Intermittant Rough Idle HELP !

[lighttech]

Hi all,

I purchased a 1995 Ford Explorer XLT with about 160K miles. I managed to fix all the issues except for two that are driving me crazy:

1. After driving the vehicle for a bit allowing it to heat up, park it and shut off engine. Wait twenty minutes and go to restart and it idles really rough, major mis-firing for about 30 seconds. ONLY will do this after completely warmed up. - kind of suspect injector leak down, but why only when hot ?

2. Slight misfire when in Park with no load. Putting on A/C and putting it into drive and misfire goes away. Many other Explorers that friends of mine have the same issue.

No check engine light or codes. (111), as well as KOER (111)

What I have done: (pertaining to engine)

1. Clean EGR valve. - also checked contol solinoid
2. Clean IAC valve (idle air)
3. New plugs and wires.
4. New O2 sensors
5. New fuel filter.
6. Multiple treatments of Sea Foam. (5)
7. Fuel pressure is at 32 PSI idle, 40 PSI engine not running, pump on.

I am beginning to suspect ignition module. How often do they fail ?

If anyone has any ideas please let me know. Thanks in advance.

Craig Sherman

 

[Axial32]

Possibly check the TPS, throttle position sensor, or PCV, is worth trying the little things. Check and or clean the air filter, the throttle body. Which motor do you have in your explorer.??

 

[lighttech]

4.0 liter engine. Been through all the things you mentioned. I guess its time to buy a better fuel pressure guage (mine has leaks) and see how long the pressure holds after turning pump off.

Thanks for your help.

 

[Axial32]

hmmm... you said you cleaned the IAC, but sometimes cleaning doesn't always fix them. You could have a bad one still. Get one from a junkyard, I think I paid 13 bucks for a v8 one.

 

[lighttech]

I could see the IAC if it was just low or high idle, or perhaps even hunting, but when the failure occurs, pressing throttle to bring up the idle does not immediately clear the problem. While holding the throttle part open , say to 1200 RPM, you can clearly hear a rythmic misfire, then all of a sudden the misfire goes away and the RPM jumps up to 1400 with no changing of the throttle.

I just had a thought: I need to determine for sure whether the rough idle / severe misfire is due to ignition or something else. I am going to make a jig that attaches (not directly) to all six ignition wires and sample them with some computer software. After the failure occurs, I can play back on the computer to see if there was a misfire or not.

Axial again thanks for your help and will let you know what I come up with. Will work on this later today if the rain ever stops.

Craig

 

[Rick]

I moved this thread into the Stock 1995-2001 subforum.

 

[lighttech]

Rain been intermittant all day Sunday. Basically what I plan to do is to wrap five turns of #18 solid wire around each ignition lead. Combine all the leads together and attenuate them with a 10K pot. Attach output of pot to microphone input of computer (and of course ground). Use Cool Edit Software on laptop to record pulses picked up by "dummy capacitors" on ignition wires. Record pulses while engine is failing and later look to see if any are missing. If all pulses are present and amplitude is consistant from pulse to pulse, we will have to conclude its something other than ignition.

Only thing that I have thought about is that a fouled plug will cause the amplitude to drop 50% due to it being a "waste spark" system. Maybe will have to due even and odd cylinders seperately.

Craig