MXRIDER55

So I have developed a misfire on cylinder #5, after I had the trans rebuilt. I have swapped the coils and cylinder 5 is still the issue. I also put in a new plug and and new injector. I'm at a loss as to what to try next. It shakes at idle and lower rpms, but cleans out at high rpm which was why I was thinking fuel was the issue. I just did the fuel filter and ran some fuel system cleaner through it as well. i haven't driven the truck after putting in the injector just started at run it in the garage. BTW its a 2000 with a 4.6L. Any ideas?

akdoggie

What did the old plug look like? How many miles on the engine? If you swapped the coils and nothing changed, I'd assume plug first. You did that. After the plug, them maybe a compression test to see if you have a leaking cylinder or some carbon under the valve. Seems like maybe the next step.

You could have a flat lobe on the cam, but doubtful. Do you have one of the small cameras for the computers that is a snake? Ebay has them with up to 15ft of lead, and it has a built in light. I bought mine for $26 with 15' lead. You can look right in the plug hole to see the inside of the cylinder. It's USB powered. I bought one for St's & Gn's and the damn thing works great. I can look into most cylinders and record the look of everything. Works great. Anyways, just a thought on doing the compression test next. Good luck and keep us posted..

MXRIDER55

the old plug looked at little discolored, possibly lean i have a hard time reading these plugs but i'll try and get a picture of the plug. the motor has 150K on it. i'm thinking about just driving with 91 premium till it throws a code.
Could the weather affect it? it just got cold here (went from 70-80's to about 50's in about three days) so could condensation in the gas tank cause it to miss?

Frank_Ford

I have seen problems as you described when you are getting coolant in the plug hole or when the hole is full of oil, grease, dirt ect. Also when oil is leaking from the valve cover gasket and getting in the plug socket. It doesn't cost anything to clean the plug socket so you are sure of getting a good seal between the cylinder head and plug. Also, if the threads in the head are worn and the plug is loose you can be loosing compression and getting a misfire. If the plug threads are worn, you can try a little thread locker on the plug threads so you get a good seal. You should also use Motorcraft plugs. Hope this helps.

jday47

Could be coolant getting in cylinder or maybe a bent or burnt valve, has same issue with an s10 only missed at low rpm ignition system was good. Put air in the cylinder and checked for leaks and it deff had a leak, pulled the head and it had a bent intake valve

Jbrew

I'd compression test it real quick, sounds like you lost a follower, - easy fix.

MXRIDER55

I think there is a loss in the plug threads as it has spit a plug in this cylinder. Compression test is the next thing im going to do as soon as i can get my hand on one.

Jbrew

Then you will need to Time Sert it. I know someone who rents those. H'ell send you what you need to do it. No head removal required. Then send it back.

Other than that, you may get away with taping the threads on the C-Tester

MXRIDER55

Well i'd thought i'd give an update on my truck.
I finally got time to get a compression tester and it read 90psi, on the two times that i tried it. one other thing that i noticed is that there was carbon build up in the plug threads, and also on the tester when i used it. It just makes me think it is a loss through the plugs. I've looked it the time sert a little bit, but not much.

Jbrew

Great post, very true. Specially about the thread locker. IF you know which to use. - Not Permatex lol..

You just don't hear thread locker mentioned anymore, but it works great with these heads for tapered seat.