houston944

I have been trying to troubleshoot my cruise control for sometime now. The things I have done so far.

Took out the servo, cleaned it and put it back.

Took out the cruise control brain. All the solder connections on it are good.

Check the voltage and resistance on the connectors as per the repair manual.
All the voltages on Connector 1 are good.
All but one of the resistance values on Connector 2 are good.
The one between terminals 5 and 6 is supposed to be between 20 - 30 ohms and it comes out as about 250 ohms. As per the repair manual terminals 5 and 6 and the engine positive and negative.

Does anyone have any idea as to why it is coming up with such high resistance values. Does it mean a failed sensor? If so which one?

scular

Did you reflow all of the solder connections or just look at them? Sometimes the joints look good, but have tiny cracks. I would suggest ebay to find a new one, all the time put in to fixing will surely surpass the price of a working unit.

SCular

houston944

I looked at the solders under a microscope. But my concern is that the connector is the problem rather than the cruise control brain

Shutemup

mine has had the servo replaced, the brain replaced, and the switch replaced and it still doesn't work

Granite 944

I resoldered my control unit and it worked great.......for about a week, then went into a intermitant, sometimes surging mode. Cleaned the servo, replaced it with another.....no change. Replaced my control unit with another used one, worked better for a while, back to strangeness. Resistance checks all show good according to FSM. Problem seems to be directly related to heat expansion somewhere. When I drive it for extended periods (especially with heater running inside, the CC works better if not perfect. I still need to investigate/try other routes with this. I need to look at switch, and harness real good. Then start diagnosis all over again. I haven't messed with it for a while now. Good luck!

By the way, some time back, Sid V sent me some conformal coating for coating the circut board with after reflowing the solder joints. I still have plenty left in a tube. Let me know, and I'll send it to whoever is wanting to use it. (thanks again Sid!)

Shutemup

I've got a whole list of things I want to do before worrying about the cruise myself

Chris_924s

It is extremely difficult to visually inspect for a cold solder joint, even to a trained eye.

Better off to resolder each and every connection - even connectors..

I do and I've built boards since I was 15.

theedge

<Whispering> Mine works great

Porsche-O-Phile

I'm having similar intermittant problems with mine too (works when it wants to, but when it does, it works great). I've got a new brain on the way, so we'll see if that fixes it. . .

Odd thing is it works about 25% during the day and about 95% of the time at night - how the hell a cruise control computer could tell the difference I have no idea. I even thought it might be temperature related, but nope, interior temps are about the same for my morning (day) and evening (night) jaunts, and it doesn't seem to be related to whether the headlights are on or not either. Just weird I guess.

Rich Sandor

does the cruise get engine speed from the reference sensors? or from the gauge cluster?

Bri Bro

The one between terminals 5 and 6 is supposed to be between 20 - 30 ohms and it comes out as about 250 ohms. As per the repair manual terminals 5 and 6 and the engine positive and negative.
All the connections on Plug 2 go directly to the cruise drive motor. Plug 2 has the signal you listed above. My guess is that these signals command a increase or decrease in throttle cable position (car speed) to the drive unit.

I would check the connector at the drive unit to make sure it is seated and all the pins are in good order. Then you might want to slip in another drive unit (lots of people have removed them) and see if the reading go to nominal.

does the cruise get engine speed from the reference sensors? or from the gauge cluster?

The speed input to the cruise comes from the trany, it is the same input that goes to the speedometer. The speed signal for the cruise comes in on Plug 1, pin 1.

buckshot

re-solder, re-solder, re-solder!!!
i run an office equipment company, have an electronics degree, and
believe me solder connections that look good are not always as they seem!
i re-soldered mine after same symptoms as above, it has worked like a champ ever since... this would be my first thing on the list to try...
you will need to remove the coating off the board before you solder the connections, use only rosin core solder, some people actually tried
"plumbing' solder which has an acid flux in it and ruined their circuit boards!
good luck!
buckshot wi

dme

dang, what's left?

Peckster

One of the replacements? Were they used?

Shutemup

All of the replacements were used. PO replaced the Servo and the Switch (at least he told me he did) and had another cruise computer which he had bought but not swapped.

I just swapped the computers, still doesn't work.

I'm alot more concerned about getting the water to quit leaking in and replacing the interior and my surging idle while in drive atm though.