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RPM Relay - Fuel Priming
#16
Just a thought, why not stick a few of these around the cables randomly until it works:

[Image: 31YB4WD713L._AA250_.jpg]

Just don't forget to fit them so they are exposed to water spray from the road. Behind the wheels in the wheel arch is ideal or at the front frame underneath so they get road salt spray and/or in a position where speed bumps can whack them about. The wise amongst you will realise that the headlamps are a good shield against water so use them plentiful behind there too !

Or for the electrical savvy amongst you who dis-like scotchloks for some unknown reason, fit some in line crimps to extend wires and coil it around the exhaust silencer/ manifold or near a belt so the wire bounces on it all the time:

[Image: p1733620_l.jpg]

Ideally fit them using a pair of old knackered pliers instead of the correct crimp tool so the wire falls off if you sneezed on it and/or the plastic insulation is partially removed, all causing random against bodywork that will give you a challenge for hours........

ONLY MESSING Big Grin

Nick-has.some.issues.with.sorting.peoples.dodgy.wiring-T
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#17
Dan1986 Wrote:I have a green cased one and an original black one, neither do the prime function. Someone, I can't remember who looked at the circuit and said it can't do a prime, it can only do it because of a voltage spike or sudden drop caused by flicking the key about or flashing lights.

That'll be me then

I've banged on about this one ad nauseum, I've tried three RPM relays in my D including ones that 'prime' other owners cars. Non of them prime mine.

Anyone who wants a full technical (and somewhat boring) electronics explanation of why the RPM dosen't, hasn't and never will prime the fuel system intentionally is welcome to email me.... Mr Green
Richard H.
http://www.deloreans.co.uk
DOC Technical Advisor VIN 1274
In theory, theory and practice are the same. In practice, they are not.
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#18
Rich, with your electronic know how I am sure you can easily mod one that does initially run the fuel pump for a sec or two regardless which car it is in Big Grin It would definately solve starting issues like in Dan Shanes fix.

I was interested to see if the prime thing works to a certain VIN number if the car ever had a wiring loom/ earth point change or not etc.

NickT
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#19
My car did prime on the final turn of key before ignition and then after 5 years of ownership the rpm died. After replacement the ignition behavior changed. I accept that the RPM relay doesn't prime but that is one heck of a co-incidence.

So what makes some cars have their fuel pump prime for that bit longer? We know they didn't all leave the factory the same but to have wired some up differently?

So what is the best way of having the pump prime the extra second or two before actual ignition?
Regards,

Chris Hawes
DOC 138
Vin 5255 Grey, 5-speed
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#20
Chris Hawes Wrote:My car did prime on the final turn of key before ignition and then after 5 years of ownership the rpm died. After replacement the ignition behavior changed. I accept that the RPM relay doesn't prime but that is one heck of a co-incidence.

So what makes some cars have their fuel pump prime for that bit longer? We know they didn't all leave the factory the same but to have wired some up differently?

So what is the best way of having the pump prime the extra second or two before actual ignition?

If somone could design a little add on which jumpered the rpm relay for a couple of
seconds when it received voltage from ignition position 2 then that would certainly
aid the starting of cars like mine.

Surely it can't be that hard to do for somone with electrical knowledge.

James
www.classicdelorean.com
Colchester - Essex - UK
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#21
Quote:That'll be me then

I've banged on about this one ad nauseum, I've tried three RPM relays in my
D including ones that 'prime' other owners cars. Non of them prime mine.

Anyone who wants a full technical (and somewhat boring) electronics
explanation of why the RPM dosen't, hasn't and never will prime the fuel
system intentionally is welcome to email me.... Mr Green

So is another component in the chain feeding 12V to the pump temporarily?
just seems such a random problem.

I'm no electrical expert but....

If it's not the rpm then an interesting experiment would be to remove the RPM relay,
on a car which is known to prime before starting, and put a multi-meter across
the +tive terminal on the wiring harnes (where the rpm normaly connects) to earth
and see if there is a voltage spike when you turn the key to pos 2.

if you tried this accross the terminal that is normaly live only when the car ir running
then you could prove that the RPM is not responcible for the priming.

