how DOES a fuel pressure relay work? was 1988 245 no start (well still not starting!)

Hi all. Still trying to figure our why our (until now) trusty 1988 245 won't go.

Looking through list after list of Volvo info, I thought I would check our fuel pressure relay. It looks like it might be the culprit.

Can someone explan to me how this is supposed to work? I understand how relays work, here is the scenario for ours (observed in the car just now (it's minus 32C, so excuse the rough sentences, talk about lousy weather to diagnose a stuck car!!).

If you are looking at the relay installed (BTW, we have the white plastic relay in our 1988), but with the cover off, there are two coils. The left and the right. When I turn the key in the ignition to position three ("on"), this relay clicks. The other relay remains motionless and there is no noise from my fuel pump. Being a bit of an idiot, I figured what happens if... So carefully inserting a tiny screwdriver to close the second relay (the right hand side), I noticed that then I could in fact hear the fuel pump merrily whirring away. Still the car will not start.

Can someone explain just what is supposed to be the sequence of operation in a functioning fuel pressure relay? Which side should be closed? Opened? When?

The car is still cranking wonderfully, but it just won't catch. It ran so wonderfully when I parked it last Thursday night, wish I knew what happened that night!

Chris Mears Charlottetown, PEI

1988 Volvo 245GL "Daisy"
Reply to
chris mears
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I have a similar problem with an '88 here (it's a parts car, so it's not a priority to fix). In my case, the left relay clicks in then drops straight back out when the ignition is turned on. The solution is to hold the left relay in whilst cranking. Once the engine starts, there appears to be sufficient power to hold the relay in?!?

Of course, this is a RHD car, so the technique involves sitting in the driver's seat and lying across the gearshift so that I can just reach the relay with the left hand while turning the key with the right hand!

I don't know whether the fault is in the relay or in whatever circuit drives it.

Reply to
athol

In the run position the main fuel injection system relay closes (powers up the injection control unit). When you turn to the crank position a ground signal from the injection unit closes the fuel pumps relay provided an ignition pulse from the ignition control unit is seen by the injection unit, whereupon the pump relay latches until power to the main relay is interrupted.

Bob

Reply to
User

So looking at the top, and replying in the most simple of terms:

(Described looking at relay with plug at top of unit and relays facing user)

-Left relay is MAIN and is the on/off for the entire unit.

-Right relay turns fuel pumps on and off, and is dependant on LEFT being on.

Have I got this?

Thanks Chris

Reply to
chris mears

Yes, but to clarify, the fuel pump part is also dependant on the fuel control unit receiving pulses from the ignition control unit (i.e. working ignition, engine rotating) before it will ground the pin that turns the fuel relay on.

Reply to
Mike F

Since you have had the fuel pump running by manually forcing the relay, and still no start, I would suggest that you had a look at the connector for the Hall sensor. Another cause could be the output circuit for the fuel pump relay on the injection module itself, this is a bit harder to verify though, but soldering could be inspected if opening the module.

Regards

Per Hauge

"chris mears" skrev i en meddelelse news: snipped-for-privacy@g44g2000cwa.googlegroups.com...

Reply to
Per Hauge-Nielsen

Hi Folks..

Rather than spend countless hours studying the workings of the relay, take a look at the date stamp on the case. If it's approximately the same date as the vehicle year then just replace it. In my shop the symptoms you describe plus the date confirmation would require replacement of the relay simply for maintenance purposes.

regards

wharf rat in Ashland, Oregon

Reply to
dupree8995

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