What to try yet to fix my cruise?

tomiki · 09-06-2009, 10:58 AM

Hi,

I purchased a used complete cruise system from an ’84 944 and installed it to my ’86 924S. Fortunately the cabling was all present in the car, so I didn’t need to rewire. And of course, after installation the cruise did not work… As it’s a very complex system and very hard to test (coz you gotta be moving the car at least 30 mph while testing…) I went step-by-step in the following manner (long, but might be an interesting before-sleep reading

):

First I checked the stalk by the steering wheel, and it had contact problems, not all functions worked properly. Therefore, I disassembled it, cleaned all the tiny metal contacts, reassembled – works perfectly. But the cruise? No.

Then I tested all the wiring, following the instructions of the Workshop Manual I measured the voltages on the 16 pole multiple-pin plug – everything was perfect. All switches (steering column stalk, clutch and brake) work perfectly. The cruise? No.

Then I disassembled the drive, located by the engine. Surprisingly the little electric motor could not rotate inside it. So I disassembled that one too and found out that two pieces of the wall magnets just broke off…and of course locked the motor. Thus I removed them, tested: motor works perfectly. Then I cleaned the whole drive, all contacts, fed in grease, reassembled and measured its electrics according to the Workshop Manual: every single resistance value was perfect. But the cruise still didn’t work.

Then I continued with checking the Hall-Sender inside the speedometer. This was the trickiest one, but fortunately the Workshop Manual had an excellent hint: cars with electric targa hardtop (like mine) can be checked easily. One needs to simply unhook the top holding slides just like when wishing to take the roof out from its place, and then start up the car and start moving. As soon as the speedometer sends a signal that the car is moving (already at 2-3 mph), the roof slides hook themselves automatically. I checked this feature on my car, and it works! Of course it was not only great news that my Hall-Sender is working, but also that my car has this cool re-hooking feature

But the cruise is still not working.

Then I uninstalled the cruise control unit, which is most likely the last chance and thus probably the faulty unit. Following the instructions on Clarks Garage I inspected the board, but couldn’t really see anything faulty inside. This is where I am now.

Thus my questions are: what else should I check? Or how should I check the brain further? Are there any typical parts that can die in it? Are there any testing/measurement points on it, which could be tested? Its part number is 944 617 127 00 as it’s the early 944 version. Also, does anyone have such a working brain for sale, if I can’t fix this one?

Thanks for reading and thanks for advices!

Porsche-O-Phile · Porsche-O-Phile's Garage

In my experiences, it's either the computer under the center console or the servo unit under the hood. Not much else it can be.

I'm 99% sure I have a spare early c/c brain - I'll take a look. If you want it you can have it cheap.

kdjones2000 · kdjones2000's Garage

Oftentimes the brain is faulty due to cracks in the solder joints. Carefully re-melt all of the joints in the brain and see if that fixes it or not.

If it's "Or not", then it's time for another brain...

Good luck, Keith

tomiki · 09-07-2009, 12:43 AM

Hi Jeff,
I'd appreciate if you could take a look. Thanks.
Hi Keith,
Yeah, I shall consider that too, just redoing all of them will take some 2-4 hours (for me

) so for that I need to allocate this amount of time

Mike in Everett · 09-07-2009, 06:33 AM

Related troubleshooting on a 1997 NA 944: trying to reconnect teh cruise an use it results in a blown fuse. Sounds like I need to go into the cruise servo.

maxiblu · 04-07-2010, 06:27 PM

Can you send me instructions to check the cruise control wiring on my 84 944 from the factory repair manual? What voltage or resistance should be present at certain times? Any help would be appreciated.

tomiki · 11:30 PM

Old cruise cabling (-85)

tomiki · 04-07-2010, 11:29 PM

New cruise cabling (85-)

maxiblu · 04-15-2010, 06:59 AM

Thanks for the cruise control test procedures Tomiki. That is exactly what I was looking for.

tomiki · 04-15-2010, 07:04 AM

You're welcome.
BTW, my personal favorite is the test to be done with the lifting roof

and it really works!
Actually, once I went through all these steps and it still didn't work, I myself had to replace the control unit.