UK Car Repair: Vauxhall Senator Problem, vauxhall senator, fuel starvation

Question
QUESTION: We have a 1993 3.0 24v Senator and have a problem. When driven at full throttle the power phases out at about 4000rpm.  It struggles to increase in speed and wont change up the gearbox until I back off the throttle.  There are no warning lights on the dashboard, as far I know the dual ram system is working corrently, could it be the transmission holding the car back. When in Neutral the engine will rev to 6500rpm without problem.

ANSWER: It sounds like a fuel starvation problem, The first thing I would check is the fuel filter.  It won't change as there is too low a vacuum until you reduce the throttle opening. Also, make sure none of the fuel lines are restricted.

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QUESTION: Hi,

I have changed the fuel filter but there doesn't appear to be any improvement. It's really hard to diagnose this one, I have owned the car 12 years and know it pretty much inside out. This is the first time I have experienced this problem.
Upto 3500 rpm the car drives smooth and responsively, but beyond that there's no more power. The engine has a dual ram intake system, and there is a butterfly valve that effectively splits the 6 cylinder engine into two 3 cylinder ones. This valve is closed upto 4000 rpm, to provide low end torque, and is designed to open via an electronic solenoid above 4000 rpm, to provide further high end torque.
I don't know of a way to manually open the valve at 4000+ to test if the power delivery changes.
Any thoughts???


ANSWER: Clearly you know the car better than I do. I would still suspect a fuel problem, how hard would it be to check pump volume?  as for the secondary butterfly usually they are not completely closed, can you give it an external feed to activate it or reach it to physically hold it open?

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QUESTION: The pump is inside the tank unfortunately. I could try wedging the valve open as a test.
If the engine revs to 6000+ in neutral, would you still suspect a fuel problem?

Answer
To test pump volume you would do it at a convenient location, usually where the supply line fits to the engine. As for off load, yes, there is no load demand on the engine so it will rev up freely, once it has the car to pull it needs much more energy thus more fuel.