Hey all - I've pretty thoroughly gone through the cruise system using Oliver Scholz's writeup and determined the following:

- Clutch switch was bad; opening it and cleaning it made it good
- brake switch was bad; opening it and cleaning it made it good
- ground at servo was poor, showed 30 ohms; new ground established
- vacuum can is leaking; work in progress
- vacuum dump solenoid was sticking; cleaning it made it good
- swapped a servo from another GM vehicle; both servos behave the same and tested good per Oliver's instructions
- Cruise stalk set switch tested bad and was replaced with a new Standard part

As you can see...just about every part of the system tested bad, but the system still doesn't work with the new and repaired parts. I'm suspecting the cruise module BECAUSE:

With the ignition ON, the servo is only receiving 0.96 volts across both the vacuum solenoid (Terminals A&C) and the vent solenoid (Terminals C&E). I believe they should be receiving 12 volts each, as this is how they were tested per Oliver's instructions. Can anyone confirm this? Would this point to a bad module?

Anything else work checking? The vacuum can was riddled with pinholes, I'm trying to patch it but the cruise didn't work with the can bypassed either.

Thanks all. BTW its a 1986 GT V6.

Key on, engine off, foot off of the clutch, cruise control on - does the vacuum valve click when you start to depress the brake?

[This message has been edited by phonedawgz (edited 12-08-2010).]

Vacuum valve does click. I have been using a multimeter for diagnosis.

EDIT: sorry didn't answer your question...I only have a volt meter, not a test light.

[This message has been edited by masospaghetti (edited 12-08-2010).]

Do you have a download of the 86 GM service manual? If not download it here under 86. I'll make reference to it so it will be good if we both have it.

http://www.fieronews.net/fusion/downloads.php

sweet, thanks.

I have the 86 FSM hard copy that i've been using. The online one is downloading but I assume they are the same? I've gone through the troubleshooting tables and all of the tests show good (this was how I found the bad ground, though)

I have some experience with electrical troubleshooting...ive been going through the diagrams in the FSM.

[This message has been edited by masospaghetti (edited 12-08-2010).]

It will be nice to try to reference page #s - well see how it goes

My hard copy had the cruise control wiring and troubleshooting in chapter 8, section 34.

Although the download hasn't finished, the link you gave me appears to be the same manual as the one i've got.

[This message has been edited by masospaghetti (edited 12-08-2010).]

Speedo works fine? no SES lights right?

quote Originally posted by phonedawgz: Speedo works fine? no SES lights right?

Correct, and correct.

And yeah it just pulled out...wasn't mechanically fastened at all. I cleaned the contacts and looked at the circuit board, it doesn't appear damaged but it was loose in there.

[This message has been edited by masospaghetti (edited 12-08-2010).]

So on 340-0 there are several wires that get power if the cruise switch is on, or depressed or whatever. Grey - Brown/White - Dk Blue - Grey Black. Can you unplug the connector from the cruise control unit and verify that each of those wires gets power when the associated switch is on or depressed or whatever? I'm assuming you can understand when each of those should get power depending on what is happening with the stalk switch. If not say so and I'll baby step you through it.

You can always just slap an electronic cruise module off of mid 90s GMs. You just have to buy a new end, clamp it on and run the wires to the cruise stalk. It is a ridiculously easy upgrade.

But if the stalk is bad it still won't work. Still needs to be wired to the brake an clutch. The way I look at it, with some logical troubleshooting it's easier to get the old one working.

quote Originally posted by katore8105: You can always just slap an electronic cruise module off of mid 90s GMs. You just have to buy a new end, clamp it on and run the wires to the cruise stalk. It is a ridiculously easy upgrade.

What's involved in this? New digital servo with new control box?

quote So on 340-0 there are several wires that get power if the cruise switch is on, or depressed or whatever. Grey - Brown/White - Dk Blue - Grey Black. Can you unplug the connector from the cruise control unit and verify that each of those wires gets power when the associated switch is on or depressed or whatever? I'm assuming you can understand when each of those should get power depending on what is happening with the stalk switch. If not say so and I'll baby step you through it.

