'97 Mounty Cruise Control Problem

[parad1mg]

ok, i'm going to need my cruise control really soon and i have not found the cause of the problem yet as to why it wont work properly..

here's the stats:

vehicle: 1997 mountaineer v8 AWD

tests done:

> cruise control self test via switches (press off then turn key to "on" position then press on..etc..)
result of test: 1 flash
cruise control servo motor only engages for a second and does not complete the full retraction test. a snappy disengaging sound follows after.

other things noted:

1. my abs works perfectly / no abs light
2. speedometer works for about 5 minutes then dies
3. digital speedometer works flawlessly (vss signal was tapped from the wire under the dash near driver side kick panel)
4. odometer works fine (top and bottom one)
5. cruise control rarely works. in the event that it does, it cannot hold a speed and rather maintains a speed 3-5 mph lower than set originaly
6. no codes/dtc
7. it is properly connected to the TB
8. no loose wires on the servo

um, help? i dont exactly know where/what to troubleshoot next..

could it be the servo? how do you test the servo then?

the protective plastic housing of the cruise control cable is a little bit cracked and a bit brittle already but the cable does not bind..

 

[parad1mg]

the snappy/disengaging sound was my accelerator pedal being released by the servo..

 

[budwich]

IF your test "results" are aligned with other years, then my search says that a "1" flash is a static test passed... I assume this means that your basic system components are functional.

 

[parad1mg]

i'm thinking all the basic components (switches, fuses, cables, servo..) are ok too..

but it still wouldnt hold a speed properly and even start losing speed and most of the time, it wouldnt work..

 

[budwich]

based on your first post about speedo.... is the instrument cluster / gauges stock?

 

[parad1mg]

yup, theyre stock.. i just have a separate digital speedometer..

 

[budwich]

not sure that I understand... you added the digital??? or the connection to it? The output from the vss is AC. If all the gauges are stock, I would expect both to work. A "non-working one" is probably an indication that the AC signal is being compromised somewhere and since the CC uses this signal to "help it". I would say that you need to track this "condition" down (ie. loss of analog reading).

 

[parad1mg]

added a digital speedometer.. its getting signal from a vss signal wire from under the dash righ next to the driverside kick panel.. no wires wire cut, only tapped into..

 

[budwich]

OK.... but I don't think that you can "just do that".... because that signal is a "measured signal"... meaning that its "characteristics" are "well defined"... by things like impedance. By adding another system, there is no longer a known electrical characteristic and in fact, I think that what your analog gauge is trying to "tell" you. I would temporarily disconnect the digital and track on getting your analog functioning continuously (ie. longer than 5 min) and then see if your problem goes away.

 

[parad1mg]

so you're saying that its competing for the signal?

i've installed an off switch for the digital speedo and i did turn it off for a few times while on the highway but the original speedo still doesnt work.. sometimes it does but sometimes it doesnt..

i'll probably unhook it from the vss wire and see what happens..

 

[parad1mg]

if it is competing for the signal, then that means that there is no way you can hook up any additional accessories that requires tapping into a vss signal wire like a double din gps deck, digital speedo, etc?

 

[budwich]

I didn't say that "exactly", what I said was the VSS signal characteristic is "well known" ... by the Ford designers and they take that into consideration when using the signal for "their systems". "Modifying" that signal is probably not "supported" by ford. It could work or it could not. Further, the signal may not be a "bridge" in the overall system design (ie. "Y coupled"), it could be a "feed thru / buffer / output to another component" (ie. cruise control controller).... I don't know the specifics.... but note that an "open Y" connection will act as antenna which probably isn't good for a "specialized control signal". They don't really provide much on the various references that I have seen (I use the ford truck cd).... basically the circuit inputs to the PCM.... but IIRC on some models, there is a "form of daisy chaining" involving the ABS system among other things. I guess my question ultimately is.... was your speedo working OK before you "tapped into the line".... and then further was your CC working back then????

 

[parad1mg]

now that you mention it, yes, everything worked fine before i installed the digital speedo..

do you know a place where i can tap into the vss signal safely? i tried tapping it from the wire on the CC harness but there was too much engine noise interference that it made the digi-speedo fluctuate.. i couldnt find the vss wire from behind the radio panel that was why i went with the one on the driver side kick panel..

 

[budwich]

I don't have enough info on the signal... other than its AC and that the speedo unit takes the feed and converts it for the meter. As you have found, the "conversion" for either the stock or the "add on" is susceptible to noise "impediments". From the circuit diagrams, there are only "blocks" for a lot of the circuitry. Basically, I would get the stock system working reliably and then try moving the "tap" around for least impact. Is it possi ble that your "tap" isn't very good... how are you doing it... "squeeze coupler"? (its a blade that you push onto a wire to break the insulation and contact the wire inside). You might have to track down a small transformer for some isolation. I don't know... heck... I don't even know what frequency the AC signal is running. Sorry... not much help. I guess the other thing, if you get your hands on a "portable scope" (ie. hand held one)... you could look at the waveform, before and after to get idea of what you are dealing with.

From the diagrams, I don't see any "test point" / "takeoffs" for connecting to.

From a "quick search", I found this "comment"... VSS Signal Coupler.
The VSS (vehicle speed sensor) wiring in Ford cars and trucks is different than that of other vehicles. This coupler amplifies the speed pulse in Fords, bringing it to a level that's compatible with a navigation unit.

What that tells me is that the output (fords) is very low and any "disturbance" of this signal will be quite easy. That usually implies that you need a very "high impedance coupling" system that doesn't take much signal away. Not sure what that is but it sounds like they (gps people) are aware of it and provide some things to get around it. By the way, that was a "cutout" from a crutchfield page so maybe you can find a coupler which maybe you need to add to your system.

Other searches reveal that some "recommend" using the ABS signal.

 

[parad1mg]

i dont use the squeeze coupler things as they tend to come loose by my experience.. i cut away the insulation material wrap around the wire thread the wire in then solder and shrink wrap it..

as for the abs signal route.. will it have the same effect if i tap on to that? i mean will it make the abs malfunction if i tap into its signal?

 

[budwich]

Don't know... just "quoting" searches. The thing that you have to remember is that your 97 vehicle was designed in "95" when a lot of this "add on stuff" wasn't around. The "add-ons" guys don't always get all the info from the car mans... so they kind of try to "reverse engineer" things as they just want to sell you something whether it works or not... or affects other systems. Does your unit have a "signal coupler"? IF not, then perhaps you need something like that. On the ABS side of things, if you cause a signal problem there, then it is likely that you will see a flashing ABS warning / code... and likely a abs "shutdown" but still have "normal" braking. Again, though I know that the ABS system changed over the ex years in terms of feeds... for instance, my 96 abs shows feeds to the GEM while I believe other (newer) years feed an ABS module which then feeds the instrumentation.