So I finally got my cruise control working in my '97 D1. I have an CC ECU from a D2 in my D1. Just took a long trip and I noticed after about an hour into the trip using CC, the UltraGauge MPH was jumping around some but the speedometer was working fine.
Twice, the UG gave me a high speed warning. I think it said I was going 91mph or so the speedo showed 75ish. At a traffic light, the UG showed me going 40mph while at a red light. It did go to zero in a couple seconds.
The speedometer never fluctuated or bounced around.
Is my VSS going out or is it just the CC ECU?
thanks,
dcphotos

 

On my 96, CC gets speed signal from RR abs sensor. Speedometer get it's signal from the alternator. I am not sure where the Ultragauge gets its signal, but if it is from the VSS that could be your problem.

 

John, I'm not sure that is correct.

From the 1997 RAVE (B5-2) (could be different on your 1996, but I doubt it)....
"Speed Input
Terminal 11 of the Cruise Control ECU (Z121) monitors the Vehicle Speed output signal from the Instrument Cluster (Z142) through the YK wire. This signal is a pulsing voltage, and its frequency changes with vehicle speed."

The Speedo is fed by the VSS. (RAVE E1-1)

IIRC there is a calibration that needs to be done with Ultraguage.

 

Tach = Alternator Driven
Speedo = VSS Driven

 

Best4x4, where does the UltraGauge get it's MPH from?

WaltNYC - my UltraGauge was/is calibrated to the Speedometer. I used an app on my iPhone to check and did the adjustment on the UG.

I'll be heading back home and I'll be able to see if it still does this. So far around town the CC has worked great. It was working fine till about an hour into the trip so wondering if heat is a factor. When it did go haywire, the UG should for example 65mph, 40, mph back to 65 where the CC was set then maybe 80mph then 30, 90, 65. but the Speedometer needle was at 65.
But when it was going haywire the vacuum pump wasn't constant, I could see this on the TPS. The engine slowed because the vacuum wasn't holding for 65mph as set.
Thanks for the input

 

I'm sorry. I really messed that one up.

 

Following up on this, on my drive home, the CC worked flawlessly. It is a bit slow to react but I kind of expect that out of an analog vacuum pump system.
I have the TPS% displaying on my UltraGauge so I could see how S L O W the CC reacts to input.

Not sure why it flaked out on me but I am heading up to Palo Duro Canyon in a couple weeks so an eight hour drive more or less. I'll put it to the test for sure then.

Cheers!

dcphotos