Presumable the RPM relay looks for current from the alternator to confirm that the
engine is running so is the alternator the key?

hope that sort of makes sence, it seams like an easy experiment

J
www.classicdelorean.com
Colchester - Essex - UK
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#22
NickT Wrote:I would have to disagree with you on this one I'm afraid Dan even though I agree with you regarding the inertia switch cutting the fuel supply and the fact the normal relay is a working solution that overcomes the problem.

Thats ok mate, It's something I did on my car and it worked. I didnt need the CPR as I had a volvo one on mine.

Im not recommending it but I've had other cars that run the pumps all the time and the inertia switch was the only safety on the pump. My old S3 Esprit was like it as was my dads Austin Healey Sprite.

Im all for safety, I'd highly recommend a fire extinguisher in a D Mr Green

Dan
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#23
Daniel Shane Wrote:
NickT Wrote:I would have to disagree with you on this one I'm afraid Dan even though I agree with you regarding the inertia switch cutting the fuel supply and the fact the normal relay is a working solution that overcomes the problem.

Thats ok mate, It's something I did on my car and it worked. I didnt need the CPR as I had a volvo one on mine.

Im not recommending it but I've had other cars that run the pumps all the time and the inertia switch was the only safety on the pump. My old S3 Esprit was like it as was my dads Austin Healey Sprite.

Im all for safety, I'd highly recommend a fire extinguisher in a D Mr Green

Dan

No worries,

NickT
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#24
NickT Wrote:I think Blimey Ben has ChrisS's solid state one. It would be good to get his feedback on it.

NickT

Hi Nick...... and everyone else.

Not sure about the RPM relay, but it's defo got the modified central locking box. I'm sure ChrisS will add if the relay has been modified.

My car NEVER primes unless you turn the key to position 2, then back to 1 then back to 2 again. Dont matter if its hot or cold. But only through experimentation have I found this out. If I actually manually prime it from cold, say after a few weeks, then the engine will turn over several times before it will start, whereas if i'd have started it normally without priming, then it would go first turn of the key - strange that.

However, it does prime if it fails to start after turning over a few times, ie you hear the pump priming when you release from position 3 (Start) - Having had recent problems with the starter motor, this is how I found this out.

Needless to say, since i've changed the starter motor for a NOS one, and fully charged and put the battery that was on the car when I bought it, i've not had and issues. That old starter had been getting tired even when Chris still had it.

Ben
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#25
The RPM relay detects the coil making a spark, so your cranking the engine Ben would of made the pump run which is probably why you just heard it running when releasing the key from position 3.

One thing though James, my car does not prime but starts ok, so why does yours not start as well? Surely there is another problem causing the dodgy starting?
VIN: 6511
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#26
Dan1986 Wrote:The RPM relay detects the coil making a spark, so your cranking the engine Ben would of made the pump run which is probably why you just heard it running when releasing the key from position 3.

One thing though James, my car does not prime but starts ok, so why does yours not start as well? Surely there is another problem causing the dodgy starting?

Well it's probably fuel pressure related, I've changed alot of the injection gear on my car and as yet haven't got round to setting up/testing the pressures, that will be my 1st port of call.

J
www.classicdelorean.com
Colchester - Essex - UK
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#27
I have asked Mike to borrow the club fuel pressure tester, and I am sorting out some shims for Eurotec.
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#28
... arh yes fuel pressure tester ! .... will give Nick a call later and find out where it is atm..
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#29
A Van Wrote:I have asked Mike to borrow the club fuel pressure tester, and I am sorting out some shims for Eurotec.

I didn't know the club has a fuel pressure tester ! However, I have a spare fuel pressure tester (in my garage somewhere) that I don't mind anyone in the club borrowing. I just need to make one end up so it fits the fuel system. Genuine volvo one it is too and it works exactly as per workshop manual.

Sorry Ben, I thought ChrisS was the RPM not the central locking. Doh !

I have a spare green volvo relay and I might have a look at the weekend, if I am not working on this project again..................

NickT.
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#30
Dan1986 Wrote:The RPM relay detects the coil making a spark, so your cranking the engine Ben would of made the pump run which is probably why you just heard it running when releasing the key from position 3.

One thing though James, my car does not prime but starts ok, so why does yours not start as well? Surely there is another problem causing the dodgy starting?

It detects the earth switching from the ignition amplifier, grey cables. This is connected to low tension "1" on the coil and the fuel pump relay.

As a thought, I will check tonight if mine still primes if I disconnect grey cable from coil first.

NickT
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