Random Misfire Issues 2002 Silverado

nei00755 · February 11, 2008

Hello everyone,

I am having an issue with my 2002 Chevrolet silverado. I am getting a high amount of misfires out of cylinders 1 and 3. Cylinders 5 and 7 are also misfiring but nearly as bad as 1 and 3. 2,4,6, and 8 are not misfiring, just the odd side. I have an Autotap so I can see history and live misfires. The only codes I have thrown are the misfire codes. I actually cannot take the truck over 3200 rpm's because it is misfiring so bad that the SES light will flash at me. I have already replaced the plugs and wires and also a coil pack and have had no luck. I am not sure where to go next. I am thinking a few different things.....possibly a bad fuel pressure regulator, o2 sensor on that side, MAF, or clogged cat.....way too many things to think about. I can do all the repairs myself which is nice but would rather not dump 3-400 bucks into it before I find the problem. Any suggestions or tests I can try to make this function properly again would be greatly appreciated.

Thanks in advance

Jeff

gmtech4 · February 11, 2008

Hello everyone,

I am having an issue with my 2002 Chevrolet silverado. I am getting a high amount of misfires out of cylinders 1 and 3. Cylinders 5 and 7 are also misfiring but nearly as bad as 1 and 3. 2,4,6, and 8 are not misfiring, just the odd side. I have an Autotap so I can see history and live misfires. The only codes I have thrown are the misfire codes. I actually cannot take the truck over 3200 rpm's because it is misfiring so bad that the SES light will flash at me. I have already replaced the plugs and wires and also a coil pack and have had no luck. I am not sure where to go next. I am thinking a few different things.....possibly a bad fuel pressure regulator, o2 sensor on that side, MAF, or clogged cat.....way too many things to think about. I can do all the repairs myself which is nice but would rather not dump 3-400 bucks into it before I find the problem. Any suggestions or tests I can try to make this function properly again would be greatly appreciated.

Thanks in advance

Jeff

had a truck do the same thing,replaced the HO2S sensors on that bank,(one had no MV on scanner)they were covered with soot,change them both ,clr the code(s),88 ,out the gate.

MKWA · February 11, 2008

I had same similar prob. on my 99 and I had fuel injector service which my have helped a little and then I replaced the EGR valve and all is good now. Hope it helps.

nei00755 · February 11, 2008

The weird thing is, my scan tool will show MV on both O2's. I can't tell if they are acurate because i cannot open it up wide open to see readings. I don't think its an injector issue because I run cleaner through it frequently and I have never ran the tank dry so its not like it would have sucked up a bunch of junk. I am thinking its going to be an o2 but when I haven't thrown a code for it I am a little leary about spending 70 bucks on one.

nmw75 · February 11, 2008

The weird thing is, my scan tool will show MV on both O2's. I can't tell if they are acurate because i cannot open it up wide open to see readings. I don't think its an injector issue because I run cleaner through it frequently and I have never ran the tank dry so its not like it would have sucked up a bunch of junk. I am thinking its going to be an o2 but when I haven't thrown a code for it I am a little leary about spending 70 bucks on one.

Had nearly the same problem with my 04 Sierra. Replaced the upstream O2 for the bank giving the misfires, switched coils, plugs & wires. Did not help. Had 3 bad injectors. Replaced them & the misfires went away.

bobcat5544 · February 11, 2008

Before spending any money. Swap the front O2 sensors see if your problem moves to the other bank. If it does then it is an o2 sensor.

If it doesn't make a differance then you will have to look at fuel related problems. When the ses light flashes it does mean to much fuel is being dumped into the exhuast system.

Try the swap 1st and let me know if that fixed it. If not then we can go from there.

nei00755 · February 25, 2008

**UPDATE**

I swapped the O2's around from bank to bank with no luck. I also took out the fuel rails today and swapped injectors from right side to left side in hopes of seeing misfires on 2,4,6, or 8 but no, still cylinders 1 and 3 but 3 being the worst.

So far tried / tested or replaced

Spark Plugs

Wires

Injectors

O2's

Coil - on cylinder 3

Not sure what is next. Could it be a fuel pressure regulator or cat or blinker fluid resevoir? Not sure, anymore help would be greatly appreciated.

Thanks

nei00755 · March 2, 2008

Well replaced the fuel pressure regulator today, and still have the same issues. Two things I can think of, Intake leak, or bad cat. Is there any easy way to know if the intake is leaking? I looked around the top of it and didn't see any signs of leakage, but I know that is not always relevant.

Thanks

Jeff

poorboy · March 3, 2008

I just replaced the intake gasket on my 2002 5.3 with 95,000 miles this weekend. The truck was missing and thowing codes. Mine went away once the truck was warmed up but I decided to do the change anyway. I would suggest doing the intake. I'm a shadetree mechanic and with the exception of a in. pound torque wrench it was a very easy repair. Got the new gaskets for $100 bucks at the dealer and was off to the races.

If you decide to go for it here are some general observations and times.

1. Remove intake - about 45min. Taking your time and cleaning up as you go.

2. Cleaning for the head/mounting surface - about 30min.

3. Ceaning of the intake mounting surface, intake risers, TB about 45min.

4. Reassembly - about 45min, again taking your time.

Believe it or not the single hardest part of the entire project was removing the wire harness from each of the injectors...take your time...they will come off.