I have a 95 Aerostar AWD 4.0. 125k miles. I just went on vacation and while in the mountains if i was going up a hill the torque converter would lock and unlock several times. If i pressed the accelerator it would shift into 3rd gear and unlock and work fine. However, i would gain too much speed. The check engine light never came on. I am thinking it might be the TPS or the ignition module.


The transmission was rebuilt last year. It is not slipping and otherwise is working normal. If i shift into drive instead of overdrive, it still unlocks and locks so I think that would rule out the overdrive solenoid. If i press the gas further it will stay unlocked and work fine. The lockup solenoid was replaced when the tranny was rebuilt. It locks up fine at 45 mph and stays locked up. It is only doing this under load while maintaining speed. For example cruise set at 65 mph going up a hill.

It is also idling rough like it is missing after it heats up but as soon as you rev the miss goes away. I read in the EVTM that the ignition module is one of the controls for the lockup and 3-4 shifts.

Any ideas?
Brett

 

[updated:LAST EDITED ON 21-Jan-02 AT 04:01 PM (EST)]I'll admit upfront, transmissions are not my forte. However, after reading your post, I will offer these comments for discussion. In your first paragragph, the transmssion sounds as if it is working correctly, i.e. downshifting in response to load conditions. In this model, the transmission should not be "hunting" for proper gearing, that is, not rapidly shifting back and forth between OD and 3rd. If yours is hunting up and down more than 3-4 times a minute on grades, then you do have problem.

Your second paragraph is puzzling, in that there should be no OD lockup when just Drive is selected. Drive is for times when you do not want overdrive engaging, such as towing, or lugging under loaded conditions. (Steep uphill grades) If your OD is truly engaging even in Drive, then you may have a problem with the linkage adjustment, kickdown cable or vacuum line.

Lastly, the third problem sounds less like the ignition module than either the mass air flow (MAF)sensor or possibly the manifold absolute pressure (MAP) sensor. (The MAP has a lot to do with determining proper shift points) You should run a scan to see if there are any error codes held in memory.

Post again with any findings. Hope this helps.

 

Aerocolorado,
Don't get torque converter lockup confused with OD. They are independent. Torque converter lockup can occur in 3rd (1:1) and 4th (OD). In essence, what you end up with is a six speed transmission: 1st and 2nd (both without torque converter lockup) and 3rd and 4th (both with and without torque converter lockup).

Alpineswampman,
My 95 4.0 4WD had a miss that was detectable at idle which was not noticeable at other speeds except for low engine speeds with the torque converter locked up. With the torque converter locked up, engine speed low, and the throttle gently rolled on (so as not to cause a downshift or TC unlock), I would just barely notice the miss. I troubleshot the problem as much as I could, then broke down and had two shops (one was a dealer) run diagnostics and couldn't pinpoint the problem. Although close to finding it, the dealer said I had a bad cylinder and tried to sell me a new engine for $4500. Then, I ran a leak down test and found I had a bad exhaust valve. If you've checked everything else out, don't rule out a compression check. Disclaimer: Just because this was my experience, doesn't mean that you'll have the same problem. For your sake, I hope you don't. Getting the heads off is a big pain in the rear.

Good luck and post back with results so we all can learn from this.

 

Mikeman, you are correct re:TC lockup in both 3rd and 4th. For some reason, I thought only OD had TC lockup, but the Ford manual agrees with you. Good catch!

 

I'm looking at the Ford manual for the '89 A4LD, and it has this to say about CC operation:

==============================================
In the A4LD transmission, converter clutch upshifts and downshifts are scheduled electronically. The converter clutch is inhibited from engaging during the following driving modes:

* engine coolant below 128 degrees F or above 240 degrees F

{look at faulty coolant sensor, coolant temp out of range?}

* application of brakes

{bad/fluttering brakelight switch? Bad pedal cluster bushing? Misadjusted stop bracket for switch?}

* closed throttle

* 23.5 Hg or below absolute barometric pressure.

* quick tip ins

* quick tip outs

{bad TPS?}

* when actual engine speed is below a certain value at lower vacuums( this insures all 4-3 torque demands will be make on an unlocked converter)

During the above driving modes no current flows through the solenoid. To illustrate the operation of the system refer to the following illustrations {etc.}

==============================================

I do not know if any of the above applies to the later A4LD, and yours is probably an A4LD-E anyway?

Regards,
Al S.

 

The hunting i was referring to in my original post was between lockup and non-lockup. The problem I am having is with the lockup and un-lock under load.


Here's an update on what I have done and found. I had a cracked boot on one of the spark plugs that was arcing (causing my miss). I also replaced the ignition module. The plastic on mine on the fender side looked as if it had overheated. My EVTM says that the ignition module controls shifting. I am thinking that with the cracked boot the computer would unlock and lock the torque converter when it would arc.

I hooked it up to a Snap-On Mt2500 scanner and ran all the tests. No codes were found. The tps is working over all positions of throttle. The brake switch is properly adjusted. The MAF sensor is working. The mt-2500 doesn't pick up the MAP sensor. Is there any way to test this without a diagnostic computer? Also, where is the MAP sensor located? I couldn't find a location in the shop manual or any reference to it.

Since there are no hills around here, I am going to hook up my boat and go up the steepest bridge around to see if this has fixed my problem. I will post my resuts.

Thanks,
Brett

 

There shouldn't be a MAP sensor on your 4.0. They may have used them the first year of production, but none of my 4.0s ('91 and '95) have one.

 

I hooked up my boat this weekend and went over a very long and steep bridge. I had the cruise set at 50MPH and the torque converter seems to be working fine now. It unlocked and stayed unlocked until i was over the top of the bridge. No more hunting between unlock and lock. I also set the cruise at 55 and then held accel to 75 and no unlock\lock bumping either. It just stayed unlocked until i let off the accel button. Since we dont have any hills around here this was the only way i can think to simulate a loaded hill climb. I don't know if the cracked spark plug boot was causing this or not. But that's fixed along with a new ignition control module and it seems to be working fine now.

Thanks for the info!

Brett Molaison

 

[updated:LAST EDITED ON 04-Feb-02 AT 07:01 PM (EST)]Now that you mention it, my '95 4.0 AWD exhibited similar behavior on hills when it had a bad exhaust valve. Going over the Cascades, it would be in and out of OD, even if I let the speed drop (which in some cases was unavoidable). It didn't seem too bad, so I didn't worry about it. Then, after I put new heads on, I noticed that the tranny never downshifted over the same hills and I was able to maintain my speed. I suppose that now that all cylinders are good and it's got more power, I don't have to put my foot in it as much so there's no downshifting like it did before the new heads.

The other thing that I've noticed after the new heads is that it's much more difficult to feel the torque converter lock up in OD, unless I really have my foot in it. With the bad heads, I felt the lockup a lot more, especially at light throttle settings. And, the vibration that I thought was coming from the front driveshaft while coasting has now disappeared.