jaybee

My 1998 f-150 V8 Triton 4.6 runs rough only when accelerating - in any gear including park and neutral. It is sporadic too. I changed oil and filter, fuel filter, and all spark plugs. After changing the plugs I took it for a ride and the issue seemed to be solved. The next day it was back again. Just put in additive and filled tank. It ran perfect at first acceleration, then rough again on the second. Then smooth again and rough again. It seems to drive and idle perfectly normal. If you step on the gas quickly in park, the engine shakes a bit. If you accelerate slowly, there seems to be no issue. I can't figure this out. Any ideas?

highmilesf150

Same thing my f150 did it was a bad coil. It would idle fine but when under any kinda of load it would miss and "buck" or jerk while accelerating.I bought a set of 8 off ebay for 89.00 and they have been on it for almost a year with no issues. I bet when you changed the plugs and you pulled that coilpack off it could have bridged any crack or gap in the coil where its bad from the pressure you put on it pushing it back on. Assuming you have coil over plug and if im not mistaken I think you do.I would be willing to bet this will fix your problem. Another you could try first thats a little cheaper would be to clean your EGR valve if you have one with some brake cleaner.

jaybee

Thanks for responding Highmiles. No coil over plugs, but the EGR sounds like a great idea. I'll take a look at that.

highmilesf150

If cleaning the EGR dosnt help it could still be a bad coilpack or plug wire whichever you have.

jaybee

Thank You. That makes sense. Since EGR is a cheap fix, I'll look at that first like you said. Okay, I now have 3 things to check out. Excellent! I'll post back tomorrow with some results. Thanks again,
Jaybee

highmilesf150

No problem

jaybee

Well, I took off the EGR Valve. It is black and dirty inside so I cleaned it through the two openings. Since you can't take it apart and I don't have a vacuum to test it, I guess I'll put it back on and see what happens. I didn't see any major clogs so I don't think anything will change. I can't really afford to keep changing parts - I hate this diagnosis stuff! The wires probably have over 100k miles so I guess I should just get some new ones. Any tests anyone can think of that won't cost too much?

jaybee

Okay, could this be the problem? I just discovered a little of the brand new oil I put in the truck pooling on top of the engine near the front spark plug on the passenger side. Looks like I need a new gasket or something. At least I hope that's all it is. Anyway, I pulled that plugs boot and found oil all around the outside of the boot. Could that be causing my engine to run rough at acceleration? Makes sense to me but I would like to know what you think.

Pete37

^^that's definitely a problem

jaybee

Steam cleaned and wiped down the area by the plug really good, thoroughly cleaned the plug boot, inside and out. Drove the truck for a few minutes and it showed no signs of the problem. I didn't see any new oil either - it must take a while to accumulate. I think it's a very slow leak in the manifold cover gasket but I'll know for sure once I see some leakage again. Closing this thread for now as SOLVED. Thanks all.
Jaybee