Acceleration jitter

[johnad]

I have a 99 Explorer 4X4 XL 4.0 with no modifications. When I accelerate from a standstill the vehicle acts like its going over small speed bumps. My first inclination is that the transmission is faulty as it changes gears. I've taken it to the Ford dealer and their comment was "if the computer says it's okay then there's nothing wrong with it." I just don't agree with this, it just does not feel right. Also, as I go up a steep hill, you can hear what seems like the engine backfiring some where in the engine compartment. I don't know if these are related, but I would appreciate any help.
Thanks in advance.

 

[mrboyle]

The unfortunate problem with having computer diagnostics on today's automobiles is that many "technicians" will only belive what they see, not what is really happening. It sounds like you may have a fuel delivery problem or something similar. Did the "technician" drive your Explorer to confirm the complaint? If not, make him! There are numerous things that can cause and engine to not run properly, yet fail to set a code in the computer.

 

[TPLYNCH]

The speed bump feeling could be a problem with the control trac 4x4. If the computer is getting incorrect info from faulty sensors, it may be engaging/disengaging 4x4. The GEM module controls the Auto 4x4 function, and there is a recall on the '99 GEM's (see phantom windshield wiper posts). If you haven't had the recall work done, have it done and see if there is any change in the situation. Don't know about the misfires.... Haven't had that with mine, but it does have change of pitch in noise and a vibration while doing 70+ (~2500rpm) up a hill. Not sure if it's done this all along or if it's a new quirk. (paying $1.75+ for gas, I try to be as economical as possible and usually do 60-65.) I'll probably bring this up next trip to dealer if it continues or gets worse.

 

[RocketMan]

I have the same problem with my '99 XLT. I took it to the dealer (Lincoln/Merc) and they verified the problem (even took out another '99 they had on the lot and had it do the same thing) but didn't know what was causing it. I have an appointment with a Ford dealer next week to have them check it out. I'll mention the GEM recall to them and see if that doesn't help them.

johnad, if you get yours fixed, please let me know what it was. Thanks!

 

[-=DaemoN=-]

O.K. I think I have the same problem. When I'm taking off and hit around 20mph it tugs back(if that's the right word to describe it), like it won't shift up. It does it for a couple seconds and then it shifts. This sometimes happens at high speeds. At first I thought it was only when my car's running hot but then I guess not.

This started happening after I got my fan clutch replaced, if this have anything to do with it. Any suggestions? Thanks....

 

[Jim F]

Well johnad I have a 98XLT 4x4 4.0L SOHC and have the same small speed bump feeling going up hills at slower speeds (pulling hard under 35MPH). It feels like the front tires are trying to go faster than then rear and are bouncing slightly. I don't see any tire wear though. I have not had it looked at since I have read posts here regarding it unsolvable state. Acceleration from stop on level is smooth, but occasionally I feel a slight vibration. I remember a post on this board (that I can not find again) regarding someone having this problem solved by having the "clutchpak zeroed" by Ford. Does anyone else remenber this post?

Oh one other thing, I have not had the backfiring under the hood problem.

 

[briantf]

Fixable, known problem

It's a GEMS unit problem, and its supposed to be fixable with a software upgrade. Considering my wife's 98 XLT has had it from the beginning, you'd think Ford would be resolving this problem.

The TSB database entry for my wife's VIN said that it's caused by the GEMS unit "recalibrating to zero" under medium acceleration. The CDROM or downloadable fix was not available at the time the report was printed, and the dealer I have it at now is hedging about whether it's out now or not.

Right now it's in the shop for final warranty work; I was very concerned when I did the 35K oil change to find red sticky fluid in an arc around the front driveshaft where it leaves the transfer case. I've been worried about the damage/wear and tear that may be ocurring as a result of the constant engagement of the electric clutch in the 'case.

The dealer said this is normal grease coming out. Bu!!$hit. It's red, it's new (no dirt, trust me, if it had been there before, it would be filthy), and it's right at the seal - why would there grease at a seal like that???

I'll post if this clunking under acceleration gets resolved. As it is, I have two calls into 3rd party extended warranty services.

Brian in CA

 

[croess]

acceleration jitters at 40MPH +

I've had a similar problem with my 96XLT. It shakes/buzzes when accelerating at speeds of 40MPH+, especially when going uphill. If I punch the gas, it jumps out of the episode. I have noticed that this always occurs around 2000-2300 RPM. Anybody else notice this? I took it in, but the shop only changed the fuel filter (no help), and said they could not diagnose anything on the lift. What now???

 

[RocketMan]

FIXED!

Well, the acceleration jitter from 25-35 is DEFINATELY a GEM problem. I took mine in with a complaint of that (to Ace Ford in Woodbury, NJ) and a "buzzing" in the accelerator under 2000 rpm and after 4 hours, my truck was vibration/jitter and buzz-free. The RO says that they reprogrammed the GEM in accordance with a Special Service Message (slightly different than a TSB) and the accelerator cable was replaced (referenced in another SSM). So now I'm happy once again with my '99 XLT. I still have a resonance vibration at idle, but I've seen a TSB about that. It says that a Y-brace is to be installed to stop the vibration. I will look into it and probably have it done soon so my Explorer is good (better?) as new.

Thanks for the help guys. Hope I can be as helpful as I get more experience with these trucks.