Random misfires only when cold and letting off the gas

[BackInA88]

OK maybe someone else here has seen the same issue and can guide me down the right path?
I am getting random misfires (mainly 6 or 8) only when I lift off the go pedal and the engine is cold, I mean like under 30 degrees cold.
Once the engine warms a little, no more misfires.
A warmer day and no misfires?

New plugs
New wires
Cleaned the MAF
No coolant loss.
Head gaskets replaced about 35K ago at which time the heads were done.

No other codes just the standard misfire codes.

Runs great while accelerating and cruising.
Even getting 13+ MPG in mixed driving.

Steve

 

[adriatic04]

You'll get the "cracked block" answer probably.

 

[BackInA88]

OK so that's it?
Replace the engine?
I did want a 4.6 anyway!


Steve

 

[I HATE PONIES]

If it's temp related I would start by checking the temp sensors.

 

[BackInA88]

So is there an incoming air temp sensor I should check?
Is it built into the MAF?
My coolant temp gauge seems to be working correctly.

Steve

 

[adriatic04]

I would guess something to do with the plug, wires, or coil. When cold something might be loose due to shrinkage or something. Maybe a weak spark, loose connection at coil, bad plug?

 

[kyleduncan]

My guess would be coils. My 01 had similar misfire issues. Coils fixed them. Getting the damn things out isn't too much fun though. If you go that route, I suggest a jack under the tranny. Remove the nuts on the tranny mounts so you can jack it up or down to gain the room where you need it.

 

[BackInA88]

So yours was only giving you the misfires when cold?
Than running fine after it warmed up?

I was thinking coils as well as I had to jack the engine up pretty high to replace the motor mounts at the begining of last summer.
I am fearing I cracked them on the firewall. I kept checking while I was jacking up the motor and never saw them hit but who knows?

My guess would be coils. My 01 had similar misfire issues. Coils fixed them. Getting the damn things out isn't too much fun though. If you go that route, I suggest a jack under the tranny. Remove the nuts on the tranny mounts so you can jack it up or down to gain the room where you need it.

 

[kyleduncan]

After checking out the coil pack wiring diagram, I guess my recollection was skewed. I was thinking that 6 and 8 were on the same coil. It appears they are not. My misfires were had nothing to do with being on or off the gas. But they did seem to clear up a bit after the engine warmed up. If it were me, and I changed the plugs and wires already. I would definitely try the coils next.