'04 Lightning not running right under boost

[WA 2 FST]

My son's truck ... runs fine at cruise, but under decent throttle it starts to spit and sputter... unburned fuel out exhaust. Coil pack, right? Maybe plug or two... but I would think it would run poorly also at low-speed or idle. Thoughts are welcome.

[BigBobsL]

Yes, most likely cause is bad coil or plug. Losing a single cylinder makes the motor run real poor since the computer adjusts fuel (richens) on that entire bank to compensate for the extra O2. Their is a good tool for quickly telling you whether it it is a plug or coil and which cylinder for <$100. Looks like a small "flyswatter" that you play on top each COP coil (one at a time)with motor loaded. Best way to load is with someone lightly power braking the motor to make the motor "miss a little>

[WA 2 FST]

I just went and drove it. Under light or moderate throttle input it is fine. Would never know there is an issue. But downshift it and it bucks and surges...then intermittently it will clean up and pull. It is not throwing a MIL, but I pulled the codes. I'm getting a 403 and 406... EGR circuit malfunctions, but the EGR is removed on this truck and Terry tuned it out of the equation, so I do not believe that is related. Motor runs fine at everything but WOT....even gradually building rpm, seems ok.

[dboat]

any chance its a fuel filter?

[WA 2 FST]

I thought about that, but it has been only 6k miles since it was replaced. It's at the dealer now. I really do not have time to mess with it. My other thought is a faulty TPS sensor. It really feels like something I experienced when there is an ignition problem under load. It's not a sluggish acceleration issue, its a misfire-type issue. I am just surprised it is only at WOT and not at part-throttle acceleration, though. Idle and part-throttle are perfect.

[WA 2 FST]

They say it is the NGK's blowing out under boost and the COP's are fine. They want to install OEM plugs. I took them some new NGK's gapped down to .030" (right now they are .035"). I run these plugs in both my TT Z06 and CTSV. They are good plugs. However, the 6# pulley is probably taking a toll on them, so my son and I will reinstall the 4# pulley once I get it back. Never had issues with the NGK's with the 4# pulley and 20k miles on the plugs. These NGK's only have 6k miles...so it must be the additional boost creating the issue.

[L8 APEX]

It is probably spark related. If you can simulate it by power braking it in the driveway then one brave soul can unplug the coil packs one by one until you find the dead one. if you have driven through heavy rains lately the rear coil packs could have moisture in the boots. The boots shrink over time and get condensation in them. You can also Google Ford coil pack test and it will show you how to check them with an ohm meter. The plug hold up to everything but detonation. I have never had misfire or blowout with anything under a 40 gap, out of the box is 36. When spraying over 75 I have closed them to 34. 15 pounds from an Eaton should not affect a plug unless someone gapped them very wide 44 or more.
Start with power braking, check fuel pressure 35 at idle and 55 at WOT, check coil packs and plugs.
NGK is a great plug period.

When a fuel pump lays down or the tubing in the tank splits the truck will lay down as soon as you tip into the boost.

[WA 2 FST]

Thanks Terry... as always you are a wealth of info... wish you still lived in DFW. For now, the plugs are gapped at .030 and the truck runs fine again. So it was a spark-related issue (getting blown out under heavy boost... part-throttle, tip-in boost was fine), but I still think we could have some weak coil packs. Dealer diagnostics said 1,2,8 were giving us problems, and they checked the coil packs and reported that they are ok. We could not simulate the issue with powerbraking.

If I ever have to get into the tank, its going to be way over my head, the twin big pumps you installed are still in the truck and about 8yrs old, but only about 20k miles. They should be good.

I completely agree about the NGK plugs, so I'm glad we stuck with them... still considering swapping the 4# lower back on for the cooler weather, although detonation was not the issue, I don't believe.