fuel pump relay again.

[Ian Fife]

I gather the relay is dual function, but I'm not sure what the second function is.

I may be mistaken here, but I think these relays are in fact two relays - one which works when cranking and then switching to the second when the engine fires.

I was told this when I had a fault with my 945, it would fire and run very briefly and then cut out. So a fault with the second relay was diagnosed. Changing the (white) relay effected an instant and permanent cure.

Ian F

[classicswede]

Originally Posted by Ian Fife

I gather the relay is dual function, but I'm not sure what the second function is.

It operates as a relay for the fuel pump. The second function is a safety car relay. Should the rpm signal to the relay stop the relay cuts the fuel pump, that is the reason of the rpm signal wire going to the fuel pump relay

[Offgrid]

Classic Swede is in agreement with the information that I discovered when I replaced the relay on the B230E, but it doesn't seem to agree with the information I have discovered recently. I've also tried to discover what will happen if I use a white relay on a 1990 B200E - that is the one Ebay seems to think I should be using.
I'm also concerned by the small amount of heat I detect on the relay, and I wonder if that is the result of a faulty sensor. causing the relay to oscillate or something. That would explain the failure in heavy traffic.
I'm also considering the implications of the secondary shut off relay. When I switch on the ignition, I can hear the fuel pump for a second or so, and then it turns off. If I turn off the ignition and turn it on again, then the pump will run again for another second or so. This would seem to be a good way of priming the fuel line rather than possibly draining the battery by cranking the engine.
I think I'm going to cut the top off one of the broken relays, and see if I can repair it. I could then keep the repaired unit for emergencies.

[Ian Fife]

I got my information from a Volvo trained mechanic who now runs his own Volvo business,

Ian F

[Offgrid]

Originally Posted by Ian Fife

I got my information from a Volvo trained mechanic who now runs his own Volvo business,

Ian F

You were lucky to find someone who knows about car components. Most so-called mechanics these days seem to be either software engineers, or fitters.

I've taken the covers off the two failed relays, and they are very different ( although they are both green ). The one that failed in the traffic jam has got a wire that has become de-soldered, and the insulation has melted slightly at the end. This ties in with the fact that the case became red hot. I'll resolder it, and see if it works, if so, I'll keep it as a spare. I'll have a look at the wiring diagram, and see if I can work out where the heat came from. Since fitting the replacement, the car seems to be a bit friskier, and the starter disconnection hasn't returned. I'll give it another couple of days before forming a conclusion about that issue.

The reversed functionality of the earlier failed relay will require a bit more research. I'll keep you guys posted when I get round to doing that.

The white relay has arrived, and it appears to be identical externally. The connectors and lugs are all in the same locations. I haven't had the courage to try it yet. I might do that on the saloon, but it doesn't have a back box right now, and the neighbours complain if I start it too often.

[Offgrid]

OK
Here is the definitive answer for a 1990 B200E engine.

Green ( mechanical ) is the correct relay. With it fitted, the pump runs for a couple of seconds on turning the ignition key, and the engine starts.

White ( electronic ) doesn't work. The fuel pump run continuously when the ignition key is turned, and the engine doesn't start.

Apologies to anyone who's opinion I called into question.

[classicswede]

Told you so

The relays do get hot as they are a high load relay and that is why the soldering can let go. As the soldering starts to fail the relay gets hotter

The covers unclip easy enough to look at them. You can sometimes repair them

Stop looking for information in the US as it does not apply to UK cars