Random Cylinder Misfire...

[Dannk]

My truck has been periodically missing out - but then seemed to go away. I kept driving it waiting for a Check Engine light to help my diagnostics. Well it came on today with a P0300 (Cylinder Misfire Detected - Random) code. I recently changed plugs, wires, cap and rotor. What is next?

[BlazerLT]

What year do you have?

What plugs did you use and how much gap did you gap them too?

Did you install a new fuel filter lately?

Changed gas stations recently?

[Fireplug]

OMG not the P0300 That is a GM techs nightmare.
It could be just about anything from the change over in gas from summer to winter(if you live in that type of area) to a piece of carbon on a plug.
Did you use all AC Delco parts?? Please say you did
Do you have any of the scan tool readings or was it just a code reader??
Fireplug

[Dannk]

It's a 1996 S-10, 4.3W. I cannot recall what brand I used - but it was not the cheapest available. I gapped the plugs to the spec under the hood too. I have changed the fuel filter withing the last 3 months (along with the fuel pump).

I change gas stations all the time - but it's been doing this for 3-4 tanks now.

I have all the DTC info and Freeze frame data, but not with me now...

I just inspected the coil and it has some severe discoloration around the housing near the "iron bar" that wraps around it. Almost like it's been arcing to ground??? Too bad I cannot watch it while I'm driving! Could it be a bad coil?

[Dannk]

I thought P0440 (EVAP system) was a GM tech's nightmare!!!

[BlazerLT]

Originally Posted by Dannk

It's a 1996 S-10, 4.3W. I cannot recall what brand I used - but it was not the cheapest available. I gapped the plugs to the spec under the hood too. I have changed the fuel filter withing the last 3 months (along with the fuel pump).

I change gas stations all the time - but it's been doing this for 3-4 tanks now.

I have all the DTC info and Freeze frame data, but not with me now...

I just inspected the coil and it has some severe discoloration around the housing near the "iron bar" that wraps around it. Almost like it's been arcing to ground??? Too bad I cannot watch it while I'm driving! Could it be a bad coil?

Aha! This is have heard of before!

Yes, it is probably your beast! Replace the coil and try that out.

The arcing can definitely be the problem.

[Jeremy-WI]

I would try a new distributor cap with brass contacts

[Fireplug]

A very easy test is to take a small spray bottle with water in it and MIST the entire system while looking for any arcs. Also look at the ing wires and see if there are any white patches spots on the wires . That is a tale tale sign that they are arcing to ground.
Fireplug

[Fireplug]

Dannk
yep
po440 and put that stupid evap machine and do all the stupid tests and then get paid .3 time for and hours work and then find a loose gas cap.
I just lived for a evap code.
Fireplug

[BlazerLT]

From past reading, most people with this problaem have the arcing coil pack.

Best to look at it at night with no lights on and look for the blue light from the arcing.

[Fireplug]

Good point.
I found what works nice is to take a mixture of washer fluid and water and mist it on .Then I day The mixture was too much washer fluid and it flashed (can we yell FIRE) It did no damage to the car because it was just a little puff. I did find the problem and had to change my shorts after I was done.

[Dannk]

I replaced the Coil Pack and it seemed to fix the problem. $32.50 aint bad! It actually runs a lot better now too! It was not real easy, but I probably saved $100-$250 by doing it myself. You have to remove a bracket to remove a bracket to remove a bracket the coil is fastened to. Thanks GM for designing POP RIVETS into the coil pack bracket assembly....freekin interns.

[BlazerLT]

Good to see you got it fixed.

[Dannk]

Well, I was wrong - again. A few days after my last reply, it started missing out again. I have been putting up with it but now I have to get it fixed (I need a dependable car for the winter). For review, I have replaced the following within the last 2 months:

1. spark plugs
2. cap and rotor
3. plug wires
4. coil pack

When it's real bad the Service Engine Soon light will come on with a code of cylinder misfire detected (random) P0300. It will go off on it's own. It really only misfires under normal driving conditions. When I mash down the gas it seems to run very strong. It really feels like crossfiring in the distributor BUT it's a brand new cap???

PLEASE HELP!!

[BlazerLT]

Sounds like you should do some fuel system diagnosis.

Fuel Filter
Fuel Pressure test etc...