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V8 running problems


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Well ill try & make this quick so you clever boffs can help :blink:

TVR 500 Rover V8

2 New red top facets to feed new efi inline pump.

Ive bi passed the fuel tank & returns by using Jerrys cans so to eliminate tank problems.

All new leads plugs etc .

The problem is,

1st i run the red tops to charge the fuel lines & gives around 10psil.

2nd turn the ignition key & injection the fuel pump relay comes on the pump goes up to 40psi -relay shuts off & normally unless you start the car the fuel pressure gauge stays around the same !

But now the as soon as the relay shuts off the pressure drops to about 10psi .

Turn on ignition same again & so on.

If i run the car the same happens but obviusly runs a little pooey but the fuel pumps are all running & getting 12.5V ish so the relay is coming back on. :huh:

So my question is can it only be my power boost valve{regulator} or can it be electrical ,before i just go out & buy another one.

PS still wont go diesel before someone says it

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There are a couple of possible answers to this,

1) Because you have always had a steady 40psi (once the pump has charged) then it may be that the non return valve in the EFI pump is leaking. This will allow the forward pressure to drop as it will feed back through the pump. The valve is usually on the output end of the pump and is usually a serviceable item.

2) This could also be caused by a leak in the fuel rail (but you would notice that because fuel will be raining out ) or a dripping injector (if they get plop in then, then sometimes the injector will refuse to seal in its off state and drip fuel into the inlet manifold. A dripping injector is harder to diagnose without lifting off the fuel rail complete with the injectors. Sometimes you can detect it, as the excess fuel will often cause popping in the exhaust on over run …… but not always.

Hope this helps


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Is there a fuel regulator at the end of the injector rail? Where the fuel return line goes from? I am sure Ian would have mentioned it if so or if it were likely to be the problem - our 3.9 RR had one. If it were to fail then fuel pressure could be lost - either totally or partially.


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Good point Chris :) …… I suspect that Pete has an aftermarket high rise adjustable reg…………………. the reg is on the return line and vacuum controlled. If it were to leak back to the tank return, then yes, pressure would be lost………. But I would have thought this would also show up as lower then normal pressure when the engine is running……….. unless Pete has a mighty powerful EFI pump (and I expect he has) that could keep up with the lost pressure ……..


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I was thinking perhaps some small item of debris stuck in the valve. Since there is no accumilator in the system (is there?) then a tiny leak could cause a drop in pressure.


Thanks for that guys but as Ian said i have a after market regulator no return leaks etc the fuel pump is an external inline type rated to 500hp & will run up to 90 psi .The drop in pressure was so fast that it cant be anything apart from an external leak plus all the plugs are dry !!

Anyway i fitted a new external regulator today & it seems to solve it , well at least in the garage anyway :D until that was the throttle linkage pin fell out :angry:

At that point i thought i better walk of & come back tomorrow :rolleyes:

Thanks though :D

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