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I have written recently about the problems with acceleration and low power with my 93 940GL (non-turbo), wondering if my problem might be fuel system related. (It has been getting steadily worse after acquiring the '93 several months ago.) One of the luxuries of having a 2nd 940 (a 94 non-turbo) is that I can switch parts to identify problems. To that end, I rigged up a pressure gauge to check fuel pressure at the fuel rail and measured fuel pressure for the following 4 combinations:
'94 940 with its fuel pressure regulator = 38-40 psi (runs fine)
'94 940 with the '93 model's FPR = 40 psi (runs fine)
'93 940 with its FPR = 32-34 psi (sluggish acceleration and low power at 1000-2500 rpm)
'93 940 with the '94 model's FPR = 32 psi (stumbles badly on acceleration)
Since the fuel pressure is supposed to be ~43 psi and allowing for some inaccuracy of my gauge, I've concluded that the problem is not FPR related, but in the supply of fuel to the fuel rail. I recently changed the fuel filter on the '93 without any improvement. I'm pretty sure the in-tank pump is working since the car will not run with its fuse unplugged (and does with it in place). This leads me to believe it is either the main fuel pump or the check valve. I'm OK with replacing either or both but would like the input of forum friends as to the most likely cause. Specifically, is it probabe that the main fuel pump could be providing low pressure without failing completely? Is this a common problem? I have read of check valve problems causing these symptoms.
Also (showing my ignorance and humility), where exactly is the main fuel pump? I spent about 15 minutes searching for it without success. I know it's held in a cradle. The Haynes manual is no help. Specifically, is it on the drivers side? Is it adjacent to the fuel tank? I would appreciate a nearby landmark.
Thanks in advance,
Ron
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