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Fuel issue?

4055 Views 22 Replies 9 Participants Last post by  Kyle844
Got the Nova running and driving finally, Ran well for a bit but would throw a P0300 random misfire code when Idling, after a few 5 mi trips around the neighbor hood, the walbro 255 in-line pump started having a high pitched squeal to it, it's made this noise before when my pre-filter was clogged, cleaned it, and still makes the noise, also since the noise from the pump, the car only responds well from 0-50% throttle, after that, it seems to miss or stumble and lose power. Fuel rail pressure idling was around 45psi and when revved it went to around 52psi, this is taken from a aeromotive fuel pressure guage right before the fuel enters the rail.
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Pressure needs to be up at 58psi for an LS motor.
x2 ^^^^

Your probably running out of fuel due to low pressure. Which is also running your engine lean. I know it's a total PITA but you might want to look into using a factory style GM pump in the tank.

Good luck Kyle.
Your fuel pump is probably toast. Bad thing about external pumps. Once you starve them for gas, the vanes get hot and lose their ability to maintain pressure. Fuel cools the pump amd vanes. Try to eliminate the prefilter and see if that helps. Bari is correct, the pump HAS to maintain 58-60 psi at all speeds to feed the engine. If it sees a drop in pressure it will run lean as Dhamen said, and make adjustments in timing, AFR etc. to protect the engine...if severe enough, could even go into limp mode...

Why would the pressure go up when the engine is revved? Unless it is going up on decel? Even then the difference shouldn't account for it :no: There may be something wrong with the regulator set up.

Try closing off the return line and cycling the pump then see what happens with the fuel pressure.
Thanks for the suggestions guys, I live away from the car so next time I go down, I'll start diagnosing.

I'm running a LM7 with lq4 return style fuel rail and factory regulator.

Now, earlier in the day before the pump was acting up, when priming the fuel system, pressure would go up to 58psi and i could hear the return start flowing, maintaining that 58psi. I didn't pay attention to the pressure once I lit it off, mid 50's or 58, didn't seem terribly different (could of been 58 but I just cant remember :yes: ), but now it is a significant difference on the gauge with the pump screaming at me.

I've heard a lot of people say how they can hear their walbro over their engine. When my pump wasn't actng up, I never even heard it besides when priming. Maybe I got lucky? When the pump first started being louder, I figure hey! That's what everyone complains about! but now it's effecting drive-ability so something is amiss.
id say the pump is on the way out. Another way to diagnose a PO300 is to watch the fuel trims,If the ecm tried adding fuel and cant quite get it where it needs it will often set this code along with at times lean fuel codes. If yoy have a scanner give it a look might be suprised to see what you find.
Currently the only scanner I have just pulls the codes, its a real cheap piece. Doesn't show real time data or anything.

I've had issues with my pre-filter clogging from crap in my tank, probably have cleaned it out 10-15 times. Maybe finally it's taken it's toll on the pump..
More info:

-6an feed and return lines
Walbro 255 mounted level with bottom of gas tank
Jegs 40 micron pre-filter (Should I step up to a 85 Micron earls filter instead?)
Jegs 40 micron post-filter
If you havent allready, either clean the tank or get a new one or this will keep happening.
I pulled the tank and gave it a rinse a few weeks ago, a lot of orange scaley/flakey material came out. (which is whats clogging my 40 micron pre filter) This is all new because when I prepped my tank to have the sump welded on, I rinsed it out also. I think its just some rust scale from the welded area from sitting with no gas in it after the sump was welded on. I'm HOPING that its %95 cleaned now and the rest will be filtered through. I just filled up the tank after running about 1/4 tank through the engine.
You could seal the tank and have no more issues? I do this to every gas tank I use or make. Lasts forever.,167_POR-15®-Fuel-Tank-Sealer.html

I would highly recommend sealing the inside of the tank. Even if you still have loose junk left in there this will capture it!:yes:
If yopu're not already I would recomend useing a fuel pump sock at the pick up/sump inside the tank.
I have a competition engineering weld in sump, where would I apply a sock? Also, how well does sealing work? I've heard these horror stories of it breaking down and messing up the fuel system. Is that all myth nowadays?

Still havent gotten down to work on it more.
Your prefilter is not correct.

Selecting the correct filter to prevent lean-out and pump failure.

STOP!! If you are selling or installing a fuel filter on the inlet of an Aeromotive fuel pump, be certain you do not use a filter that causes more problems than it solves. For pump inlet filtration, use only Aeromotive 100-micron P/N #12304, #12302 or an acceptable equivalent (see specifications below). Do not install the Aeromotive P/N #12301 or 12310 filter with 10-micron fabric element on the inlet of any Aeromotive fuel pump, they are however perfect for
use on the outlet of the pump, and this is the only location for which they are recommended. You may run any brand of filter you choose on your car, just be certain that it meets the following requirements: The filter element used on the inlet side of any Aeromotive fuel pump may be no finer than 100-micron (no number smaller than 100), with a surface area of 60 square inches or more.

You may want to read this intire page:
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I think your on to something, I only have about 1 square inch of filtering area. :no: not good!
Placing a order in to Summit for a new Walbro GSL392 255LPH external pump and KRC Racing 4706BK 100 micron fuel filter. This filter is 7.5" in length and 2" in diameter. This should prevent the filter from cavitating like my old one did.
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