ford 4.2 motor misfire

[mike14837]

I have a 2001 f150 2 wheel drive 5 speed with the 4.2 litre. I have had a skip or misfire for about a year now, it hasn,t got worst or better. It also seems to be at lower rpm's. I have changed the plugs, wires and coil pack and didnt help, any ideas would be great thanks

[tempfixit]

Welcome to AF.

Have you checked for any codes?

[mike14837]

Yes i have and there is none.

[discnik]

Have you tried doing a manifold vacuum test ? Should be 19 - 21 in. HG @ idle.
You could have a small vacuum leak.

Have you performed a compression test on the engine ?
I have seen instances where carbon build-up on the valve lip can cause a misfire.

Have you tried running Sea Foam through the engine ?
Some people swear by this for cleaning up carbon deposits.

Try checking and cleaning the EGR and IAC valve

Do a fuel pressure test , should be 35 - 55 psi.

Just some starting points.

[mike14837]

thank you for the ideas i haven't tried any of them. ill let you know how i make out after i do some of your ideas thanks again

[caribbeankruzer]

How can I find how to run sea foam through an engine. Where do you buy the foam at.