MicroSquirt.com read only forum (Jan.15,2018)

I have been trying to set up a racecar with MS and ran into what I think is a falling fuel pressure under full load. What does everyone think of this test for fuel flow?

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The motor has a FP gauge on the end of the fuel rail, I am thinking of a 100% DC/load test on the fuel system.

1) Bypass the fuel return hose to a large bucket/can

2) disconnect the power to the ignition coil

3) disconnect the injector wires the go to the Squirt

4) turn on the fuel pump on. I should get 43 psi with a strong steady stream of fuel out of the return line into the can

5) now ground the two injector leads so that the injectors goto 100% DC for about 1 sec (worst case fuel demand)

6) watch the FP gauge an hope the pressure remains close to 43 lbs (41 possibaly would work 15# is a total failure)

7) see if the fuel is still flowing out of the return line even at the 100 load test

What do you think? If this all passes find bigger injectors is the only fix.

AW

Maybe try five or ten second full load test, check the pressure at the reg and also measure the amount of fuel released to work out the real fuel flow under full load? I did it for 30 seconds with my WI setup just to be sure I was getting enough flow.

If you`re getting falling pressure at the fpr the pump may not be man enough to supply your current injectors?, also the pump could be failing over time (say 10 mins of use). Best bet would be to log fuel pressure against MAP to see what`s really happening under race conditions?

How about a pressure switch at the fuel rails to light a bulb when pressure drops below 35 psi or so? If the pressure falls at full load you need a bigger pump/lines, if it falls under cornering you need a better surge tank. If MS isn't running your injectors at 100%, bigger ones would be no help.

Well it could be fuel flow or pressure? Is there a difference? Lol I don't know.
But I what I noticed in my saturn is that at 15PSI (turbo) my 86# injectors made me around 280 hp at the wheels. I tried turning it up to 17PSI, and it made 311hp but it was fatally lean. I found that no matter how I adjusted the fuel values for that level, it was always lean, it would fall on it's face.

Is that what is happening to you? If so I think you should just replace your fuel pump with a higher output/pressure model and save yourself the time
-teb

The issue is that we have a late model Corvette pump in a relitivly tiny tank feeding an inline fuel filter that could be restricting. The fuel rails and connecting hose size could be an issue. Possible we could have a venting issue in the tank. Bottom line is the 8 x 24# injectors should be enough to run a 300hp motor to 7000 RPM. I have the VE table jacked to 130 in the upper ranges and we are getting 100% DC1 at about 5500 RPM. The motor is acting lean and every time I jack up the fuel things get better. In the driveway all appears fine. It realy appears that the pressure is dropping to about 15 PSI at full power. Packaging of any more data sources is no small issue.

AW

Hi Andy... a simple test is to remove the return line and measure the fuel returning to the tank @ 43 psi, if you can pump .5 US gallons per min them your system should just make it.
See Magnaflows site here:
http://www.magnumforceracing.com/store4 ... _notes.htm

Brad J.

We think we found the issue. It appears that a fair amount of trash found its way to the injectors. We have yet to find the true source of the trash. Nothing a quick flushing and a swaping of all 10 filters wont help giving us that false sense of security that all is good.

AW

ahah good luck