powdrhound

I finally got my fuel system upgraded with the final few parts that solve the remaining issues I was dealing with. Several months ago we installed a Motec fuel pressure sensor so that we can constantly monitor and log fuel pressure under various conditions as we had a fuel pump failure after only a few thousand miles. This has allowed us uncover a couple of interesting findings. First of all, as fuel temperatures go up, the output of a fuel pump will slightly decrease. Fuel temperatures go up when you add larger pumps due to the increased fuel bypass resulting in increased fuel recirculation. The bigger the pumps you install, the greater fuel heating will become as you have more fuel recirculation. High G loadings acting on the pump will also slightly decrease fuel pump output as we have experienced at the track in highly loaded turns.

The most significant finding however is the fact the if you have upgraded your fuel lines or added additional pumps, you MUST replace the OEM check valve that is part of the OEM in tank plumbing just aft of the fuel pump in line with the plastic corrugated tubing. The OEM check valve has a very small flow through opening and severely restricts fuel flow no matter how large your down stream fuel lines are or how many fuel pumps you are running. The OEM check valve is designed to handle the rather meager output of the OEM VDO pump but becomes a restriction when more flow is required. All else unchanged, by simply removing the factory check valve our idle fuel flow jumped significantly from 3.3 bar to 4.5 bar at idle when using a high output Walbro 450 pump and high flow AN fuel lines. We used a billet Aeromotive check valve and a billet Aeromotive fuel filter (with easily replaceable 10 micron filter cartrage). I already had an aftermarket -AN8 fuel filter but decided to replace the filter while at it. Both of these Aeromotive items are high flow items designed to handle up to 3000hp applications. The check valve is about $100 and the filter about $130. They are top quality and extremely free flowing unlike the factory check valve or filter. It is now clear that the early Walbro pump failure was caused by the OEM in tank check valve severely limiting flow thus causing a restriction that the high flow pump had to constantly work against. Essentially the OEM check valve was choking the pump causing it to operate under a constant strain.

With the additional fuel flow uncorked by removing the OEM check valve, we ended up having to scale the 450 pump down to 55% output at idle to arrive at the correct idle fuel pressures. We use a Motec fuel pump controller to control the fuel pump completely bypassing the factory fuel pump relay. We then scale up the pump output tying it to RPM and boost to limit the amount of fuel bypass (thus reducing fuel heating). We are essentially running a simplified on demand fuel system with limited fuel bypass. We spent 3 days last week testing the new system at the track and fine tuning the programing of the fuel pump controller to get pump output just right for all conditions. Temps were approaching 100F and I can say that the engine has never run better and fuel pressures were absolutely solid through out.

Long story short, there is a lot more to it than just throwing larger fuel lines and larger pumps in there. If you upgraded your pumps and external fuel lines, make sure you address the restriction of the OEM in tank check valve. If you haven't, also address the restriction of the OEM fuel filter and the quick disconnect fuel line fitting in the tank lid. Those are very small and restrictive also. Even with the stock fuel pump, if you address the above mentioned restrictions you will free up some more fuel flow.

Aeromotive check valve connected to an Aeromotive fuel filter via female/female AN6 coupler.

[url=https://flic.kr/p/J9uUmE]

[url=https://flic.kr/p/J9uTVu]

[url=https://flic.kr/p/HgAPPV]

T10Chris

Good info here that I think many could benefit from are missing out on based on the response/lack of.

Always enjoy your posts/threads, thanks for sharing with us

powdrhound

I posted this on 6bling and there is a lot more interest there. More straight line guys there doing higher hp set ups that this info is more up their alley than here...

http://www.6speedonline.com/forums/9...m-upgrade.html

T10Chris

Ahh yeah that makes sense. I bounce back and forth between the sites. I am not much of a straight line only racing guy. Obviously I want a fast car, but I am more interested in HPDE builds, optimizing what is available, trying to stay with factory stuff as much as possible.... As such, I have found a ton of valuable info from your posts

powdrhound

I'm not a straight line guy either, only road course. There is good info on both sites including a ton of misinformation. You just have to pick and choose. I only go with aftermarket stuff when absolutely necessary. The factory fuel system has it's limitations for sure if you retain the in tank lines as we found out.

jumper5836

lol, did you also enlarge the gas tank because these cars drink gas.

2jzhx60

powdrhound do you have these pictures still available?

