I'm troubleshooting the cruise control on my 92 D250. The FSM makes mention of codes 34, 15, and 11 in the speed control section but not 24 (TPS).

I know the TPS is shot. That's why I use governor pressure to trigger OD.

There hasn't been time to thoroughly test the electrical function. I was hoping Saturday would be slow enough for me to play with it but I haven't been able to yet.

Will a bad TPS prevent cruise control operation?

Yes,
If the ECM doesnt know where the throttle is, cruise is dis-abled

Oops!

I should have specified that this is a Cummins with mechanical injection. Only the automatics have a TPS. It is used to throw the OD and that's it as far as I can tell.

The 5 speed trucks do not have a TPS.

Cruise is not mentioned in the Powertrain Diagnostics Manual.
My factory service manual makes no mention of the TPS in the speed control diagnostics.

Since you don't have a TPS maybe you need to restate the cruise control problem.

I agree that TPS does effect the cruise control

My ctd is newer than yours, so I don't know if it operates the same, but I lost cruise when the vacuum line split.

On the diesels, cruise is getting an RPM signal from the crank sensor. That's the 91-93 trucks, not positive on the 89-90.

If the CPs is out you'll also be missing AC and charging.

Verify vacuum to the can on the fender.

Clockspring and switches are common problems oon these.

Thanks for the suggestions.

I found a dodgy resume switch on the steering wheel. It is no longer available so a friend and I took it apart and ordered a replacement microswitch for 59 cents.

I've questioned my clock spring in the past when the horn was iffy but that hasn't been a problem lately.

Once the repaired switch goes back in I'll move to the next step in line.

The vacuum is great. It feeds directly off the brake booster and that was replaced not too long ago.

The CPS is okay since I have no problem with the A/C or charging.

The 59 cent switch landed. Kirk enjoys electrical fiddly bits more than I do so he soldered it onto the board for me. We got together for some grub tonight and he gave me the repaired switch.

Being kinda curious, I installed it while sitting in the parking lot of the restaurant. I had cruise control on the way home! Of course that only involved a half mile or so on the freeway so I diverted in order to play with it a bit longer. The truck didn't want to resume after I hit the brake pedal but all other functions worked fine.

The brake switch is touchy and has occasionally left the brake lights on so I imagine it may be at fault there.


Other than that, I'm kinda excited to have the cruise control working again. It's been inop for the better part of the last ten years.

Clock spring? What is that? I have a recall on my 99 Caravan for that.

the clock spring is the round, electrical device under the steering wheel that controls the airbag and all the function buttons on your steering wheel. it is not visible unless the wheel is removed.

A clock spring connects the steering wheel to the rest of the car. It is a flat multi-conductor cable in a round can under the steering wheel. It replaces sliding contacts.

Opened clockspring picture below:

R.

Thank you

when replacing your clock spring, it MUST be done in exactly the way the FSM instructs, or you will have some nasty problems crop up. and there is also the possibility you will mess up or ruin the clock spring in the process. the one you show looks like a newer model than the one i have on the bench for a 97. 2004 ish or so ?