Confused 4.0

BrokenVet · Aug 28, 2007

Need some help guys. My 1994 Explorer has been acting funny and I am totally confused. My problem is the engine sometimes acts like it is not getting fuel. It runs fine but then all of the sudden it starts running like the fuel is fluctating. If I accelerate, the problem goes away. I primarily happens between 1000-2000 RPM. Below that/Above that there is no fluctuation. I found the vacuum line to the Fuel Pressure Regulator off one time and replaced the rubber boot that hold the line on and it resolved the problem. I am now thinking that the Fuel Pressure Regulator is the culprit but not sure.

Any Suggestions would be sincerely appreciated.

MAKG · Aug 29, 2007

It might be -- measure the fuel pressure at idle and WOT, and make sure it holds vacuum.

Run the self tests and inspect the spark plugs.

BrokenVet · Sep 25, 2007

Still Confused

Fuel Pressure is fine.

I also changed the spark plugs.

Vehicle runs good 95% of the time also, I used an Actron Code Scanner and ran the Key On Engine Off tests and everything fine.

Also did a visual and could find nothing. Still looking though!!

I also ran the Key On Engine Running tests including the WOT test and every time comes up with code 111. System Pass.

I still need help. I will explain the problem a little more.

First when I start in the morning, it idles a little rough but it quickly starts running smooth. It runs excellent until it gets hot (normal temp).

When driving down the road after car is completely warm, between 1000-2000 rpm, the engine seems to miss a little for a few seconds but below/above the 1000-2000 rpm it is great. The miss however is a sporadic thing. Sometimes it does not do it.

I can't really tell but it may be at a point where the transmission is shifting. I originally thought that it may be related to the overdrive however, when I use normal drive without overdrive, the same thing occurs.

When it does, I bump the accelerator and it goes away. It does come back later however. Bear in mind, this is in city traffic, stop and go, stop and go. On the highway, there is no indication of anything, everything is great.

Any help or ideas would be great.

michowski · Sep 25, 2007

how is your timing?

BrokenVet · Sep 26, 2007

timing

Fine

Bob Ayers · Sep 26, 2007

michowski said:
how is your timing?

Timing isn't adjustable on a 4.0L without a tuner.

MAKG · Sep 26, 2007

Yes, but if it's wrong, that might be a bit of a clue.

Normal advance should also be checked for.

Did you INSPECT the old spark plugs?

Bob Ayers · Sep 26, 2007

MAKG said:
Yes, but if it's wrong, that might be a bit of a clue.

Normal advance should also be checked for.

Did you INSPECT the old spark plugs?

When is the last time you saw a PCM throw the timing off?

MAKG · Sep 26, 2007

Usually, you get no advance. But crosstalk between the coils or spark plug wires could give you very wrong timing. It's not just the PCM that determines when spark plugs fire. You could also get incorrect timing from bad inputs, especially cam and crank sensors.

Bob Ayers · Sep 26, 2007

MAKG said:
Usually, you get no advance. But crosstalk between the coils or spark plug wires could give you very wrong timing. It's not just the PCM that determines when spark plugs fire. You could also get incorrect timing from bad inputs, especially cam and crank sensors.

I disagree, sensors normaly fail with a weak or no signal, not an out of phase signal.

Again, when is the last time you have seen a timing problem caused by the PCM or sensor with an EDIS? Even with crossfire, the plug that's supposed to be firing is firing at the correct time.

Bird · Sep 26, 2007

Dirty MAF elements or a bad TPS would cause those symptoms.

Bird

BrokenVet · Sep 26, 2007

Confused still alive

It has also been suggested that it might be an injector since it runs rough in the mornings.

I will check all that has been suggested by you guys and at the same time check the wiring to the injector and clean the contacts.

Maybe adding som techron will clean up the injectors while I check everything else.

What do you guys think about the injectors ??

MAKG · Sep 27, 2007

I take all complaints about injectors with a wheelbarrow of salt.

They are just solenoid valves. They will usually outlast the vehicle. They are not AT ALL temperamental.

You might go there after you rule out everything else.

fireguy12117 · Sep 27, 2007

i've had issues with a coolant temp sensor that wasnt throwing a code, but was not giving an accurate feedback and was causing all sorts of weird warm start problems for me. just throwing my 2 cents in.

speed_demon · Sep 28, 2007

So only at low rpms? It sounds like a vacuum leak. When cold the fast idle and rich mixture can mask a vacuum leak then when warm it causes one or more cylinders to run lean creating rough idle and higher depending on the size of the leak. You can usually hear a vacuum leak if you know what to listen for. You can diagnose a vacuum leak by spaying brake cleaner, wd-40 or whatever around the intake manifold sealing points and hose connections. If the rpm fluctuates more than usual it means a vacuum leak is sucking it in.
I have plenty more ideas but this is where I would start.

Confused 4.0

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