Misfire at high RPM's

Truck was running great, after a few hundred miles I cleared all codes and was heading for the inspection station when my friend the CEL came on. I had noticed what felt like a miss around 3000 RPM on the highway but it was running so well otherwise that I figured I'd see if it just got better. Went home, shows a cylinder 4 misfire. I immediately realized that that was where my bad injector had resided.
I swear it didn't look that dirty at the time!!! I did dry the fuel pool before reassembly.
Anyway, that code didn't show up for a while and the engine wasn't missing either.
But, I thought that maybe I should pull the plug, I had put 500 or so miles on the car trying to figure it out. Then I thought that I should check my gap, but it was perfect at .060. Couldn't see a cracked insulator.
BUT, 2 things,
1) the plug has carbon on one side, clean on the other. About 140 degrees.Plug has the 500 miles on it

2) it's the wrong plug, I think. It calls for a AC 41-932 but I bought 41-993. At least this one is. Guess I should start pulling plugs. I have a bit of Dupuytren's Contracture going on and doing so is some
what ......uncomfortable. And my strength isn't the best. So I'll do a few a day I guess.
My question, should I just clean the plug as best as I can and put it back? Get the right plug? Is it an acceptable plug anyway. Did I cook a valve (no oilly smoke BTW nor noticeable oil loss) ? Can't see a rich condition doing that but I'm not that smart.

41-993 is acceptable, unless it is from amazon or ebay chineese. I switched to NGK because of counterfit ACDelco. Cap/wires suspect if 2+ years. Add a can of Berrymans to gas tank. Was Spider ever changed?What codes show up?

Check for vacuum leaks. Inspect inside of Distributor. Rust, vent plugged, wires rubbing, carbon tracking, burn thru. Fuel pressure checks, compression test.

exp500 said:

41-993 is acceptable, unless it is from amazon or ebay chineese. I switched to NGK because of counterfit ACDelco. Cap/wires suspect if 2+ years. Add a can of Berrymans to gas tank. Was Spider ever changed?What codes show up?

Click to expand...

Got the plugs from Autozone
Wires replaced 500 miles ago, Delco,
Rotor replaced 500 miles ago, Delco
Cap replaced 200 miles ago My son broke the new delco cap,Couldn't find a Delco got a BWD
Spider replaced 200 miles ago Delco

Had to clear codes so had to drive until the went away, which they did. Then this P0304 showed up.

exp500 said:

Check for vacuum leaks. Inspect inside of Distributor. Rust, vent plugged, wires rubbing, carbon tracking, burn thru. Fuel pressure checks, compression test.

Click to expand...

Evap code last to clear
Distributer looks good and clean, vent not plugged
no tracking
Fuel pressure correct and steady, new fuel filter.

One issue I have is the wires sometimes touch one another. Cannot get them in all the looms, several of which are broken

Still have the old cap?

Swap the plug with another cylinder, see if the code follows. Repeat with a similar length wire since that’s all free.

Exp500 is correct - that part number plug superseded the original one.

I forget - did you replace the intake gaskets as well? Any coolant loss or leaks? Check the front and rear block/intake interface and in the small valley between the valve cover and intake.


Sent from my iPhone using Tapatalk

I would still do a complete compression test with all plugs removed. You want to know the engine itself is sound before you assume it is. Likely no problem but I like to KNOW.

east302 said:

Still have the old cap?

Swap the plug with another cylinder, see if the code follows. Repeat with a similar length wire since that’s all free.

Exp500 is correct - that part number plug superseded the original one.

I forget - did you replace the intake gaskets as well? Any coolant loss or leaks? Check the front and rear block/intake interface and in the small valley between the valve cover and intake.


Sent from my iPhone using Tapatalk

Click to expand...

re: the old cap.
No, my youngest son was visiting and I opted to have a "father/son work on the truck moment". Let him put the cap back on, next thing I knew he over tightened the screw and broke the "ear" off the cap. He has long maintained that he doesn't have the hands of a surgeon, I am inclined to agree. Still, had a great few hours with him doing it, certainly worth a distributer cap!


Plug swapping sounds good, if it doesn't follow then I'll swap wires.
I'm glad, I was concerned about that being the wrong plugs
Yes, I replaced the plenum gasket, the spider gasket, and the throttle body gasket. I did spray all areas liberally with carb cleaner, got nothing though.
No coolant leaks, I really thought I was getting too much water from the exhaust to be just condensation so I marked my expansion tank. It has remained consistent. On the plus side, although I am still getting condensate out the pipe, there are noticeably fewer carbon particles in it! I also sopped some up with filter paper and compared it to what I got out of the expansion tank, looks like just water.

It looks like you don't have a code reader. That is a Must Have! BAFX has a decent cell phone bluetooth unit.
And Amazon usually has wire loom clips. RockAuto sometimes.

Donf said:

Evap code last to clear
Distributer looks good and clean, vent not plugged
no tracking
Fuel pressure correct and steady, new fuel filter.

One issue I have is the wires sometimes touch one another. Cannot get them in all the looms, several of which are broken

Click to expand...

based on the age the fuel injectors are dirty put some lucas fuel injector cleaner 5 oz per gallon of fuel will do the job