Hello everyone.

I've been chasing this misfire for about two months now. I have changed all eight plugs, changed the coil and even paid $3,300 to change head gaskets. After all of that I'm still getting a misfire on cyl3 code. I've inspected the resistance from the fuel injectors, they are all about 12ohms. What else do I need to check before I sell this thing off?

Background: It has just under 130k miles and I have had zero problems until it got cold this season. Once the mornings hit about 20F degrees I had a check engine light come on. Maybe a little bit of a shake at first but after it warms up it drives excellent. It has never sounded like there is a misfire, it has always ran smooth.

What else do I need to look for? Thanks,

KC

 

I chased one around for a similar problem last year. I turned out to be a bad O2 sensor of all things. I finally caught it on the scanner, it would run rough only in the morning after first startup and would shake the whole truck like it was missing, then all of the sudden it would smooth out and run fine for the rest of the day...A lot of parts were changed on this one too.

 

I would first try a bottle of techron or seafoam, I had an o6 with 5.4 and 44,000 miles would get an intermittent check engine light and engine would start funky, it was a leaking injector, just because the coil on the injector ohm's out, dosent mean that the injector is not dirty or partially plugged, ultimately, I wound up changing gas stations ant the problem went away, it sounds like you went after all the usual problems, although head gaskets are not usual on the 5.4!

 

I had a misfire like symptom on my '04 Expy a few years ago. I went to AZ and bought a $150 code reader and it was indicating an issue with bank one. Still not fully convinced I took it to my mechanic and he found a small vacuum leak from a hose, replaced it and viola.

 

I forgot to mention that I have used Techron on 2 occasions. I used three of the 12 gallon of centrates with no luck.

My mechanic said he saw fluid on the head. I was working 60hr weeks before Christmas and never got to see this for myself. He assured me the head gasket was in fact the problem. Despite a perfectly running truck after the reoair, the kight still pops up. I've done several hard resets myself since then to clear the code.

On the topic of gas stations, I ONLY use QuikTrio because they are top teir but I've noticed soot in/on my tailpipe. Is "top teir" really that great?

Thanks for all the info guys. I appreciate it

 

Would an o2 sensor give a misfire code for a specific cylinder? This has been consistantly giving me the Cyl3 code.

 

No, I don't believe you would get a p0303 code because of an o2 sensor, have you replaced the coil boots? An injector is about 35 to 40 bucks, since its all been apart the fuel rail should come apart without too much fuss, I would move a coil and or plug/injector to another cylinder and see if the code moves moves with it. Understand the part about not enough hours in the day!

 

The plugs are all new. I put a new boot on cyl 3. When I got the truck back from the mechanic, the new boot was on #2. I am still getting #3 misfire. If it's not an o2 sensor (or any of the above variabkes) then I suppose it has to be the injector???

 

Unless the wire is bad. How probable is it that the wire is bad?

Do you think the gasoline is causing problems?

 

Wire bad? no, I don't think so, try making the problem move to another cylinder, I use shell or BP, you have no idea what the store manager does to the fuel once the tanker drops off, try switching stations for 2 or 3 tanks.

 

I will move the injector from #3 to #1 and try that. If a P0301 pops up then I know to replace that injector.

What would I check if cyl 3 keeps misfiring after that? Bad wire or something internal? The mechanic sent the head to a machinist when he pulled the head gasket. If it was cracked I should have known about it.

 

If you can't make the misfire move to a different cylinder by moving parts around, try checking the coil harness and injector harness for a chafed wire.

 

Thanks!

I test drove it last night after cleaning some electrical connections and then took it for a test drive. This morning it won't start. I think it is the 4yo battery that died but I won't know until my wife gets home with our other car for a jump.

I want to test one hypothesis at a time so I can pinpoint the culprit.

 

Found out the battery was not 4 years old. It was only 2 years old but it wasn't the correct size. The AZ guy tested the batt and said it was bad. He said the alternator was on its way out, too.

 

That's good. A bad battery will make a lot of weird things happen. Does it run alright now?