This isn't FI related, but it's on an FI build so I'm hoping somebody can provide some insight. Thanks in advance for the help!

I just did a total rebuild on an 07 Z06. I'm running a Fore triple hanger, and 3x AEM 320 pumps, 8AN feed line to billet rails, Aeromotive boost pressure regulator, and 6AN return line. Cold start my fuel pressure is 50 psi (per my tuner for start-up/break-in tune). Today I drove about 20 miles and my pressure started dropping. By the time I made it home (50 miles), my pressure was down to about 10-15 psi. Car is very hard to make take fuel before it burps it back out. It did this yesterday too but never left me stranded like it finally did today.

Gauge says I have 3/4 tank of fuel... can it all be in the passenger tank and not crossing over? Why am I losing pressure after driving for a while. I put about 80 miles on it this morning (just trying to put some miles on the build [YSi ERL Superdeck 427]) and the pressure was absolutely perfect the entire time.

On a side note, I'll be adding pics, build info, and numbers soon... if I can. Get the fuel issue handled! Thanks again guys! Any and all help is greatly appreciated!

 

How are the pumps being triggered? i.e. are they all on all the time?

There is a vent on one of the tanks, I can't recall which one.. it is supposed to close when both tanks are full, and that's what makes fuel back up into the pipe and makes it "burp" like that.

Do you have access to HP Tuners? You can log how much fuel is in each tank to see if fuel isn't transferring properly if you do.

Has the passenger side tank regulator been replace with the bypass valve from LPE? If not, it won't transfer fuel at 50psi more than likely. It needs more pressure than that.

 

Thanks! The pumps are on all the time...my thinking was that a Hobbs switch was just something else for the engine to be reliant on under load. I haven't messed with the passenger side tank at all. What pressure do you run your system at? I've been trying to all the research I can and I've run across your knowledgable answers a lot! I don't have access to HP Tuners, only a Snap-On scanner. I ran across the same info on a vent valve in the passenger tank and assumed that was my problem that it was closing my driver's tank vent, but now I'm thinking that's not it.

 

I would recommend putting the second two pumps on a hobbs switch. That's a lot of fuel to keep sending up to the engine compartment and back.. it will get hot, vapor lock, and voila, fuel pressure sucks. To check--try adding some nice cold fuel when you have the low pressure problem and see if it goes away for a bit.

I would bet the fuel is getting too hot

If fuel pressure isn't high enough the system that transfers fuel from passenger to driver tank won't work. There's a valve built into the passenger side tank that stops it from working under a certain pressure (somewhere in the low 50's psi).

If the vent that lets air out while filling up with fuel is in the passenger side tank.. that could explain that issue too. Passenger tank is staying full, so the vent is staying closed, and that creates the burping issue when filling

So.. try turning it up so that it's at least 56psi or so minimum and see how it does.

 

Exactly the kind of info I was looking for! Thanks a million...that makes perfect sense. I read that the valve in the passenger tank could be my issue, but you just confirmed it with the pressure readings. This morning when it ran fine the air temp was around 50, and this afternoon was around 80. So I'd say you've figured out my issue.

Next question...I'm breaking my engine in and not getting into boost for now. Can I get by with one of the pumps until the Hobbs switch arrives or should I leave 2 running?

 

Do you have a wideband or fuel pressure gauge?

 

Just a pressure gauge for now

 

Yeah I'd just leave one pump on then and keep an eye on it. I think it'll be fine but not 100.000% sure

 

Perfect, thanks! We ever cross paths and I'll buy you a steak dinner and a beer or 5! Lol. Thanks again!

 

lol, didn't notice that you were in NC!

Good luck with it

 

you should get a wideband on that thing asap imo but for just breaking it all in and with no boost and very light driving one of those fuel pumps should be more than enough assuming everything is running right. but you need the afr proper to break the engine in right though, if its far too rich you can actually wash the cylinders with fuel and cause break in problems. assuming you had a real tuner on that since obviously not a budget build but just throwing that out there

 

Schpenxel this is my old setup.

Unless a 3rd magically changes everything, I ran those 2 pumps on all the time, in 120+ weather with ZERO issues. Sounds like the transfer issue. That is why there was the block off in the package I sent you to use. If cold FP is 50 with no vacuum on the reg, that probably means it is only transferring fuel when you are in or near boost. You need to either bump the base fuel pressure up so it doesn't drop below ~52-54 (even when in vacuum) or install the regulator block in the passenger tank.

Considering I've driven 8 hour plus road trips with those pumps, I doubt 20 minutes is doing anything with the fuel heat.

If car isn't taking fuel, then that also indicates that the one tank is probably full still and you have an issue in the tanks.

 

Good to hear from someone else who has actually ran those pumps in stupid hot weather

I was basing the overheating thoughts on the issues a lot of people had on the Aeromotive setups a few years back. Hopefully that isn't even an issue here

Regardless... first things first, fixing the fuel pressure so the transfer system works correctly is #1. I think we all agree it probably isn't working right at 50psi. Can't hurt (IMO) to try only one pump and see if it helps on anything else while you don't have the blower installed. Just keep an eye on fuel pressure.

Unreal makes a good point.. it needs to be a minimum of mid 50's, at idle.. not mid 50's at 0 psi boost

 

Like Unreal said, stupid me had the passenger side block off and didn't put it in. However, I put it in yesterday and nothing changed whatsoever. As I expected, the passenger tank was completely full when I dropped it. Drove the car from work again last night and ran into the same problem at around the same mileage. So I'm assuming it's still not transferring. Gauge still says almost full and can't get it to take gas. Next step is drop the driver tank again and make sure I don't have the crossover tube inside the tank pinched. Thanks guys

 

Yah, if it won't take gas you have an issue with the tanks/vents/lines. There is a shut off valve when it gets near full that causes the pump to shut off. You need to fix that.

One thing I found that really helps is JB welding the crossover lines in the tube, to reinforce them and make sure they don't pop out of place when installing.

Fuel stuff on these cars is a pain. I had to drop my tank 5-6 times before I got it working great, then I didn't touch it forever. I haven't even ran my new setup yet to see. I hope it went in well, but who knows. Makes me wish I never touched it.

 

Haha. Yeah, I should have left well enough alone. I put in everything you sent me (minus the plug) and got my fuel pressure perfect. I got stuck waiting for another piece of the build and decided I'd rather overkill the fuel and be set for the future and have had issues ever since. But I never drove it on just the 2 pumps either, so I could'be had the same issue within too. But I'll drop the driver's tank for a 4th time and see I guess.

I got the car with a blown N/A engine and in boxes...it kills me that the motor runs flawless now and I'm too stupid to fix the fuel! Lol

 

Take your time. You will get it.

At least you don't have the fore wide setup. That is what I put in, and it makes that setup look beyond easy. You have to assemble the wide setup inside the tank a piece at a time.

 

Good lord! I can't imagine what a PITA that is! Patience is about to get trumped by urgency...dyno tune is scheduled for Friday and I've got plenty of break-in miles on it now. So it's getting fixed asap now.