I changed the fuel filter and spark plugs today and it did nothing.

Only thing that I can say is: I was driving home from Lauderdale and stopped at a rest area for gas after driving fine for 2 hours. About 5 minutes after I left the station it started losing power and kind of gradually losing power. The only way to keep my speed up is to accelerate. It only runs smooth if I'm accelerating. If I cruise steady with a set throttle setting it starts to lose power and missfire. Its at a point where I can't drive it, it sounds hoirrible, backfiring and **** and during acceleration it stumbles the whole time on its way up the rpm's. But every once in a while it'll accelerate smooth and normal, than a couple seconds later its horrible again. 90% of the time its bad.

Do coil packs fail slowly or all at once and they're dead????

Maybe a bad tank of gas


.

 

You throwin' a code?
Sounds like a fouled plug or a vac leak or messed up spark plug wire if you ask me. I really don't think that it is a bad coil pack.

FYI: Most of the time on a 346 stock bottom end with stock PCM you will find this kind of problem on #7 coil pack. I have seen it on about 5 occaisions. (I don't know if this would be the same in your case.)

 

No codes, but I think the codes are turned off for misfires.

I changed all the plugs today. The wires look fine. I can see one going bad but the entire engine is missing and running rough. I've left a spark plug wire off by accident once and drove around and it ran and idled great. I noticed when I returned after the test drive when I saw it sitting in my driveway near all my tools

Maybe its an electrical problem???? Can something get fried all of a sudden?

 

I would take in in to your tuner and have him log some data while driving. Probably won't do it while they drive it. Only when you get back home

 

Sounds coinsadental to me. Car runs fine, stop for gas, car runs bad...... I'd be looking for water in the fuel.

 

Check the grounds on the heads, cam sensor, crank sensor.Make sure the wires
aren't pinched , damaged, or loose.

 

Ever find your issue?

 

Unplug one 02 sensor and go drive the car...Do one at a time until eventually both are unplugged in the front. Sounds like a sensor crapped out on you....Soon as it stops the jerking you'll know which one it was that you unplugged.

As long as you are past X amount of throttle the 02 sensors are cut off...They are in use during cruise mode when fuel trimming is necessary for economy. That is if you are still using them for that and not in speed density mode. Reconnect the new ones with dielectric grease to keep moisture out. It really does help.