Car struggles to make fuel pressure
 

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.

Dirty fuel filter?

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

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?

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.

Little bit of **** in there
http://img.photobucket.com/albums/v2...psouqc7t19.jpg

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.
http://img.photobucket.com/albums/v2...ps9xbmmuku.jpg

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.

http://img.photobucket.com/albums/v2...ps6nladwk9.jpg


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

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!

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.

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.

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.

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?

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?

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.

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

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

Ive never seen a regulator react to heat, it would probably take some really extreme heat - they are rather simple devices and if constructed with quality materials they are not very prone to failure without debris making it in. It wouldnt hurt to try swapping the regulator out just to test with another, although its unlikely the problem.

For hose clamps, smallest you can find probably, its a 1/4" ID hose. Thats the return side that blue hose I was looking at. If it leaked the over-tank siphon and canister refill would be weakened.

If there is pressure problems even with a full tank when the car heats up, its probably a bad pump. The pump in your photos is red, Walbro doesnt make any red pumps. If that isnt an Aeromotive Stealth pump its an ebay pump that probably needs to be replaced.

Charles,

I dont have another regulator to test at the moment but I dont think it would be that either if its unheard of.

Would you clamp the supply side black tubes as well? I noticed there is no clamps on them, can they leak? Should I upgrade them now that im pushing ~70PSi at times?

The pump is not Aeromotive, I bought a Aeromotive 340 and am going to be installing here once i burn some fuel out of my tank. Had a vendor account and could get it locally so that worked out nicely. Just dont want to have issues with our trip down the vegas next week.

The factory black tubes dont need any clamps. They are either Nylon or PTFE and press fit very tightly on their barbs.

I bet that fuel pump will solve your problems. Just watch for a possibly idle pressure spike unless you already opened up the swirl jet orifice enough to accomodate that large of a pump.

Ok I wont worry about them then, thank you.

Should the regulator along with the pressure dampener be sufficient with these spikes? Ill have it apart anyways I can always drill it out with the link you provided me earlier. Im not to concerned about a bit of a fluctuating idle the car does it right now anyways.

Its unrelated to the regulator and dampers. You can read about it here: http://www.the370z.com/forced-induct...ml#post2784717

I see so its actually on the return side of things coming back to the tank after it passes through the regulator? Makes sense I will drill it out as per that thread.

Thank you sir.

Mitch

So after changing the pump I had a close look at my wiring and it appears to have gotten pretty hot which I think was what was causing my issues all along. That said I am going to run some 10-12GA back from the battery today. However I am still not happy with how it has to drop down to some ~22ga to get through that plug, I think this is very insufficient as according to the pump spec sheet I can expect a constant draw of about 16-18 Amps.

Has anyone every modified the top housing to run the 10-12GA directly into the fuel tank? I want to try and bypass that plug all together if possible.

Something like this would work but our car needs 5 pins for the bulkhead.

Racetronix - Fuel Pump Wiring Kit MP150/280, Generic - Kit Configuration Page

With the aeromotive pump I was overheating the wiring due to bad connections at the terminals, I redid them all and soldiered them and havent had any trouble. Since the top is plastic, you dont have to do anything fancy to get larger wires through to your pump, you can just run a hex screw through the top and use them as power/ground lugs. The connector you linked would need some sort of bung to insert it into.

I thought of that, the only concern I have is I have to find copper bolts to keep the conductivity up otherwise the bolts will get hot and melt the housing and make a mess. Did you end up going through your housing like this Charles? I just have a 1600 mile road trip coming up next week and don't want to introduce any issues.

Thank you sir

Nope I am still using the stock plug and stock wiring. Just upgraded the wiring inside the tank and soldiered up the terminal to reduce hot spots.

The stock wiring back to the tank gets really hot and I am surprised it never blew a fuse. If it were a customers car, I would have put in a relay kit.

Stock wiring? wow. I ran 10Ga back to the tank yesterday and got it to the point where it gets warm to the touch but it is no longer hot. I attribute that to soldering my connections instead of using splices as I imagine the internal resistance of a buttsplice is significantly higher and thus got hot.

That said after the car warmed up the idle fuel pressure dropped again. I was doing some reading and have read that fuel pressure gauges can easily be affected by heat and that this is normal. I do know that regulator gets hot to the touch when the car is driving around.

For example the fuel pressure when cold sits 58-60PSI, hot at idle it sits around 55-57psi. I am going to do some more research when I get time this morning to see if thats normal and if it is a possibility that its the heat affecting the sensor.

Just got to Vegas, fuel pressure was fine till the temps got up to about 210-220F and the idle fuel pressure dropped down to 40-50PSI and I could confirm that it was low because my AFRs were showing leaner than it was when it was at 58PSI.

I am really starting to think this regulator is being affected by heat and that spring that regulates pressure is getting weaker with the heat.

Possible?

Stay outta high boost, have a good time in Vegas! And a safe trip back.

