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911st 07-17-2010 06:40 AM

930 fuel pumps operation?
Are both fuel pumps on a 930 on all the time?

Is voltage increased with load at anytime?

I have learned that some cars have provision to increase voltage to the fuel pumps with load.

There has been some indication that on a built CIS 930 the stock fuel pumps have not been able to maintain full system pressure at the fuel distributor contributing to our lean condition.

I am wondering if this might present some opportunity. I think I also read that GSF has some type of controllable voltage reg on hit EFI twin turbo fuel pumps.

lucittm 07-19-2010 04:46 AM

As far as I know the 930 and 965 fuel pumps are on all the time. They build pressure and the pressure regulator in the fuel distributor sends excess pressure (flow) back to the tank.

Voltage will not increase with load because you only have what the battery/alternator can send, about a max of 13.8V. However current will increase with load in the form of higher resistance in the pump motor as the motor slows down under load, but this is slight due to the dumping of excess flow as described above.

Do a flow test on your fuel pumps. The pump should flow 51 oz. in 30 seconds from the output hose on the filter. That is a qualitative test. For a more quantitative test get a pressure gauge and measure 91-94 psi at the same point, this is your system pressure.

Then you have to test the control pressure as the fuel leaves the warm up regulator and goes into the top of the fuel distributor. It should be 50-60 psi depending on the ambient temperature and elevation above sea level.

The system pressure can be adjusted with shims in the fuel head, but only after determining that there is no other cause for reduced pressure such as a clogged filter, worn out pump, etc.

Good Luck,

911st 07-19-2010 06:47 AM

Thanks Mark.

What I thought.

My understanding is there is a chance our fuel pumps may not be able to fully support maintaining system pressure under higher HP operation.

Maybe a higher duty pump could be run at a lower voltage untill needed.

Just a thought.

lucittm 07-19-2010 04:24 PM

I had the same thought. I looked at all the Bosch fuel pumps and our rear pumps have the highest output pressure and the highest flow. 930-608-113-00, Bosch P/N 0-580-254-044, 300 liters per hour, 5 bar pressure.

For more flow or higher pressure you would have to look at drag racing pumps!


911st 07-20-2010 07:04 AM

The motor sports ...044 I heard can go there.

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