# bad speed sensor?



## ZooYork (Jun 23, 2004)

why would my 90 240 no engine mods cut out cauz of a faulty speed sensor?

its a intermittent problem, some times the speedo will work or it will not.

when it works i can go as fast as i want and go up to any rpm

when it dosent i am limited how high i can rev it. and how high in the revs i can be in gear.

does the vss tell the ecu how fas im going or is it just limited by 4th 5th gear sensors+ rpm in those gears?

also if i pull the sensor out will a crap load of trans fluid come out to?

any trouble shooting ideas?


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## ZooYork (Jun 23, 2004)

ANY ONe??????????????????


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## rogoman (Dec 16, 2004)

Are you having a problem with top speed or an RPM limit? If it's only an RPM limit, then either the 4th or 5th gear sensors may be bad.


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## ZooYork (Jun 23, 2004)

it is rpm limit, 
but its is only limited when the speedodometer is not working.

when the speedo works the rpms are not limited


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## rogoman (Dec 16, 2004)

ZooYork said:


> it is rpm limit,
> but its is only limited when the speedodometer is not working.
> 
> when the speedo works the rpms are not limited


Do an ECU code readout to see if any fault codes are set; if so, it may help you diagnose the problem.


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## ZooYork (Jun 23, 2004)

no codes in the ecu


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## rogoman (Dec 16, 2004)

Could be a bad ECU; but first reseat the ECU harness connector.


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## ZooYork (Jun 23, 2004)

i put a dif ecu from a friends car in. it only happens when the speedo dosent work. when the speedo works its all good.

do u have a wiring diagram for the VSS circuit?


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## rogoman (Dec 16, 2004)

ZooYork said:


> i put a dif ecu from a friends car in. it only happens when the speedo dosent work. when the speedo works its all good.
> 
> do u have a wiring diagram for the VSS circuit?


Sorry, don't have a 1990 wiring for the VSS.

If you unpluged the speed sensor harness connector at the tranny, what effect would that have on your problem; by unplugging it should have no effect on the RPM; many guys have disconnected the speed sensor so that there is no top speed limit by the ECU.

If you don't run into a problem by disconnecting the sensor, then there may be an intermittent short either in the instrument panel wiring or the connecting harness.


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## ZooYork (Jun 23, 2004)

i tried that a while ago, it is just does it all the time with the vss unpluged.but if i unplug the trans sensors and keep the vss connected, no differnce. only when the speedo works i can go high in the revs.

i did take the cluster out a while back. how could there be a short in there?


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## rogoman (Dec 16, 2004)

ZooYork said:


> i tried that a while ago, it is just does it all the time with the vss unpluged.but if i unplug the trans sensors and keep the vss connected, no differnce. only when the speedo works i can go high in the revs.
> 
> i did take the cluster out a while back. how could there be a short in there?


The only thing left is the wiring between the cluster, ECU and the VSS. There might be some insulation that's wore off some place causing a short intermittently.


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