I have a 94 XLT with 84K mi.

Problem with Torque Converter Lockup at the wrong time.

When at operating temperature, I accelerate normally in Drive to about 35 mph. As soon as car shifts into 3rd, the torque coverter wants to locks up. This draws the RPM's down to about 1000, which is too low. This may be normal if I coast at this point, but I am still continuing with gradual acceleration. This car is now bogged down. I then push more gas and the torque coverter unlocks roughly (bangs out). It then keeps trying to lock again. This is very unpleasant for around-town driving

This also happens in Overdrive, but at higher speeds.

I had into the tranny shop for this problem about 6 mo ago. They put it on the diag machine and found no problem. They said a spark plug wire was loose and that the engine was not developing enough power. I wasn't sure I bought that because the engine seemed fine (no rough idling or loss of acceleration). Nonetheless the problem was gone and has not returned until now. I checked and "reseated" all plug wires and the problem did not go away.

Is there something I can check or even change at the "home mechanic level" before I take it in? Do these cars have an external torque converter lock solenoid that may be faulty?

I look for vacuum lines and a modulator valve, but I doubt this tranny works like my old C4 that was in my 1967 Mustang Fastback. I see there is a vacuum diaphram. Could this be a possible cause of the problem?

Any suggestions?

Thanks
Chris

 

I would do the following.
1. Disconnect the wiring harness at the transmission that controls the 3-4 upshift and Torque converter lockup solenoids in the transmission. Go for a test drive and verify transmission mechanical/1-2 &2-3 shifts seems fine except, there will be on 3-4 upshift or torque converter lock-up.
If this seems fine then reconnect wiring harness from above:
2. Disconnect the wire harness from the speed sensor (speedometer cable at transmission tailshaft). Go for another test drive and verify no torque converter lockup occurs at the low speed you indicated (also may not get a 3-4 upshift).

Doing the above may cause the computer to set a fault code(s), but can be manualy verified and cleared later.

Lockup and 3-4 upshift are under programed control of the computer. The speed sensor is main input to determine vehicle speed and when these events should occur in conjunction with other engine sensor inputs based on engine load demands (throttle position sensor, etc.).
I would be sooking at the VSS sensor, TPS sensor and then to the transmission solenoids/valve body lastly.
Dialtone

 

something else to look for, could be an odd chance of a ground in the harness for the lock up solenoid. the computer turns the solenoid on by grounding the return from the solenoid.

 

Thanks Dialtone,

I assume the VSS sensor is Vehicle Speed Sensor.

Would you happen to know where on the transmission I will find the connector to the harness that controls torque converter solenoids?

Also, is the VSS located on the tranny and is it easily changeable?. I believe the TPS is up in the engine compartment.

Wife drove it tonight.. she said it did not act up. It appears to be intermittent.

Thanks
Chris

 

Just got in from trying the following:

1) disconnected the solenoid control harness on tranny and test drove..no luck... reconnected

2) disconnected speed sensor harness on tail shaft.. test drove.. no luck.. reconnected.

3) disconnected throttle position sensor harness on engine.. ... test drove.. no luck .. reconnected.

4) rechecked spark plug wires.. engine appears to be running OK

5) disconnected battery to reset EEC... test drove.. no change.

Could there be anything else? or do I need to go to the "dreaded" garage?

Thanks
Chris

 

hello chris, i seem to be having the exact same lockup problem as you did on my 91 f-250 deisel. what did it end up being? i'm so frustrated as i have had the truck in and out of the tranny shop 4 times already. I JUST WANT IT FIXED! any input would be much appreciated.

thanks: Sweetisuzu