The more I keep working on my Ex, the worse it runs!

[sabasigh]

2000 Explorer Sport 4x4, 4.0 SOHC, 188,000 miles.

Up until recently the truck was running decent. Every once in a while, hard to start but drove great.

At 185,000 I put in a new air filter. At 187,000 I put a new serpentine belt, tensioner, plugs & wires. Old plugs/wires were original and plugs looked good. Wow, like a new truck. Great power and fuel mileage. After a few thousand miles, then it started feeling kinda pokey...not much power. And it idled really low. Both in gear and in park...about 500rpm. Sometimes it would drop and catch itself before stalling. I did run a bottle of fuel injection cleaner thru it. Seems like that tank of gas is when my problems started. Even though it seemed to be running kinda weak, gas mileage was still decent.

Had a tranny flush and new fuel filter. No change. So reading all the forums I cleaned my MAF sensor, my IAC, and my throttle body. No change. I changed my plugs, just in case, new PCV valve and new IAC. The plugs I pulled out still looked new.

Plugged in the battery, started right up and revs up nicely at 1000rpm then drops a bit. Put in gear and it drops down to about 500rpm. Ok, doesn't look like anything's really changed. Took it for a ride and seems to be about the same power wise. Get going and cruising about 35 in fourth or OD, I don't know...give it gas and woah, stumble, stuttering, sputtering bucking...wtf?!

Put on a new TPS, re-attached the negative cable. Starts great, idles the same. Takes off from a start ok, but kinda weak. Shifts thru the gears fine...but once you're cruising in a higher gear and get on the gas...then it sputters and sounds like it backfires thru the intake.

I should mention that Check engine light hasn't come on. I bought a code reader and there were no DTC codes. When I reset the battery, it takes a while for all diag tests to complete but when they do...no codes.

I can drive the thing around town but if you get on it in a higher gear, it will sputter, jerk and pop. Rev's don't change...and if you mash the gas to get it to downshift it will do it but feels like it's really straining.

Sorry for the long post but better to give all info up front. The truck's obviously not worth much but has been a good daily driver the last 70,000+ miles. If anyone has some ideas, would appreciate them.

I have yet to check the Fuel pressure or do a vacuum test. If the freaking thing would just kick off a code to point me in the right direction, I wouldn't be so frustrated.

 

[2000StreetRod]

perform tests

It appears that you have tried all of the normal corrective measures with no success. I suggest that you revert to pre-OBD days and perform an engine compression test and a fuel pressure test. If they pass then I would look for something subtle like a faulty crankshaft or camshaft position sensor. I've been fighting what appears to be a faulty knock sensor on my 2000 Sport since I purchased it from a tow truck operator in May 2009. The vehicle was abandoned on the highway because it quit running. It just needed a new camshaft position sensor.

 

[sabasigh]

Thanks 2000SR.

I went ahead and put new Autolite wires on there and a new Crankshaft Position Sensor.

Idles the same, has some giddy up but still the problem exists...though not as bad.

Standing start and hard acceleration to 60...revs up to 5000 no problem. Feels good...but if I'm cruising around 35-40 in higher gear and get on the gas...it sputters. If I let up off the gas and get back into it...it will downshift.

Got it on the highway and acclerated fine...though it did feel a little shaky at 60.

Last weekend while changing my plugs, noticed that my corroded Tranny dispstick had actually rusted thru and when the shop did the tranny flush, some fluid got on the frame. I put some muffler tape on it and didn't think much of it. Checked it tonight and my tranny fluid is really clear...weird.

 

[motorkingracing]

Thanks 2000SR.

I went ahead and put new Autolite wires on there and a new Crankshaft Position Sensor.

Idles the same, has some giddy up but still the problem exists...though not as bad.

Standing start and hard acceleration to 60...revs up to 5000 no problem. Feels good...but if I'm cruising around 35-40 in higher gear and get on the gas...it sputters. If I let up off the gas and get back into it...it will downshift.

Got it on the highway and acclerated fine...though it did feel a little shaky at 60.

Last weekend while changing my plugs, noticed that my corroded Tranny dispstick had actually rusted thru and when the shop did the tranny flush, some fluid got on the frame. I put some muffler tape on it and didn't think much of it. Checked it tonight and my tranny fluid is really clear...weird.

Hey dude, '
Sorry to hear your having so much trouble running this down. I am a mechanic, I am also the tech manager at Autolite spark plugs. There is a service bulletin from Ford that kinda sounds like what you have going on. It is about fuel pressure drop out. The problem is you need a fuel pressure guage hooked up and drive around having a passenger watch the guage to see if you get a pressure drop when the problem occurs.
Another approach is to find a mechanic with a data logging scan tool who will hook up and drive around recording scan data, when the problem occurs, one or more of the data parameters will go out of range.
It may be a crank sensor drop out, fuel pressure or something else but that is a way to track it down and you have spent alot of time on it allready. Try looking on your local Craigslist under automotive services, you might find someone who will do this for a reasonable fee. I would also do a "wiggle check". With the engine running, wiggle wiring harness near each connectors to see if you have loose or corroded connections.
Best of luck to you.

 

[sabasigh]

Well, I tested the coilpack last nite and it was reading 13.25 ohms across the secondaries. I then tested the coilpack on my 4.0 SOHC Mustang and it read virtually the same.

I went ahead and replaced the coilpack anyway. No change. Seems a little down on power too.

Still no Check Engine light/code or nothing. When I unplug the IAC while idling, it will sputter and die. Is this a reasonable vacuum test?

*Update: Just drove it prolly 60 miles of mixed driving...highway, stop/go, etc. Ran decent but still sputtered and hesitated when giving it gas under load. Parked it and still no codes.

 

[sabasigh]

Problem solved?

Well it looks like it may have been a cracked insulator on a plug...probably from over-tightening them.

Runs pretty decent now...still got a low idle but it's had that for quite a while.

 

[2000StreetRod]

Congratulations!

Glad to learn you found the problem and thanks for posting the solution.