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Pre-Pump Posted by Bill Homer [Email] ![]() ![]() In Reply to: Which is the pre-pump?, Andrew W., Sun, 10 Apr 2005 23:04:59 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Since no one answered you yet, I'll give it a shot, despite my unfamiliarity with the early (1986) 9000 - I assume that the 9000 uses a similar pump setup as the 900 of that era, which I am familiar with.
The fuel pump on the mid-80s 900 has a large main pump and a very small pre-pump. The main pump sits in a plastic canister (cup) which resembles a small open coffee can; the point of this is to cool the pump and have a constant source of input fuel that will not slosh around in turns, acceleration, braking, etc., particularly when the tank level is low, leading to "starvation" of the pump. This canister is filled and fed by the pre-pump. If the car acts like it is starved for gas when the fuel level is low, yet runs properly with a full tank, the fault is probably the pre-pump. This does not appear to be your problem.
Since you did the pressure test and found that you have zero pressure on startup, I would guess that the check valve or the Fuel Pressure Regulator (FPR) is defective. Perhaps the FPR has a pinhole leak in its diapragham? An easy test is to CAREFULLY suck on the vacuum hose connected to the FPR - if it's leaking you will know about it! On later 9000s, the check valve is located on top of the pump, plugs into the assembly, and is difficult to remove without breaking - not sure about the '86.
posted by 136.182.2...
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