A442F shifting from 1st directly to 3rd (1 Viewer)

[SmokingRocks]

So I found the right page in the FSM. 83-85 point to the ESA (Electronic Spark Advance) Circuit link between the ECU and TCM.

But since its the entire ESA circuit from the TCM is throwing a fault I'm thinking that the TCM is having an intermittent input from one of the sensors.

 

[ppc]

So I found the right page in the FSM. 83-85 point to the ESA (Electronic Spark Advance) Circuit link between the ECU and TCM.


But since its the entire ESA circuit from the TCM is throwing a fault I'm thinking that the TCM is having an intermittent input from one of the sensors.

The other possibility is a faulty TCM which might be easier to diagnose by swapping in a known working part.

 

[panamacruiser]

Not related, but I love your gauges!!! Could you tell me where to get them and a better pic of the whole thing

 

[SmokingRocks]

Not related, but I love your gauges!!! Could you tell me where to get them and a better pic of the whole thing

Custom Gauge Cluster

 

[SmokingRocks]

Look what I found.....

Replacing the ECU is expensive. Checking the TPS is not.

Quoting Christo:

"The computer is looking at the idle circuit. So you might think the problem is at the tranny, but more than likely the throttle position sensor is faulty or misadjusted and it is not telling the tcm that the truck is idling. Use the FSM and check and adjust the tps if needed."

That sounds quite likely.

 

[SmokingRocks]

I readjusted my TPS per the FSM and so far so good...

 

[panamacruiser]

Well, kindda what I told ya in previous post, TPS, in my case, the plug came loose!

 

[SmokingRocks]

Yup that was it. The codes are misleading because they pout to a transmission problem in the FSM and a ECU problem on mud.

Took a second to uncover what that circuit is doing and which inputs it was using to find it pointing back to the tps.

 

[SmokingRocks]

Well I think the problem is that the sensor fails when it is heat soaked. It happened again today on my way up the hill to assist in some recoveries.

Except this time I got code 041 TPS signal. Also the TCM was putting out pulses to the diagnostic light but it wasn't enough to trigger the light... could the TCM be going down too?

 

[Mark3406e]

Well I think the problem is that the sensor fails when it is heat soaked. It happened again today on my way up the hill to assist in some recoveries.

Except this time I got code 041 TPS signal. Also the TCM was putting out pulses to the diagnostic light but it wasn't enough to trigger the light... could the TCM be going down too?

I chased TPS code to, I ended up running a new wiring overlay for all four wires to the TPS. Left the factory wires and ran new ones along with it.

All is well, now.

 

[Eicca]

Subscribed

 

[SmokingRocks]

It was a combination of two factors:

1) Failing TPS Sensor caused the TCM to freak out and grab the wrong gears / go unresponsive. This condition magnified when the engine got heat soaked.
2) A secondary issue was noticed, it felt like the trans was popping out of gear then slamming back into it. You can only imagine how terrifying this was to me. Well it did it on a climb in the mountains I happened to be along a rock wall which allowed me to hear the rapid clicking sound of a worn hub splines popping in and out of engagement. The culprit was a failing AVM 4x4----4x2 hub on the front axle. I locked the center and unlocked the hubs and the problem stopped. (In the middle of a 4x2 conversion)

So it turns out the TPS CAN AND DOES trigger codes 83,84,& 85. And HEAT does affect this sensor (even noticed at the end of a 5 hr drive in 100 degree temps that my new sensor was out of adjustment a bit due to the heat)

I'd bet that the later ECU addresses this issue by broadening the tolerance limits and possibly conditions the signal some.

 

[amagnono]

Custom Gauge Cluster

A quick comment on this thread, many years later. My ‘93 was exhibiting similar problems over the last week or two - transmission worked fine until the truck warmed up and then it started going from 1st to 3rd (skipping 2nd) and downshifting from 3rd and 4th directly to 1st when accelerating resulting in scary high RPMS - not good. It was also starting to kick codes - flashing the OD light, but I never got around to decoding those. I fiddled with a bunch of stuff overt a period of days, including the kick-down cable but nothing had any impact at all. I finally found this thread and decided to swap out the TPS from another truck and BOOM - totally fixed! Transmission is running like a champ again. Appreciate all the work that went into this by the OP and others. Hope it can help someone else!

 

[amagnono]

A quick comment on this thread, many years later. My ‘93 was exhibiting similar problems over the last week or two - transmission worked fine until the truck warmed up and then it started going from 1st to 3rd (skipping 2nd) and downshifting from 3rd and 4th directly to 1st when accelerating resulting in scary high RPMS - not good. It was also starting to kick codes - flashing the OD light, but I never got around to decoding those. I fiddled with a bunch of stuff overt a period of days, including the kick-down cable but nothing had any impact at all. I finally found this thread and decided to swap out the TPS from another truck and BOOM - totally fixed! Transmission is running like a champ again. Appreciate all the work that went into this by the OP and others. Hope it can help someone else!

Well, I have to report back that the TPS replacement did *not* fix my transmission issues. The problem came back shortly after posting here (of course!). The ultimate issue turned out to be a faulty shift solenoid 2, as diagnosed per the shop manual. I had to drop the transmission pan - which was a nasty PITA of a job - and while I was in there I went ahead and replaced all 4 of the solenoids. It’s been several days now and everything is shifting normally. Good luck to anyone else who is dealing with this!