The car has been running great*. Last night out with friends, hop on the highway and give the car maybe 1/4-1/3 throttle. As soon as I do the check engine light comes on and the car runs a bit rough and is down on acceleration (not that I am into the throttle at this point). Get to a point where I can stop and pull the cars - code 300, 301, and Random Misfires. So if I remember correctly code 300 is misfire cylinder 1 and 301 is misfire cylinder 5.

When I restart the it seems fine, a couple of revs and it seems like its normal self. When I drive home a couple of hours later the car seems 95%. Although I am now driving like a grandma.

The plugs have maybe 20k miles on them.

The astrix up top is that while the car is running I do suspect a leaking IC that I am in the process of addressing. I popped the hood and did not smell any coolant or see anything amiss.

Any thoughts why I would suddenly throw these codes and what to check? My first thought was the IC leak getting pretty bad but the coolant did not drop noticeable and if there was no smell of coolant.

 

SRT 6 Roasdster, I had the same codes back about six months ago. I was told PO 300 was multiple misfires and 301 thru 306 indicated individual cyclinders. My coupe would run rough under accelleration around 90 mph. I checked with Rob at Needswings. First check your plug wires to see if you have any loose connections. Then check your plugs for fouling. I ended up getting new plugs and magnacor wires and it solved the problem.

 

Thanks for the advise. I was thinking I need new plugs after this but was not thinking about that being the root cause.

Will go check the wires now.

Any idea what the cause of your fouled plugs was?

If it is fouled plugs do people recommend sticking with the standard heat range or 1 step colder. I went with 1 stop colder plugs due to running a 185mm pulley and the very hot summers around here.

 

I just started getting the same missfire codes right after my retune and 181 install. Pulled one of the offending cylinder plugs out and it looks nice and brown. I'm going to try regapping from .039" to .035" see if that stops it.I have 1 step colder iridiums also.

 

Tuna, I gapped my 1 step colder plugs to .035" when I installed them a couple of years ago.... no misfires yet.... (knock on wood)

 

The current plugs are gaped to .035.

Car is running great today - no issues. Did not beat on it but gave it more gas than last night when the misfires developed.

All the wires are tight. I will pull a couple of plugs tomorrow and look at them.

 

I did end up regapping the plugs today went out for a thrashing. No missfire codes and it was only 40F today.