Hesitation, stumbling; End of my rope.

[LukeDog3D]

Hesitation, Stumbling at WOT - 92 X

Greetings

I am having a problem with my 92 Explorer. It hesitates and "misses" at or near WOT. Sometimes it doesn't do it, and runs perfectly. Sometimes it stumbles just a little bit, then takes off good. Sometimes it stumbles for a long time, until its moving i guess at about 40+ mph. It seems like it does it worse and more often when the weather is hot and muggy. The truck generally only stumbles when I take off from a dead stop and floor it, or from a slow roll. When I punch it at highway speeds, it runs well. I've been having this problem off and on for perhaps a year. I'm at the end of my rope. I've searched all over this site, and replaced every part that I thought could be the problem. The whole thing started when the truck melted the electrode of a spark plug about a year ago. I replaced the plug and it ran fine. Then about a month later, it started running bad. I replaced a few things, then found a cracked ceramic insulator on one of the plugs. I replaced the plugs again. About 2 months ago, it started running bad again. I started searching for info and replacing stuff. I don't know what to do anymore, except go to the Ford dealer. Any suggestions would be helpful. I don't have a check engine light on. I did numerous compression tests, and all the cylinders read between 180 and 190. The gauge went up like it was supposed to, indicating no stuck valves.

Stuff I've replaced:

-fuel pump relay
-fuel pump/strainer
-fuel pump
-fuel filter
-coil pack
-spark plugs
-wires
-TPS
-FPR
-alternator -(upgrade to 130 amp)
-battery -(t was bad)
-Fuel injectors (used; ebay)
-Vacuum Modulator on the tranny (autozone)
-MAF (autozone)
-Throttle Body (aftermarket)
-crankshaft position sensor (autozone)

I've also changed the head gaskets, valve stem seals, and all of the top end gaskets that go with a head gasket replacement. I put headers on when I took the heads off. The exhaust system is relatively new, and is sealed up well. So, no exhaust leaks. I did all that before the problem started. I've checked for vacuum leaks. I've talked to mechanics, and they say that a computer code reading won't do anything for me since I don't have a check engine light on.

I've also:

-changed gasoline brand
-changed octane
-reset computer many times
-cleaned MAS
-cleaned IAC
-Took the IAC off my brother's '91 X and tried it on mine
-checked all of my fuses, underhood and under the dash

Also new (but unrelated):
-Fender solenoid
-starter
-water pump
-fan clutch

could it be:

short in wiring harness?
Capacitor near the coil pack?

any suggestions?

Sorry that this is so long...I love the truck, but this is just getting ridiculous.

updated 1/15/04

 

[88vert]

sounds like what happen to my 92 sport when the computer was messing up

 

[dogfriend]

One thing that you didn't mention is the ICM (ignition control module) also known as the TFI (thick film ignition) module. You could have an intermittent problem with this module. It is possible to have it bench tested; also since it appears to be heat related, you could heat it with a heat gun to see if you can reproduce the problem.

Here is a thread with some more info:

ICM problem

 

[LukeDog3D]

Thanks for the suggestions. Can you bench test the ICM at the dealer? Maybe I can pull it off and bring it there.

 

[LukeDog3D]

O.K., replaced the ICM with a junkyard one. No dice. Any suggestions appreciated.

 

[scott_gunn]

A leak in the intake somewhere after the MAF? It happened to me, and since I didn't get it fixed in time, it led to lots of other expensive damages...

 

[dogfriend]

This is a page out of my EEC-IV book on troubleshooting. The first column in the chart represents the most likely cause of the problem (1=very likely, 10=much less likely). Ignore the second column, MECS is for Mazda Engine Control System (Ford Probe, Mercury Tracer, etc.)

 

[dogfriend]

I was going to post these yesterday morning, but my cable connection was down. You may still want to test the ICM with a ohmmeter to verify that it is ok.

 

[dogfriend]

tfi second page

 

[Tat2dExploder]

any updates i have the same problem

 

[LukeDog3D]

Here's what i've done lately:


-rebuilt MAF
-different throttle body
-junkyard computer

when i took the Throttle body off to change it, i noticed some tranny fluid inside the upper intake manifold ( a small puddle in the corner.....this seems like a possible problem...apparantly the fluid came in through the vacuum hose going to the tranny. I'm gonna search around on here and try to fix it. If it works, ill post back.

 

[IronIndian]

If the trans is controlled by vacuum, then the modulator could be faulty. Check your trans fluid level to make sure youre not short some. IF it is, then I'd replace the modulator. This would only pertain to a trans that is vacuum controlled, but from what youre saying it is...

 

[Billy177]

how old are your o2 sensors also clean your fuel pump relay contacts

 

[LukeDog3D]

thanks guys

I already replaced the fuel pump relay. I haven't gotten to change the modulator yet. The o2 sensor is less than 2 years old...


edit: also recently replaced the air intake charge temp sensor and the gaskets between the upper intake and fuel rail, and fuel rail and lower intake. Checked the torque on the lower intake.

 

[Billy177]

is the fuel pump original

 

[LukeDog3D]

nah, i replaced it. its an autozone special.

 

[Billy177]

the only thing that i can think of is either a crankshaft position sensor or bad alternator/battery cables

 

[LukeDog3D]

okay, i forgot to mention that I also recently replaced the CKP (autozone). Maybe I could try replacing the battery cables...

I'm hoping its the vacuum modulator.

 

[IronIndian]

Wow LukeDog,
Looks like you've done alot of work to the truck already! Fix the things that you know need fixin' ( ie. vacuum modulator). A faulty modulator should not allow ANY trans fluid back into the engine. It's a PITA to do it the "hit n miss" way .

 

[IronIndian]

Re: Hesitation, Stumbling at WOT - 92 X

Originally posted by LukeDog3D
The whole thing started when the truck melted the electrode of a spark plug about a year ago. I replaced the plug and it ran fine. Then about a month later, it started running bad.

Was the melted electrode the result from normal driving? And you're sure that no metal was left in the cylinder? When you changed the head gaskets, you didnt see any damage to the piston or cylinder walls? I'd check the cylinder that had the melted electrode. Take out the spark plugs next to that cylinder and do another compression check on the cylinder with the melted plug. Could it be possible you poked a hole in the piston?