Strange behavior- ECU/ignition?

[Frederick Smith]

DGraber460 at aol.com wrote:

>I have over the years had my car (83 URQ) on rare occassion behave very  
>strange with no clue as to why.
>What happens is out of the blue, driving down the hiway at 60-70, the tach  
>will suddenly to drop to zero and bounce up & down as it comes on and  off 
>line. The car then backfires violently at the same time. It starts with once  
>every 15-20 seconds and becomes more and more frequent until the car finally  
>stops altogether. Switching the car off, and restarting (rebooting the computer)  
>and all seems fine.
>It has only happened 4-5 times over the years, but did it twice yesterday  as 
>I was returning from the West Coast UPG in the middle of Utah, and western  
>Colorado (miles from anywhere). It is not heat related, and pedal input &  
>jiggling the ignition switch have no effect. Is there anything in the ECU maps,  
>programs, or electronics that could cause such a thing?
>This has me totally stumped!
>It will go months or years between episodes- although yesterday it was 3  
>hours and 240 miles apart.
> 
>Dennis
>Denver
>
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>  
>
Dennis, I experienced the same problem a few years ago and it was 
maddening to track down
due to it's intermittent nature. I did replace one of the fly wheel 
sensors (speed sensor, on top of
the bell housing for WX motor). I would recommend buying new ones, 
(both) since they do not have an
infinity life. I replaced my ign. distributor as well, bought a new one 
for $90.00, and never had  another
issue.
Since the refference sensor is out of the loop after starting, I doubt 
that that is the problem.

Good luck