It has been a while since I have been on here and I know that there was a picture of the fuse box and which ones go to what, but I can't find it again. I am trying to troubleshoot my Cruise Control on my 86 Mark VII and I wanted to start there. I was reading some of the other posts about what they have done to check the cruise control and I have another question. I pulled the servo assy away from the inner fender well so I can work on it and understand that there is a vacuum dump valve on the back side of the brake pedal, that tells me that I should have vacuum there at the brake if I understand this right. I pulled the incoming line off of the servo and it has vacuum there but if I pull the one off going to the dump valve no vacuum I would say this is pointing to the servo is bad. Any thoughts on this and let me know if I missed something.
Cruise Control Troublesooting
- Thread starter gramps
- Start date
OldSchool1
Dedicated LVC Member
Welcome back.
We normally loose the bladder in the servo in the fender well for our 1988 - 1989 Mark VIIs. This is the first time that I've heard of a pre 1988 unit going bad. The 1990 - 1992s normally loose the clock spring. Also, if the servo is serviceable, we'd love to see pictures!
No. You are correct. The definitive answer though would be to test for vacuum at the pedal connection via an additional hose leading up to a hand held vacuum gauge and read while the vehicle is moving faster than 28 miles per hour.
We normally loose the bladder in the servo in the fender well for our 1988 - 1989 Mark VIIs. This is the first time that I've heard of a pre 1988 unit going bad. The 1990 - 1992s normally loose the clock spring. Also, if the servo is serviceable, we'd love to see pictures!
Assuming the '86 and '88s are the same, which is likely..
The fuse is in the Number 1 position.. it's down (or up) in the corner on the hazard flasher side...
It's a 15 AMP (light blue) fuse that is always "hot". It's service includes Cornering lamp relays, Stop/Hazard lamps, Speed control Servo, and the Electronic Control Assembly (ECA).
I've got the '88 Mark7 "Electrical and Vacuum Trouble shooting Manual". It pretty well explains the operation of the speed control system, has electrical schematics, component locations, and has trouble shooting tips.
It might be helpful if you describe whatever symptoms the car is experiencing.
For instance, if the Speed Control doesn't work, or works but shuts off for no apparent reason, know that the Resume, Set Accel and Coast button contacts are sliding contacts. Sliding on rings of copper inside the steering wheel. Just turning the steering wheel might break the electrical connection. Those rings can be cleaned to provide better contact.
If "operation is erratic or unstable" it could be that the linkage is binding or too loose.
"System does not operate" ..
Possible causes:
Open Modulating valve. (check resistance between certain wires)
Open circuit to Speed Control Switch (more resistance checks..)
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The vacuum portion does seem to be relatively simple. Either there is vacuum available at (functional) vacuum devices, or there isn't.
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Originally posted by OldSchool1
"...test for vacuum at the pedal connection via an additional hose leading up to a hand held vacuum gauge and read while the vehicle is moving faster than 28 miles per hour...."
...while the vehicle is going over 28mph?
OldSchool.. i have a question. While this manual states the car must be moving at 30 MPH minimum for the system to function it also points out that the Vehicle Speed Sensor is an electronic device, down at the transmission, and it has no vacuum component as far as I've been able to determine..
If it's purely electronic and signals the ECA of the +30 mph speed, and the speed control system is then available, why would it have an effect on vacuum availability at the brake pedal's dump valve? Where or how does that Speed Sensor control vacuum?
The fuse is in the Number 1 position.. it's down (or up) in the corner on the hazard flasher side...
It's a 15 AMP (light blue) fuse that is always "hot". It's service includes Cornering lamp relays, Stop/Hazard lamps, Speed control Servo, and the Electronic Control Assembly (ECA).
I've got the '88 Mark7 "Electrical and Vacuum Trouble shooting Manual". It pretty well explains the operation of the speed control system, has electrical schematics, component locations, and has trouble shooting tips.
It might be helpful if you describe whatever symptoms the car is experiencing.
For instance, if the Speed Control doesn't work, or works but shuts off for no apparent reason, know that the Resume, Set Accel and Coast button contacts are sliding contacts. Sliding on rings of copper inside the steering wheel. Just turning the steering wheel might break the electrical connection. Those rings can be cleaned to provide better contact.
