very urgent mountaineer misfire!!

[monkeydude3]

Hello all~
very urgent here. My girlfriend's mom has a 2001 mercury mountaineer, v8 awd automatic. Only 45000 miles on it.

the problem is a misfire. We got a check engine, p304 which means cylinder #4 is misfiring. There is also a funny smell emitting from the mid to front of the truck that smells like very hot metal. It is not a trans problem, it misfirse no matter if it's in neutral or gear. Primarily though the misfire is very very noticable under load.

I put in a new set of spark plugs which seemed to be needed to be done anyway, and some octane boost and fresh premium gas. No change. We are thinking it is an injector sticking. Friday it will be computer diagnostic tested to determine what will be needed. Any ideas please let me know. this is my g/f mom's daily driver that needs to be working right. Thanks!

George

 

[falls guy]

Three things cause a misfire. Compression, fuel or spark problems. Burnt wire perhaps? If it has spark, do a compression test. If that checks out, it must be an injector problem. Either it is clogged, or it isn't getting a signal from the computor. Try listening or feeling for an injector pulse, if you feel one, and the compression and spark check out, the injector is most likely clogged.
Good luck
Peace

 

[monkeydude3]

Okay thanks. it's no longer in my posession, as she took it home. I will definitely take those factors into account. As far as I know the compression is good. Has had regular maintenance (ME! ). I am very leaning towards either a clogged or shorted injector. Ithink one injector may be heating up and causing the smell and problems. I will report back on friday, thanks for the help.

George

 

[section525]

I'd check the coil packs. I've had a couple go out on my 5.0s. I also have 150k on my stock injectors with no problems. Did you change the wires along with the plugs?

 

[Glacier991]

I'm gonna guess electrical not fuel. Why? That smell you smell is probably the CAT getting super hot from the unburned fuel charge from CYL #4.

 

[410Fortune]

Is the spark plug wet iwth fuel after it runs for a few?
Have you checked for spark at #4?

 

[CDW6212R]

Good thoughts Chris and 410(name?). How often has fuel injector cleaner been used?

A quick poor man's method of comparing fuel injectors is to place a long screwdriver onto injectors, and your ear. Be careful, use a long screwdriver, and rest your ear against it. The sound of that injector should be very clear, and they should all sound alike.

Swap a couple of the adjacent plug wires, both ends, to see if the missfire moves. My bet is on the plug wires, try Magnecor if it is a keeper.

Of course all of these ideas are in place of an expensive dealer diagnostic. Good luck,
Don