I have a 1999 F-150 4.2L with a misfire in #5 cylinder. I have replaced plugs, plug wires and coil pack, checked compression (147 psi) and ran 4 cans of seafoam thru it and still getting misfires on acceleration. It'a a 5 speed and it sounds rough and runs a lil rough as I go thru the first 3 gears, then it runs good as I get up to speed and cruises fine at 80mph.
I'm thinking a bad fuel injector???

Any ideas would be appreciated.

 

First you need to know that the 4,2 uses a waist spark system.
That means the cylinders are paired with another cylinder hanging on each end of it's coil windings.
Try disconnecting the EGR to disable it.
If the trouble goes way, there are two issues involved as the cause.
Good luck.

 

Thanks Blugrass, I will try this in the morning. Could you explain what i might experience? And what the two causes may be.

Thanks

 

The two possible issues from what you described are;
1. The EGR is opening when it should not, under the conditions you describe.
2. The EGR ports in this engine are inside the intake manifold where they likely are nearly all plugged. The one/s left open/unplugged is getting Exhaust feed back making that cylinder misfire.
If the problem stops with EGR disabled you likely have the conditions.
If the EGR is stuck open by itself after being disabled, that's a problem.
You have to carefully differentiate what you see as reactions to this logic testing.

Otherwise it's still an ignition problem your missing.
Good luck.

 

Did you mean to unplug the egr silenoid or to unhook the vacuum hose from the egr valve?

 

I unplugged the silenoid and the got a 0443 code thrown, but it seemed to run better. BUT still misfired. Not for sure if I unplugged the right thing.

 

So I plugged the solenoid back in and unplugged the egr and now it really runs better and idles much quieter and only shows a 401 code. Is it ok to keep this disabled? or what would be the action to resolve the problem and how costly would that be?

Thanks for the fix!

 

If this results in a definite change then it proves the issue with the internal EGR ports.
It is ok to run without EGR until inspection time comes.
The thing is in a normal trouble free system, EGR helps with fuel mileage but at this point you may not notice any difference.
Good luck.