Fuel pressure dropping?

[gmcmotorsport]

Got a strange problem with my C20XE redtop Manta........

Start the car and fuel pressure sits perfect at 37psi and will remain the same for ever if I left the car ticking over. Drive the car and over a mile or so the pressure drops to a point the car is undriveable, to around 15psi. it'll continue to tick over at 15psi, but the pressure won't rise again until the car is stopped, fully cooled down and then the same scenario happens again?

I've replaced the following;

Fuel pump (twice - brand new Bosch pump fitted now), pressure regulator, filter, supply fuel line.

I've also checked the tank breather - all fine (no vacuum)

The only part of the fuel system I've not replaced is the return line, but dont see how this could be linked.

Anyone came across a similar problem?

Cheers

[owelly]

Does the pressure regulator have a vaccuum pipe on it?

[mitsuru]

Check the fuel line and it's connections.

I don't know what your fuel line is made of but the neon
came off the production line with mild steel pipes.
I replaced mine as well as the brake lines when I found
that they were rotten.

And some of the clip connections were leaking by spring
apart a bit under high pressure but not enough to come
totally apart, and would pull themselves back together
when no pressure.

(On later Neon models they change the pipe metal and the
connections)

[gmcmotorsport]

Yes, vacuum pipe connected & sealed.

Fuel pipe is high pressure plastic - 10mm feed, 8mm return.

I'm stumped!

[owelly]

Have you tried clamping the return to see if its the reg valve thats passing.

[TeamTotalWankel]

Is the pump getting a constant 12v? Just a thought

[gmcmotorsport]

Yes, permanent 12v available when running & petrol pump relay ok (a known fault on fuel injected vauxhalls of this era)

Good point Owelly, will clamp return & check regulator (although it is a new adjustable regulator)

[Relentless Rob]

I had a similar problem on one of my bikes after the tank was resprayed. Paint had got into the breather holes and as the bike used fuel the vacuum pressure of the fuel dropping make the bike cut out completely. I doubt this is the case here but try running the car without the filler cap on and see if it still happens.

[gmcmotorsport]

Cheers Rob, but breather pipe 100% clear

Planning spending a few hours on it tomorrow evening, will post update afterwards

[owelly]

Can you get a gauge on pipe from the pump to check that? The other thing worth checking, is have you got an air leak before the pump?

[Renrut]

Sounds to me like the regulator isn't regulating. This is probably an obvious statement.

What controls the adjustment on the regulator? Is it electronic or mechanical? Or pressure?

[mjslonergan]

Sometimes its less technical, have you tried flushing the tank, we spent ages on a friends car, went through all suggested above, turned out to be very fine dirt in the tank, it built up and blocked the filter after a bit of running, but was fine enough to wash back from the filter when the system was not under pressure... gave the exact symptoms you describe and had us stumped for a while...

[andrewg1323]

Its possible a pipes collapsing internally restricting flow too...

[gmcmotorsport]

Thanks for all your suggestions.....I'd checked many of then already and further checked the ones I hadn't, but still no luck!!!

The one thing that i haven't checked since fitting them is the injectors. They are new (remanufactured).......unlikely, but I'm wondering if these, or one of these, is causing a drop in pressure. I really don't think so as the engine is definitely suffering from fuel starvation, not flooding but to be honest everything else has been replaced (literally)!

Anyone had any problem with re-manufactured injectors?