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Weird Binary Fuel Pump Starting issue..?
#1
Hi All!


Recently noted a bit of an oddity with my car on starting.

Having had old cars before, I have a habit of turning key from off to first position then second position slowly, then waiting in second position to hear fuel pump going - leaving for a bit to make sure system pressurised and fuel is in all lines, before finally turning to 'start'.  Hopefully avoiding unnecessary fuel-less cranking..

Currently, however, in my D;
Turn key through first position to second position, and there's an odd buzzing noise from somewhere behind me on the LHS.
And the fuel pump appears not to be going.
Turn key back to 'off', then turn back through first to second position.  No problem, pump is going as normal.  Continue turning key to 'start', no worries, off she goes.

However, even after a bit of running, if I then turn her off (at a petrol station, say) - the whole malarkey happens again!

So, I call it a binary pump issue, as every time I get in to start her up, there's a first turn of the key to position 2 with no fuel pump (0) and an odd buzzing noise, then on the second turn of the key to position 2, fuel pump winds up perfectly normally (1) 'cos I can hear it, without the buzzing noise.

Any thoughts?

Yours confusedly, 
Ivan
Huh
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#2
I get exactly the same issue. I think it's the frequency valve.

Sometimes the speed of turning through key Position 2 affects whether it happens or not! I have noted it as a quirk and continue to ignore it.

I'm pretty sure it's always done it, but I've become more conscious of it post restoration.
Richard Hanlon
Derbyshire
DOC 393

1981 DMC-12 VIN 06126
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#3
The buzzing behind you on LHS is the idle speed motor which is normal.

I have had different behaviours with different fuel pump relays in the past.
Some Fuel pump relays (RPM Relay) can prime on position 2... some not... but still start the engine.
If it primes it will only pump for 2 seconds ( sometimes I turn the key off and on to prime again... )

I have also heard some owners can prime the fuel pump by flashing the headlights once... whether this is normal or not I'm not sure. Give it a try.
Also try a different RPM relay and see if it behaves better for you. Volvo 260/760 ones fit and work.
DOC 116
VIN 6237
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#4
Cheers guys, good to know it's not a unique problem at least (which seems to be a common theme with these, thankfully - any problem you've got, someone else has had it before [and often found a solution as well!]).
So, some things for me to try / have a look at - failing that, I might also go the 'ignorable quirk' route..! :-D
Thank you!
:-)
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#5
That's true, Freq valve is RHS. I've not really tracked it down! But yeah,it happens whatever it is and has no noticeable influence on starting or not. It's always been a pretty good starter FWIW.
Richard Hanlon
Derbyshire
DOC 393

1981 DMC-12 VIN 06126
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#6
Perfectly normal, I seem to remember long discussions around if the fuel pump should prime on the key or not, seems the jury is out on it. Me i always make it prime!
Chris
Membership Secretary DOC UK
2021's DeLorean event: http://www.deloreans.co.uk/forum/showthr...p?tid=6056
VIN#15768 Ex VIN#4584
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#7
My car primes randomly. What i mean by that, is sometimes It does, and other times it doesn't. I've changed the RPM relay as an experiment some time in the past. Didn't make any difference. I put the original one back. Even without priming, the car starts on the button or quickly if it feels lazy any particular day. No pressing of the accelerator to "aid" things along.
Rissy
Chris M. Morionem qui loquitur multus sine cogitatione.
(Forum Member 288)
(DOC Member 663)

May 1981 vin#1458
"LEX" aka "Wonkey" - Officially used in Britain's Greatest Machines (80's episode) with Chris Barrie.
Grey Wheels
Grooved, flapped Bonnet
Black Leather Interior
Chassis: #1073
Engine: #2839

Main Car(s):

2005 BMW M3 E46 Shape 3.246 Straight Six in Velvet Blue
1999 Honda Civic MB6 Shape 1.8VTi VTEC in Pirates Black
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#8
Quote: I seem to remember long discussions around if the fuel pump should prime on the key or not, seems the jury is out on it.

I think I'm well known for my opinions on it  Big Grin

My car has never primed, with any RPM relay (and I've tested many), including those that supposedly do it on other cars. But I won't bang on about why. Again

The loud buzzing is the Frequency Valve. Not always guaranteed to operate at ignition time. Sometimes it will buzz for a second, sometimes longer, sometimes not at all.

The faint humming noise is constant with ignition on, and is from the idle motor. Usually it's too quiet to hear inside the cab.
Richard H. DOC 365 VIN 1274
http://www.deloreans.co.uk
In theory, theory and practice are the same. In practice, they are not.
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