think of, and nothing. I don't even have headers. I've had it show up with 2 different scanners, a Snap-On and I can't remember the other one. The only thing I haven't changed is my o2 sensors, I'm waiting on headers to do that.

 

the heaters can and do ware out. when mine went up the misfire was the first code to show. if this is happening you can use exhaust wrap to wrap the o2 sensors to help keep them warm enough.

 

Mine has set a P0300 a couple of times. It misses regardless of engine temp. Looking at the history counter, it seems that about 5 cylinders miss, some alot more than others.

It doesn't seem like it should be o2 related, my car only has 20k miles, so o2 sensors shouldn't go bad that soon.

I got my plugs and wires today, haven't had time to put them in yet. Hoping maybe the plugs got damaged at some point during the header install..

 

seems everyone with the problem has exhaust...someone with lots of time on there hands put the stock one back on and see if it cures it...something just doesn't add up...20k cars 50k cars...no reason to have to pay 50 for plugs 50 for wires both added together for 02 sensors, now if we had 120k 150k I can see the point. If it was a wire it'd be consistent, not every now and then on a different plug, I cant seem to get a pattern its like a woman it does what it wants, different symptoms each time.

 

it is definitly your o2 sensors, I had the exact same problem after a header install on my car and a customers car. especially with new headers, there is a coating inside them that comes off and ruins the o2 sensors, if you still dont believe it call Bob at EPP he runs into this problem all the time

 

I thought that was with the ceramic headers...anyway, Ive been doing some reading, I dont have cats to hold and pressure in and hold heat, will the O2's heat up enough?

 

I don't have headers, and have had the problem since day one.

 

Most of this will be o2 related sometimes people have even had to grind down the bung hole on the header to allow the o2 sensor to set deeper inside to heat properly and read properly, this may be another option for you. Also you may want to purchase new sensors as others have said the coating can ruin them. The o2's should still heat up ok even w/o cats although some have had problem with them. I personally dont run cats and they heat up just fine with my pacesetter's.

 

yeah, i was reading and saw that some people were shaving the bungs down. Thanks for the info....probably hasnt helped since its been in the 30's-40s here, wonder if it will be a different story in the summer?

 

Could be a possability, but its been the same temp as you stated here as well and no problems here or with a few other guys locally that i know that arent running cats.