I have had a misfire problem and can not figure it out. My 3rd cylinder is misfiring(P0303) and I have already replaced the spark plugs and my coil. Havent changed the plugs yet but the mitsubishi dealership said the plugs look good. I was going to buy new ones to see if it would fix the problem.

Has anyone came across this or have any suggestions? I would reallt appreciate it.

It started after we tuned and dynoed it.

I know there are other forums out there about this but some jump back and forth about other stuff.

 

it just suddenly happenned on one nice day or there were some untold events prior to it?

 

We tuned, it dynoed, and that when it started to happen. After the dyno

 

At what rpm does it start to misfire? At higher rpms my turbo miata would misfire & break up hardcore... new plugs fixed it. Pull the plugs & see what they look like.

 

try load back the old map prior the tune to see if the problem is caused by the tune. This help eliminating other variables to easy on finding the cause. But in your case, it's very likely that's the tune as you mentioned.

I got p0300 after a tune as well and found that my idle and low-load cells were too much of ignition. Lowered it a bit and the problem went away.

 

Put some BR8ES in there if you run higher boost. Otherwise BR7ES. That should fix it.

 

I am running BPR7es at the moment

 

I would say at least bout 4k rpm. It only does it when I push more than 50% of the throttle

 

A mechanic told me that P0303 is not just a random misfire but it is coming directly from cylinder 3 which means it could be the spark, tune, compression or fuel

 

A bad coil would cause a misfire in both 2 and 3. Plus there isn't much plug wire going to 3. So, my guess would be the injector.

 

What would cause a loss of compression? I think it may be either compression or fuel

 

im having this same issue. did you figure yours out? only my problem occured after several hundred miles of driving prior to tune. mine wont let me past 2500 rpm.

im leaning towards a fuel issue myself.