SleeperZ Posted May 9, 2003 Share Posted May 9, 2003 My fuel pressure was dropping off at boost with RPMs climbing, so because I had no time to buy and take delivery of a single pump that will deliver the fuel, I plumbed two pumps together (high pressure Bosch units, flow 145 l/h at 60 psi each). At idle and cruising, I get a good constant fuel pressure, but as soon as I start putting load on it, my fuel pressure makes wild swings between 30 and 45 PSI, and naturally it starts hesitating and backfiring into the intake. Does this sound like the two pumps are fighting each other? I also took out the pressure dampener (damper ) as I needed the room. The pumps are both fed from the tank through a "Y", and both outlets are plumbed together into the stock hard fuel line. I'm sure the easiest way to fix it is to get one good pump, as I obviously can't run it at the strip today , my whole reason to do a rushed, ghetto job. Anyone looking to sell a fuel pump, like a T-Rex or a in-line Walbro 255hp? Quote Link to comment Share on other sites More sharing options...
mobythevan Posted May 9, 2003 Share Posted May 9, 2003 Can you just run two check valves on the pump outputs so they can't fight each other. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted May 9, 2003 Author Share Posted May 9, 2003 These pumps have check valves built into the outlets, similar to stock pumps. Just seems like something in the flow dynamics, or possibly pressure waves in the way the outlets (or possibly inlets!) are T'd together. I would imagine I could keep futzing with it, install a dampener or two, and smooth it. Much easier to get rid of the dual crap, I'm sick of it already Quote Link to comment Share on other sites More sharing options...
Guest Aaron Posted May 10, 2003 Share Posted May 10, 2003 Given the scenario as I undertand it, two pumps being fed from one outlet on the tank, I would guess the problem is actually a partially clogged outlet on the tank, or the line simply isn't big enough to supply the fuel the pumps need. Quote Link to comment Share on other sites More sharing options...
Guest z1 performance Posted May 10, 2003 Share Posted May 10, 2003 Why not jsut fit the proper sized single pump? So much easier. We use one from an old Volvo in mine...I've yet to reach its limits, though I cannot seem to locate the specs on it. Adam Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted May 10, 2003 Author Share Posted May 10, 2003 Given the scenario as I undertand it, two pumps being fed from one outlet on the tank, I would guess the problem is actually a partially clogged outlet on the tank, or the line simply isn't big enough to supply the fuel the pumps need. I appreciate the input, but the system works fine with one pump, except I lose fuel pressure at boost with the RPM climbing. I have reached the limit of the one pump. And the fact the pressure is stable with two pumps at idle and cruising suggests to me it is not a flow problem, but a dynamic problem having to do with a rapidly changing pressure demand on the pair of pumps. Keep in mind the fuel flow actually goes down with an increase in pressure, so the greatest pump flow happens at idle. My fuel pressure did not increase when I plumbed in the second pump, indicating the return line is adequate. Indeed, I am currently trying to find a new SINGLE pump to do the job, I just wanted to put my experiences out there in case anyone else was contemplating using two cheap pumps instead of one good one. Quote Link to comment Share on other sites More sharing options...
Bernardd Posted May 10, 2003 Share Posted May 10, 2003 Voltage problem?? Wiring can't supply the current/Voltage. Just a thought. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted May 10, 2003 Share Posted May 10, 2003 you might be having a problem due to lack of dampner. My fuel line pulsate like crazy without a dampner. I was also thinking that you should put a boost active switch for the second fuel pump, that way, there shoudn't be a problem with feul pressure off boost. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted May 11, 2003 Author Share Posted May 11, 2003 Voltage problem?? Wiring can't supply the current/Voltage. Just a thought. Heheh, not with 10AWG wire from the battery, through the fuse box and relay Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted April 17, 2004 Share Posted April 17, 2004 Two pumps in parallel will double the flow and keep the PSI the same as one pump was. Two pumps in series will double the pressure and keep the flow the same as one pump was. These rules of thumb apply to positive displacement pumps (almost like our fuel pumps) and are NOT factoring in plumbing losses due to pipe friction so when I said "double", I don't mean EXACTLY double. And when I say "the same", I don't mean EXACTLY the same. I think thats what I think. Dave Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.