Cruise control tried to kill me!

Topic: Cruise control tried to kill me! (Read 2294 times) previous topic - next topic

Cruise control tried to kill me!

July 06, 2007, 12:12:51 PM

Ok, so it's about 7 years after the 5.0 swap in my Turbo Coupe. Cruise never worked after the motor swap until one day last spring, on a road trip from WI to CA, I pulled up on the clutch pedal with my foot (89 mustang pedal assembly, must have a weird notch that keeps the pedal from using the full travel) and turned on the cruise no problem. So I use it for the next 3-4 hrs when suddenly it grabs the throttle... 80...off button....90...brakes, BRAKES HARD...100...110...kill ignition, coast to a stop.

Ok, so I got the car stopped... But when I refire, the engine revs sky high... still grabbing. So I pull off the cable and continue with no cruise. Next day, reconnect, use cruise for 3-4 hrs... grabs, kill the motor.

So basically, it just grabs the accelerator and nothing will turn it off... Not the off button, not the brake pedal, not the clutch pedal, not even turning the key to off!! To me, it doesn't sound electrical (what are the chances all the cancel functions don't work, especially turning the key off and killing power to the unit)... so perhaps the servo is just bad and getting stuck somehow... I don't mind replacing parts but how can I test or be sure without just driving in the crazy CA traffic and waiting for it to happen again? Any ideas?

Cruise control tried to kill me!

Reply #1 – July 06, 2007, 04:21:35 PM

i had the same problem with my stock 5.0..whenever im on an empty highway and i want to cruise with my destination being at least 70 miles away,i used cruise control..5 minutes maximum and then it would floor the gas,if i was pushing the button persistently it would turn off,never used it again..heck converted the motor to carburetor ;P

Cruise control tried to kill me!

Reply #2 – July 06, 2007, 04:55:59 PM

Yeah, it sucks... And I really want to get it figured out but now that I'm in CA there's no safe, open places I drive to test the cruise... Stuck cruise in 80 mph bumper-to-bumper traffic=no fun

Anyone else have any insight?

Cruise control tried to kill me!

Reply #3 – July 06, 2007, 05:57:10 PM

Strange problem, maybe some type vacuum leak in the servo... I believe I'd swap it and cross my fingers...

Cruise control tried to kill me!

Reply #4 – July 06, 2007, 06:14:14 PM

LOL, yeah... I was thinking that, too... only a leak seems it would fail to grab... Does anyone see anything that might point to the amplifier instead?

Cruise control tried to kill me!

Reply #5 – July 06, 2007, 06:26:36 PM

kinda off topic, but i use cruise control 80% of my driving. i make trips routinely down 55mph 2 lane hwys. the only thing thats strange about my CC is every so often, like when i would come into a town that goes to a 45mph zone, when i hit the OFF button, the car will floor itself. it just takes an extra button push, and im in the habit of pressing it twice or thrice, but i experience what seems to be the same deal... just not as bad. well its a faded memory but i think one time i couldnt get it to come off with the buttons but the brake pedal did disenguage the CC. i've never actually seen what it does when i hit the off button and it accelorates b/c the speed limits (gotta keep it at least 10 over :hick: ) so as my contribute to this thread would be that its not an uncommon problem, but i'd say your's is a bit more concerning. (also i can get CC to get my car up to 110 no problems, so the CC unit turning off when someone presses the accel button too long and it shuts off is strange to me)

Cruise control tried to kill me!

Reply #6 – July 06, 2007, 07:18:56 PM

Yeah, I've never had any Ford cruise shut-off from hitting accel too long (unless I'm going up a hill in 5th or some situation where it can't keep up and cuts out).

But yeah, my situation is a bit extreme and just down right dangerous. The thing that confuses me is, like you say, if the off doesn't kill it, the brake pedal should (or clutch, or taking all it's power away and turning the key off!!). So I know it's not a simple electrical problem, like the off button being bad, or a bad column connection.

I guess I'm just gonna go with the assumption that if ALL the electrical "offs" do not work it's a mechanical problem and replace the servo and not the amplifier...

Cruise control tried to kill me!

Reply #7 – July 06, 2007, 11:45:42 PM

Yes it sounds like the servo motor is stuck in the WOT position.
It stays there with the engine off when there is no vacuum to hold it there. It must be mechanical.
But it sounds like it only sticks when it goes to WOT.

