760 GLE V6 starting fault

I have an intermittant hard start fault when hot and occasional engine cutout.
Tests have determined there is no spark, there is system voltage at the positive side of the coil, have not had a chance to check at neg side for pulsing yet as engine started nor have I checked for injector pulse.
Strangely I have found no power at the coil positive on a couple of occasions which contradicted the previous test.

Have checked coil secondary and primary windings, visual of distributor cap and rotor looks ok and coil HT lead resistance good.

The TDC sensor at rear of RH head has lost its insulation leaving only bare sheilding wire although I don't believe this should cause a problem.

Can anyone tell me how this ignition system works, the TDC sensor works off the flywheel, does it pick up cam and crank angle pulses for the ecu? there is no connector at the distributor so no sensor in there.

The rear plug leads of each bank have a 3 wire plug also, I have no idea what they are for and have been unable to locate the ignition module (it must have one though)

Although not ignition related I would like to know the location of the fuel pump relay as I have heard it can cause problems, there are 2 relays between the right hand wheel arch and ABS hydraulic unit, if I disconnect the left most relay the engine won't start, swapping relays did not fix the fault.

The problem must be heat related I just hope there is not more than one fault present.

[BillB]

I'm only familiar with the B230 4cyl but I think the principles are similar. A common failure is the crank sensor (semiconductor hall effect),which will fail when hot if it is on its way out. As you have no spark, this seems likely. Next time it fails, watch the tach needle while cranking. If it's dead, either the RPM sensor is dead (most likely) or the power stage (ignition amplifier) or possibly the ECU (ignition module) but this is least likely. The RPM sensor can be substituted using a function generator, if you happen to know an electronics person.

The chain is: RPM sensor, ECU, power stage, coil, distributor, plugs.

I have a 760 280E which had a similar problem. That turned out to be that fuel pump relay, it has 2 coils and one gets fried. Replaced it and the problem mostly went away.
However, I still have a weirdness;
Cold start is almost instant.
Hot start when stopped for 5 mins or more, cranks for ages then fires up. During this cranking, there is no spark, (as detected by a strobe), then it sparks and bursts into life immediately. I thought this was something to allow the fuel vapour to purge out first, (like an industrial boiler will).
If I crank for 2 seconds or so, then stop and recrank, it will start instantly. Is this because it thinks it's only stopped for a few seconds ?.
This has been happening for the last 100k miles at least.
Hope this may go some way to resolving yours.
Paul.
'89 760 GLE Est 220,000. Good as new.

Paul,
I had\have the exact same problem as you. The car would fail to restart sometimes for hours afterwards this was cured like yours by having the fuel fump relay replaced.

The hot start problem sounds very familiar, mine started around 118K miles its now got 132K. Starts fine first thing in the morning. If I stop and restart within a couple of minutes it is ok.
The problem comes if it's been sitting for a little while it then takes ages to get it to fire.
I have mentioned it at every service it has had with my local Volvo dealer, and they still have not cured it, instead it always comes back with no fault found.
Have got used to it now, but ideally would like to know of a fix

Malcolm
1990 760GLE Saloon

[Derry]

On my one it was the fuel pump relay.