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Cruise Control problem

11/17/2008 5:00 PM

I have been trying in vain to find out why my cruise control on my 1995 Mustang coupe seems to 'slip'. It works, but actually 'slips' from the speed setting. If I set it at 65 mph, it will slowly drop down. You can feel it actually disengage, when you do turn it off. How can it slip?

I was told it is not operated by engine vaccuum. One control goes from the control unit (buried behind the driver's side door pilaster) to the fuel injection control under the head and the rest of the cabling to the steering wheel.

Any help you can provide is greatly appreciated! The car only has 151,000 miles on it.

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#1

Re: Cruise Control problem

11/17/2008 11:04 PM

mach1qtx,

Suspect impedance factor, DC current, small wires.

Try connecting jumpers to bypass lengths of original wires.

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#2
In reply to #1

Re: Cruise Control problem

11/18/2008 8:36 AM

Hello bwire!

Interesting solution, I never would've thought of that, but makes a lot of sense. Just one last question. Why did it work for so long, but now the wires are offering more resistance than before? Does the age of the wire have anything to do with it?

Thanks for your help!

Mach1GTX

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#3
In reply to #2

Re: Cruise Control problem

11/18/2008 8:54 PM

Hi! mach1gtx,

Face it auto's are designed for a seven year life span and components are spec'd to that norm.

Resistance builds in wiring carrying DC voltages and over time the diminished flow becomes perceptible by characteristics of the components powered.

It can be seen in older cars when the running lights are dimmer than should be.

ubetcha

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#4
In reply to #3

Re: Cruise Control problem

11/19/2008 8:42 AM

Hi 'Ubetcha'!

I've had enough older cars to know that's true. In fact, I can see that my 'lights' aren't burning as bright as I get older......I just hope that I don't hit too hard of a bump where they suddenly glow brighter.........thank you for your time and help!!

'A pig without lipstick is like a day without sunshine' (confuse-us)

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#5

Re: Cruise Control problem

11/19/2008 10:33 AM

Not sure if this will help but my sister's was doing the same thing .. turns out Ford sent out a recall notice on the cable.....she never got.... but when took to Ford , replaced for free despite age.

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#6
In reply to #5

Re: Cruise Control problem

11/19/2008 10:37 AM

Hi,

Thanks for information! You might've saved me some time and $. Have a Great Day!!

Mach1GTX

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#7

Re: Cruise Control problem

11/19/2008 10:59 AM

I would also look it the brake switch. The control has an input signal from the brake to disengage it. Bad switch may be causing the intermittent disengagement.

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#8
In reply to #7

Re: Cruise Control problem

11/19/2008 11:06 AM

Hi ozzb!

I just talked to the Ford dealership and they said it could be a 'servo'. They did check and there was no recall on my '95 Mustang. The control actually 'slips', gradually decelerating. Would the brake switch do this? You can see on the site, that 'bwire' thinks the wiring is old and providing impedance on the circuit. I can check both and find out. What do you think?

Thanks!

Mach1GTX

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#12
In reply to #8

Re: Cruise Control problem

11/19/2008 11:29 AM

Hey mach1gtx,

Assuming you have cleaned the contacts and eliminated dust?

How much does it slip? 3-5 mph or it falls to zero?

Is there any reason suspect moisture being involved, it is a time of seasonal change?

Resistance is my first thought though

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#16
In reply to #12

Re: Cruise Control problem

11/19/2008 11:38 AM

I haven't tackled trying to fix it yet, until I hopefully know what to do first. It slips gradually about 1-2 mph/second or so. When I disengage it, using the switch on the steering wheel, you can 'feel' it disengage, so I think it works, just slips. Is the Ford dealerships idea of a bad 'servo' credible?

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#18
In reply to #16

Re: Cruise Control problem

11/19/2008 11:42 AM

You need to eliminate contact corrosion and the antics of dusty boards before any credible remote diagnosis can be had.

Is the Ford dealerships idea of a bad 'servo' credible?

How long is a piece of string?

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#19
In reply to #18

Re: Cruise Control problem

11/19/2008 11:45 AM

I think your right, it has to be something with loss of voltage, bwire, leaking somewhere, dirt, dust.

"How long is a piece of string?" I like that....so when talking to Ford experts...'bware'!

Thanks!

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#20
In reply to #19

Re: Cruise Control problem

11/19/2008 11:52 AM

it has to be something with loss of voltage, bwire, leaking somewhere, dirt, dust.

Maybe but is the first consideration and nothing can imitate a fault as well as dirty contacts dust enabling stray voltage.

you're welcome

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#22
In reply to #8

Re: Cruise Control problem

11/19/2008 12:46 PM

The brake should disengage it completely. Thats not to say what low input voltage from the brake switch would do or how the control would react to it.

