Running Terrible

[dusty20]

Hi, New here, have read several posts but have a problem of my own.

I have a 1996 4.0 Explorer, It has just a hair under 200,000 miles, doesn't drink oil or anything!

I bought this off my uncle and know it was taken care of. It sat for around 4 years and maybe being driven around 1-3 times a year. When i bought it, it ran great, but then began having problems with a rough idle, I started with the general stuff since it had sat for so long.

I changed the fuel filter, spark plugs, recently changed the alt (not related?) and i changed the passenger side upstream O2 sensor also (check engine light came on and said that it was bad.

right nowthe check engine light is coming on and saying that there is a mis fire in cylinder 4, i checked the resistance in the wire and it is around 13,900 Ohm. I put in Autolite platnum plugs in and gapped them to .054.

Right now it will idle at around 600 and it is rough. it will run roughly up until around 3,000 rpm and then it is like a switch is flipped and it has plenty of power and runs great. Once i stop it runs rough again and then does the same thing.

Any help is appreciated, I am stuck!

Thanks,
Dustin

 

[dusty20]

The more i Read it looks like cracked heads are a pretty big problem, I had never heard of this before. I have been losing a little bit of coolant over time but I didn't really think anything of a cracked head. My big question is that if I had a cracked head, wouldn't more than a single cylinder be having problems? That is the only thing that would make sense to me.

I am still thinking I am having a problem with the fuel injector. Is it very common for the platinum coating to get scratched off while gapping the spark plug? I never thought about that when I gapped the plugs with the keychain style gapper.

Thanks!

 

[2000StreetRod]

Misfire sources

The PCM computes the power of each cylinder and when one is low reports a misfire for that specific cylinder. Typical misfire sources are ignition, fuel injection and compression.

Ignition problems could be due to a bad plug, wire or coil.

Fuel injection problems could be due to a bad injector, pressure regulator, fuel filter or pump. The only problem that is cylinder specific is a bad injector.

Low compression could be due to worn/broken rings, worn or sticking valves, blown head gasket or cracked head.

Since you've changed your fuel filter I suggest that you add fuel injector cleaner to your tank. (I use only Techron).

I would also temporarily swap #4 and #5 plug wires at both ends if they will reach to make sure the wire isn't bad or shorting out.

Then I would pull the plugs and check the compression (make sure the throttle plate is wide open).

My guess is an injector problem. There are lots of things to check before assuming that you have a cracked head.

 

[dusty20]

The PCM computes the power of each cylinder and when one is low reports a misfire for that specific cylinder. Typical misfire sources are ignition, fuel injection and compression.

Ignition problems could be due to a bad plug, wire or coil.

Fuel injection problems could be due to a bad injector, pressure regulator, fuel filter or pump. The only problem that is cylinder specific is a bad injector.

Low compression could be due to worn/broken rings, worn or sticking valves, blown head gasket or cracked head.

Since you've changed your fuel filter I suggest that you add fuel injector cleaner to your tank. (I use only Techron).

I would also temporarily swap #4 and #5 plug wires at both ends if they will reach to make sure the wire isn't bad or shorting out.

Then I would pull the plugs and check the compression (make sure the throttle plate is wide open).

My guess is an injector problem. There are lots of things to check before assuming that you have a cracked head.

Thanks for the reply, I was going to check everything before jumping on the head being cracked, it was just another variable in the equation.

My next steps are pretty much like you said test the compression and check the spark plugs. I checked the wire with the multi meter and it is supposed to be within range but that is a really good point about switching the number 5 and number 4 wires to double check.

I ran a bottle of the gumout fuel injector cleaner through it in the last tank which seemed to help a little, still having problems but not as frequent. I wonder if trying to run a different cleaner through may make a better difference.

If I do have to change out an injector is it alright to just change one and how long does it typically take to do?

Thanks.