I have a Walbro 450 and OEM K24's and the car is tuned with E85 and it seems like I am loosing a little fuel pressure up top. I'd like to try out swapping out the check valve before uprading the fuel lines as I just need a little more flow.

What's the purpose of the check valve if the fuel pump has it's own check valve? Can it be removed completely?

T10Chris

The purpose of the check valve that is above the fuel pump has to do with the functionality and maintaining pressure for the jet pump/venturi system that pulls fuel from the legs of the tank up into the fuel pump basket in the saddle so it can't be just deleted or you'll run into issues cranking once fuel gets around 30-40% remaining. I chased this for a while before figuring it out. Unknown if it causes any issues when the car is running and fuel gets low, I never saw it but doesn't mean it isn't possible.

You might be running out of fuel pump, back when I ran E85 I had to switch to the 525 to keep fuel pressure from falling above 500 whp and I had upgraded the fuel lines already.

There are some small sections of the stock fuel lines that are rubber hoses which aren't E85 compatible if you weren't aware. One is submerged in tank, the other runs from one side of the engine bay to the other. Keep an eye on those if you don't plan to change them.

2jzhx60

Hmm... so you think I might be out of pump? My friend made 700hp (crank hp) with a single Walbro 450 on a MKIV Supra / 2JZ with the same fuel pressure, but the venturis will of course lower the output on the 996.

I actually even put a relay on the 450 pump as i was seeing 12.4 volts at the fuel pump connector and now its hard wired straight from the battery with a 75 AMP relay so now its almost the same as battery voltage when the car is running (13.2v) but it still seems like I am dropping fuel pressure. I'm at 80% injector duty cycle with 1150cc EV14 injectors which is high for estimated 600 crank hp.

Im planning to go to a dyno and measure the fuel pressure there with a gauge as its a little hard on the road without rigging a go pro to film the gauge or some other creative solutions. Suggestions are welcome.

powdrhound

I don't unfortunately. I run an ON-demand fuel system on the car now with not fuel return utilizing the BKS-1001 pump with the system operating at 5.0 bar. What I posted in this thread 7 years ago still rings true however...

2jzhx60

When you posted this originally did you have the AWD fuel tank or the GT2 one?

So you removed the stock check valve from the tank and put one in the fuel line outside of the tank if I understood this correctly?

On some cars with upgraded fuel systems I never ran check valves other than the fuel pumps own built in check valve.

powdrhound

GT2 tank. Yes, the check valve and filter were located on the -8AN line in the center tunnel. If I recall, we eventually removed the check valve altogether because we put a 2nd fuel damper in it's location and simply programmed Motec to prime the fuel line just prior to starting with a second or two delay prior to starting. On my current set up we use a -8AN check valve located up front. We use 3 fuel dampers on the current system. One up front, one in the tunnel, and one at the engine.

Here is the link to the checkvalve:

http://www.radiumauto.com/Universal-...its-P1872.aspx

If I recall, both the TiAutomotive (Walbro) 450 and 525 pump had checkvalves of sorts. Not really true check valves as they would bleed down but at a slow rate, maybe 10-15 seconds if I recall. The TiAutomotive BKS-1001 bleeds down instantly. It absolutely requires a checkvalve or you need to have the pump running prior to starter engagement.

2jzhx60

Upgraded the stock check valve yesterday and installed this one with some barb fittings:
https://www.finjector.com/eng/sytec_...a-p-733975-153

Results were that the base fuel pressure rose from 3.8bar to 4.0bar and ECU now removes fuel from the map at WOT and not add like previously.

Previously:


Now:


I've yet to check if the fuel pressure still comes down at full boost as I need rig something to check the gauge. If it still comes down, I think it's the 525 Walbro / fuel line updrade time or upgrade the fittings on top of the tank as the ID on those are only 4.8mm, but this check valve definitely made a difference.

moburki

John, based on this, I assume you are saying that the stock ecu does not prime the fuel system at every start? In other words, it will prime the system at cold start, but not after the engine reaches operating temperature? This may answer a starting issue I have been having without driving with my fuel pressure gauge attached (always a risk).
TIA
Mo

powdrhound

I’m not saying that at all. Honestly I don’t know how the stock ecu handles the fuel priming but would assume it does so on every start with key ON. Just a guess however. Easiest thing to do is to attach a fuel pressure gauge and look at it during key on/ and start. When I ran the stock ecu, we used the Motec dash to operate the fuel pump via the Motec DHB instead of the ecu.