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#25
In reply to #22

Re: Cruise Control problem

11/19/2008 1:09 PM

Thank you!!

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#9

Re: Cruise Control problem

11/19/2008 11:10 AM

I had thought that most cruise controls used a vacuum ... perhaps it is losing some vacuum? Maybe thats the way older vehicles worked.

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#10
In reply to #9

Re: Cruise Control problem

11/19/2008 11:14 AM

Hi,

I was told by Ford that it was all electric control and did not use engine vaccuum.

thanks!

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#11
In reply to #10

Re: Cruise Control problem

11/19/2008 11:26 AM

Just for your info you can Google " tsb 95 mustang " and get a lot of info the dealers get reguarding recurring problems with a certain vehicle. This is a technical service bulletin the manufacturer sends to the dealers. You can "tsb" any model or year US car and get the most problem issues. I did this on my truck and got all new brakes installed free.

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#15
In reply to #11

Re: Cruise Control problem

11/19/2008 11:37 AM

GA for you, very helpful

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#17
In reply to #11

Re: Cruise Control problem

11/19/2008 11:39 AM

Thanks for telling me that, I had forgotten all about that.

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#14
In reply to #10

Re: Cruise Control problem

11/19/2008 11:33 AM

Hello,

Most of the old cars use to have vacuum operated cruise control with vacuum diaphragm. It was control by the vacuum. Most of the new cars have electronic cruise control. I had both types of cruise control in cars over the years.

Thanks.

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#13

Re: Cruise Control problem

11/19/2008 11:30 AM

How can it slip?

Stray voltage...

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#21

Re: Cruise Control problem

11/19/2008 12:45 PM

The resistance in the wiring is not the problem and a vacuum leak is not the problem. Setting the cruise control nulls out all the offset errors.

Cruise controls are electronic. Typically a speed to voltage conversion is used. When the control is set, the speed voltage is sampled and stored in a capacitor using a sample and hold circuit. Circuits comparing the set point (voltage stored in the sample and hold capacitor) with the current speed (speed to voltage converter) determine if the servo should be driven up or down. Pushing the accel button adds charge to this sample and hold capacitor and pushing the decel button removes charge from the capacitor.

Now the problem: When a capacitor ages it looses its ability to hold a charge. (This is mainly due to heat drying out the capacitor's electrolyte.) You need to find the cruise control box and replace the sample and hold capacitor.

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#23
In reply to #21

Re: Cruise Control problem

11/19/2008 12:58 PM

GA

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#24
In reply to #21

Re: Cruise Control problem

11/19/2008 1:07 PM

Do you know if the capacitors will be mounted on a circuit board?

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#26
In reply to #24

Re: Cruise Control problem

11/19/2008 1:21 PM
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#27
In reply to #26

Re: Cruise Control problem

11/19/2008 1:32 PM

THANKS, I WILL HAVE TO TAKE TIME TO READ IT. I JUST PRINTED IT OUT.

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#28

Re: Cruise Control problem

11/19/2008 3:49 PM

The only thing I can think of is that the 'Nudge down' or lower the speed by xx ml/hr button has dirt or condensation in it.

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#29
In reply to #28

Re: Cruise Control problem

11/19/2008 3:53 PM

Thanks, that's kind of what someone else had mentioned. I'm going to check on it.

Thank you again!

Mach1GTX

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#32
In reply to #28

Re: Cruise Control problem

11/19/2008 6:46 PM

Is that the #1 dip switch?

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#30

Re: Cruise Control problem

11/19/2008 4:44 PM

Check your speed transducer.On most vehicles the signal branches off and goes to the tranny control module, and the engine control module.Any problems with the tranny shifting?(If auto)

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#31
In reply to #30

Re: Cruise Control problem

11/19/2008 5:21 PM

I haven't had any shifting problems. Where is the speed transducer?

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#33

Re: Cruise Control problem

11/24/2008 3:17 PM

I had the exact same problem on a vehicle 2 years younger and different manufacturer but in my case it definitely was a vacuum issue. If you're absolutely sure there are no relationships to a vacuum system somewhere then good luck. However, I know it's super easy for a technical mind to over-look the simple on a quest for a major troubleshooting victory. Good luck!

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#34
In reply to #33

Re: Cruise Control problem

11/24/2008 5:39 PM

So it could be vaccuum.....I think I can check under the hood for a diagram, if there is one and hopefully figure if it is one way or the other. Thanks for your information!

Mach1GTX

(2 of my past and favorite cars!)

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#35

Re: Cruise Control problem

11/25/2008 7:00 PM

Vacuum leak at the master .

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#36
In reply to #35

Re: Cruise Control problem

11/26/2008 8:04 AM

Hi,

Vaccuum leak at the 'master'?

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