Never heard of it happening before but I suppose anything is possible. I'd still bet on the mystery brand pump. Unfortunately its unlikely to be diagnosed fully until you begin the process of elimination.

Sub'd just cuz there's good discussion going on here:tup:

Charles, I swapped out the pump with the aeromotive 340 so its got a brand new good pump in it with 10ga running all the way back to the tank.

Its so bad that when heat soaked and hot it struggles to start. Cold it fires up just like stock. I will get another regulator to try while im down here if I can find a place with one. Makes me wonder if I should be mounting it somewhere away from the heat, although there isn't many other choices on our car. The other thing I can try is setting the idle pressure with the system hot. That means however that it will idle at a much higher fuel pressure when colder.

I found a guy who is having the exact same sort of thing going on. Its weird I am the only Z with this issue. This guy in particular re adjusted his regulator when hot which worked, till it got cold and overfueled hard on cold starts.

https://www.youtube.com/watch?v=q8MO5Ag73oE

Spoke to Aeromotive just now and the guy knew his ****. Said there is no way its the regulator itself its the heat of the fuel. He said anything over 130F is iffy when your running high flow fuel pumps as the fuel will cavitate while the pump is trying to suck it in and send it back to the engine.

He suggested trying to reroute the lines and move them to the outside of the frame rail at the front then cross over to the engine. Or possibly purchase a fuel cooler with a fan on it to cool the fuel on its way back.

Fuel heat can definitely cause problems but considering you are returning before the rails and only running a single pump, you are hardly pushing it as far as fuel system work goes and things that contribute to fuel system heat. I dont know what the weather is like there and if you have a vented hood or not, but you could always try reducing heat in the bay, heat wrapping some things, etc, and see if that helps your case.

I used to have the same problem regarding fuel pressure dropping after it got hot under the hood. I have a liquid filled gauge and the pressure would build up inside the gauge and lower the reading (actual fuel pressure is unchanged). It dropped up to 10 psi when compared to cold start up. I fixed this problem by draining the oil inside the gauge and left the drain/fill plug open. It fixed my problem completely. It's possible your warm start up problem has to do with uprev start up setting and not with fuel pressure.

So im ready to pull my hair out over this one. Its really cutting into me enjoying the car at this point because I only get one good run down the track before it starts to lose fuel pressure and cut boost (the new innovate boost controller I have is awesome for cutting boost when she starts to go lean).

I upgraded the wiring all the way to the bulkhead of the tank, altho I might cut that apart and go all the way to the pump. There are no leaks and the regulator is set at 58psi cold hooked up with the 1:1 to a boost only source as per reccomendation.

When its heat soaked its hard to start, I have to turn the key to acc let the pump self prime itself for 2-3 seconds then she will fire right up. If I get in and just turn the car on in one button push she does crank for about 4-5 seconds and struggles to start. When the car is cold or cool this does not happen.


What I am starting to think is happening is that basket of fuel is getting warm and fuel is not entering the basket as fast as it needs to under WOT (under wot down the 1/4 mile ive seen it drop to 38psi, at 10lbs of boost thats only a 28psi pressure differential, not good). I am thinking that this 340 pump is just moving to much fuel for that basket to keep up with, and now it is returning hot fuel to that basket and causing cavitation at the pump.

Has anyone ever cut holes in their basket to help with this issue? Ive even thought about adding a fuel cooler to the car but im not convinced that will help me either as its just because the loop circuit is so small.

It all started after doing the fuel return system, and I know its getting hot because that regulator the fuel travels through is cooking (it is installed on my firewall just beside the battery). Normal driving up here its cool enough that it usually doesnt happen, but when we were down in vegas with the cars it really had a hard time.



At a loss....

I have run that pump and larger in the factory basket without having to cut holes, along with others. If this problem even occurs when the fuel level is high, than its not likely an issue with fuel getting in the bucket... if the fuel level is higher than the bucket than it will rush in there no problem.

You could try pressure testing your fuel pump module. Perhaps it has an internal leak and when it heats up it leaks more. If you use a leakdown tester and put like 60psi of air pressure into the outlet of the fuel pump module, it should have zero leakage.

Charles, by fuel pump module you mean the fuel pressure regulator or just the fuel pump itself? It would make sense that its returning to the tank because I can shut off the car for 30 seconds to a minute and you can hear the pump in the tank repriming the system, you can hear the air working its way out.

I was thinking the same about the fuel level, but I'm starting to rack my head on this one. You dont think its that stock line between the pump and the bulkhead do you? If there is a leak there that could do it.

I mean neither... I am talking about the entire fuel pump module/housing/assembly that is inside the fuel tank. Disconnect the quick connect output on top of the fuel pump module, and apply pressure inward. This will test the entire pressure side of the fuel pump module for leakage. It will check the hose connections, it will check the filter housing for any cracks/leaks, and it will check the regulator delete assembly for leaks (like if it was missing 1 of the 2 orings or something).