Jake_Goldstein Posted January 10, 2010 Share Posted January 10, 2010 Hi, I'm installing a new Walbro 255LPH pump on a 1982 NA 280ZX, in preparation for adding a turbo. I'm running MegaSquirt, and that's working OK (thanks to this forum, where I learned a lot). I added the Walbro fuel pump, and the pump: 1) primes OK with the first key turn, and sounds good (whirring noise) 2) starts making a low-pitched noise during cranking, and stops making the good whirring noise. It's a quiet, low-pitched hum or moan, like my stomach rumbles when I'm hungry. Voltage on pump drops from 11.7 to 10.7V. If the engine catches, it dies within 30 seconds, presumably due to no fuel! 3) Once I stop cranking, the fuel pump will still make the low sound during priming. 4) If I let it sit long enough, it will prime again OK. I'm now connecting the pump straight to the battery to eliminate any bad connections / relays / fuse problems, during testing. My questions: 1) What causes a fuel pump to make a low-pitched, quiet, humming, moaning sound? I think the pump is not spinning well, and I assume this is either low voltage or too high pressure. I'm connected straight to the battery, and I still see 10.7V when it's making the low sound, so I don't think the voltage is the problem. The low sound suggest to me that the pressure is too high. But if the engine isn't cranking, I don't have this problem, so I know my lines and fuel filter and all are OK. I've also disconnected the return line, and it pumps fine into a gas can. Could high pressure in the return line cause the pump to make a low sound? 2) Could the fuel regulator cause this? Could it be closing up during cranking, closing off the return line? Then when I leave the car sit for 15 mnutes, the pressure bleeds off, and I can prime it again. 3) How can I tell if I've damaged the pump somehow? My thought is to go get a fuel pressure gauge, put it before the regulator, and see what the pressure is. If the pump is moaning with less than 37PSI, then would I conclude that the pump is bad? And if the pressure is going higher than 37PSI then I would conclude that the pump is OK, and look to the lines and regulator to see why the pressure is too high? The car worked OK last weekend, with MegaSquirt and the original fuel pump. Then I changed the fuel pump, changed some of the hoses that were old, and now the new pump is not happy. I'm off to get a fuel pressure gauge, but if anyone could suggest other tests to help me narrow down the problem, I'd appreciate it. Thanks, Jake Quote Link to comment Share on other sites More sharing options...
Jake_Goldstein Posted January 10, 2010 Author Share Posted January 10, 2010 When I prime, and the pump's going well, the pressure between the filter and the fuel rail input is 50PSI. When I crank, and the pump stops pumping and starts making the low moaning noise, the pressure is off my 60 PSI gauge (pegs the gauge, maybe 80PSI). When I stop cranking, the pressure remains pegged, gradually falling. When I try to prime again, while the pressure is 60+PSI, my pump makes the noise. So the noise is related to too much pressure. I'll go back through my lines and see if I can find where the blockage is. Can I idle the car with the regulator bypassed, just to test whether the regulator is the problem or not? Quote Link to comment Share on other sites More sharing options...
Jake_Goldstein Posted January 13, 2010 Author Share Posted January 13, 2010 Looks like the problem is a sticky fuel pressure regulator. Too much pressure makes the pump not turn and make that terrible moaning noise. Quote Link to comment Share on other sites More sharing options...
woldson Posted January 16, 2010 Share Posted January 16, 2010 So much mention of pressure and moaning is making me laugh a bit;) Quote Link to comment Share on other sites More sharing options...
LIVauto Posted January 21, 2010 Share Posted January 21, 2010 walbro 255 are known to be noisy Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 24, 2010 Share Posted January 24, 2010 For gawd's sake man! Check your tank for snakes! Black ones in particular. Theys be very pesky and cause all sort o'trouble when theys commence t'moanin'! Oh, and BTW: " I'm connected straight to the battery, and I still see 10.7V when it's making the low sound, so I don't think the voltage is the problem." I think voltage like that will burn up your pump quicker than you can say 'overamperave from undervoltage' --- these high draw items are designed to run on 13.8 vdc nominal, 14.2 optimal. You run it on 10.7vdc, and you're asking for lifetimes shorter than the gas company employee looking for leaks with a match! If it's not cabling related, figure out what is wrong that you only get 107V at your pump under load. That is FAR BELOW ACCEPTABLE! Quote Link to comment Share on other sites More sharing options...
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