Trouble shooting cruise ctrl...

Nine9six · Nine9six's Garage

I have an 87 Carrera with cruise control. The cruise control will engage, but will not hold speed, and bleeds down rather rapidly.
Does this system work on vacuum? What might be the problem?
Thank you in advance for any assistance.
Paul

PCA7GGR · 06-04-2005, 09:26 AM

Could be your cruise control "control" module. It is a small retangular box that sits under your radio. So if you can borrow one from another Carrera and swap them out. If the new box cures the problem, your original box is bad.

Por_sha911 · Por_sha911's Garage

Do a search! I had the same problem last year. Posted where I found the best deal on a rebuilt module.

porschenut · 06-04-2005, 06:14 PM

It doesn't make sense to me that it would be the CC brain. If it keeps working but the speed slowly decreases, it can't be the fault of the electronic memory. Much more likely that there's a problem with the vacuum line or servo unit, IMO.

Nine9six · Nine9six's Garage

Thanks for your input Dave...Kinda what I was thinking. Would you happen to know where the servo unit is located on an 87. I will be pulling the carpet out of the trunk to check the vacuum line tomorrow.
Regards,
Paul

Por_sha911 · Por_sha911's Garage

I had EXACTLY the same problem and I totally agreed with Dave right up till I swapped out the brain with one from a friend's car and all the problems went away (we put the brain from my car in his and the problem went to his car). It could be the capacitors are leaking (I tried replacing those first but no go).

rickdm · 06-05-2005, 03:51 PM

I had the same issue with the speed bleeding off. I had Beckman Technology rebuild the cruise control module, and now it works just fine. I believe the folks at Pelican can also send it off for a rebuild.

rickdm

Por_sha911 · Por_sha911's Garage

I had mine done by Beckmann as well. Pelican sends theirs to Loren to rebuild.

PeteBrown · 06-06-2005, 06:14 AM

Mine worked sporatically after my clutch was replaced. Turns out pelicanite vesnyder found one of my vacume lines was half attached when he replaced my rear shocks. The vacum solenoid is located on the drivers side of the engine compartment towards the front of the car (right above the LR shock). Vance properly installed the line and now my cruise works better than ever.

david914 · 06-06-2005, 08:13 AM

Quote:

Originally posted by porschenut
It doesn't make sense to me that it would be the CC brain. If it keeps working but the speed slowly decreases, it can't be the fault of the electronic memory. Much more likely that there's a problem with the vacuum line or servo unit, IMO.

Actually, it's the most common problem with the 911 cruise controls and it IS the brain box most of the time. I sure wish someone could find out which component in the brain box is the one that fails and post it here. It must be a closely guarded secret as no one seems to know.

Superman · 06-06-2005, 08:37 AM

Warren?

FrayAdjacent911 · 06-06-2005, 10:49 AM

If you have trouble shooting your cruise control, try moving closer, concentrate on your sight picture and squeeze the trigger, do not pull it.

david914 · 06-06-2005, 02:05 PM

Funny, that very thought crossed my mind when I first read this post...

Nine9six · Nine9six's Garage

I had no idea so many comedians were logged onto Pelican...All must be "Little Jerry Seinfeld's" in training :-)

island911 · 06-07-2005, 11:40 AM

Nine9 (for a serious post, for a change)--

I have quite few threads on the topic. (search under island911)

Your prob is most likely the brain. ....if accelerating, using the CC, works, then the prob' is definitly the brain-box. (all the servo needs to do is hold throttle, increase or decrease throttle.) The brain-box is under/fwd the wiper-motor-ish. (behind the cover)

The guys over on the benz board say the prob's with the brain are usually nothing more than solder points gone bad. That all you need to do is systematically retouch all the solder points and re-install.

Having said that, I'll start timing how long it take loran to chime-in to say "don't do that ... you will ruin it . . send it to me, along with some cash, and I'll fix it with magic"

david914 · 06-07-2005, 04:42 PM

I have actually tried re-flowing any suspicious looking solder joints on SC's cruise brain with no joy. I'm inclined to believe it's a component that's value drifts as it heats up.

As I said before, it sure would be nice if someone who knew what the problem component is would post the fix here!

don911 · don911's Garage

I also have an 87. My I unhooked my cc when I replaced the motor. It's been unhooked for a year and a half but worked fine before.
Everything is still on the car but you're welcome to any parts that I can easily remove.

Porsche80 · Porsche80's Garage

I have an 80 911SC and just had the brain redone by Beckman, but still does not work. The 1980's used a servo for vacumm and I have tested the servo and it holds vacuum. One ?? I have if you ohm out one of the connectors on the servo-one lead on connector of servo and other grd should it show a short?

Thanks
C