Cruise Control challenges

[Richwro1]

Hello all,

I have a 87 3.2 carrera and the Cruise Control suddenly stopped working - can't set it to hold any speed.
I went through the Bentley's troubleshooting guide and it showed a bad clutch switch, which I replaced. Showed same ohm nil with clutch in or out. Should have showed 10 ohms with the clutch pressed down. new switch in and still no -a -worky. Re-tested and it shows a bad clutch switch again! Tested both old and new switch with an ohm meter on the bench and they both seem good. The tests passed on the column switch, the solenoid in the back, and the brake light switch. So I am now dumbfounded. Any additional thoughts or is it most likely the module as a default. If so, who do you know who can fix it?
As always, much appreciated!

[86 911 Targa]

Originally Posted by Richwro1

Hello all,

I have a 87 3.2 carrera and the Cruise Control suddenly stopped working - can't set it to hold any speed.
I went through the Bentley's troubleshooting guide and it showed a bad clutch switch, which I replaced. Showed same ohm nil with clutch in or out. Should have showed 10 ohms with the clutch pressed down. new switch in and still no -a -worky. Re-tested and it shows a bad clutch switch again! Tested both old and new switch with an ohm meter on the bench and they both seem good. The tests passed on the column switch, the solenoid in the back, and the brake light switch. So I am now dumbfounded. Any additional thoughts or is it most likely the module as a default. If so, who do you know who can fix it?
As always, much appreciated!

Your well done analysis is pointing towards the control unit located in the boot.

There are several companies that will repair the unit.

Including:

Beckman Technology

3333 Industrial Dr.

Durnham, NC 27704

Give them a call.

Also, do a search "cruise control repair".

Good luck,

Gerry

[Geneman]

if the problem is the mechanical control box in the engine compartment with the wire sticking lout of it that goes to the throttle.. ( I just removed a [perfect one from a low mileage 88 ...worked fine last week.. can sell it to you along with the electronics if you show me where they are Best Frank email best rauscher@wistar.org

[Richwro1]

Thanks for the info on the repair place - that's a key piece of info.
I did look at the connections - cable to the throttle and the vacuum lines and visually they all look correct. The solenoid in the back showed 14 ohms, which is the right reading in the Bentley test so I don't think that is it.
So far, the module is becoming the default.

[Hendog]

My '87 coupe had the same problem. I reflowed solder at various suspicious spots on the PC board of the control unit: works fine now. They are prone to cold solder joint breaks.

[Richwro1]

Not an electrical engineer, but it's worth a try to pull the board out and re-solder. Worse I do is destroy it and spend more bucks on a rebuild from our sponsor?

My biggest question is why the Bentleys troubleshoot result of the clutch switch - really testing the wiring, not the module, shows it isn't functioning, even when I replaced it and made sure the adjustment was right - clutch lever tab moves the switch lever when the petal is non-engaged (no foot on it) and is not touching the lever when I press the clutch pedal (engaged). The switch (new and old ) both work (show they are switching on and off via ohm meter). The troubleshoot guide next had me test the solenoid in the back to remove that as a problem and it passed on the ohm reading (14 ohms), meaning the switch is the problem, but its not.

Got me scratching my head, so I will go the module route and re-solder to try that.

Any other thoughts are appreciated!

[Chuck.H]

Make sure the clutch tab is actually pressing on the switch, one way to try this is by using your foot to pull the clutch pedal back up to see if you then can engage cruise. Also check your brake lights are not on for some reason, that will also disable it.

Chuck.H
'89 TurboLookTarga, 340k miles

[Hendog]

Originally Posted by Richwro1

My biggest question is why the Bentleys troubleshoot result of the clutch switch - really testing the wiring, not the module, shows it isn't functioning, even when I replaced it and made sure the adjustment was right - clutch lever tab moves the switch lever when the petal is non-engaged (no foot on it) and is not touching the lever when I press the clutch pedal (engaged). The switch (new and old ) both work (show they are switching on and off via ohm meter). The troubleshoot guide next had me test the solenoid in the back to remove that as a problem and it passed on the ohm reading (14 ohms), meaning the switch is the problem, but its not.

I see. Is it possible the wiring from the switch to the module has a break in it?
I hope I understood you correctly...

[Richwro1]

I actually was thinking the same thing - boy I hope not. I guess the key is if anyone else followed the Bentleys troubleshooting guide and did in fact get a 10 ohms reading when pressing down on the clutch peddle? If so, then it could be the wiring.

[rgrimm]

I did go through the Bentley guide on my '84 and it pointed to a bad clutch switch. I asked my wrench and he replied "those never fail." He was right...a replacement control unit fixed it.

[Richwro1]

Thanks Roger, you brought my confidence level to a new high to focus on the control module and I agree. I replaced the switch with a new one and the fault is still there, as well as the result of the Bentleys troubleshoot result.
From what I can see in the wiring diagram, the clutch switch is normally closed (when the clutch is pressed down and the lever on the switch is in its unpressed position.
This completes the circuit and energizes the relay, which is also normally closed, opening the relay switch and killing the circuit to the module. When you release the clutch, the little lever presses the switch lever and keeps it open, de-energizing the relay, which makes its switch closed, keeping current to the module. So, you only need to make sure the clutch switch is slightly pressed by the clutch peddle lever when the clutch peddle is unpressed by your foot, to keep the it open, when adjusting the switch position. That's the way I see it.

[atc_marty]

I fixed the cruise control on my 87 Carrera last month by taking the electronic box under the dash to a small local electronics repair shop to have the capacitors tested and the soldering points redone. A week and $80 later, I had my cruise working. Way cheaper than a $1000 new unit!