Hot Start problem on DGS here we go :(

[Dan6457]

Its back together now with my original relay back in but with a new 555 timer chip. Still exactly as it was, no priming, starts perfectly when cold, takes a while then sputters to life if warm. Will leave it alone now till eurotec and get the pressure tester on it. The other relay will go back to gsf.

[Rich H]

Quote:So why are there so many references to fuel pump relay priming on the forum if this is a myth?

Well, perhaps myth was the wrong choice of word.

Many, if not most DeLoreans do this priming thing, but more by accident than design I'm sure. There's certainly no circuit within the RPM relay to generate this initial pulse.

As my car has never done this priming thing I figured I had a 'fault' with my RPM relay even though I've never had a problem with starting. I changed it for another and it still didn't prime, so replaced every single component in the relay with new and still no 'priming'

I can simulate the priming effect on the test bench by spiking the supply to the RPM relay and I guess thats where the effect comes from inside the car. I think it could be classed as a fault, but if it aint broke.....

Bet you're sorry you asked now! :lol:

[NickT]

RichH Wrote:

Quote:So why are there so many references to fuel pump relay priming on the forum if this is a myth?

Well, perhaps myth was the wrong choice of word.

Many, if not most DeLoreans do this priming thing, but more by accident than design I'm sure. There's certainly no circuit within the RPM relay to generate this initial pulse.

As my car has never done this priming thing I figured I had a 'fault' with my RPM relay even though I've never had a problem with starting. I changed it for another and it still didn't prime, so replaced every single component in the relay with new and still no 'priming'

I can simulate the priming effect on the test bench by spiking the supply to the RPM relay and I guess thats where the effect comes from inside the car. I think it could be classed as a fault, but if it aint broke.....

Bet you're sorry you asked now! :lol:

I would have to disagree with you on this one Rich I'm afraid.

When you say "......I can simulate the priming effect on the test bench by spiking the supply to the RPM relay ..." , surely this is when the power is first applied to the fuel pump relay when the ignition key is set to position 2? A question to ask is what voltage did you apply? Was it 12v exactly or slightly more? I'm not discounting what and how you have tested as I know you have experience in fixing these relays and other electronic parts successfully.

I would definately say that the fuel pump relay should run the fuel pump for a couple/ few seconds to prime the fuel system.

http://www.auto-solve.com/mech_inj.htm

http://www.volvoclub.org.uk/tech/fuel_i ... ection.pdf
(copy of the autosolve probably!)

http://www.swedishbricks.com/faq/figeneral.html#restart

With the initial priming , the 'effect' would benefit starting the car as the fuel line pressure would be at operating pressure rather than rest pressure (if any pressure at all). I don't think I have looked at a car that doesn't do this priming but then again there are far more cars about. I am going on experience on these and other K-Jet cars I've worked on.

In any case, to sort out Dan's hot start, Dan, can you confirm if you have:

ran the car until it is warm
turned the engine off
added the (TEMPORARY FOR TESTING ONLY) link in the fuel pump relay (this will run the fuel pump continuously even with key out)
tried to restart the engine.

Let me know if this helps the car start or not.

NickT.

ps Rich, we could swap relays over at EuroTec and see if this priming is car or relay dependant and measure appropriate voltages.

[bozzzydmc]

Be interesting to see what 'make' of relay doesnt 'prime' as I have 3 different manufacturers of fuel pump relay here and they all do .

Their only difference is the length of time they prime the pump.

[Rich H]

Quote:I would definately say that the fuel pump relay should run the fuel pump for a couple/ few seconds to prime the fuel system.

And I would definately say not :lol: at least not according to the circuit diagram... One to thrash out at Eurotec over a nice cold pint I reckon 8)

Oh, one thing about jumpering the RPM relay - it might start, but it'll run like a bag of nails 'cause there'll be no power to the Lambda system

[NickT]

RichH Wrote:

Quote:I would definately say that the fuel pump relay should run the fuel pump for a couple/ few seconds to prime the fuel system.

And I would definately say not :lol: at least not according to the circuit diagram... One to thrash out at Eurotec over a nice cold pint I reckon 8)

Oh, one thing about jumpering the RPM relay - it might start, but it'll run like a bag of nails 'cause there'll be no power to the Lambda system

True but at least it could narrow down the hot start test.

Definately over a nice cold pint Thanks for the offer

It would be interesting to see which ones do and don't as there wil be quite a few cars there !

NickT

[Rich H]

Quote:Definately over a nice cold pint Thanks for the offer

Me and my big mouth :?

[Dan6457]

NickT Wrote:In any case, to sort out Dan's hot start, Dan, can you confirm if you have:

ran the car until it is warm
turned the engine off
added the (TEMPORARY FOR TESTING ONLY) link in the fuel pump relay (this will run the fuel pump continuously even with key out)
tried to restart the engine.

Let me know if this helps the car start or not.

Hi Nick, Yes running the pump helps start the car when hot. You hear the pump run fast then it sort of slows down after a couple of secs as if its clearing air out of the line...? then it fires right up.

[Dan6457]

RichH Wrote:Oh, one thing about jumpering the RPM relay - it might start, but it'll run like a bag of nails 'cause there'll be no power to the Lambda system

Theres no lambda system on my car. :wink:

[Rich H]

Quote:Yes running the pump helps start the car when hot. You hear the pump run fast then it sort of slows down after a couple of secs as if its clearing air out of the line...? then it fires right up.

The pump slows down as it pressurises the system, which (when hot) if the accumulator was working it wouldn't have to do.

Without a proper check it's hard to say, but it does sounds like the accumulator to me.

[NickT]

RichH Wrote:

Quote:Yes running the pump helps start the car when hot. You hear the pump run fast then it sort of slows down after a couple of secs as if its clearing air out of the line...? then it fires right up.

The pump slows down as it pressurises the system, which (when hot) if the accumulator was working it wouldn't have to do.

Without a proper check it's hard to say, but it does sounds like the accumulator to me.

I agree. Mind you I don't fancy changing it, my fingers can be like a bunch of bananas at times !

NickT

[bozzzydmc]

yes definatly not a job for a oem jack and a gravelled carpark

Hopefully it is just a check valve ...

[Dan6457]

At last I have had time to do some work on this today. I have replaced the check valve as a precaution and also done the O-rings in the metering head as suggested by Mr NickT. Here is a before and after picture of the o-ring:





Unfortunatly I can't get the D out of the garage to test it for a few days as the driveway has just been re-laid and I cant drive on it for a bit. The old ring does look pretty shot to me though so I'm hoping this was the problem.

[NickT]

Useful pic for others:







Taken from Specialtautos' web site:

http://www.specialtauto.com/delorean-pa ... ulator.jpg

Let's hope this fixes the hot start issue.

While you have it apart you could re-shim the primary pressure while you are at it It was 4.8 to 4.9 bar when we checked it at EuroTec. You can set it up to 5.5 bar according to my book. The base fuelling may need re-setting (2% +/- 0.5% CO) if you do this.

I will have a look in my book tonight for approx increase in shim versus increase in fuel pressure.

Nick.

[Dan6457]

What will I gain by increasing the pressure Nick?