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

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chris mears - 20 Feb 2006 03:01 GMT

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"

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athol - 20 Feb 2006 04:44 GMT

> 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
[quoted text clipped - 5 lines]
> that then I could in fact hear the fuel pump merrily whirring away.
> Still the car will not start.

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.

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Athol
<http://cust.idl.com.au/athol> Linux Registered User # 254000
The state of infrastructure in New South Wales is a disgrace.
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User - 20 Feb 2006 04:46 GMT

> Hi all. Still trying to figure our why our (until now) trusty 1988 245
> won't go.
[quoted text clipped - 28 lines]
> Charlottetown, PEI
> 1988 Volvo 245GL "Daisy"

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

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The goal when driving is to miss the maximum number of objects.

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chris mears - 20 Feb 2006 05:11 GMT

> 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
[quoted text clipped - 4 lines]
>
> Bob

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

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Mike F - 20 Feb 2006 16:10 GMT

> > 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
[quoted text clipped - 17 lines]
> Thanks
> Chris

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.

Signature

Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

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Per Hauge-Nielsen - 20 Feb 2006 20:15 GMT

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

> Hi all. Still trying to figure our why our (until now) trusty 1988 245
> won't go.
[quoted text clipped - 28 lines]
> Charlottetown, PEI
> 1988 Volvo 245GL "Daisy"

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dupree8995@msn.com - 21 Feb 2006 06:10 GMT

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

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