Running badly.

[jclose11]

As per my post in another section Can someone look at my tune and see if it has anything to do with it.
I did a complete tune up on the 1990 mustang and its developed a miss, breaking up when going about 2000 rpm and idles rough. I double and triple checked my firing order and timing and both are good. My question is has anyone ever gapped a spark plug too much and had problems. I've messed with plug gap before in my s10 with a 350 and never had any issues. Now this car has gt40p heads ,engine is a 302 and I'm running autolite 764 plugs in it which old owner had in it. I gapped them at .054like I have on my other mustangs. Did a google search and search on here people are all over the place with the gap with these heads and plugs. Anyone run a setup like this or have any suggestions , Going to pull out whatever hair I have left. I have a ms2 ecu not sure if that effected the tune .

Did plugs ,wires ,cap and rotor. double checked plugs yesterday and gaps are what I set them at.
I just put another set of new plugs in and same result.

 

[a91what]

Let's start from the beginning. When did the ECU go in and did you have it fully tuned properly before this issue occured?

That gap is fairly wide if the coil has become weak, what color tfi are you running.
My suggestion is to close the gap down to 44 and see if it clears up.

 

[jclose11]

Let's start from the beginning. When did the ECU go in and did you have it fully tuned properly before this issue occured?

That gap is fairly wide if the coil has become weak, what color tfi are you running.
My suggestion is to close the gap down to 44 and see if it clears up.

I just installed 8 new plugs and they came gapped at .044 which I left but checked to make sure they were at that gap. No change.
Ecu went in 4 weeks ago or so, been driving it since and no real problems. Properly tuned no. Just doing auto tune.

 

[Foxbodyguy49]

So the miss started after the tune up? If so check the plug wires could have gotten a bad one