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Rover V8 Fuel Pressures from EFI Pump


Hybrid_From_Hell
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Maybe something maybe nothing

Last night I mused the problem over.

Basically the engine has a std PRC8318 EFI 3.9 HP Fuel pump in it, plus an adjustable PRV.

I wandered into the garage and tested the fuel pressure by removing the cold start injector hose and with the ignition on but the engine not running saw 38 psi

HMMM I though

Started engine..

Its sits at 30 psi

Something in my mind says this is too low, but I can't remember, all the books I have say 36-38PSI non running engine flap open, but the drop is significant.

Just to prove a point I wound up the PRV higher, but engine running still at 30 PSI.

Hmmmmm

Anyone know the numbers, I also have some memory that the pressure will go up when engine is being driven ie foot down on the road moving, as oppossed to reving the engine stationary ?

Wondering if I might just have a lazy fuel pump ?

Any figures anyone ?

Nige

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  • 7 years later...

Just reading this old thread and realised what is going on - thought I would just close it off.

To ensure constant flow through the injectors the pressure regulator is referenced to the plenum. The pressure guage is referenced to atmosphere.

When you start the engine the regulator is happily maintaining the pressure at 38psi above the pressure in the plenum, which is 8 psi lower than atmospheric pressure. That's why the gauge drops to 30.

If you had minimal inlet vacuum (low revs, high gear, WOT) the gauge would go back up to 38. Makes me think people running forced induction must need a pretty decent pump...

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They do, because not only do they need LOTS of fuel, they need to stop it getting blown back down the fuel rail :o

Although, many OEM pumps are capable of good pressure and flow, most of which is delivered back to the tank via the return at all times.

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