Misfire Issue

[lilpeep3]

So I have a 98 ford explorer sport that has had a bad misfire issue for awhile and cannot find out why. I have replaced all plugs and wires,coil pack and fuel filter I even replaced a bad injector on cylinder 3. worked good for about a month and started acting up again but when i unplug the negative end of the battery and let it sit and plug it back in it goes away for a little bit???

Would really like to get this fixed

 

[koda2000]

Fuel injector wiring problem? PCM problem? Put a noid on the #3 fuel injector and see if it's firing while you're experiencing the misfire.

 

[J_C]

I'm wondering if you might have a minor vacuum leak whether it be hose or manifold gasket or whatever, then disconnecting the battery just makes it run in open loop, richer fuel for a while.

See if an OBDII code scanner can pull a code that isolates where it's misfiring or any other trouble codes.

 

[fast_dave]

lilpeep3,

Welcome to the forum.

To help us better help you, what V6 4.0 Liter Engine does your Ex Sport have?

*Is it the SOHC or the OHV?

*Another good piece of info to provide is how many miles are on your Ex?

Note 1: Like J_C suggested, have you hoooked up an OBD2 Scanner and seen if there are any codes stored in your computer?

Note 2: koda2000 also had a good suggestion.
I'll add to what he wrote, not knowing what was the original problem with the #3 injector, maybe another injector is beginning/starting to exhibit the same issue? Most Fuel Injection problems are associated with dirt (non-frequent fuel filter changes) and water in the gas. I believe (from memory) there is a fine mesh screen on the top of the fuel injectors, maybe one (or more) are showing signs of being clogged?

With all that said, given the parts that you have listed that you have already replaced, and if your engine is an OHV, a common "problem area " (of this otherwise very reliable engine) that is associated with rough running/load problems/perceived misfiring & hesitating under load is vacuum leaking upper intake plenum gaskets.

In the picture BELOW, it's the (3) Black Rubber Gaskets that compress over time that require replacing. They're under engineered for their job, and frequently require replacement around 70,000 Miles.

 

[lilpeep3]

Sorry about the long reply. But it is a 4.0 dont know if its ohv or not im kinda new to all this. I also know when i have gotten it scanned it either says that an 02 sensor is bad or cylinder3 is missing. I had a compression check done to it and i have great compression. Also has 139k miles

 

[lilpeep3]

Whatever the E.F.I engine is thats what i got

 

[Tech By Trade]

98 had both an overhead valve 4.0l and a single overhead camshaft 4.0. both are injection. Which do you have?

 

[koda2000]

What is the 8th character of your VIN number? an E or an X?

 

[J_C]

Assuming the engine still has the removable plastic shroud (cover) over the top, if it's SOHC that is stamped in big letters onto it.