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Fuel pressure drop when in boost

 
Old 11-21-2018, 01:49 PM
  #21  
junk c5
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That’s what I did. I’ve got a new in tank walbro 450 and AEM pump sitting in my cabinet. I was having a cavitation problem with the in tank pump .
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Old 11-21-2018, 02:47 PM
  #22  
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Have you tried lowering base pressue and adjusting in the tune? I found things run much better, for me, with a 44# base pressure versus a 56#. 13.2vdc isnt bad but your better off at 14vdc, imo.
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Old 11-21-2018, 09:04 PM
  #23  
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Originally Posted by JoeyG View Post
Have you tried lowering base pressue and adjusting in the tune? I found things run much better, for me, with a 44# base pressure versus a 56#. 13.2vdc isnt bad but your better off at 14vdc, imo.
I thought about asking my tuner that. Pretty new to forced induction so I don't know what dictates whether you can you start at base pressure of 43.5-44 or 58. I saw the specs on the pumps and at higher pressures their flow really drops so I've been wondering why not just start at lower base.
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Old 11-22-2018, 02:47 PM
  #24  
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Record voltage at the pumps or as close as possible to the pumps....system voltage at the ecu may not be the same....most likely is not the same.

run 1 pump to test and monitor pressure...then switch on the other pump. Does pressure change ? That might give an indication of the regs actual ability to control with varying amounts of fuel flow.

Absolutely ensure the pressure line to the reg is good, and does not leak. Test this with a Mityvac. Lots of people dont like the Magnafuel regs as they claim they dont see reliable pressure increases...no real reason why they shouldnt though.

Most Walbros start to nose dive around 75psi, their bypass would be well and truly open at 110psi if they can even get that far ( unless you have the 274's, high pressure 450's vs the normal 267, 450's )
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Old 11-22-2018, 04:28 PM
  #25  
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Originally Posted by dopefedz View Post
Might be time to stop d!cking around with these walbros and run an external magnafuel.
You ran out of fuel pump. Change the point that you get voltage for the pumps to the back of the alternator to ensure you get 14.5 volts to the pumps

Last edited by gearheadib; 11-22-2018 at 04:32 PM.
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Old 11-22-2018, 09:36 PM
  #26  
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Originally Posted by stevieturbo View Post
Record voltage at the pumps or as close as possible to the pumps....system voltage at the ecu may not be the same....most likely is not the same.

run 1 pump to test and monitor pressure...then switch on the other pump. Does pressure change ? That might give an indication of the regs actual ability to control with varying amounts of fuel flow.

Absolutely ensure the pressure line to the reg is good, and does not leak. Test this with a Mityvac. Lots of people dont like the Magnafuel regs as they claim they dont see reliable pressure increases...no real reason why they shouldnt though.

Most Walbros start to nose dive around 75psi, their bypass would be well and truly open at 110psi if they can even get that far ( unless you have the 274's, high pressure 450's vs the normal 267, 450's )
To test the voltage at the pumps can this be done with the car just idling and the pump on or do I need to be driving around? I took a couple half assed videos to show what's going on that I'll post up in a bit. When I turn the second pump which I do with a rocker switch the fuel pressure increases by several psi. I searched all last night and interesting enough found multiple threads on the yellow bullet where guys had similar issues with the same magnafuel 9950b regulator. Tomorrow I will buy the fitting that Im missing to install the fuelab reg from my formula onto the corvette to see what happens. Im pretty pissed at myself because I honestly cannot for the life of me remember what is the highest pressure I seen on the fuel gauge before this issue came about. I'm pretty confident I've seen something in the 70s before but have no proof of it which is pissing me off. Highest I'm getting now is 63 psi. These are the walbro 274 pumps and they only have a few months of actual use and fuel through them.
Originally Posted by gearheadib View Post
You ran out of fuel pump. Change the point that you get voltage for the pumps to the back of the alternator to ensure you get 14.5 volts to the pumps
I want to believe that to but I didn't have this issue up until the point that I dropped the tank to fix a leak in my fuel hat and add some wiring bulkheads at the top of thank and I also changed the blower pulley to a 4" from a 4.25". Whether its just a coincidence or not I honestly don't know. I'm running a fore fc3 controller and it has a 4 gauge power cable to it that does come from the back of the alternator. I've been monitoring my voltage on the cars display and it is always right around 14 volts. I'll check to see what Im getting at the actual pumps tomorrow.

Last edited by dopefedz; 11-22-2018 at 09:38 PM.
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Old 11-29-2018, 11:18 AM
  #27  
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Originally Posted by dopefedz View Post
Last night me and a buddy conducted a few more experiments lol that lead me to believe the pumps are ok. I couls be wrong but maybe you guys can tell me what you think.

First test was running each pump individually thru the external filter also and comparing how much fuel they could push into a bucket in 10 seconds running off just battery power. I was hoping one wouls be drastically less maybe proving it was either weak, failing or maybe its fuel sock was clogged. Well they both filles the bucket to the same mark.

Second tests my buddys cousin did some calculating and told us the pump should be able to fill a one gallon jug in 30 seconds. Tried this with each pump individually and they both filled a jug within 30 seconds.

So at this time both pumps can make the pressure and from the two half assed test appear to be moving the same volume of fuel.

i was hoping the voltage logged would show maybe a drastic drop but it holding at 13.2 volts according to my tuner.

