boosted motor fuel pump problem?
boosted motor fuel pump problem? I was playing around on the dyno a little bit today again and im loosing fuel pressure at around 6000 rpm and up. im running a twin walboro intank setup with 8an feed, 6 an return with a magnafuel boost refrenced regulator. ive got a set of 60lbs injectors in there now but I dont think that could be the issue. im able to keep my AFR at 11.0 until around 5800 then it spikes up quickly to 12.1-12.2 as the fuel pressure drops under 60 even when my regulator is set at the injectors max recommended pressure of 85psi. duty cycle also increases to 98% accordingly with everything else going wrong. i disconected the boost ref. line and set it at 85psi for the whole pull and its doing the same thing. im sure if I could keep fuel pressure up I could get my duty cycle back down. does this sound like a lazy or a bad pump to anyone else?
if my dc was high with good fuel pressure I could see the injectors being a problem, but it seems like in my case everything falls off on a linear basis with fuel pressure
Whats the op range on the regulator?
If I understand this, you have the reg set to 85psi, base pressure??
What's the relief pressure in the Walbros?? AIRC somewhere near 90??
How much boost are you putting to the reg?
Here's what I see on the Magna website:
Two models are available. The Standard MP-9925 is good for applications of up to 700 horsepower. The Large MP9950 is for use in applications of up to 2,000+ horsepower. Both pressure control units are available in three different pressure ranges: 6-20, 18-50 and 35-85 psi.
If I understand this, you have the reg set to 85psi, base pressure??
What's the relief pressure in the Walbros?? AIRC somewhere near 90??
How much boost are you putting to the reg?
Here's what I see on the Magna website:
Two models are available. The Standard MP-9925 is good for applications of up to 700 horsepower. The Large MP9950 is for use in applications of up to 2,000+ horsepower. Both pressure control units are available in three different pressure ranges: 6-20, 18-50 and 35-85 psi.
Last edited by Old Geezer; May 25, 2008 at 07:58 AM.
First, how much power are you making? Without knowing this info, it is very hard to help you.
1. I can tell you, those pumps are not designed to be run at 85psi & will flow significantly less at that pressure.
2. If you need 85psi, I'm guessing you must have 58 base pressure, plus 27# boost. If you are truely doing this, you are not approaching the fuel system correctly. If you have this much boost, you should be starting at 43psi base & boost referencing upwards to no more than 70psi. Forcing any pump to make in excess of this pressure is not typical & generally they are not designed to do so.
3. If the above example is not your situation, then I would assume that you are running high pressure to make up for a lack of injector. In this situation, you need to consider buying a larger injector.
4. The other possibility is that there is still a pump problem..... as it should be able to hold over 60 psi even with 1000rwhp.
Here are a few things to look for.
1. Did you buy it from me? If you did, call me & I'll will talk you through this problem until we find a solution.
Otherwise, here is some info.....
2. It sounds like the regulator is OK.
3. If it only holds 60psi it could be a bad pump, or a leaking internal line, or something else is causing a significant restriction in the system.... such as improper fuel socks, filter etc.
4. Are you using an upgraded wiring harness? What voltage is presesnt at the pumps? What size wires? This has a huge effect on pump output.
5. What is your alternator voltage at 6000rpm?
Hope this helps.
1. I can tell you, those pumps are not designed to be run at 85psi & will flow significantly less at that pressure.
2. If you need 85psi, I'm guessing you must have 58 base pressure, plus 27# boost. If you are truely doing this, you are not approaching the fuel system correctly. If you have this much boost, you should be starting at 43psi base & boost referencing upwards to no more than 70psi. Forcing any pump to make in excess of this pressure is not typical & generally they are not designed to do so.
3. If the above example is not your situation, then I would assume that you are running high pressure to make up for a lack of injector. In this situation, you need to consider buying a larger injector.
4. The other possibility is that there is still a pump problem..... as it should be able to hold over 60 psi even with 1000rwhp.
Here are a few things to look for.
1. Did you buy it from me? If you did, call me & I'll will talk you through this problem until we find a solution.
Otherwise, here is some info.....
2. It sounds like the regulator is OK.
3. If it only holds 60psi it could be a bad pump, or a leaking internal line, or something else is causing a significant restriction in the system.... such as improper fuel socks, filter etc.
4. Are you using an upgraded wiring harness? What voltage is presesnt at the pumps? What size wires? This has a huge effect on pump output.
5. What is your alternator voltage at 6000rpm?
Hope this helps.
i started at 60 psi and let the boost ref. raise pressure for me and I was loosing pressure so to try and eliminate the boost ref. as a sourse of the problem I disconnected the vac. line and raised the base pressure to 85 to see if the pressure would remain steady and they did not. im low 700s right now with a lot to go, but im going to have to figure my pressure problem out before I go cracking 800. I may need injectors but I dont think that has anything to do with this problem. If I had 72lbs injectors wouldent it make my pressure go even lower?
Trending Topics
i started at 60 psi and let the boost ref. raise pressure for me and I was loosing pressure so to try and eliminate the boost ref. as a sourse of the problem I disconnected the vac. line and raised the base pressure to 85 to see if the pressure would remain steady and they did not. im low 700s right now with a lot to go, but im going to have to figure my pressure problem out before I go cracking 800. I may need injectors but I dont think that has anything to do with this problem. If I had 72lbs injectors wouldent it make my pressure go even lower?
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Topdon ONE vs. Artidiag 800 BT2: Which is the Diagnostic Tablet For You?
Pouria Savadkouei
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo With only 700rwhp, you have a problem with something other than the injectors. Check the items I listed above as a starting point. You either have a line, pump or voltage problem.
Does it hold pressure when you shut it off?
Does it hold pressure when you shut it off?
Only if so if my regulator is set at 60 psi when I turn the car off it should hold 60 psi indefinatly? both of my gauges (in car and under the hood) are reading off the regulator
I have another twin setup that I just put in so I will get these pumps tested and I will block the return line like Lonnie suggested and see if I can get the system to hold pressure. my regulator is a magnafuel pn s/m 2312. i got all my stuff thru nate at nasty perf.
Nope.. Instant zero tells me:
You got a leak in the intank plumbing.
You have pump[s] that have no check valves in them.
You have a bad check valve.[s]
Are the pumps hard line plumbed, or w/ hose and clamps?
Check valves used to prevent back flow when only 1 pump is on?
Volt meter on the power stud on the alt to ground, will tell you what the alts putting out. Do the same test at the battery. This will tell you if you have a volt drop in the charging circuit that feeds the batt.
Check w/ the meter at the plug near the pump. Should be very little drop from alt volts..a 1 volt drop can/will result in a significant loss of pump output.
Check w/ the meter at the plug near the pump. Should be very little drop from alt volts..a 1 volt drop can/will result in a significant loss of pump output.