Fuel pump relay /CPS
 

Had an intermittent no start problem that after advice on here I managed to trace back to the Crank Position Sensor. I fitted a new sensor in January and all has been great.
Just serviced the car getting ready for winter - new plugs, leads, rotor arm, cap, oil etc. Went to start the car - won't start. Checked everything, still won't start. Put all the old plugs, cap etc back on. Still won't start. There is a spark.

Guessing that it's either the new CPS or fuel pump relay. Have ordered a new white relay but in the mean time is there a way of testing the old relay to see if it's gone.

Alternative is the CPS has gone again :(

Use a short length of wire with a clip on each end and connect together the terminals of fuses 4 and 6. This bypasses the relay and causes the pumps to run continuously. If you can then start the engine then it proves the relay was faulty.
If you still can't then it's something else. In my experience this is quite commonly a failed ignition amplifier.
There's a recent thread on various non-start faults.

If you have access to the relay tray you can tap the FPR with a knuckle while trying to start the car : a dodgy relay sometimes comes to life that way, which finds the problem but obviously still needs replacing ASAP.
If the car does start, and you have the panel open, a dodgy FPS can get TOO HOT, revealing its inherent evilness.

Thanks for that. While I'm waiting for the new relay and sensor to arrive I pulled out the fuel pump relay, popped the cover off, ran a multi meter through it. It all seems to work OK. Looks OK. Popped it back in. Turned on ignition - heard pump charge the system. Car started - ran - stalled. Restarted. Tick over seems a bit low.

Will try again this morning after another damp evening. The thing is I did so many things getting at once - aside from servicing it I'd had an area welded on the underside that was pointed out at last MOT. Also then cleaned the engine with engine cleaner as it was pretty disgusting.

Going to order an ignition amplifier in any case.

Ignition amplifier - Remove and check that the heat sink paste hasn't dried out. If looking dodgy, clean and renew. It's the same paste as used for fitting the processor chips in PC's so a PC shop a good place to try if you don't want to shop with Amazon or similar. Maybe the screws holding it on are loose. Amp will overheat and give unpredictable signals if loose or the paste is bad.
Scroll down about 2 thirds down this page.
https://www.volvoclub.org.uk/faq/Ele...lIgnition.html