Hi guys. never done a forum but looking for help. my 2002 diesel excursion has a low speed surge that no one has been able to figure out. It starts and runs fine unless your trying maintain a slow speed ( 20 - 40 mph). Oddly enough, if you turn on the cruise control it smooths out perfectly. I've pulled a 10,000 lb trsailer with it as well with no problems. Has new transmission, but did the same thing with the old. any ideas?? dealership charged me $400 to do nothing.

 

You are in the wrong forum, this is for 94.5 back engines. Put the same question in two forums above where it says 99-03 7.3 and they should be able to help you.

 

thanks!!!
sorry.

 

in case anyone sees this: I found the problem.

It was the throttle position sensor. Problem is, it never showed any code.
Runs great now.

 

How did you figure this out? I'm thinking mine might be bad too

 

I don't know how to test the tps other than with autoenginuity or a similar diagnostics program. The tps is part of the throttle pedal assembly and i bought one a couple months ago at the dealer and it was only 90 bucks, surprised at the price coming from the dealer. I don't know what the dealers return policy is but you could probably buy one and switch it out and see if that was the problem. It is only 3 bolts and a wire harness to switch them, it took me about ten minutes to switch them out. Maybe someone else will come on that knows how to test them.

 

Don't they need to be calibrated too after they're installed????

 

I have never read anything about calibrating out tps and the ford service manual didn't say anything about it either. I just put the three bolts in and plugged it in and it ran perfect and i tested the new one with my autoenginuity and it was fine.

 

I replaced mine about a year ago, just unbolt the old one and bolt the new one in. I figured that was my problem by using the cruse control, it would do it with it off then hit the cruse control and it stopped... Just my 2 cents

Joe

 

I just got lucky in figuring out what it was. My wifes navigator has been giving us fits and the TPS came up in that conversation. I had it at the Diesel shop ( I'm not much of a mechanic) and the guy was telling me he wasnt getting any codes on it.; I said to give it a try and I'll roll the dice. It worked. Best $200 bucks I ever spent. It had me at a point where I was very frustrated driving it and now I love it again. Amazing the dealer couldnt tell me what it was and charged me $400.00 to replace some other component that didnt do anything.

The navigator is a whole nother story if anyone is having strange problems with a bucking engine.

 

To Ford Dad:

The cruise was the big clue for me too.

 

OK guys, I have the opposite problem. When I set the cruise at 40-45, and the TC is all locked up, I feel a little surge. It happens on and off, and it's done it since it was new. Of course the dealership could never "duplicate the problem" even when I took them for a ride. It's not a bad surge. There is no acknowledgement from the speedo, the tach, or the pyro guage, but you can feel it. Kinda like when you get "the bobs" after being on the boat all day. Any ideas??

 

Mine does this at 70. Only thing that comes to mind would be the VSS in the rear diff.... I have yet to check mine. It's a mag pickup like the CPS is, so it's prone to failure.......

 

HMMM, I'll have to check that out.

 

I'm not sure how the speedo circuit is on the Super Duty's but on my 94 F150 the VSS signal was sent to the speedo module and the speedo sent the cruise module it's speed command. I had a real bad surging problem on my F150 and replacing the VSS made it 10 times better, but it still had some drift due to the speedo. Once the original speedo failed I swapped in a used one and the problem was almost non-existant.

If the SD is the same way maybe the speedo is partly to blame as well?? Also, follow the VSS harness on the frame and check the plugs too. I have heard of those being corroded, etc... causing problems.

The tone ring, the ring with multiple teeth that is pressed onto the carrier inside the differential, has been known to lose some teeth on the old F-series. They have also been known to "clog" with fine metal shavings. Basically the VSS can't "see" the teeth because the gaps are filled with metal shavings that are magnetically attracted to them.

Popping off the cover back there for a quick inspection wouldn't hurt if all else turns out to be good. If your truck is like mine it's due for a diff fluid change anyway!!!