Cruise Control Fail above 40mph: need Sherlock Holmes help!

reesnick · 09-15-2018, 07:51 PM

Seeking Answers/Ideas: 1996 E-350: Cruise Control fails above 40mph.
1. Over last 3 years, since we picked up our Beast, speedometer has always bounced some at Hwy speeds, and cruise worked fine up to 95+mph. Does your speedometer bounce at all (is this normal)?
2. Fall 2017: Cruise suddenly stopped working at higher speeds and a periodic tranny down shift and back to up shift started occurring over 70mph but not always. Been here? Solution?
3. Story&Question: It’s been at my local Ford dealership for approximately 6 months total (2 periods: we took it back for a couple week summer trip) with the request to fix the cruise control and told them of the periodic shift down/up at high speeds. They said they’re unrelated. In these months in the shop, they repaired and/or rebuilt the speed cluster 6 times, confirmed all electronic/wiring is good, did something in the rear axle, and ultimately made no improvements (cost me $1,300 in parts and they covered labor: FWIW we think they also damaged a ring too because we started leaking at the end of our trip and the mechanic later told me his apprentice may have damaged it on install: ug! ...another $1,500 rebuild in a shop). Ford demands the cruise on steering wheel was aftermarket. 1st owner was oil field (100,000mi), 2nd owner (miles 200-300,000) says cruise and wheel were always in it. I don’t think it makes sense: looks same, etc. What else can I consider and try? Is cruise and tranny linked? One old mechanic friend says it may be a tranny sensor. I’m 100% ignorant.

Ok all you Sherlock’s and all you consumers who have been as unfortunate as I, what next?!?!?
Thanks!!!!

carringb · 09-16-2018, 12:53 AM

Probably the rear speed sensor in the top of the diff is fouled. You can try cleaning it but it's cheap enough you might as well replace it.

The shifting problem may be a bad Throttle position sensor. It's easy enough to test with either a DVOM or monitoring the TPA data channel with a good scan tool.

reesnick · 10-11-2018, 09:04 PM

Carringb, thanks for your advice.
Speed sensor: Diesel shop tried to replace that speed sensor about a year ago, and the speedometer bounced like crazy at all speeds, so he put the old one back in and it only bounced at high highway speed’s.
Ford replaced it too. See images. No changes. If you look at the two pictures of ford’s invoice, you might make sense of the rest of what they did.
Thanks