If "operation is erratic or unstable" it could be that the linkage is binding or too loose.
"System does not operate" ..
Possible causes:
Open Modulating valve. (check resistance between certain wires)
Open circuit to Speed Control Switch (more resistance checks..)
----
The vacuum portion does seem to be relatively simple. Either there is vacuum available at (functional) vacuum devices, or there isn't.
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Originally posted by OldSchool1
"...test for vacuum at the pedal connection via an additional hose leading up to a hand held vacuum gauge and read while the vehicle is moving faster than 28 miles per hour...."
...while the vehicle is going over 28mph?
OldSchool.. i have a question. While this manual states the car must be moving at 30 MPH minimum for the system to function it also points out that the Vehicle Speed Sensor is an electronic device, down at the transmission, and it has no vacuum component as far as I've been able to determine..
If it's purely electronic and signals the ECA of the +30 mph speed, and the speed control system is then available, why would it have an effect on vacuum availability at the brake pedal's dump valve? Where or how does that Speed Sensor control vacuum?
OldSchool1
Dedicated LVC Member
It's simply the closest and most convenient place to read that particular system (ever try doing this kinda stuff in the rain?) My 1984s through the 1989 cruise controls kick in at 28 mph. I forget when the 1990s kick in. As for it being purely electronic, have you ever noticed the vacuum lines on the drivers side of the intake? <g>
The main manuals have a section on speed control. Group 37. I read through it and learned a little.
While the servo certainly has one, my thinking was that the speed sensor at the tranny had no vacuum component. But... turns out that there's no need for that speed sensor on electronic cluster vehicles.
Aside from that, it makes sense that there's no vacuum available at the brake-pedal dump-valve at low speeds. To have vacuum there would mean there's a vacuum leak every time you hit the brake.
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This 88 manual says Mark7 minimum speed is 25mph, while all others are 30mph.
One (electrical) test says to jack up the rear end, tires off the ground, to simulate driving at 30mph.. which might be good for someone who doesn't want to drive around with vacuum gauges and multimeters on their lap...
Warns about MPH suddenly increasing into the red zone and how to shut down quick which, since you're messing with cruise control, seems reasonable enough.
This system is a bit more complex than i thought. There are several pages of troubleshooting, and I dunno how anyone could diagnose a broken system without a guide..
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btw.. last time speed control was discussed, i noticed an electrical connection to the horn, suspected the horn was an additional way to shut it off, and planned to test it. I did test that on a lonely stretch of highway and the horn did not shut off the speed control.
While the servo certainly has one, my thinking was that the speed sensor at the tranny had no vacuum component. But... turns out that there's no need for that speed sensor on electronic cluster vehicles.
Aside from that, it makes sense that there's no vacuum available at the brake-pedal dump-valve at low speeds. To have vacuum there would mean there's a vacuum leak every time you hit the brake.
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This 88 manual says Mark7 minimum speed is 25mph, while all others are 30mph.
One (electrical) test says to jack up the rear end, tires off the ground, to simulate driving at 30mph.. which might be good for someone who doesn't want to drive around with vacuum gauges and multimeters on their lap...
Warns about MPH suddenly increasing into the red zone and how to shut down quick which, since you're messing with cruise control, seems reasonable enough.
This system is a bit more complex than i thought. There are several pages of troubleshooting, and I dunno how anyone could diagnose a broken system without a guide..
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btw.. last time speed control was discussed, i noticed an electrical connection to the horn, suspected the horn was an additional way to shut it off, and planned to test it. I did test that on a lonely stretch of highway and the horn did not shut off the speed control.
OldSchool1
Dedicated LVC Member
Mechanically Controlling Electrical Vacuum Speeds
You're kindasorta on the right track.
Think BRAKE LIGHT SYSTEM.
Yes, depressing the mechanical brake pedal will open the dump valve and remove vacuum from the system telling the cruise control module to stop monitoring and reacting to, the cruise control set point and the actual ground speed of the vehicle. On the ELECTRICAL END, our BRAKE LIGHT SYSTEM* (second element in the bulb in the tail light) will electronically tell the cruise control module to stop monitoring and reacting to, the cruise control set point and the actual ground speed of the vehicle. The same goes for the ON/OFF switch for the cruise control.
