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C20Xe Manta - Dropping Fuel Pressure

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Got a strange problem........

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?


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Cheers Kevin, but thats ok. Like yourself it was one of the first things I checked ;)

Another thing I should have mentioned...

No fuel leaks & new injectors

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have seen same problem on Calibra's over here and they all turned out to be perished hoses, no evidence of fuel leaks, but same symptoms are you describe

new fuel lines and problem solved.

Edited by opelmantagsi
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Thanks again, but all new hoses fitted.

What I don't understand is why the problem only occurs when the car is driving as the delivery of fuel remains the same. When under load, it simply returns less to the tank.

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  • 2 weeks later...

I would suspect the fuel pressure regulator on the fuel rail. It may have a weakened diaphragm which gets worse when hot. This reg is what determines how much fuel is to be returned to tank, so if the return line is blocked for example the pressure would be high. In normal use when the reg sees vacuum (low load part throttle) the reg is open more to allow the pressure to escape to tank. When on full power (or getting near it) the vacuum in the manifold all but disappears the reg is more closed allowing more pressure to be maintained.

A quick test to see if there are any changes would be to disconnect the vac pipe from the reg and block it (to avoid air leak). The pressure at idle "should" increase over what it was before with the pipe on. Drive it like this to see if the pressure drops the same. If you see a noticeable difference i would change the reg to a known good one. hth


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