No prob, all four inputs (A, G, L, & M on the wiring schematic) showed +12v when probed at the module connector when compared to J (ground).

[This message has been edited by masospaghetti (edited 12-08-2010).]

All the time or just when you pushed or turned the switch?

They should not have +12 on them when the switch or button associated with them is off.

quote Originally posted by phonedawgz: All the time or just when you pushed or turned the switch? They should not have +12 on them when the switch or button associated with them is off.

Correct...A & G have +12v when the "cruise" switch is turned on. L has +12v only when the set button is depressed. M only has +12v when the R/A slider is moved.

OK

So now back at the trunk can you verify you have +12v on the purple wire at the cruise control vacuum release solenoid (just two wires on it, purple and black)

Can you also verify you have good engine vacuum on the vacuum line leading from the engine. You have the vacuum resivour just disconnected and the line plugged right now right?

quote Originally posted by phonedawgz: OK So now back at the trunk can you verify you have +12v on the purple wire at the cruise control vacuum release solenoid (just two wires on it, purple and black)

11.49 volts at the connector...the solenoid clicks when the connector is unplugged or reconnected. I also tested the dump solenoid with a vacuum pump, it holds vacuum until the brake is depressed, in which the vacuum is dumped.

quote Can you also verify you have good engine vacuum on the vacuum line leading from the engine.

17 in-hg of vacuum at the vacuum line with the engine running at high idle.

quote You have the vacuum resivour just disconnected and the line plugged right now right?

Right now I have the vacuum line running directly to the servo to prevent a vacuum leak. I don't plan on leaving it this way for long, I am in the process of repairing the vacuum can.

[This message has been edited by masospaghetti (edited 12-08-2010).]

There's an interesting post on the "tomato can"

anyways

So now if you have some little allegator jumper leads this would be the time to use them

Unplug the connector from the servo unit. Unplug the dump valve at the dump valve and plug the vacuum hose with a golf tee. ( You could also just leave the dump valve connected and powered with the key on)

Run +12 to the two outside pins of the servo unit. Apply ground to the center pin. The other pins leave disconnected. Now apply vacuum to the "engine/input" side of the servo The diaphram should retract as you do this. The diaphram should stay retracted.

See if this works.

[This message has been edited by phonedawgz (edited 12-08-2010).]

quote Originally posted by phonedawgz: Unplug the connector from the servo unit. Unplug the dump valve at the dump valve and plug the vacuum hose with a golf tee. ( You could also just leave the dump valve connected and powered with the key on) Run +12 to the two outside pins of the servo unit. Apply ground to the center pin. The other pins leave disconnected. Now apply vacuum to the "engine/input" side of the servo The diaphram should retract as you do this. The diaphram should stay retracted.

Servo does exactly what you say it should.

quote Connect a digital volt meter to pins B and D of the servo diaphram (wiring disconnected) With the meter set to read DC voltage - lowest setting push the diaphram in. Then release the diaphram. One way you should get a positive voltage of about 0.3mV and when moving the other way you should get a negative voltage of the same (-0.3mV)

I only got 0.01 mV on the multimeter but its pretty slow to respond, I don't think it had time to get a good reading.

Try it just a little slower. Make sure one way its positive and the other way it's negative.

I tried goin a little slower, most I could get was 0.01 mV and -0.01 mV. Both servos I have behaved the same way. I'm guessing there's no easy way to test the module, besides eliminating everything else?

BTW thanks for your help...and the soup can threads are hysterical.

I have a "reman" module (more like, salvaged and tested working) on order but it probably will take a few days to get here.

[This message has been edited by masospaghetti (edited 12-08-2010).]

Installed the reman module and the cruise is now working. So modules do sometimes go bad.

Also, note that the cruise worked without the vacuum canister, although it didn't operate as smoothly..this might be useful to some at troubleshooting if you have a leaky canister.

Thanks for the help.

Cool cool cool

Well it should have worked, you fixed every other part of the cruise control before you got there. Cool to see you got it fixed. Sucked that there was so many things up with it.