I've got a 92 auto that once in a while drops out of OD for no apparent reason. After reading quite a few posts, I'm convinced I have a TPS on the way out. I'll probably go the route of replacing it with a pot that I'll mount inside, but here is my question.

Can I add a grounding switch to the solenoid wiring without disconnecting the wire coming from the ECM? In other words, will I risk damage to the ECM if I manually ground the wire that it is grounded by the ECM when IT makes the tranny to into OD?

I'm shortly heading out on a road trip and would like to add backup to force OD if the TPS starts acting up while going down the highway.

 

That's a good question, and one I had myself awhile back. I spliced into the ECM lead wire with one of those blue trailer light adapters and ran a wire into the cab temporarily to see if/when the ECM was grounding(unplugged from solenoid). It checked fine with a test light, came on at correct speeds, off with throttle, etc, so I plugged it back onto the solenoid to check further. When I plugged it in(while grounded), I heard a slight high-pitched 'squeal' up top, I assume from the ECM. I have heard other electronic stuff do that, and figuring the ECM must have a switching transistor or diode that supplies the ground for the o/d solenoid when activated, I didn't think it would damage anything in the ECM being grounded to switch it off/on manually to be sure the solenoid is grounded. My solenoid did end up being stuck in the closed position, but unfortunately the valve body has further issues. :-( But I did ground the ECM lead and ran around a couple weeks with it grounded with no apparent bad results. Hope that may help, good luck! :-)

 

Yes, you can manually activate the solenoid. DON'T ground the blue wire, ground the other one.

 

Thanks guys. Just didn't want to hurt the ecm.

 

Thanks for reminding us, Dave, I should have said that too!! lol Once again, wannadiesel to the rescue...I'm not sure I'd even still HAVE my truck if not for Dave especially(and all the rest of the great people here!). Thanks y'all!! :-)

 

Yup, Thanks for the info. New owner, learning quite a bit on this site.... It's going to be fun....