Miss at idle

[Petey]

My 4.2 has developed a miss. No SEL light

It is random and not all the time, but more pronounced when its in gear and warm. It is either not noticeable or non existence at all when at any rpm higher than idle.

Coil going bad or throttle body needs cleaning.

 

[budwich]

get a scanner / data logger and check the "miss counts" to find out how bad and which / all cylinders involved and go from there.

 

[Mektek]

I had two causes for a miss. A continuous miss was caused by a bad coil. A random miss was caused by a cracked rubber elbow to the fuel pressure regulator and a rubber plug on the intake plenum. So check for vacuum leaks.

 

[Petey]

My scanner does not have a miss fire counter.

But today pulling out into traffic it had no power and was running like turds, then like started blinking whenever I goosed it. It quickly cleared up and went back to its random miss at idle, no light.

Pulled a P0301 code, I guess now I'm looking into coil or injector on 1.

 

[Maverick6587]

If the CEL started blinking that is a random misfire code P0300. It might still be pending or in history. I would buy a cheap $12 scanner off of Amazon and use the Torque app (if you have an Android device) to see where you're misfiring at, like budwich suggested.

Otherwise you're just guessing and throwing money at it. Which is fine if you haven't changed the spark plugs in 100k miles and your spark plugs are ACDelco. Only use ACDelco 41-103 spark plugs. They'll last you 100k miles.

I had a "misfire" feel awhile back and it ended up being a cracked hose causing a vacuum leak, just like Mektek.

 

[Petey]

If the CEL started blinking that is a random misfire code P0300. It might still be pending or in history. I would buy a cheap $12 scanner off of Amazon and use the Torque app (if you have an Android device) to see where you're misfiring at, like budwich suggested.

Otherwise you're just guessing and throwing money at it. Which is fine if you haven't changed the spark plugs in 100k miles and your spark plugs are ACDelco. Only use ACDelco 41-103 spark plugs. They'll last you 100k miles.

I had a "misfire" feel awhile back and it ended up being a cracked hose causing a vacuum leak, just like Mektek.

I surly do not want to shot the parts cannon at it.

New AC 41-103 plugs between 95-100K

SES light was blinking on hard acceleration but then stopped and it went back to its random miss at idle. Only code was a pending P0301. Live data is showing Short term FT between -2 and +2 with long term FT around the opposite for an avg of 0 at idle when its missing the avg of 2 is in + numbers if I recall.


I do have the Autel ap200 just have not gotten the GM specific software yet for it. I couldn't figure out how to get the freeze frame data from the Autel and didn't have access to my other scanner before the pending 301 cleared.

 

[budwich]

if you have access to an android tablet, get the torque app for $5 and a bluetooth interface another $10-20. From there you can look at the miss data for each cylinder to check for patterns. the 301 code gives a "start" as it indicates a threshold has been crossed but doesn't tell you about others that might exist. Further, continual misses may take out you cat in time as the fuel dumps into the exhaust. of course, the other method is to swap out the one that is currently indicating difficulty and go from there to see if there is any improvement.

 

[Petey]

Well I cured the symptoms but now to fix the initial problem....

I activated the GM software for my scanner and found the misses limited to cyl 1.

Cylinder 1 and 2 plug hole had water in them, the rest were dry. Dried them out and let it idle for 10 min while I played around with the Autel and there were no misses. Now to figure out the water issue.

Did the 06's still have problems with the hood gasket?

 

[christo829]

Thought they'd fixed the gasket issue by 2006 already. Usually, the leak would drop water in to #4 though. Glad you were able to narrow it down and dry it out! I can't remember if the hood gasket could be modified like the door weather strip could. When I'm back out there tomorrow fixing the rodent chewed wiring that has me shut down at the moment, I'll check my truck and see. You might be able to slide some smaller diameter weather strip in or alongside the existing gasket and cut down on the water getting on to the engine.

Oh...and did you use dielectric grease on the plug boots when you replaced the plugs? That can help seal the boots from water infiltration.

Cheers-

Chris

 

[mrrsm]

ATTN: Mods... For @christo829 ... A Small h/j...

Chris... This is THE BEST Automotive Quality High Temp Wire Bundle around for your Repair:

Amazon.com: High Temp GXL Cross-Link XLPE Stranded Wire, 14 AWG, GA, Gauge, SAE J1128, Automotive, Motorcycle, Electrical, 10' Each of 12 Solid Colors (120' Total): Automotive

Buy High Temp GXL Cross-Link XLPE Stranded Wire, 14 AWG, GA, Gauge, SAE J1128, Automotive, Motorcycle, Electrical, 10' Each of 12 Solid Colors (120' Total): Wiring Harnesses - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[christo829]

Took a closer look at my 04's cowl seal while I was soldering wires. There is a channel in the leading edge that you could pull some additional tubing of a slightly smaller diameter through, or you could lift up the edge of the seal and put some of that narrow, flat door weatherstrip down along the metal lip the seal sits on.
Either one of those options would make the seal seat more firmly against the hood and hopefully cut down on water getting in to your engine.

Good Luck!

Chris