BlackShark

There's been a lot of threads related to this, but didn't find my particular symtom.

Background:
1987 S4 Auto. Cruise didn't work. Tests according to the WSM are good. The day before SITM 2007 I tried the brain resoldering. Didn't work.

I ordered a used unit because I didn't want to pay for a rebuild one. Maybe that's the problem, but here's my current symtoms.

When you hit the "set/accel" (move stalk forward) the car accelerates and just keeps accelerating. It disengages by brake or using the stalk. I went through the WSM tests again and all seem to work. The only thing I might question is that when it says the result should be "battery voltage" I am seeing around 10vdc?

Anyone experience anything like this? Maybe it's just a bad brain?

FlyingDog

You have the James Bond edition like me. It's not really cruise control, it's the instant acceleration/get-away button.

BlackShark

Update: I've tried two additional cc brains and the results are the same. When you try to set the speed it accelerates and keeps accelerating. Thinking now I need to verify with a known good cc brain. If it's not the brain what could cause this?

FlyingDog

vacuum? The throttle servo is vacuum actuated. I've never really looked into the cruise system, so that's all I can come up with...

joejoe

Could the set/accel contact be bad in the stalk? If cc brain is good and car goes to acceleration only then maybe the stalk is getting stuck when trying to only set speed. The brains that accel might be good candidates for resoldering.

85fortheDrive

[QUOTE=BlackShark]There's been a lot of threads related to this, but didn't find my particular symtom.


When you hit the "set/accel" (move stalk forward) the car accelerates and just keeps accelerating.
QUOTE]

My first suspicion here is the stem in your switch. 10 vdc seems fine and it indicates that voltage is turned on. The vaccuum system is actuated methinks because you to get a message to the servo. So too, the brake cuts off the system as it should.

Have you tinkered with the switch stem? Is it possible that it is not releasing quite right? I've had issues with my blinker/washer assembly so I can testify that other areas of that multifunction part can deteriorate.

BlackShark

I haven't dug into the stalk, but when you run the test at the plug to the brain you get the correct reading when activating the set/accell. Believe you see voltage when you push the set/accell and it goes away when you release. Also the using the pushbutton switch you can obserb the vacumn move the throttle forward and back. Maybe the servo under the fender has an issue, doesn't know when you quit once triggered until to disable via brake or stalk.

85fortheDrive

Blackshark:

The part that confuses me is the dual nature of the set/accel switch. I'm not sure how the two functions relate to the 5 and 7 pins on the brain. You want the set part, but get accel instead. If you've got vacuum at the servo, my sense is that that part is okay. You've done some good testing here.

Maybe we should call Alan!

Glen McCartney

I am having the same issue after installing a cruise control brain (used).
The cruise control stopped working completely at the end of last season. Performed all the tests, and everything checked OK, so figured the brain.

Got a used cc brain during christmas special from Mark

Took car out today and tested....keeps accelerating.

Was there any resolution found?

Thanks
Glen

rjm65

If resoldering doesn't work, great writeup on replacing some of the caps on the 78-87 cruise brain here:

http://forums.pelicanparts.com/porsc...ntrol-amp.html

sikes

I'm in the same boat with my 87 S4. It either does not work, at all, or it goes into "James Bond getaway mode". Found this Cruise Control Computer rebuild service on eBay:

http://www.ebay.com/itm/911-928-PORS...53d5e4&vxp=mtr

He's supposedly done 36 928 CC computer rebuilds. Gives a LIFETIME warranty. Anyone ever use them?

sstrickstein

My 84 does the "James Bond" mode too. I have tried a rebuilt unit, resoldered mine, tried a known good used. All the same. Good vacume at servo. I used deoxit on the connections and the switch. I think I've got a bad servo.

jeremymilo

soontobered84

I don't know if this will "cure" your James Bond mode issue, but Roger@928sRus is offering rebuilt CC brains now.