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Fuel delivery issues

Old 07-20-18, 03:57 PM
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Fuel delivery issues

Fuel delivery cut out issues just purchased a 91 RX seven built for ITS SCCA racing

Took the car to the track for some testing had a few issues came home changed a few things went back to the track new parts we just installed a brand new hundred psi fuel pump that mounts in side the fuel cell With brand new foam in the cell
brand new primary fuel injectors new plugs new coils

also run an aftermarket fuel pressure regulator and gauge on the firewall in the return side of the fuel system where it comes out of the motor returning back to the tank

now hereís the issue

take the car out runs great for a lap maybe two and then it feels like the motor quit pulling !
like youíll go to shift gears hit the gas and you can just tell itís struggling to get fuel and it slowly gets worse until youíre down to first gear at about 10 miles an hour when this happens the fuel pressure gauge fluctuates a bunch and goes all the way down to 10 or 15 pounds

so while it did this on track one time I reach down shut off the fuel pump switch flipped it directly back on in the car took off again like nothing was wrong. So we continued to drive the same problem continue to happen about every lap to lap and a half we would flip the fuel pressure switch off right back on the car would take off again we did this for an hour long in Deuro and every time we flip the switch and a car ran perfectly fine for about another lap

things we changed at the track where we swapped out the fuel pressure regulator the aftermarket one we have installed on the firewall and at the track is where we actually installed the new primary fuel injectors as we only had two with us so we could not change the secondaries

It almost feels like thereís a sensor or relay going bad and when we flip the switch it kills the fuel pressure to the motor lets the relay or sensor reset or maybe the computer reset somehow and then it takes about another lap for it to go bad again any ideas what this could possibly be or has anyone ever ran into this issue before

than it almost feels like thereís a sensor or relay going bad and when we flip the switch kills the fuel pressure to the motor lets the relay or sensor reset or maybe the computer reset somehow and then it takes about another lap for it to go bad again any ideas what this could possibly be or has anyone ever ran into this issue before
thanks
Bryan!!
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Old 07-26-18, 01:57 PM
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Hi Bryan,

I think I would have a look at your fuel filter, sounds like it could be clogging up.

Good luck,

Guy
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Old 07-26-18, 02:28 PM
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Thanks !! We had a new filter on car !! But we did find a wire that wasnít crimped together right and through some moving of wire it came apart!! So we are hoping this is the problem!!
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Old 07-26-18, 10:14 PM
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fuel cell? we ran a 25 hour where we had a mismatched pump and box in the fuel cell, and it would let the pump suck itself to the bottom of the box.

possible issue #2 was that we didn't wash the foam before we put it in.
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Old 07-30-18, 09:04 AM
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We had the exact same issue running at NHMS one year. Insanely frustrating. Interestingly enough we found, similar to you, that when we pitted and refilled the fuel it would run great for ~5 laps, and then start the slow drop in power/revs.

My main hypothesis at the time was that the fuel pump must have been on the edge of bad, so that when we refilled with ambient temp fuel from our jugs the fuel was dense enough so the pump could work, but after a few laps the exhaust heats the tank and thins the fuel enough that the pump starts having trouble.

Replaced the pump and the issue went away but who knows.

Also, I have installed a brand new mazda fuel filter that was bad right out of the box. It's a bit of thing I believe. So you may want to to ditch that to eliminate a potential issue.
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Old 08-03-18, 12:38 PM
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I would be very curious to see how much voltage you see at the pump as it starts to lose power. You may want to consider wiring a direct positive wire with a new relay so the fuel pump always sees 12V. Also, you mention you installed a 100 psi fuel pump. That doesn't really mean much as the flow of the pump at a given pressure is what is important. What kind of pump is it and are you sure it flows enough at your set fuel pressure to meet the demands of the engine?
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