I have and 88 E30 M3 that has an S52 swap and today was the first drive over a couple miles that i took it on. About five miles down the road i started to loss power and my fuel pressure gauge is down to 20psi so I knew exactly whats wrong. How can i tell which pump is going out? Both buzz when i turn the key. I also clamped the return line to see if the pressure regulator may be bad but it still was at 20psi clamped so it has to be one of the pumps. I just want to get the right one as both are over 200$. Thanks.
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It's the high pressure pump?
tnow, sometimes I just mess with people. It's more entertaining that way. george graves -
The word "High Pressure" should explain it all. The transfer pump cannot create that much pressure.Comment
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The transfer pump only produces a few psi. It's purpose is to lift fuel to the high pressure, so it can't directly cause low fuel pressure. However, if the transfer pump is dead the high pressure pump will be starved for fuel below about 3/4's of a tank.
Another possibility would be a rusty tank with a layer of sediment in it. When the car is driven the fuel sloshes and stirs up the sediment, which collects on the inlet screen of the transfer pump and starves the high pressure pump. The fix is to replace the tank or to remove the tank, acid clean it, and seal it.The car makes it possible, but the driver makes it happen.
Jim Levie, Huntsville, ALComment
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So after pulling the in tank pump i realized my fuel gauge is broken. The tank was completely empty and the gauge read 1/2 a tank. I pulled the level sensor and rocked it back and forth and the fuel gauge went from full to half empty. Whats funny is the low fuel light would come on but the needle only went half way down. I thought i had figured it out but after putting 3 gallons in i still only had 10psi of pressure so i am back to square one. I wonder if I killed one of the pumps testing them earlier.Comment
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Thanks for the info, that could be the case my cluster was swapped before i bought it. I am kind of at a loss with the fuel pumps. Both come on with key on and i have removed both and tested both on the bench and both seem to work fine but i still have about 10psi of pressure. I clamped the return line to the pressure regulator to see if it spikes and nothing so i am just not building pressure. Maybe my high pressure pump is just not building enought pressure.Comment
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When i ran the lines i paid attention to that and it ran for a good month idling in the driveway and running around the neiborhood a few minutes at a time so i think if they were reversed it would have affected the pressure before now.Comment
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I think i have finally figured it out. Last night i verified the lines to the FPR are correct and tested both pumps again but this time on the car. After both pumps tested fine I went back to the FPR and realized when i tested it the first time it was before i found out my fuel gauge wasnt reading correctly so now with fuel in the tank and in the lines i clamped the return line and sure enought the pressure came right up. So a new question, would running out of fuel kill your FPR or could it be just a huge coincidence that my FPR failed right when my tank ran dry? I am also wondering if the FPR are is still good and that the running out of fuel caused it to malfunction until i reestablished system pressure. I removed the clamp and so far its holding the correct pressure. I guess i can just let it idle on and off for a few days and see.Comment
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Could have had air in the lines somewhere, cause what looked like a drop in pressure. Now that everything is primed and full of fuel, pressure is back up. It will generally take a lot of cranking to get a car that ran dry started back up again. There is quite a large volume of fuel in all the lines.Comment
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