Working on Cruise Control

[Tom Kelly]

Nothing to do today so I started checking out the cruise control in my 86 GN. Nothing happens at any stage. So I checked switch. Seemed fine but installed the ne one I have had for awhile. Fuse OK. Brake switch checked and adjusted. Vacuum actuator vacuum line has vacuum ten minutes after shut down. I did notice that the throttle body end of the cable had fallen off the little stud. When I put it back on and depressed the rubber boot, the throttle moved nicely. Despite three tries I have not been able to get a fastener to work and it keeps falling off before I can retest the system.. I will get that fixed (anyone know of the PROPER fastener for that?) but if that is disconnected will the system not work? If so, I will wait til I get it connected to move on.
If that isn't causing the problem, what's left to check. I think there is a controller somewhere but I don't know where. Also how can I be sure the actuator is functioning? I only have a voltmeter. What electrics are there to test? As always, all advice welcomed. Pictures always helpful. Thanks guys.

 

[RmvBfrFlght]

The cable retaining clip at the throttle body (TB) is the same as the throttle cable at the TB. IIRC, the same clip is used on the cruise cable at the servo.

The controller is up under the dash sorta' in the area between the steering column and radio. A simple black plastic box with an edge-card connector.

Need to be above 25 MPH to test/set the cruise to be active. Does the Cruise light on the dash light up when activated?

RemoveBeforeFlight

 

[Tom Kelly]

Thanks for your reply. I will try to get the cable secured tomorrow. Nothing happens at any speed. Light doesn't come on and cruise doesn't work. Question:Would it TRY to work with the cable not connected at TB or would it sense no back pressure and not operate.? Is light supposed to come on when you turn cruise on at the switch or only when you activate it by pushing the set button?

 

[Coelacanth]

Subscribed; looking forward to additional troubleshooting steps. This is on my to-do list too, the cruise in my GN hasn't worked in decades.

 

[BMR]

Light only comes on after pressing "set/coast" button. The cruise system should still try to work, cable or not. Is your ecu getting speed signal?

 

[RmvBfrFlght]

What BMR posted about how the CC works. Here is a zip of the FSM CC operation and troubleshooting. Note that I'm only re-posting it. It likely came from another thread here on TB.

RemoveBeforeFlight

 

[Mattthias]

Thanks. Having the same issues. Have been for awhile now even after purchasing a new stalk, checked the fuse and have vacuum.

 

[Tom Kelly]

What BMR posted about how the CC works. Here is a zip of the FSM CC operation and troubleshooting. Note that I'm only re-posting it. It likely came from another thread here on TB.

RemoveBeforeFlight

Thank you for the jpg's. I only wish I was smart enough and had the tester they mentioned.

 

[Tom Kelly]

Thanks. Having the same issues. Have been for awhile now even after purchasing a new stalk, checked the fuse and have vacuum.

Yeah, we are definitely not alone. But even my friends ho have had their GN's from new say that they never worked right from day one.

 

[Tom Kelly]

Light only comes on after pressing "set/coast" button. The cruise system should still try to work, cable or not. Is your ecu getting speed signal?

Yes, speed is showing up on the scanmaster.

 

[Tom Kelly]

Subscribed; looking forward to additional troubleshooting steps. This is on my to-do list too, the cruise in my GN hasn't worked in decades.

Nice ride!

 

[No disintegrations]

If the cable falls off I imagine it won't see the tps rise or fall in correlation to it's command. It prob gives up at that point. Lol.

 

[Coelacanth]

Nice ride!

Thank you, and thanks to RmvBfrFlght for sharing the JPG files...that'll come in handy!

 

[Turbo6inKY]

If the cable falls off I imagine it won't see the tps rise or fall in correlation to it's command. It prob gives up at that point. Lol.

The cruise doesn't see TPS. It only sees the speed sensor output and the brake pedal. So if the cable were disconnected from the throttle, and the car fell below the set point, the servo would WOT trying to get the car back up to speed.

Mine quit working a bit ago. Replaced the servo to no avail. Tried to replace the module, but can't get one new or reman. I did go junkyard diving and came up with three boards that might work. The one I have in now has the same P/N printed on the board, but several jumpers are in different places. It tries to work with that board. I can set it, and I feel the servo moving the pedal, but it doesn't move it enough to maintain speed.

I have good vacuum at the servo and the brake switch isn't the issue. Cruise light comes on and everything. It just doesn't yank hard enough. Haven't been able to tell if the servo is weaksauce, or I need a different module.

I may look into adapting a newer cruise setup. Parts for this one are just hard to get.

 

[Tom Kelly]

If the cable falls off I imagine it won't see the tps rise or fall in correlation to it's command. It prob gives up at that point. Lol.

Definitely won't control cruise without the cable but I wish it would come to life. Gonna leave it alone til I get cable reattached and then move on. found a set of used original clips on ebay motors. I'll move on when they arrive and cable is snugly attached.

 

[No disintegrations]

The cruise doesn't see TPS. It only sees the speed sensor output and the brake pedal. So if the cable were disconnected from the throttle, and the car fell below the set point, the servo would WOT trying to get the car back up to speed.

Mine quit working a bit ago. Replaced the servo to no avail. Tried to replace the module, but can't get one new or reman. I did go junkyard diving and came up with three boards that might work. The one I have in now has the same P/N printed on the board, but several jumpers are in different places. It tries to work with that board. I can set it, and I feel the servo moving the pedal, but it doesn't move it enough to maintain speed.

I have good vacuum at the servo and the brake switch isn't the issue. Cruise light comes on and everything. It just doesn't yank hard enough. Haven't been able to tell if the servo is weaksauce, or I need a different module.

I may look into adapting a newer cruise setup. Parts for this one are just hard to get.

Try a mityvac to simulate operation?

 

[Turbo6inKY]

Try a mityvac to simulate operation?

Vacuum isn't the issue. The pedal moves, it's got and holds vacuum. It's simulating VSS inputs to the module and simulating outputs to the servo that I need.

That's what the diagnostic tool in the FSM troubleshooting guide does. It replaces the module under the dash so you can test the servo and the brake switch without the car moving.

 

[GNRick]

My cc works intermitantly. Has done this for years. It might work for 5 minutes and then shut off. Then 10 minutes later it starts working again by itself.

 

[Buckshot G/N]

Sounds like your GN is posses

My cc works intermitantly. Has done this for years. It might work for 5 minutes and then shut off. Then 10 minutes later it starts working again by itself.

Sounds like your GN is possessed and is in need of a old fashion Exorcism, but you do drive your GN a lot.
Tom seems like you have check everything associated with the CC. That vdo speed sensor module in the left corner behind your dash panel may be bad , it still will show mph on your SM even if bad. Good luck.

 

[Tom Kelly]

Sounds like your GN is posses


Sounds like your GN is possessed and is in need of a old fashion Exorcism, but you do drive your GN a lot.
Tom seems like you have check everything associated with the CC. That vdo speed sensor module in the left corner behind your dash panel may be bad , it still will show mph on your SM even if bad. Good luck.

Yes Rick, maybe possessed but coming together. I guess I need to wait for the lip to attach the linkage at the TB end before I proceed. It was so much easier with the GS. No electronics anywhere.