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Thread: Cruise control doesn’t work

  1. #1

    Default Cruise control doesn’t work

    Is there any way to diagnose this system? All fuses are good and it doesn’t throw a vss code so my guess would be either the servo or transducer but how could I test either one?


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  2. #2
    I'm an air-conditioned gypsy gadget73's Avatar
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    on what? the 87? VSS doesn't actually connect to the ECM in 87 so you won't get a code for that. If you have a tripminder that works, that proves the VSS works.

    does the horn work? Cruise buttons are powered through the horn relay so if thats dead the CC will be too
    do you have LED tail lights? Gets dumb if you do
    beyond that check the vacuum dump valve above the brake pedal. Easy way is to unplug it at the cruise servo to see if it holds vacuum. If you look on the servo you'll see a short hose that goes from one side of the can to the other with a Y connector going off someplace else. Thats the vac dump line. If that does not hold vacuum the CC will not function.
    also make sure you actually have vacuum supply to the servo, and that the cable from the throttle body to the servo is not broken internally.
    also make sure the tail lights work as expected. If the brake light switch failed and the brake lights are stuck on, the CC will not work.

    There are more detailed diag processes in the manuals but those are the easy and likely things for it to be. Personally I've had more issues with vacuum dump valves than anything else. usually just out of position after working on something under the dashboard.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  3. #3

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    I second the vacuum dump valve. Many of the cruise/speed control modules have labels for the wiring connections so you can figure out what goes where pretty easily.
    Also make sure the connectors are tight on the controller itself; they aren't the stoutest connectors out there.

    Gadget, I think the VSS connection on EEC-IV is used to prove the car isn't coasting (coasting is a different condition from sitting still in neutral or drive) so the computer knows it can pull fuel but not go to full idle mode. I'll have to look that up, though, now that I'm thinking about it.

  4. #4

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    I’m sorry yes its for my 87. Its a gs so no tripminder too. No leds, brake light switch and horn work. I’ll check the dump valve when I can, thanks. I bet thats the issue as it seems everything else is fine but with the car being 33 years old I’m sure the diaphram in the servo is leaking.


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  5. #5
    I'm an air-conditioned gypsy gadget73's Avatar
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    haven't had that, but unless the diaphragm is completely ripped it would still work even with a leak. Might surge tho. Leaky vac dump valve does the same thing. If its not holding at all though it flat out won't work.


    as for the vss, I know 86 has no vss connection to the ECM, pretty sure 87 didn't either. I had to add those pins on my 86 when I converted it to mass air in order for the EGR to behave itself.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  6. #6

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    The dump valve is where exactly?


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  7. #7
    Member Arquemann's Avatar
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    Im subbing this thread, my cc worked a couple times and stopped.
    The shaft broke later though, so the fix won't be as simple.

    Is the cfi cruise setup similar to the efi one?
    1985 Mercury Grand Marquis LS
    1997 Volvo 850 GLE Estate

  8. #8
    The Brown Blob 87gtVIC's Avatar
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    Quote Originally Posted by 87GrandMarq View Post
    The dump valve is where exactly?


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    They are talking about the dump valve directly above the brake pedal...above steering shaft..shitty area to access.

    It has a large vacuum line going to it.

    If you follow the brake pedal pad upward its brake pedal lever you will see a white (should be white) piece of plastic next to the brake light switch. that white piece of plastic makes contact with the dump valve in question. The dump valve threads into a hanger. It has a plunger that releases vacuum from the servo mounted under the hood on the drivers side inner fender once the brake pedal is applied. Brake pedal not applied the plunger is closed and vacuum is stored in the servo...I Believe that is the gist of it.
    ~David~

    My 1987 Crown Victoria Coupe: The Brown Blob
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    Quote Originally Posted by DerekTheGreat View Post
    But, that's just coming from me, this site's biggest pessimist. Best of luck

  9. #9

    Default

    Oh ok I’ll take a look. There is something leaking under the dash but I thought it was the parking brake release, perhaps its not.


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  10. #10
    I'm an air-conditioned gypsy gadget73's Avatar
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    the dump valve only has vacuum on it when you engage the cruise control.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  11. #11

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    So if I were to engage it and not hear a hiss its probably electrical because its not getting vacuum?


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  12. #12
    Beater gonna beat sly's Avatar
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    No. There should be no hiss from the dump valve at all until you press the brake with cruise engaged and then only long enough to break the vacuum in the cruise solenoid. If you hear a hiss already near the floor, it will probably be the half moon shaped valve at the bottom of the steering shaft that actuates the parking brake release. The leak could also be coming from the actuator itself. Pull the black line off the valve on the steering shaft and plug/cap it and the leak should stop.

