Cruise Control Problem
 

I have finally decided to tackle a problem that has persisted for years! The cruise control on my 1983 928s automatic either works perfectly or not at all on a given trip.I have followed the workshop manual trouble shooting procedure and have discovered that instead of getting a 0 ohms reading between terminal 12 and car ground I am getting a reading of 3.5 ohms. Has anybody had this problem ? Where should I start looking for the problem?

Sounds like you may have intermittent, bad connection somewhere. This may also be defective switch(brake, control lever) or grounding issue..
There are some write up's I have followed to fix my issues.

http://members.rennlist.com/pirtle/svc_cc.html

http://jenniskens.livedsl.nl/Technic...0/MyTip022.htm

The known issue with control unit is that soldered connections on the foil side become loose due to vibration or heat.
You may need to inspect the circuit board and possibly resolder the components again. Check everything else first, before resoldering.

Cheers,

Simo

Had the same issue. Re-soldered every joint on the board and it has worked perfectly for 5 years. If you have checked everything else, then I would recommend re-soldering.

not to hijack the thread, but mine works, but slowly looses speed...
if i touch the gas pedal it will catch back up.. almost seems as if the vac servo is not strong enough to overcome the return spring for the throttle...

You have loose speed?

Sounds like you are losing vacuum.

for the OP try resoldering the control unit it is behind the right console cover and under the heater box held with one 7 mm screw, the box is silver and its about 4 inches by 6 inches and 1 1/2 inches high

Vanster try plugging the black line for the HVAC system at the booster then drive the car if the CC works then you have a leaking pod in the HVAC system

Thanks for the input. It is John Pritle's posting of the workshop manual that I am using to help solve the problem. Point number 16 of the workshop manual is the present problem....getting 3.5 ohms instead of 0 ohms.Could a failing speed censor or neutral switch be the cause?

NO, just resolder the box

I definitely endorse doing it yourself...but back in the day there used to be a POC that serviced/rebuilt the cruise control controllers for a decent price. He started on Mercs, from what I recall and then the 928 community pinged in. That was back with the earlier email lists though.

Wait, found it after a fun ride in the wayback machine:
http://www.nichols.nu/tip003.htm

Thanks guys......It,s working perfectly!!
Bought a soldering iron and some solder from Radio Shack for less than $20.00, removed the circuit board, discovered that the board was manufactured in 1982 and rebuilt in 2002. I re-soldered all the joints and then inspected my work under a magnifier to make sure no solder had run between circuits, re assembled everything and went out for a drive.
That was 2 days ago and the cruise control is still working flawlessly.
My next project is the sunroof which does not always open and close. Can it be anything other than a faulty switch?

Nice work! Love a successful fix!

Congradulations on the cruise fix! Mine just quit last week, so I'll be doing the same soldering this week.

If the roof gets no movement what-so-ever, first check for current at the motor. If no current, then it will most likely be the switch. The most common problem on the roof is dirty rails and cable, along with poor adjustment. The motors are rarely the main problem.

...., this may be of some use, re the sunroof ?
http://www.kondratyev.com/porsche/te...or/sunroof.htm

Ken
80 928 S
5 Speed

UK

1989 928 cruise control issue, stopped working - Solved
 

A quick one for prosperity.

I read a lot of the cruise control threads and my issue was one I did not find.

I did all the steps in the WSM, all food other that I am high on the ohms for the 4-6 ohms. It was 11 ohms. Not sure what that means...

After validating everything I could find good I opened the connector. Turns out the 14 pin wire is a bit short and had broken free of the pin.

Soldered in a new extension into the pin and then all was good.

This has been a 4 month hunt. Intermittent problem that I have swapped brains three time and then it quick working all together. Today I finally found it.

There was no test for the 14 pin, so not sure how I would have found without opening the connector...

For the record, a current link to this company. Doesn't mention 928's, but ...
http://www.perfanalysis.com/electronics/cruise-control/