Help me track down what feels like a misfire.

[Chris_Red_V8]

Under full load/accel, my engine feels like its breaking up. Its not pinging, but you can feel a misfire. Under normal load its ok. Its not air, and I don't think its fuel.

When I got wot in 3rd it really just stutters the whole way up. The problem worsens if I bypass my MSD 6A box, and I just installed fresh plugs gapped at .054" and a new cap/rotor.

Ignition is as follows:
~2year old F150 distributor
MSD 6A box
Taylor Wires (8mm?)
MSD coil
new msd cap/rotor
copper plugs at .054" gap (maybe I need to be at more?)
stocker TFI

A local shop mentioned that I should replace the taylor wires as they've seen a lot of them start to gap internally until they get to the point where there is too much resistance. I hadn't checked continuity and reistence on the wires, but that's on my todo list.

 

[BlownFiveLiter]

I'd pull codes and see if any pop up as a good starting point. You may have some present even if the CEL doesn't illuminate. Do a cylinder balance test while you're at it to see if any particular cylinder is causing the problem. Your .054 gap on the plugs should be good and I wouldn't open them up any more than that. How do all of your plugs look? I also didn't notice any injectors listed in your mods. Still running 19's? You may be going lean under hard acceleration.

 

[divit250r]

This sounds exactly like the problem I had a couple weeks ago, and someone else on the board here had last week. I bet you've got a plug that's cracked somewhere along the porcelain. I had that happen, ran the cylinder balance test three times and got a pass code each time. Turned out the lights in my shop one night and saw a light show from the #1 cyl. Changed the plug (It was snapped right at the base of the porcelain and the spark arced all over instead of actually firing the plug) and all was well again. For what it's worth, I run an MSD too, and I kind of think that it's extra juice allows the plug to fire decently under light / no load conditions but even it can't fix this kind of problem under heavy load.

Good luck!
Scott

 

[Chris_Red_V8]

Checked for lightshow, didn't see anything.

Could it be a loose rocker? My valvetrain is noisy, but doesn't sound like any are out, getting good vacuum, and its idling great (E303 cam, so any vacuum loss would be pretty rough).

I'll pull codes and the plugs next.