OK... Managed the 200 mile round trip to Detling with only a few problems!!

basically driving along the motorway at a steady 70 and begin to loose power/cant accelerate

firat time i got to the side of the road and swithched off then had a look - nothing to see. tried starting but fuel pressure guage shows zero.
fiddled around hp and lp pumps and fuel pump relay(fused) all semed fine then the fuel pressure came back... didnt actually find an issue but figured i must have disturbed something

on the ay home i had the same issue twice but when i pulled over for a second (didnt actually stop the engine) it seemed to clear and was fine again.....

so I have a few of theories and want your opinions on them...

1, HP fuel pump intermittent wiring fault?
2, same as above but LP?
3, LP pump not up to job of filling swirl tank fast enough for HP pump?
4, HP fuel pump is very close to the diff whihc is getting very hot, could the heat be effecting the pump?

I have a facet pump supplying the swirl pot (1.5 litre pot i think) gravity feeding HP sierra injection pump. fuel pressure reg is set at 3 bar with return to swirl pot. overflow from swirl pot back to tank.
have lp filter before lp pump and hp filter after hp pump. fuel rail has been converted to flow straight through to the regulator and return.

am thinking that i should try replacing the filters anyway as they have been on since it was pu ont the road a year ago and probably should be changed (as you say, build debris)...

Check for loose debris inside the fuel tank.

The classic symptoms for this are.

Car stops due to lack of fuel supply at a random distance.
Leave the car switched off for 20 minites + and it starts and runs perfectly.

Also check your fuel tank is properly vented and not building up a vacuum.

not seeing debris in the lp filter which i would think would be an obvious first sign...

i have a breather in place which has an inversion cutoff valve jobbie...
i dont get and rush of air when opening cap so i think it is breathing ok but will check it.


one thing i did thnk off was that at both time the problems occured at similar point of fuel level...... cant quite see how that effects thing though

Have you got a low pressure return?

When I first built mine I did not bother, the car ran fine for a while then gradually the swirl pot emptied itself, which is an impossibility as all that is happening is fuel being taken away. I added a return with a old carb jet as a restrictor which resolved things.

Later on in the year the HP pump started to leak, when I replaced this the return was no-longer required. The HP pump was introducing air at pressure into the system at a rate higher than the LP cut off which explained my initial problem.

A small airleak in the HP pickup will also create these issues.
Regards Mark

quote:

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Originally posted by mark chandler
Have you got a low pressure return?

When I first built mine I did not bother, the car ran fine for a while then gradually the swirl pot emptied itself, which is an impossibility as all that is happening is fuel being taken away. I added a return with a old carb jet as a restrictor which resolved things.

Later on in the year the HP pump started to leak, when I replaced this the return was no-longer required. The HP pump was introducing air at pressure into the system at a rate higher than the LP cut off which explained my initial problem.

A small airleak in the HP pickup will also create these issues.
Regards Mark

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BTTT

So no opinions on whether the heat from the diff could be causing the issue???

OK.....

as some of you know from the show, I spent last week relocating the hp fuel pump about 5" further from the diff and fitting a heat shield... i can confirm that the pump is now not getting hot....

however my problems continue

I bought a pressure sender at the show and fitted it to my regulator for the drive home. i had it connected to my oil pressure guage...

I was fine for the first 85 miles. it held a very steady 3 bar
then the needle started to wobble about a bit and the pressure dropped to about 2.5 bar for the next 20 miles
the needle carried on wobbling and was down to about 2bar by the time i filled up at newmarket. i swirtched off before filling up and back on again and saw no pressure at all from the priming pulse!
filled the tank completely (added 13 litres so not an empty tank!)
then flicked the ignition key again and still no pressure from priming pulse
had a coffee for about 10 mins and then went back to it and the pressure rose slowly to about 2 bar on the prime pulse
drove down the road and got about 2 miles before the pressure dropped to 1 bar and the car started really playing up
pulled over and tried removing the fuel cap in case the breather was blocked.... made no difference and after the brief stop the pressure was unstaedy at about 2 bar for the next 10 miles beofre it dropped to 1 bar again....
pulled over and unloaded the boot to look at the pumps... was trying to tell whether both were running but couldnt tell because of all the road noise
at which point the priming pressure jumped back to a very steady 3bar and stayed there for the last 35miles home without a blip

so.........

analysis anyone?

Im thinking of replacing all filters and double checking the wiring to the lp pump... then next step is to replace the hp pump - which was from the donor sierra.... if that fails then look at replacing the facet silver top pump supplying the swirl pot (that was bought new late 2007 about 1700 milkes ago so should be ok....)

I'd replace the HP pump with a decent one (non-oem). I've had fuel pumps fail in normal cars and do what your describing.

Sounds like you are on the case......

I agree it really does sound like the pump....BUT, also be aware, that things like earthing problems else where could cause the pump to malfunction......when you see the problem, get a multimeter on the gnd pin and check resistance to gnd.....

For an experiment you by pass the entire ECU, and hard wire the pump (via a switch) to the battery, that way you could be 100% confident that it's not a wiring issue.

Good luck.

PJ.

FWIW I would stick a new HP pump on, they are often on ebay silly cheap

Clicky

As jenko says, do try hardwiring it in first and check the supplies are ok. Pump relay from megasquirt ok? I would think that faultering pressure means the pump is either on its way out, or has something stuck in it.

David

PS bosch HP pumps are a nice fit in an old fashioned coil bracket with a bit of thin rubber wrapped around them

BTTT

problems continue

have replaced both hp and lp filters... holding off on the hp pump for the sec for financial reasons!

latest bit of info is > it would appear that the problem is MOSTLY restricted to when the tank 1/4 full !?
however when i filled up on the way home i took the tank to the brim and had the same problems..... tried driving with the fuel cap off incase it was a vacuum problem but no help. once i had driven 20 miles it settled down again.....

my lp pump is a facet silver top which is sucking the fuel through a generic clear filter and up a dip tube in the tank...
the filter is currently sat at an angle downwards. swirl pot is about 1.5l

thing i cant get away from is the idea that the swirl pot is emptying and starving the hp pump..... possibly due to the lp pump failing to draw fuel effectively from the tank... although that matches the symptoms i cant see how it could be related to the fuel level being eith 1/4 or brim full....

this is getting really frustrating but i dont want to shell out a fortune on new hp and lp pumps if i dont need them!

obscure thought but could the angle of the lp filter cause starvation? there is always an air bubble in there when running which grows when sropped.....

added a diagram to help explain....

see HERE

[Edited on 12-5-09 by DaveFJ]

Not sure if you answered this, but do you have a return from the swirl pot back to the tank? This is very important, otherwise the LP pump can not purge the swirl pot of air.

yup - on the diagram

of course i dont know for sure it isnt blocked............

quote:

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Originally posted by DaveFJ
yup - on the diagram

of course i dont know for sure it isnt blocked............

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