Running Problems

[Torqued2Spec]

I have a 2003 Silverado 2500HD 8.1L with about 72,000 miles on it.

 

I was running low on fuel a couple days back so I went to a gas station I don't regularly go to. After I put $65 in, the truck started running like crap. I tried to put in Dry Gas, Gas-Line Antifreeze/Dewaterizer, and Fuel Injector Cleaner and the problem still persists. I've got gas twice since then and it is slowly getting better, but still is running bad.

 

What It Does:

1) The truck has a real rough idle sometimes, not all the time. One moment it will run well, the next it will run as if the motor has been cammed. The RPMs don't move though, it stays right around 600-700 RPM idle.

2) Every once in a while the check engine light will flash a few times and then go away for a period of time and then come back, flash a couple times, then go away.

3) The truck is very sluggish at times, but at times will run like nothing is wrong. Higher RPMs and speeds seem to diminish the problem than it runs at lower speeds and RPMs.

 

I know a flashing CEL is bad and shouldn't be driven but it is my only running vehicle right now and I need it to commute. Considering the CEL only flashes about five times during an hour drive and then goes away should I stop driving it or will it be fine?

 

I don't know if maybe the gas station I went to was low on gas, or had water in their gas, or anything but it was running fine before I went there.

 

I don't want to play parts darts with the truck if the problem will just go away after a few more fill ups.

 

Any insite would be greatly appreciated.

 

Thanks in advance

~Torque~

[alvocado]

The CEL will go out once the computer completes a scan cycle and doens't detect a problem. The fact that your light is intermittant points to a failing but not failed component. You may have a bad sensor. If you're getting a dash light, you should have an error code stored even if the light goes off. Get it scanned at an Autozone or Advance Auto as a first step; the error code may point you in the right direction.

[Torqued2Spec]

Went to my buddy after work that has a scan tool and it came up with three codes. Two were the same code.

 

The first code was P0101 - MAF/VAF A Circuit Range/Performance

The second/third code was P0306 - Cylinder 6 Misfire

 

I'm assuming that the misfire is due to a bad coil because I know Big Blocks have a reputation for having coils go in really cold weather (it was -1 degress). It's not the catalytic converter because I put a heat gun on the front of the cat and the rear of the cat and they both were within variance.

 

Any thoughts you guys have would be appreciated.

~Torque~

[Torqued2Spec]

Okay, update. What I changed and how the problem got fixed. I don't like how when people solve a problem, they forget to post what it was that they fixed, so most forums in turn don't help at all.

 

What I Did:

1) Hooked up an even better scan tool this time when I had some free time and it showed that Cylinder 5,6 were misfiring. I believe that Cylinder 5 was being overworked because Cylinder 6 was missing. I came to the conclusion that the truck has been doing this for a while, just hardly noticable. I retrieved data from the scan tool that showed Cylinder 6 had misfired 66,823 times.

 

2) Decided to do a compression test just to make sure valves and everything internally was decent. Everything came back within specs.

 

3) Replaced the coil and spark plug and the truck is running like a top. Scan tool is reading no misses from any cylinders. The MAF/VAF Range DTC (P0101) reading could have been an old code or was in due fact of the misfiring cylinder. After replacing the coil and plug the MAF/VAF Range code went away and has not indicated coming back.

 

Culprit Parts:

1) Cylinder 6 coil was bad internally.

2) Spark Plug 6 was bad (foiled) due to all the misfires.