A4LD Transmission - Lock up converter

[gosub283]

Hello,

My A4LD has been acting a strange.
On the same stretch of flat highway (no wind) the unit always dropped into overdrive and the converter lockup at 50 mph or greater.
The lock-up engages and disengages as normal for the whole driving session. RPM drops to 1700 when lock up occurs.

Lately on some sessions the lock-up does not happen and the rpm (in OD) stays at 2000 and remains that way for the whole trip. No engagement regardless of speed or engine load.
Summer or winter. Makes no difference, so I don't think its temperature related.

So the problem is intermittent.

What are some of the more simple things to check without going into the transmission ?

Cheers

 

[franklin2]

Check for codes in the computer. Certain problems with the engine or it's sensors will sometimes drop it out of lockup. Is your speedometer acting normally? If you have a electronic speedometer, it's run off the speed sensor and sometimes if the speed sensor craps out, the speedo will mess up and the transmission will drop out of lockup.

 

[gosub283]

Sorry, I forgot to identify the truck

1994
4.0 V6
4x4

So it does not have OBDII

Speedo is acting normal.
Any vacuum lines, wires, or external sensors I should be checking?

 

[franklin2]

It still has OBDI. I would still check the codes. The computer delays lockup when the engine is cold to help it warm up faster. The codes may show you nothing, or they may give you a big clue, but it's standard procedure on a fuel injected truck with problems. If you are going to do your own work, you should get familiar with pulling the codes, you can do it with a testlight and a jumper wire. Your later model may even blink the check engine light in the dash, not sure about that.

 

[Mackhedq]

It still has OBDI. I would still check the codes. The computer delays lockup when the engine is cold to help it warm up faster. The codes may show you nothing, or they may give you a big clue, but it's standard procedure on a fuel injected truck with problems. If you are going to do your own work, you should get familiar with pulling the codes, you can do it with a testlight and a jumper wire. Your later model may even blink the check engine light in the dash, not sure about that.

Any luck figuring out what's going on? My 94 4.0 is acting like this too.

 

[ford4wd08]

Any luck figuring out what's going on? My 94 4.0 is acting like this too.

I believe that a temp sensor reading can prevent the computer for triggering lock up. Lots of reports of the temp sensor going out preventing converter from going into lock up.

 

[Rimjam]

On my old '88 the problem was the throttle position sensor.

 

[lil_Blue_Ford]

Could also be the solenoid for lockup. I also had an 89 that the wires ended up against the exhaust and melted through. Really hard to say without some investigation.

OBD1 is also somewhat notorious for having codes set without lighting the CEL. If it’s not a major, world ending issue, the CEL may not light. I’ve pulled 6-10 codes off them before with no CEL.

I‘ll probably move this to the transmission forum where it belongs in a bit

 

[Mackhedq]

Could also be the solenoid for lockup. I also had an 89 that the wires ended up against the exhaust and melted through. Really hard to say without some investigation.

OBD1 is also somewhat notorious for having codes set without lighting the CEL. If it’s not a major, world ending issue, the CEL may not light. I’ve pulled 6-10 codes off them before with no CEL.

I‘ll probably move this to the transmission forum where it belongs in a bit

Yeah I've pulled the OBD1 codes to no solution which sucks. It's definitely some sort of imput issue into the computer. I think I'm going to gather up everyone's imputs and replace parts one by one and report back if anyone of them fix it at this point.