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Discussion Starter #1
I bought my P38 in last December with 63K kilometres on the clock. In the last few weeks I have been the victim of a strange happening. My rev counter reads about 700 rpm when the engine is cold but reads almost zero when the engine is hot.
I started working through the electrical sticky procedure last weekend then had to go out. The alternator output was reading 14.19-14.20 V when the alternator was cold. When I got home and restarted testing I found that the output was now 14.11-14.12 V. I know that this is below the minimum system requirement.
My understanding is that the rev counter takes a reading from the alternator.

Would I be correct to assume that the low output, when hot, is reflected in the rev counter showing zero revs at idle?

In another thread I was talking about a faulty engine temperature gauge showing maximum hot when the engine is at normal temperature. That was in high summer - 28-30* outside. Now autumn temperatures are down to 13-15* and the gauge is only going to a little past the last white mark on the gauge.

Is it possible that the worn out alternator's reduced voltage is also having an effect on the gauge reading? - A few degrees lower engine bay temp is reflected on the gauge?

Can anybody recommend a good brand of alternator to put in? New or reconditioned?

Thanks Rowan
 

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Highly doubtful the alternator is worn out, my original lasted over 250,000 miles. You've got a 96 so the voltage you are seeing is correct. Early cars had an alternator rated to charge a standard lead acid battery but battery technology evolved with batteries having a higher Calcium content so able to withstand a higher charge voltage so later alternators (from 97 on) output a higher voltage. You are testing an early alternator to later alternator specs. Rev counter is driven from the engine speed output of the engine ECU not the alternator but the reading is adjustable. The rev counter and speedometer can be calibrated using small trimmer pots on the circuit board but if they are reading wrong as well as the temperature gauge, I'd suspect a bad earth connection for the instrument panel.
 

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Discussion Starter #3
Thanks Richard
Maybe somebody might add the earlier output readings to the main electrical sticky. That would prevent panic and needless worry.

My rev counter reads normally until things get hot - then they go silly. I recall reading somewhere that the crank sensor? and alternator readings combine to feed the ECU and that then goes to the rev counter. Or maybe I have it all wrong ((((

I am going to recheck my readings and see if I can get any more information.
 

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Discussion Starter #4
I forgot to mention that I have recently had a spate of weird message. ABS fault, Traction failure and Traction overheat - all when I usually am not even touching in the brakes.
I have read that these are often related to electrical gremlins so I will continue with my checking.
 

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If there is a problem with the ABS system it will also bring up the Traction Failure message as the Traction Control uses the ABS system so these messages may be due to a separate issue. Carry one with your checking, paying particular attention to the earth connections. There's a couple down in the footwells, behind the kick panels.
 

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Discussion Starter #6
I cleaned a couple of earth points under the bonnet, behind the battery, and now the temperature gauge is working properly - separate post.

Where does the instrument panel earth to? Behind the footwell kick-plates? or up behind the cluster inside the dashboard?
 
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