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I just recently went through this myself with my 85 740 Turbo. My main fuel pump was not getting any gas. To check this squirt a bit into the manifold, which one can on a turbo, and see if it will start. If it tries or does, you are not getting any fuel. Now just because you are not, does not mean it is the Fuel Pump. There are two things that I know of that control the fuel operation on and off the fuel pumps and one is the Fuel System Control Unit, located under the left hand bottom panel in the passenger compartment. Your fuel pumps should turn on when you switch on your ignition. You can stick a hose down the inlet hose filler pipe and you should hear the in-tank pump running. If not then it is either the fuel injector relay ( the other source for turning on your fuel pumps) or the Fuel System Control Unit. A defective in tank pump or main pump can cause the Fuel System Control Unit to go bad, which is not a good thing, because they are expensive. In my case, it was the Fuel System Control Unit. When I replace it, vola, my main pump started and I could start the car. However, I then had the systems you described. After much searching, I found it was the anti-knock sensor located underneath the manifold. The FAQ's describe the fuel pump and how to check for operation. But what I found out, is that one needs to also check the Fuel System Control Unit. To second another commentator I would not use the turbo pump as it is meant to pump a higher gas pressure. And I would not rely on your fuel pressure regulator and other aspects of your fuel injection system to compensate. I found out these cars are sensitive when it comes to fuel pressure. I have the other problem of a lot of 740s and not enough turbos in the recyling yards here in California. Maybe we could do some trading. Hope some of this was helpful.
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