The last thing I noticed yesterday while pressuring up the reg with air was that although the vacuum hose to it was not collapsed or split it was not anywhere near as tight on the nipple I installed it over on the side of the intake and my dumbself didnt put a clamp over it. Maybe just maybe pressure was leaking by at this connection causing the reg to drop the pressure. Its the only thing that is starting to make more sense now.
so at what pressure were you filling the buckets?

what i do is to use an restrictor adjusted to desired pressure and see what the output is. in your boost referenced case you could use your regulator. and the calculation is simple. e.g. 1000cc=1 liter, 8x1=8 liters per minute=4 liters in 30 sec. 1 gallon=3.8 liters, so cousin was right. but it has to happed at 4 bar or whatever.

Last edited by romandian; 11-29-2018 at 11:23 AM.
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Old 11-29-2018, 01:33 PM
  #28  
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Originally Posted by dopefedz View Post
To test the voltage at the pumps can this be done with the car just idling and the pump on or do I need to be driving around? I took a couple half assed videos to show what's going on that I'll post up in a bit. When I turn the second pump which I do with a rocker switch the fuel pressure increases by several psi. I searched all last night and interesting enough found multiple threads on the yellow bullet where guys had similar issues with the same magnafuel 9950b regulator. Tomorrow I will buy the fitting that Im missing to install the fuelab reg from my formula onto the corvette to see what happens. Im pretty pissed at myself because I honestly cannot for the life of me remember what is the highest pressure I seen on the fuel gauge before this issue came about. I'm pretty confident I've seen something in the 70s before but have no proof of it which is pissing me off. Highest I'm getting now is 63 psi. These are the walbro 274 pumps and they only have a few months of actual use and fuel through them.

I want to believe that to but I didn't have this issue up until the point that I dropped the tank to fix a leak in my fuel hat and add some wiring bulkheads at the top of thank and I also changed the blower pulley to a 4" from a 4.25". Whether its just a coincidence or not I honestly don't know. I'm running a fore fc3 controller and it has a 4 gauge power cable to it that does come from the back of the alternator. I've been monitoring my voltage on the cars display and it is always right around 14 volts. I'll check to see what Im getting at the actual pumps tomorrow.

The test needs done under load, in the real world...ie engine under full load/boost and high rpm. Sometimes alternators do funny things at high rpm, although that should be apparent on a regular datalog, but when having problems, you need to record at the area where the problem is the biggest concern.

Also, a good recent article

https://www.realstreetperformance.co...KE6znUMqyP7NW8

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Old 02-02-2019, 11:01 PM
  #29  
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Resurrecting this thread. I thought I had solved the issue up until we put the car back on the dyno today. What I found after dropping the tank was that for some reason the hoses from the pumps to the y-manifold where not very tight anymore. I blew air through the feed line towards the pumps and could not build any pressure. I tightened up the clamps. The feed line could now hold pressure without bleeding out.

I then tried rolling into a few times on the street and it no longer did the breaking up like it was doing on the dyno so I figured the issue was fixed. Today we put it on the dyno and tuner had to get out the pull because the car was leaning out and injector duty cycle was at 140%. There was nothing hooked up to log fuel pressure but my pressure gauge records peak and so does my boost gauge.

Fuel pressure is peaking at 65psi. base pressure is set to 58 psi and it is boost referenced using a magnafuel regulator. Boost gauge was showing a peak of 22 psi.

Fairly new to forced induction. Should I truly be seeing a 1:1 increase in fuel pressure/boost. So if im at a base of 58psi I really should be at 80psi during a pull? At this point the only thing that makes sense is something has happened to my pumps and they are both weaker that the first time the car was dynoed experienced no issue or after the pulley change Im now out of pump?
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Old 02-03-2019, 05:53 AM
  #30  
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Peak fuel pressure tells almost nothing. You need to know fuel pressure throughout the entire pull.

But in an ideal world yes you should see a 1:1 rise, but they rarely do this. But it should be close.

It could be pump, lines, wiring, reg...any number of factors.
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Old 02-04-2019, 10:58 PM
  #31  
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I was having this issue recently, base 58psi fuel pressure, fuel pressure will peak around 64psi, then fall back down to 52psi by redline, my alternator died shortly after, looked back on the old logs to see if the issue was related, I noticed battery voltage was also dropping from 14.x to 12.x volts during a pull. rebuilt alternator, voltage now steady 14.5V to redline, fuel pressure now also rock solid at 71psi at redline, instead of falling back in the 50s like before.
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Old 02-10-2019, 09:48 AM
  #32  
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Originally Posted by FourG63 97GST View Post
I was having this issue recently, base 58psi fuel pressure, fuel pressure will peak around 64psi, then fall back down to 52psi by redline, my alternator died shortly after, looked back on the old logs to see if the issue was related, I noticed battery voltage was also dropping from 14.x to 12.x volts during a pull. rebuilt alternator, voltage now steady 14.5V to redline, fuel pressure now also rock solid at 71psi at redline, instead of falling back in the 50s like before.
I just had my stock alternator rebuilt so I think that is ok. TK2K is right around the corner. I hate just spending money without being 100% sure what the problem is but Im replacing the regulator with a Fore F2I because I have seen multiple posts about issues with the magnafuel one. I also ordered a new walbro 450 and a walbro 525.

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Old 02-13-2019, 05:25 PM
  #33  
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is it overheating the fuel? Mine would be fine then after awhile when it got hot it would drop into the teens. I once put 5 gallon gas can in the deep freezer over night and when the issue happened I put the cold fuel in and voila my FP went back to 70-75 under boost. Then once it got warm it would drop back into the teens. I never did figure this out as my blower started leaking and I decided to let the car sit ever since, been about 1.5 years now that it's been sitting. I have a thread about it. Hope you find a solution
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Old 02-15-2019, 05:38 PM
  #34  
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If fuel is too hot, fit a fuel cooler. After monitoring fuel temperature of course to see if it is actually hot, and how hot.
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