Why did it accelerate in the first place?
Maybe the amplifier is getting false information from the speed sensor. This sensor is operated by the speedometer cable for non electronic instrument clusters.
On electronic instrument clusters it is a signal from the cluster.

Many years ago a friend of mine installed an after-market CC.
It had two magnets glued to the drive shaft 180* apart. A sensor detected the magnets as they went by.
One of the magnets fell off and the sensor pulses now indicated the car was going half as fast as it actually was.
Yep he had a runaway CC..

Cruise control tried to kill me!

Reply #8 – July 06, 2007, 11:46:14 PM

The brake and clutch pedals activates a vacuum dump, which is what operates the servo... AFIK its the electronics that regulate the amount of vac... So if it is hanging/jamming at full on, I'd think it'd almost have to be a vac/mech prob(assuming the dump on the pedal(s) is operating)...

Cruise control tried to kill me!

Reply #9 – July 07, 2007, 12:07:40 AM

From what I remember, the brake pedal kills the cruise when it's not going crazy. So I have to figure that system is working fine. And I think it's true that this happened when using the accel button so perhaps a hill or something caused a WOT situation and a stuck servo.

But why would turning the key off not reset it, but having the car off/cable disconnected for a few hours reset it? Perhaps the servo just gets "road-bumped" back loose...?

Also, I know my speed sensor is a bit messed up because I forgot to unplug it once when pulling the tranny and it pulled so hard the bracket and speedo gear (since replaced) bent

But the speedo works great so I'm assuming the cruise sees the same signal and that signal is fine...

Anyway, I don't know where I'm going with all of this. Since my speedo is correct, I don't see the amplifier getting a bad signal... I'm going to replace the servo...

Cruise control tried to kill me!

Reply #10 – July 07, 2007, 01:03:47 AM

Maybe the cable is hanging at a near WOT position??? Checked it for binding???

Cruise control tried to kill me!

Reply #11 – July 07, 2007, 01:43:23 AM

I made the assumption that the throttle linkage was stuck in the WOT position when you disconnected the CC linkage.
If that is not true then the vacuum reactivated it when you started the car.
A modulating valve in the servo is controlled by the amplifier and the valve controls the amount of vacuum to the servo motor.

The brake pedal disables the CC two ways. The stop lamp switch signals the amplifier to close the modulating valve.
For emergency back-up incase the electronics are out of control, a vacuum dump valve, mechanicaly operated by the brake pedal, dumps the vacuum.

So you have vacuum to the servo motor when you should not have because of an out of control amplifier or a mechanicaly stuck modulator valve.
The brake did not save the day because the dump valve is not working.

Cruise control tried to kill me!

Reply #12 – July 07, 2007, 11:43:17 AM

Hmm, well, considering I just swapped over to a fox booster and cobra m/c before it started happening, perhaps my system is no longer set up correctly...? How would I check the dump valve and where is it located in this whole system?

As for the linkage, I just thought of a binding problem yesterday... It does look kind of funny the way it's routed. But from what I remember, the throttle was closed after shutting the car off, but before disconnection the cable - but I'm not entirely sure.

The stop lamp switch is the same for the cruise and the brake lights, correct? If so, that should be working fine...

Cruise control tried to kill me!

Reply #13 – July 07, 2007, 06:09:53 PM

Yes the stop lamp switch is the same one that turns on the brake lights.
In the picture it looks like the dump valve is above the pivot point of the brake pedal. When you press the brake, the top end above the pivot moves toward you. This presses on the check valve. The valve has a white or black/white vacuum line to it.

They test it by disconnecting the vacuum line at the speed control servo and putting a vacuum pump on it to see if it holds vacuum.
Then press the brake to see if it releases the vacuum.

I notice in this EVTSM that there is a difference between 2.3L and 3.8/5.0L in the vacuum input to the servo.

On 3.8/5.0 the vacuum input goes to the vacuum distribution tee.

On the 2.3L there is a vacuum tee at the input to the servo to give you two vacuum sources. One through a check valve to the main vacuum distribution tee and the other to the aspirator through another check valve.

Don't know if any of this 2.3 stuff is still in your car or what differance it would make.

Cruise control tried to kill me!

Reply #14 – July 08, 2007, 12:57:00 AM

yeah, some is 2.3. I'll have to check a diagram to get it all connected right and check my valve once in finished building my vac pump.