A little challenge, all thoughts / comments welcome,
I have a 98 Ford Galaxy which very intermittantly stalls as you dip the clutch changing down to 1st or 2nd gear on the approach to a give way or roundabout. Sometimes won't do it for a week, sometimes several times within an hour, sometimes it nearly stalls (Rev counter hits the stop but recovers in less than a second).
It doesn't exhibit any other problems at any other times. Never seen it do it cold although its so intermittant that may be a red herring.
Ford dealer looked, changed a few bits (including coils) and I gave up throwing money away.
My own ignornace may show through in my further descriptions of whats going on :
A small local garage reset the Cars error log on its last service. It had been misfiring and a spark plug had apparently broken down. The car ran fine afterwards except for the intermittant stalling which was still present.
On the last visit to my local garage, to look in this stalling, the Cars error log now reports a code that translates into a 'Vehicle Speed Sensor' problem. They are ordering a replacement sensor as its only c. £15 and minutes to fit. Apparently it could also be wiring between the sensor and ECU which will cost a lot in labour to trace.
Why would a faulty speed sensor exhibit these symptoms ?
Also, and more interesting, my local garage spoke with a technician from Ford (or probably a dealer contact) who asked straight away, after hearing the symptoms, whether the radio / cassette had been changed !!!! and if so was it changed to the correct model !
In fact it was changed a couple of years ago and while I can't be sure the two co-incide we've certainly had the stalling for a couple of years . . . weird huh !
The replacement radio is Ford but a different model and the column mount audio controls ceased to work form the point that the radio / casette was swapped.
Now, and I have no idea what I'm talking about now, apparently the vehicle speed sensor is wired through the radio as well as to the ECU. This is so that the volume can be increased slightly as the car gets more noisy at increased speed.
The Ford Tech said he'd seen another case where swapping out the radio / cassette had led to these kinds of problems. In that instance they put the old Ford radio back in - jobs a good un !
Now, I can see that if the speed sensor is wired to Radio & ECU (possibly to ECU via radio internals) a radio swap could affect the function of this sensor / signal system.
What I don't understand is :
Why might speed sensor problems cause our Car's symptoms in the first place ?
If the problem was that the ECU speed signal is derived via the radio, and the replacement radio & wiring didn't relay the signal on to the ECU properly (or interferred with the signal), why might it be so intermittant ?
Anyone shed any light on any of this ?
Does it all sound like a load of tripe ?
Any and all constructive thoughts or comments greatly appreciated. On a serious note, my wife taxis our three young kids around in the Galaxy and a stall at the wrong moment when pulling on to a busy road could be very dangerous.
Thanks & regards
Ian
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Yes speed sensors do go to radio, and to ecu. Its possible a radio could induce interference/peaks/drops on that line. To eliminate, take radio out for a few weeks. See what happens.
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Thanks for your comments / thoughts.
What decisions does the ECU make based on the signal from the vehicle speed sensor ?
What outputs does the ECU change based on the signal from the vehicle speed sensor ?
I'm trying to understand how this signal getting messed up might cause the symptoms we're experiencing.
Is the Speedo measurement driven from the vehicle speed sensor or derived by some other means ? (because the speedo reading appears entirely stable the whole time . . . I haven't noticed it doing anything strange at the same time as the stalling episodes).
regards
Ian
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Visit www.fordgalaxy.org.uk - we have many members who have superb technical skills. You may already find answers to your problems posted there!
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What decisions does the ECU make based on the signal from the vehicle speed sensor ?
Lots. Now this is not specific for your car but
It is used for fuel consumption savings (shuts off fuel on the over run), anti stalling features (tries to fuel car if its stalling) air bag deployment (not at all, half or full) Auto box (if it has one)trip computer. Radio volume. Traction control, possibly ABS.
I'm trying to understand how this signal getting messed up might cause the symptoms we're experiencing.
See the links to traction control, consumption, anti stall. They link to the ECU and alter the fuelling to the car.
Is the Speedo measurement driven from the vehicle speed sensor
Yes
>>(because the speedo reading appears entirely stable the whole time . . . I haven't noticed it doing anything strange at the same time as the stalling episodes)
Because it might be driving the speedo directly, which may be immune to spikes, low levels or fluctuations. Also the speedo will average out speed readings (pulses) so you may not see fluctuations.
The only way to disprove the radio is as i said, take it out.
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