Engine cut out and Lambda sensor

[Laird Scooby]

Originally Posted by jlawler

Hi,
Yes I cleaned the fuses when you mentioned them. The Fuel Pump one (#11) looked a little tarnished but was sound. I have some spares anyway so I swapped it. Again no change in behaviour.

What I'm referring to as the Ignition relay is what I think people call the Radio Suppression Relay (is that the correct name?). Mounted close to the ignition amp on wing above the battery.

J

That is indeed the Radio Suppression Relay, on your car being a 98 model it does provide ignition power and injector power. If memory serves it also feeds the Lambda sensor heater. Have you unplugged the existing one and confirmed the car fails to start? I ask this because your car should have an electric cooling fan, depending on exact spec some were ECU controlled and had a special relay to switch between 2 speeds and other cars still had a single relay that simply switched the fan on and off. That one uses the same type of relay as the RSR so it's possible to mix the two of them up.

Also on the pre-95 cars (Mk1 and older) the RSR did not feed the coil so had nothing to do with ignition. When i said "Mk1 and older" i'm including the later 740s that had EFi - many of those had no Lambda sensor so the RSR literally only powered the injectors.

For this reason, the RSR is always referred to on here as the RSR so we know which one is being talked about.

When it has cut out, have you tried turning the ignition on and off several times quickly before trying to restart at all? If not, give it a try and let me know the result.

[jlawler]

Thanks for the heads up. Yes it has an electric fan.
It's a 98 model and is well speced, so it may have the dual speed fan.
I'll check it tomorrow.

[jlawler]

Yes it has the big two speed fan relay so I swapping the correct one.
Parts arrived today (post must have freed up after Christmas).
So I'll put them in this evening and see how I get on.

[Laird Scooby]

Originally Posted by jlawler

Yes it has the big two speed fan relay so I swapping the correct one.
Parts arrived today (post must have freed up after Christmas).
So I'll put them in this evening and see how I get on.

Do them one at a time and test for a few days in between so you have an idea which part was/is faulty. Also try that trick of turning the ignition on/off repeatedly several times for a few seconds next time it cuts out BEFORE you fit any news parts.

[jlawler]

So a week in without any further problems and I am tentatively going to say Fuel Pump Relay.
I'll give it another week or more before I claim a cure

Thanks again for all your advice and help on this.

[jlawler]

Ok another week and still running without a hitch.
I guess it was the demon fuel pump relay after all.
Does it run more than just the fuel pump?

J