97 f-150 4.6L
ok if i use only 1/4 to 1/2 throttle every now and then my truck will surge like a misfire but only 1 or 2 times then its fine. and sometimes if its at 40 in O/D and i give it a lil bit of gas it will make that same surgeing feeling but i look at the tach and the RPM's arent moving at all? What could be making my truck do this...dirty fuel injector? bc i noticed one day when i started it that black smoke shot out of my driver side muffler *i have true duals* so im thinking its somthing on the driver side. Any ideas? Thanks guys

 

No one really? it started after i had open-cutouts one day and i left it in 1st a lil to long and then i herd like 1-2 misfires and i let off the gas and put it into D ever since then every now and then ill get a lil misfire...could i have done somthing to my plugs/ injectors keeeping it at high RPM so long?

 

I'll take a guess, maybe a burnt exhaust valve First I would check the coil packs before jumping to any other conclusions.

 

coil packs are pretty new they only have about 6 months on them. Doesnt the exhaust valve always get burnt? So having the engine at redline for 15 seconds wouldnt hurt the spark plugs or anything?

 

I do believe I'd do a compression test and leakdown on the left bank at least
The way you descibe your driving habits, you are a little hard on that truck.

 

the cut-outs were open and i was going under a bridge and i left it in 1st a lil to long most of them time the RPM's never go over 3,000 unless the cut-outs are open or someone makes me mad. Yeah i admit ive driven the crap outta this truck but it still runs. I think i still have the compression tester. I know i sounded kinda jokeing about the burnt valve but i really dont know what that means? what does it mean to burn a valve?

Thanks guys

 

During the compresion cycle the valves are closed. Sometimes something such as carbon or other deposits can keep it from closing completly.
The the detionation begins the expanding explosion can creep past the valve and evnetually burn the edges of it where it will no longer contain the compression

 

Go here, might help:
http://www.fordf150.net/howto/diagnoseengine.php

 

if it was a burnt valve wouldnt it happen alllll the time? Some days my truck doesnt even do it at all. It only does it every now and then. Thanks guys.

 

You might want to look into the tranny.

Regards

Jean Marc Chartier

 

i don't know anything about the tranny....Thats were the magic happens to send power to the rear wheels.... The U-Joints are fine i had my buddy check them the other day.

 

At 40 mph, you shouldn't be in OD w/3.55's.

 

at 35mph my RPMs are at 2,100 at 40MPH my RPMs are at 1,100 RPMs i can feel it shift into OD at 40.

 

I'm surprised, but maybe it's a 4r70w thing or just a 4.6L thing. I would think it would shift at a higher speed than the 5.4L because of the power band. ??

I could be wrong, but that makes sense to me.

 

Thats how its always shifted. if i go half to 3/4 Throttle frist shift is at 35MPH then if i let off around 40 it will kick into O/D. But if i do only 1/4 thorttle it shifts at 20/ 35/ 40 for OD. i donno just how its always been. Any other ideas on what could be causeing this? Because wouldnt a Burnt valve happen all the time??