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  13. #13
    I'm an air-conditioned gypsy gadget73's Avatar
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    just unhook it under the hood and pull vacuum on it. If it holds, that isn't your problem.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  14. #14
    I post a lot...
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    I can say that most times the cruise failed on me it was a vacuum leak.
    "X" car 89 Colony Park LS Mods>Engine delete, SS duals magnaflow hflow cats, 2010 Must GT mufflers, auto air shocks, Posi, Tran cooler, big front brakes, 03+ rear disks, Large 3g alt, Tripminder, GS grill, 86 seats, 16" HPP wheels, winter boots=96 Cartier wheels, 215-65/16 Goodyear ULTRA GW3 snows, pi rear sway, alum driveshaft.
    03 Marauder DBP, HS, 6disk, Organizer, Silver Stars, M&Z rear control arms, Oil deflector.
    02 SL500 Silver Arrow
    08 TC Signature Limited, HID's Mods>235/55-17 Z rated Cooper Zeon RS3-A, Addco 1" rear Sway, Posi, Compustar Remote Start, floor liners, trunk organizer, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17

  15. #15

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    Hmm ok I’ll do that tomorrow thanks for the tips.


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  16. #16

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    Ok so I couldn’t get to the dump valve without burning my hand on the light bulb under the dash lol so I pulled the hose off the servo and pulled vacuum and it held. Next I pulled the hose off the check valve and check the valve and it was also good. Then I pulled a line off the servo and tested the servo itself and sure enough it would pull a vacuum then leak down within a minute. On a side note there is a missing line on the check valve, is it supposed to go to the air pump?







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  17. #17
    I'm an air-conditioned gypsy gadget73's Avatar
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    i want to say the 3 way check valve usually has engine vacuum and servo connection straight across from one another and the bottom out to the smog pump. I also seem to remember a standard 2 port one on the smog pump line. I shuffled things around on mine so the 2 port check valve is the only one in place. Just make sure if the engine side is pulling vacuum its actually getting to the servo.



    Which line off the servo were you getting leakage on? If its the one with the Y thing, thats the line to the dump valve, so make sure its the servo and not the valve. You should be able to apply vacuum to the servo and see the throttle open if its working at all.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  18. #18
    I post a lot...
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    Is the line connected to the soup can?
    "X" car 89 Colony Park LS Mods>Engine delete, SS duals magnaflow hflow cats, 2010 Must GT mufflers, auto air shocks, Posi, Tran cooler, big front brakes, 03+ rear disks, Large 3g alt, Tripminder, GS grill, 86 seats, 16" HPP wheels, winter boots=96 Cartier wheels, 215-65/16 Goodyear ULTRA GW3 snows, pi rear sway, alum driveshaft.
    03 Marauder DBP, HS, 6disk, Organizer, Silver Stars, M&Z rear control arms, Oil deflector.
    02 SL500 Silver Arrow
    08 TC Signature Limited, HID's Mods>235/55-17 Z rated Cooper Zeon RS3-A, Addco 1" rear Sway, Posi, Compustar Remote Start, floor liners, trunk organizer, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17

  19. #19

    Default Cruise control doesn’t work

    I think the po of my car messed up the lines, the bottom of the tee goes to the vacuum tree then the top right goes to the servo. I believe that line was getting vacuum and I tested the check valve from there too. Also I tested the little line from the tee to the top of the servo and thats where it leaks, so basically where engine vacuum would enter the servo.

    Edit: I see what you’re saying so if I apply vacuum to where I did it should pull the linkage back too? It did not. It seems the black piece of plastic at the end where it attached to the throttle cable can move freely compared to the linkage if that makes sense.

    Also yes the line is connected to the soup can. I actually had to buy a soup can and line for it because someone deleted it at some point.

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    Last edited by 87GrandMarq; 03-30-2020 at 05:23 PM.

  20. #20
    The Brown Blob 87gtVIC's Avatar
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    Pro tip when working inside car for long time..pull the door plunger out and unplug it. You wont burn your hands on any lights or drain your battery down to nothing.

    Also:





    Page 123 only tells you the vacuum supplied to the speed control is coming from the firewall mounted manifold through a black and brown vacuum line.
    Attached Thumbnails Attached Thumbnails cruise evtm 1.jpg   cruise evtm 2.jpg  
    Last edited by 87gtVIC; 03-30-2020 at 05:37 PM.
    ~David~

    My 1987 Crown Victoria Coupe: The Brown Blob
    My 2004 Mercedes Benz E320:The Benz

    Quote Originally Posted by DerekTheGreat View Post
    But, that's just coming from me, this site's biggest pessimist. Best of luck

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