Where does the V8 take its rev signal from?

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SpudH

Well-Known Member
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Location
County Kerry, Ireland
As per title, I'm trying to find out where the Lucas 14CUX (RRC3.9) gets its rev signal from.

I'm having a bit of a starting issue with my RRC (pretty sure its down to an earthing problem) and I'm wondering where does the ECU pick up its signal from.

Any help appreciated.
 
As per title, I'm trying to find out where the Lucas 14CUX (RRC3.9) gets its rev signal from.

I'm having a bit of a starting issue with my RRC (pretty sure its down to an earthing problem) and I'm wondering where does the ECU pick up its signal from.

Any help appreciated.

What is the issue?

ECU takes a signal from coil and Alternator if I remember well. The signal from the coil also triggers injection pulse.

I assume you've done the normal checks for fuel and sparks? Or is it the case it takes a while to fire up then runs like a bag of spanners? If you can get it started, is it running rich or is it not starting at all?

If starting and running rich then probably a sensor - check sensor values. Is efi warning light coming on?

Try an ecu reset - disconnect plug on ecu for a few seconds then reconnect it or simply disconnect then reconnect battery.
 
Issue was non-start for months since thrashing it through salt water floods (I know, but thats why I have it :) ). It drove home, parked up, then refused to start when I went to start it the following w/end or since. I finally got round to giving it some attention last w/end.
I hooked it up to Faultmate and my P38 for a jump and went cranking. I noticed on faultmate that it wasn't showing any revs. On my DSE this would indicate a failed crank sensor but the 3..9 doesn't have one. I figured that the alternator wasn't earthing properly and with a bit of prodding and excessive cranking she finally spluttered into life. After a couple of prods on the throttle she settled into a nice idle. I took it for a good spin and parked it up again.
A week later it was back to no start so I took off the alt to clean up the earthing surfaces . While taking it off I noticed one of the wires was down to a single strand. Sorted that, put it back on and up she fired, yippie!! Took it for a good thrash and parked up again.
I hooked up faultmate again to see what was different and I noticed that it still doesn't show any revs while cranking until it actually fires up hence the original question.
Incidently it appears that one of the O2 sensors is not working so even though it fired first time this morning, I'm not out of the woods yet.

So are you saying there are two signals, one from the coil and one from the alternator? Any chance one is for rev counter one for the ECU or what do you think?
 
Its a simple old system,the W term on the alternator provides an AC waveform to drive the rev counter - plus an engine running signal to the EAS ECU if the car is on air.The 14CUX engine ecu uses the switched side of the HT coil via an inline resistor to get its signal to run the fuel pump and time the injector pulses.
 
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