Engine/Transmission (1994 - 1998) Lockup unlocks when it hits 45mph

[Figor]

My 05 is down so I had to jump in the 97 to get to work. It’s been sitting a good long while. I don’t drive it much anymore. Glad I kept it though.

I noticed with the overdrive off once the tc locks up around 32 mph it unlocks at 45mph. Any ideas?

 

[DonFitzwater]

Check your tps voltage. Is your tachometer working?

 

[Figor]

Tach is not working. transmission isn’t down shifting either. It is taking off in 3rd.

 

[DonFitzwater]

The computer on these trucks is pretty simple. If I remember correctly it monitors crank signal to control charging, shifting, tach output and enable air conditioning. 97 may be a little different.....a few years back my computer failed and my trucks symptoms were trans hot, water in fuel, no shifting control, no tach and no A/C. You may very well have a failing/failed computer.

 

[Figor]

Thanks Don. I’ll keep an eye out for a computer. Hope it doesn’t leave me stranded.

 

[GrantP]

Losing the tach and converter falling out of lockup points to the crankshaft position sensor.

 

[BigPapa]

Losing the tach and converter falling out of lockup points to the crankshaft position sensor.

It’s called the Engine Speed Sensor on the 12-valves, and that’s what I’d check before going after a PCM. You need to check and clean ALL connectors related to the ESS and PCM as well as all grounds, THEN go after the PCM itself.

 

[Figor]

Will do. Hopefully cleaning will help. I was just pricing ecu’s. They’re cheaper then what I paid for my 2005 but still painful.

 

[DonFitzwater]

Will do. Hopefully cleaning will help. I was just pricing ecu’s. They’re cheaper then what I paid for my 2005 but still painful.

Get yours repaired. There is a company in Illinois that I've used with great luck. I've never seen a crank position sensor go bad on a 12 valve, only computers. Of course check it out first but I'd be surprised if that's what is wrong.

 

[Figor]

Oh good to know. I’m from Illinois.

 

[DonFitzwater]

Oh good to know. I’m from Illinois.

https://www.turbodieselregister.com...y-marketplace-ecm-dealers-potentially.271842/

 

[Figor]

Aha. Yes that’s who the local Cummins dealer recommended. Thanks.

 

[DonFitzwater]

Did you get this thing fixed yet?

 

[Figor]

No not yet. My backhoe broke down and a recently widowed woman asked for help getting her husbands tractor running for an auction this weekend. I e been bouncing between these two projects all week. I haven’t had time to mess with the old 12v. I did manage to get the alternator replaced in the 05 so I’ve gone back to driving it.