Bludy Speedo!

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Teflon

New Member
OK, '92 3.9 auto, and AFAIK electronic speedo head.
Dang thing drops out on me, like whenever it feels like it.
Usually works on start up, so bloomin difficult to diagnose, cos sat on the drive, you dont REALLY know whether its not working.......
I had near enough the exact same thing on Jaqui, and never found the source of that neither, but got to fathom it this time... and I only have four months 'till the MOT to do it....
Now, normally works......
Sometimes doesn't.
Start up, nearly always works for the first couple of miles or so....... sometimes longer.
First few times it tripped oit, was just after getting up to about 60... then dead.
But, not always; drove down to Salisbury, worked ALL the way there, and ALL the way round the lanes, and only tripped out on me, on the way home.
ONLY 'coincidence' of that was when it tripped out, was shortly after I switched to gas......
ANY-ONE got any kid of idea where to start even LOOKING for the cause of this annoying anomoly?
I really NEED to nail this one, too, becouse the gas guage is so hopeless on this one, oddometer's about the only way I can judge how much fuel I might have in the tank!
 
I don't know about on the P38, but on other cars like Volvo the electonic dash is made using a flexible printed circuit. I have repaired many which have either failed due to dry solder joints or fatige failures of the flexible circuit where it has flexed due to vibration. Hard to diagnose without a circuit continuity tracer and a bloody great bench magnifying glass
 
Teflon, I have had the same problem on my 91 RRC. I think the problem is with the electronic speed transducer and not the speedo head or the short cable that drives it.

I have not been able to properly diagnose the fault. The transducer itself is not a complicated thing and I suspect the problem is either related to a poor earth somewhere or a fault in the supply to the transducer.

It is very frustrating because when the speedo drops out there is no cruise control and the EFI warning light comes on. I have not found a specific set of circumstances that will cause the fault but if I do get to the bottom of it I will let you know.
 
Ize got a small cateye push bike speedo which is only .1 or .2 of a mph out accordin to sat nav and cost me £20...
easy to fit and accurate enough....

I wasn't going to admit to that one...... robbed one of my kids bike and fitted it to my other Rangie when that ones speedo died and I was getting desperate to get her through test..... bit difficult to read in the dark though.........
 
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