99 Explorer XLT misfires under load.

[rednblk]

I have a 1999 Ford Explorer XLT 4X4. it just hit 150,000 miles. It belonged to my wife and her ex before we got married and was parked about 5 years ago when the transmission started to fail.

I recently had the transmission rebuilt, and now I am having issues with it still. First of all we cleaned the fuel tank, replaced the fuel pump and filter, jus to get it to the shop for the rebuild.After the rebuild it ran great for a week or so, then all the sudden I could be driving and have no acceleration at all. rpms would stay at about 2000, and no amount of pushing the accelerator would change it. The problem started out as only at highway speeds and has since progressed to making it almost undriveable.

I had done the following before taking it to Ford:

1. replace fuel pump
2. replace fuel filter
3. clean throttle body
4. clean maf
5. clean iac
6. replace pcv valve
7. check with carb cleaner for vacuum leaks

I then decided instead of randomly replacing parts to go ahead and pay 89.95 for my local Ford dealer to diagnose the problem. Aside from wanting to charge me 250.00 to replace 6 plugs, they said I needed new wires and the coil pack was bad, firing more than one cylinder at a time under load, but they could fix it for 450.00! I am a former Track Vehicle Mechanic, so I figured I would do it myself... Pending codes for both left and right bank o2 sensors.

1. gapped plugs to .054 and installed motocraft platinum plugs
2. replaced wires
3. replace coil pack

problem went away for 1 day, then began again. Took it back to Ford Last night (made appointment)and they pretty much told me the parts I bought were junk and alluded that they had no interest in doing another diagnostic til i bought THEIR parts. So I left.

Went home and put a fuel gauge on. ran it over an hour, accelerating, running a/c doing whatever.Pressure was 55 the whole time. Car wouldn't hesitate. I blocked the wheels, put it in drive and within ten minutes it started missing and eventually stalled.

If I am driving I can sometimes shift into neutral, turn off the engine , coast a bit and restart it it and go another mile or so or up the next hill. then it starts again. Problem seems to only occur when driving, after car heats up for a while. it is definitely missing as the engine starts to shudder just before loss of acceleration.

I am at my wits end with this. any help would be appreciated.

 

[ZBlackBeast]

Coolant temp sensor IF you have replaced all the above.

 

[96eb96]

Pending codes for both left and right bank o2 sensors....Issues with acceleration...
You say you cleaned the MAF sensor - that does not mean it is operating correctly.

Try disconnecting it and driving around ...
What is the BARO parameter? (You would need a scan tool that could read ford codes).

 

[rednblk]

Pending codes for both left and right bank o2 sensors....Issues with acceleration...
You say you cleaned the MAF sensor - that does not mean it is operating correctly.

Try disconnecting it and driving around ...
What is the BARO parameter? (You would need a scan tool that could read ford codes).

If I disconnect the MAF, I get a MIL on the dash. Performance is unchanged. Once I reconnected the MAF, it took two or three drive cycles for the MIL light to turn off.

 

[96eb96]

Pending codes for both left and right bank o2 sensors

Are your codes P0171 and P0174? There is also OBD-2 freeze frame data that could be valuable - like the RPM/Temp/Load that the code happened. Also this is a sanity check on your coolant temp sensor.

These trucks have issues with intake manifold gaskets - 00M12 service kit -There is a kit to replace them. There is some good info in this thread(maybe not exactly your symptoms though): http://www.explorerforum.com/forums/showthread.php?t=228903 - his issues start with "after the truck is warn"

 

[frankenfreak]

My 2000 sport 4x4 had a habit of doing the same thing if I ran the AC when it was about 100 outside. It had 155,000 on it. Same symptoms and codes. Never figured it out. Only thing I can think of is how hot the 4.0 runs and the crappy E10 here. Acted like vapor lock which makes no sence.

 

[rednblk]

Okay. So I was able to borrow an OTC Genisys 3.0 diagnostic tool from a church member. After we talked a while he said he thought it was the O2 sensors, and he showed me what the graph should look like on his car. (Kind of a steady waveform going from near 0 to near 1 volt)

So I hook it up to the explorer and I get a graph that looks like a shark's mouth with dental issues on both sensors!

I replaced the sensors last night and disconnected the battery while I worked to make sure the pcm reset.

While it does run slightly better, I still have the same problem. It starts showing up once the car has been driven about 15 to 20 minutes on a cold start, sooner if it is already warmed up.

 

[Turdle]

Take a real close look at your spark plugs, looking for a hairline crack on the insulator nipple. A hairline crack in the head will slowly spray coolant causing them to crack. Not uncommon. Coolant pressure rises when it is warmer--allowing more "spray"

I hope I am wrong.

 

[my98nnj]

O2's will not cause a misfire.
The ignition system is a waste spark system

coil pack was bad, firing more than one cylinder at a time under load,

is exactly how it's designed to operate. It does indeed fire 2 plugs at a time. So much for your local FORD dealer...

Check the signal from the MAF.
Also verify that you don't have clogged cats. A loss of power under load when the engine is hot is a symptom of clogged cats. The MAF signal will be low under that condition as well and engine vacuum will be off too.

 

[rednblk]

Okay. So what I have gleaned from the info here is:

My MAF sensor might be bad.
My Catalytic converter is blocked.
My new plugs have a crack.
I have an intake manifold air leak.
My temp sensor is shot.

I really appreciate the help. I think I will take it back to Ford and have them redo the diagnostic, maybe after I tell the manager how I was treated during my so called appointment. Hopefully I get it narrowed down a bit.

I mean it sat for five years, so it was bound to have issues...I just wonder why it drove great for a week after the transmission fix, then started having these problems.

 

[rednblk]

Back to Ford.

Since I shelled out 89.95 for a diagnostic, I figured I would take it back to my "helpful" Ford dealer last night and see what expensive repairs they recommend this time.

I will update the thread as I find out the situation.

 

[rednblk]

So I took the Explorer back to ford, and left it overnight. About 4 pm the next day a tech calls and says "they have had it in the garage all day and can't recreate the problem"

So I ask if they actually drove it...

Seems to me that if the customer tells you he let it run two hours in the driveway, but it only occurs when he drove it, you would actually drive the vehicle!

So about an hour and a half later I get another call, "were right, I pulled out of the lot and it stalled less than a quarter mile down the road. I got a code, it is your MAF sensor."

Again they recommend only motocraft parts....so I go to my favorite auction site and get it for 35.00 shipped. And its genuine motocraft. Now let's see what happens when I replace it...

 

[Midwest Dually]

How frustrating.. Any chance you can hit an Autozone or something, and use their CAN scan tool to get the codes yourself?

 

[rednblk]

I have a scan tool, but for the longest time I had no codes at all.

I replaced the MAF but haven't had a chance to drive it.

 

[koda2000]

for what it's worth, any time i've had this condition on any vehicle i've owned over the years it's been ignition related.