Car struggles to make fuel pressure

Mitco39

I have a CJM stage 1 return kit on the car running a fair amount of fuel (13psi of boost). I have started to notice that when the tank gets down below half it really struggles to make even set psi on the regulator; have it set at 56-58 PSI at idle and the boost is hooked up so that it should be in the high 60's under boost. But as the fuel level goes down it really struggles and even drops down into the 40s and the car misfires.

I have a 255 in the tank which from what I have read and been told this should be enough and in most cases it is when the tank is full. It also seems to be related to heat, maybe because the fuel pump is not fully sitting in the fuel it is getting hot? The fuel pump has a dedicated power line running to the pump and a good ground.

Just looking for suggestions of things to check when I tear into her today.

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Super Werty

Dirty fuel filter?

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Mitco39

I dont think so for the main fact that it seems to happen more as the fuel level goes down.

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instroke

Yeah I have noticed similar pressure drops as the tank gets lower. And then if it's hot out - it contributes to the lower pressure. When I get over a 1/2 tank in 72 psi start up - then 65 -67 at idle. But last night as I was getting lower in fuel - and it was hot - stoplights were at 55 or so. If I get into the gas it always drops another 10 psi - don't know if this is normal.

Would have been a perfect night if you show'd at Hawrelak last night - would have been all the boosted Z's.

My z has doesn't want to start lately, I have do just tap the gas lightly - wondering if it's fuel pressure issue?

Mitco39

Boosted with larger injectors you will get a pretty good pressure drop. I have a fuel return system that is supposed to increase fuel pressure as the boost comes on. After pulling the pump and taking a look I think its just the transfer in the tank not working like it should or I use more fuel then it can transfer and empties out the reservoir. I noticed that again the filter fell off the bottom of the pump so I "engineered it" lol.

When turning on the pump and listening I can hear fuel spraying down as it comes back from the engine, I would imagine that this is aerating the reservoir and further straining the fueling system. Ill upload some pics here now.

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Mitco39

Little bit of **** in there


When I pulled these off they were very loose, considering a fair bit of amperage has to go through these two for the pump I recrimped them so they were a sug fit.


Now I dont know if this filter is falling off or if there is even room to fall off under the pump but everytime I pull it apart its free in the bottom of the reservoir so this time I put a zip tie around 3 of the legs that clip onto the pump to suck them closed and create more of a positive lock when I slid it on.




I just dont want to have her go pop because of fuel issues.

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bullitt5897

You can drill open the bottom of the basket to help it draw in more fuel. Mustang guys have been doing it for years! Drill out the main hole and filter and then do a few extra holes. You will noticed a dramatic increase in fuel flow into the bucket!

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Mitco39

Might have to do that because something is up and it makes sense that it would get worse as the tank level drops. I also think that when im at a 1/4 I probably have 3/8" on the left side and 1/8" on the right side which works against me.

Also going to change the fuel filter like was suggested, it cant hurt.

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phunk

Not normal. The stock regulator is 52psi, and you should see just about that all the time. The only exception would be a boosted car at full throttle without a return system can loose pressure towards redline.

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phunk

The over-tank transfer siphon is done with a venturi in the return line. It should put fuel on the passenger side of the tank faster than you burn it. The drivers side of the tank should be only 1" full before the passenger side even starts to go down. The exception would be if you just took a right turn and fuel sloshed over, then it would take several minutes for the siphon to recover the fuel to the passenger side again.

Fuel that comes back from the engine goes to a pair of venturi pumps, one is the overtank venturi and the other is the canister refill venturi.

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phunk

Does your regulator have a vacuum line on it or a boost only line? Where is it hooked up? Does pressure raise at idle, and go down when you rev the engine?

I see that your fuel pump is red... is that a China knockoff 255? If so, you should replace that. Your fuel pump pickup should not be falling off.. get one that attaches properly to that pump with the circular lock how its supposed to be. The one you are using is for the stock pump.

Dont put holes in the bucket, no reason to do that.

You car should be running very lean if its actually dropping 10+psi fuel pressure from how it was tuned. Is your car running lean?

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phunk

Put a clamp on the return hose in the tank at the top fitting, and make sure a clamp is on the other side of the hose.

How long does it take your fuel pressure to drop to zero with the fuel pump off?

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Mitco39

The issues I been having are in a straight line out on the highway. When I pulled the pump I only had about a inch of fuel left in the tank (2 dots). Mind you after putting it all together and filling it up it was better, but I still wasn't completely happy with its performance as it did seem to still struggle somewhat.

The regulator I have connected to a boost only line as suggested by you when I was installing the kit last year. It is connected to the boost tubes prior to the throttle bodies. It does try and follow the 1:1. Sits around 56-58PSI at idle which is what I set it for, then ramps up to ~65-66 or so under about 13 psi of boost. Maybe I am just asking for to much pressure out of that pump? It was fine for the first 6 or so months of running it that way.

I will have to check and see what pump is in the car, I was under the impression it was a quality pump but I will double check. If thats the case it could explain the issues.

When I pull it back apart I will throw a clamp on there. And I dont know as I have my fuel pressure gauge hooked up and it only comes on when the key is turned on. I can have the wife pull the fuse for me and test it that way. I will do that this evening after work.

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Mitco39

Can a fuel pressure regulator be effected by engine heat? Seems as the car heats up it cant even sustain an idle fuel pressure.

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2007 Chevy Duramax - EFILive Tuned By Me
2010 40th W/ Nav - Boosted Performance - UpRev Tuned By Me
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Mitco39

Fuel pressure takes 12-15 seconds to drop down to about 15psi. I will be putting clamps on that factory hose when I change out the pump. Do you know what size of clamps would be best?

Thanks

Mitch

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