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Darryl Watson
Frequent User
Username: inox

Post Number: 74
Registered: 4-2015
Posted on Sunday, 03 March, 2019 - 01:23:   Edit PostDelete PostView Post/Check IP

Hi,
Sorry in advance for the long post
Intermittently our 1990 Mulsanne S coughs and won't start. It will usually start at the next turn of the key although occasionally it will take two or three tries.
The blink code shows 4312 which equates to ďSpark timing sendorĒ in the service manual.
I changed the sensor that is located near the water pump and when that didnít cure the problem transposed posed it with the sensor at the back of the engine.
I have cleaned all the plugs and sockets with Servisol Super switch cleaner and all of the wired connections seem tight and the wires canít be pulled off.
I hard wired a second lead from the socket for the front sensor to the ECU utilising a(USB lead.
The connectors, pins 29 + 30, on the ECU plug have been cleaned and tightened.
Anyone any ideas?
Many thanks.
Regards

Darryl
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Jim Walters
Prolific User
Username: jim_walters

Post Number: 216
Registered: 1-2014
Posted on Sunday, 03 March, 2019 - 13:57:   Edit PostDelete PostView Post/Check IP

Check the voltage produced by the sensors when cranking. I can't recall what it should be off the top of my head but it's in the WSM. There are often shims under these to adjust the clearance too, put a piece of Plasticine on the end of the sensor to check clearance. If not close enough there won't be enough voltage generated to produce the necessary signal.

SRH8505 SRC18015 SRE22493 NAC-05370
www.bristolmotors.com
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Darryl Watson
Frequent User
Username: inox

Post Number: 75
Registered: 4-2015
Posted on Sunday, 03 March, 2019 - 20:22:   Edit PostDelete PostView Post/Check IP

Thanks Jim,
I should have thought of that myself. I checked the output years ago when I was having problems so should have checked again now.
The output from both sensors is low. (max reading digital meter - AC volts - cranked engine). The front was replaced approx. 5000 mls / four years ago.
Pin 29 (front sensor) is .02v should be 0.11v and pin 30 (rear sensor) is .319v should be 0.63v.
From memory there is a shim under the front sensor and Iíll re-install the original rear sensor.
Not confident about putting plasticine or Blue-Tac on the end of the sensor in case it drops into the engine.
Regards
Darryl

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