Hello all! I've read through the forums many times but this is my first post. I'd like to thank everyone for all the great information I've read so far. Anyways, I have a '91 Explorer Sport 4x4 which has the 4.0 v6 ohv and the a4ld transmission. The transmission was rebuilt 1.5 years and 20,000 miles ago. Heres a list of all the things I've done in the last couple months:

-changed both intake gaskets due to a nasty coolant leak.
-changed both valve cover gaskets.
-changed oil, and coolant.
-cleaned MAF, IAC, and throttle body.
-changed plugs to bosch platinums, previously autolite standard.
-changed plug wires to autolite custom, previously borg warner.
-changed air filter with usual fram.
-changed fuel filter
-got a new battery with more power than the last one

Tranny fluid still looks normal. The driveline u-joints are good, I changed them a while ago. New tires as well. Everthing I can think of checks out fine... No error codes, no engine light, no signs of a problem except this:

Except 1st gear and maybe 2nd, when accelerating, the truck shudders intermittantly. And when in OD it feels like it slips, and also shudders when accelerating hard. This came out of the blue and is rapidly getting worse. Now when I'm going up a hill on the way to my house, it starts pinging worse and worse (I am already using supreme or whatever gas it is that is the highest octane and it hasn't been pinging anyways since I changed the intake gaskets). I'm worried its the transmission, as the people who rebuilt it last (AAMCO of Olympia, Washington) were real shady, and had it 3 times in 3 1/2 weeks before they fixed it to what seemed at the time, correctly... (I would highly recommend to anyone in Olympia, washington to never take their vehicle to the local AAMCO). I'm hoping though, that it might be something else (even though its not looking that way). If it turns out that its the transmission, the only thing I can do is trade in the vehicle and get what I can for it, as I'm still paying off the bill for the last rebuild, and I can't afford to do anything else. I'm heading to the dealership tomorrow to see if they can do a diagnostics or something and see what my options are for a trade if it comes down to it. I love my X and hope theres something I can do. Any tips, thoughts, or ideas are welcome and appreciated.

ZT730

 

Transmission won't make it ping. If I had to guess, its the fuel pressure regulator. I had problems with my 92 and after changing everything else, cut open the regulator. It had worn a bevel on the side of the seat. Some of these have a spring slightly offset and they wear. Sounds like you might have a voltmeter. Pull the fuel pump fuse and measure the pump current. Should be 4A or more. I had to drive around monitoring the current because sometimes it was ok. Sorry, but unless you have a very late year 91 the regulator is wierd and harder (more expensive) to get.

 

Thanks for the reply, its greatly appreciated. The thought had crossed my mind that maybe the engine was getting too much fuel and bogging down, but it seems like I would get an error code for running rich or something. Even with this problem it's still getting good gasmileage, around 18mpg in the city. Well, I'm heading over to the dealership this morning to see what the tech guys think there (They're really nice at this dealership). I'll give the fuel pump test a shot as well and look into a fuel pressure regulator. Thanks again for the input.

ZT730

 

That was one of the things I missed when it was fixed. Don't know if it actually burned that lean. After a while the O2 sensor would correct that and give the injectors a longer pulse. There was just no extra room on acceleration. Think mostly I modified my driving habits cause I didn't want to hear it knock. After it was changed the computer wouldn't relearn (>200 miles) till I disonnected the battery.

 

That's odd. Well, the guys at the dealership weren't able to help a whole lot without doing their diagnostics. I checked when my truck was built, its from january of 91. The local schucks has two different fuel pressure regulators, one for $79.99, the other for $89.99. OE numbers are F1TZ-9C968-A and F0TZ-9C968-A respectevly. Unfortunately I can't see any numbers on the one in the truck. My voltmeter will only do 10A, I'm not going to destroy anything by doing that fuel pump test am I?

It didn't start pinging until just the last 2 times I went up that hill. It doesn't start pinging until I'm almost all the way up the hill, then comes and gets worse and worse until I level out. But its been doing that bad shudder and slipping for 2 weeks or so, granted its been getting worse by the day. Thanks for the tips.

ZT730

 

a pigtail return line and the later has a nut that threads the return line on the top of he regulator. There is a push on vacuum line on the bottom and it attaches onto the fuel rail with two bolts. Takes no more than 10 minutes to change. 1/4 inch spade lugs push into the fuse clips which makes it easy to run the wires into the cab.

 

Well, I went ahead and got the fuel pressure regulator... I changed it out and went for a test drive. It deffinetly helped... There's no more shudder when accelerating on level ground, even when I really lay into the throttle. Also the engine feels a lot more powerful like it used to. Unfortunately, it didn't completely fix the problem... as it still shudders going up fairly steep hills and pings going up steep hills (Although, not as much as it did before). I think its fair to say that it is an ignition problem after all and not the transmission (Thank god). Thank you so much for your help Opera House Works. For now, its drivable and until I have more money and time it will get me where I need and want to go as long as it doesn't involve big hills.

ZT730

 

What you describe as a ping is detonation and that is usually a lean condition. The shudder leads me to think you have a vacuum leak. I have had this problem and it turned out that a vacuum line on the drivers side of the motor that runs near the center of the exhaust manifold running vertically. There are two in that location on my 94 one had burned through due to heat from the manifold. This caused a vacuum leak that would cause the diaphragm on the side of the Trans not to operate properly causing the shifting to be as you described and a shudder in OD and pining of the motor.

I would check the following

All vacuum lines in the engine compartment pay close attention to the ones at the spider at the rear left side of the motor.

Has the motor ever backfired?? This can blow lines off and make the motor run strange, it will ping, it can also damage the diaphragm on the trans.

Check the vacuum line that connects the diaphragm on the Trans to the steel line that runs to up to the spider. Again a backfire at start up caused mine to come off.

Check the operation of the diaphragm on the trans. I had mine fail and again I had the exact conditions you describe. It was less than $40.00 from the dealer. This install is a pain you have to loosen the exhaust pipe that runs by the Trans but if your Trans was out recently it should not be that bad.


Hope this helps


Dean

 

Vacuum line to the regulator is also a good place to check. The regulator boosts pressure when the vacuum drops at high load. I would still measure the pump current. The gears in the pumps do wear but most failures are immediate when the brushes wear down and stick. As a precaution, I would pull out the pump relay and fuse to check the contacts for corrosion and heat. Poor contact will drop the pump voltage. You can easily drive around with as little as 6V on the pump but performance will suffer. Unplug/plug the electrical tank conector to clean connections. If you get a fuel pressure gauge, it should be about 33# at idle and go up to 39# when the vacuum line is removed to regulator.

 

I haave muchthe same problem as you, but only when in gear and it worsens with hard excelerartion. i have a whole list of things to check, let me know what you find out.

i have notice that this problem seems to be a reoccuring one does anyone know of an article that covers this topic and the others like it.

takecare
randall
isherwood46(No Email Addresses In Posts!)