If the dump valve failed, the brake lamp system would break cruise operation.
If the brake lamp system failed, the dump valve would break cruise operation.
* - To test this, engage the cruise control at what ever speed. Once you know that your speed is being controlled, turn on your four way flashers. Our cruise controls immediately disengage
You're kindasorta on the right track.
Think BRAKE LIGHT SYSTEM.
Yes, depressing the mechanical brake pedal will open the dump valve and remove vacuum from the system telling the cruise control module to stop monitoring and reacting to, the cruise control set point and the actual ground speed of the vehicle. On the ELECTRICAL END, our BRAKE LIGHT SYSTEM* (second element in the bulb in the tail light) will electronically tell the cruise control module to stop monitoring and reacting to, the cruise control set point and the actual ground speed of the vehicle. The same goes for the ON/OFF switch for the cruise control.
If the dump valve failed, the brake lamp system would break cruise operation.
If the brake lamp system failed, the dump valve would break cruise operation.
* - To test this, engage the cruise control at what ever speed. Once you know that your speed is being controlled, turn on your four way flashers. Our cruise controls immediately disengage
More information
When I was working on it I jacked the back of the car up and put it on jacks and the speed control does not come on at all. Elessee where can I get one of those manuals you talked about (Electrical and Vacuum Trouble shooting Manual). I have been a mechanic for over 25 years and doing the best that I can I am going to have to get some kind of schematic to troubleshoot this system. I took the vacuum line coming from the engine off of the servo and I am getting vacuum to the servo. Just not sure if it is on the vacuum side or the elictrical side. So if I understand this post right if I have vacuum at the servo I may not have vacuum at the brake dump valve until I am above 25 or 30 MPH? Another comment is if my cornering lamps and haz lights come on my fuse should be ok, and they both work. Just gonna have to break down and find a manual on the ole girl.
When I was working on it I jacked the back of the car up and put it on jacks and the speed control does not come on at all. Elessee where can I get one of those manuals you talked about (Electrical and Vacuum Trouble shooting Manual). I have been a mechanic for over 25 years and doing the best that I can I am going to have to get some kind of schematic to troubleshoot this system. I took the vacuum line coming from the engine off of the servo and I am getting vacuum to the servo. Just not sure if it is on the vacuum side or the elictrical side. So if I understand this post right if I have vacuum at the servo I may not have vacuum at the brake dump valve until I am above 25 or 30 MPH? Another comment is if my cornering lamps and haz lights come on my fuse should be ok, and they both work. Just gonna have to break down and find a manual on the ole girl.
gramps, they're just "Ford Car Shop manuals".
Published by Ford Parts and Services Division, Training and Publications Department.
They came with the car when I got it... I suspect Ford won't have them 20 years after the fact, but you never know..
Can you share a bit of history on that car? Did speed control ever work? Did it stop working after something was done to the car?
There are just so many tests, some involving breakout boxes and codes, i can't type it all.. Here's a sample of mostly mechanical stuff.
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Speed control does not work:
Check connections. (all vacuum and electrical)
Check Brake Lamp (seems like just a broken bulb might do it)
Check Clutch Switch (any Marks come with manual transmission? You got one?)
Check Throttle linkage (self explanatory)
Check vacuum at servo (2.5in-Hg is minimum vac for normal servo operation. Hose is attached to the 5/16 inch vacuum fitting port)
Check dump Valve (service, replace or adjust as required. Adjust means leave a tiny gap between it and the stop.)
Perform Control Switched and Circuit Test (a bunch of electrical tests..)
Perform Servo Tests (likewise)
Perform Sensor Test (With electronic cluster, perform speed signal test .. i haven't read through that one)
Perform Amplifier Test (substitute a known good amplifier.. the amp is mounted to the servo if memory serves...
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another couple pages related to:
Speed Control is Intermittent.
Is it? If not I don't wanna type a bunch of stuff.. Accurately describing symptoms might go a long way towards narrowing things down a bit..
