cougar

Trouble is, I have tried more than 1 TPS, known good ones including a linear actuated potentiometer. Same thing. When I can get a break from work I'll try the trim pot in the return side.

j_martin

The point is to get the TPS to give the right range of voltage for idle to full throttle. Start is 1V, range is 2.5V +- .25 V. That's what the PCM is expecting.

When you turn up your pump and have to turn down the idle, that stretches the low end. Full throttle mod stretches the high end. sum of mods puts it out of range. The trimmer is to compensate for that.

Now, if you get it in range and it acts up, I'll be officially stumped.

ricky0677

I wish you guys would figure this out... my 92 has had this problem for several years. I am the one with a wire connected to the ground side of the OD solenoid - run through the floor - insulation peeled back a couple of inches - bent with a hook shape on the end and when it starts acting up I hook the wire on the shifter shaft (metal part of the shaft) and it stays in OD until I remove the wire off the shifter.
Please keep trying.
Has anyone tried a new OD switch on dash? I haven't but I keep thinking if the contacts inside are corroded or loose they may be causing the problem... but the light in the switch should be flickering...I assume???

j_martin

The OD switch is a momentary contact switch. A pulse from it toggles OD mode on and off in the PCM. The PCM lights the lamp with a completely separate circuit. So it's either go or no, and not much to arc and spark in the switch.

Wire hooked over the shift lever? You, sir, are close to hopeless, as in terminal red neck.

ricky0677

What can I say... I am from Arkansas, and on top of that I am a Poultry farmer (40,000 birds) My day job is as an Electrician - self employed.
But i was thinking maybe even though it is a momentary switch it could be bad inside and bouncing on and off just as if you were pushing the switch on and then off and then on and then...

You sound like a very interesting guy. I would love to visit with you for a day or two and pick your brain. I enjoy your posts.

cougar

The only pump mod to the truck in question, the 92 is the fuel pin turned. That has no effect on idle. And sense it never sees full throttle, the upper end is irrelevant at this point. When the TPS is set at 1 volt at idle it will not shift into overdrive at any speed or throttle position unless I pull my foot completely off the peddle. Then as soon as I give it any throttle, OD drops back out.

ricky0677

[QUOTE=j_martin;3189399]The point is to get the TPS to give the right range of voltage for idle to full throttle. Start is 1V, range is 2.5V +- .25 V. That's what the PCM is expecting.

j_martin, what would happen, for testing purposes, to supply a 1.5 or 2.0 volt steady voltage to the varying voltage pin? Or does the voltage have to vary.
If that would work wouldn't it rule out everything but the TPS and it's circuit.

KRB

Found this on another forum I frequent. Being electronically challenged I'm not sure if this would even help or if thats what you all have been talking about already anyway?

http://www.cumminsforum.com/forum/89...e-out-fix.html

j_martin

[QUOTE=ricky0677;3189617]Funny you should ask.

https://www.dieseltruckresource.com/...&highlight=tps

It works, OD shifts at a set speed. Cruise works.

j_martin

Electrical noise is another thing. Looks like it would help.

KRB

[QUOTE=j_martin;3189661]So basically what you built is a fixed point POT? That eleminates the TPS but now it shifts at a set speed no matter what the load, correct? If so, then that little gizmo would at least let us rule out a faulty TPS which would narrow down the possibilities. I'd be interested in one of you're making them...

j_martin

[QUOTE=KRB;3189672]Actually, I'm making one today, I'll make 2. PM me.

Used it for awhile, but I either run empty or pull a double that weighs 11,000 lbs, so I need the dynamic OD control. Made the touchy TPS run an extra year with DeOxit contact cleaner. Just replaced it with the TPS off my other truck. (Blue, thelocal wood hauler and parts mine rust bucket) Now I need the resistor pack for Blue. Do you suppose I can find it?

cougar

Replaced the 3 capacitors on the original ecm board and cleaned up some solder joints and it was working beautifully for 2 days, then the OD solenoid quits. Wide open, guess it couldn't take the shock of having to work right again. Can't I ever get a break?

gadget.35-06

Who's the electronics guru, let's see... Jim Lane? Might send him a PM.

KRB

j martin seems to know his way around an electron pretty well too.