Published by Ford Parts and Services Division, Training and Publications Department.
They came with the car when I got it... I suspect Ford won't have them 20 years after the fact, but you never know..
Can you share a bit of history on that car? Did speed control ever work? Did it stop working after something was done to the car?
There are just so many tests, some involving breakout boxes and codes, i can't type it all.. Here's a sample of mostly mechanical stuff.
------
Speed control does not work:
Check connections. (all vacuum and electrical)
Check Brake Lamp (seems like just a broken bulb might do it)
Check Clutch Switch (any Marks come with manual transmission? You got one?)
Check Throttle linkage (self explanatory)
Check vacuum at servo (2.5in-Hg is minimum vac for normal servo operation. Hose is attached to the 5/16 inch vacuum fitting port)
Check dump Valve (service, replace or adjust as required. Adjust means leave a tiny gap between it and the stop.)
Perform Control Switched and Circuit Test (a bunch of electrical tests..)
Perform Servo Tests (likewise)
Perform Sensor Test (With electronic cluster, perform speed signal test .. i haven't read through that one)
Perform Amplifier Test (substitute a known good amplifier.. the amp is mounted to the servo if memory serves...
------
another couple pages related to:
Speed Control is Intermittent.
Is it? If not I don't wanna type a bunch of stuff.. Accurately describing symptoms might go a long way towards narrowing things down a bit..
OldSchool1
Dedicated LVC Member
Backgrouond
I have had the car for over a year and the speed control has never worked. I have been doing other repairs to the car for the last year that I feel were more important then getting the cruise control working. Now I am at the point to start working on some of the LUXURY items now.....lol. I had vacuum at the servo, brake light works, checked all my linkage and it has an automatic transmission. I want to eliminate one system at a time and the only thing I have left on the vacuum side is the dump valve and I am going to check it on my next attempt when I get back to work on it. If it is electrical I am going to be looking for a good schematic cause the one in the haynes repair manual is pretty poor.
I have had the car for over a year and the speed control has never worked. I have been doing other repairs to the car for the last year that I feel were more important then getting the cruise control working. Now I am at the point to start working on some of the LUXURY items now.....lol. I had vacuum at the servo, brake light works, checked all my linkage and it has an automatic transmission. I want to eliminate one system at a time and the only thing I have left on the vacuum side is the dump valve and I am going to check it on my next attempt when I get back to work on it. If it is electrical I am going to be looking for a good schematic cause the one in the haynes repair manual is pretty poor.
OldSchool1
Dedicated LVC Member
Push The Button?
One of the things that interrupts our cruise controls electronically, is the brake lamp system. Our FLASHERS will interrupt our cruise controls electronically. Even if the flashers are not fully activated, and the flasher switch is not fully pushed in, our cruise controls won't work.
Also, replace your ignition switch (see my signature).
One of the things that interrupts our cruise controls electronically, is the brake lamp system. Our FLASHERS will interrupt our cruise controls electronically. Even if the flashers are not fully activated, and the flasher switch is not fully pushed in, our cruise controls won't work.
Also, replace your ignition switch (see my signature).
Done that already
I replaced that switch way back when I was first started fixing the car for a charging problem which ended up being a broke wire actually. I am going to try and see if I can eliminate the vacuum side of the cruise control system this weekend all that is left is the brake dump valve and if it still doesn't work after that I will try and tackle the electrical side of it after I find a good wiring schematic to look at.
I replaced that switch way back when I was first started fixing the car for a charging problem which ended up being a broke wire actually. I am going to try and see if I can eliminate the vacuum side of the cruise control system this weekend all that is left is the brake dump valve and if it still doesn't work after that I will try and tackle the electrical side of it after I find a good wiring schematic to look at.
OldSchool1
Dedicated LVC Member
Cool.
I hope the weather holds out for you to be able to work on this moreso sooner than later.
A recent 250 mile trip reminded me of another reason why I drive the best American made luxury sport coupe from 1984 to 1992 ... cruise control!
I hope the weather holds out for you to be able to work on this moreso sooner than later.
A recent 250 mile trip reminded me of another reason why I drive the best American made luxury sport coupe from 1984 to 1992 ... cruise control!