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. The new problem however, if you are running multiple big pumps, will be the fact that you end up with too much fuel flow if you have no way to control it based on demand. Ah, the quest continues...

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

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Great that u share your knockledge

 

Great post. Not unsurprising however I thought extra fuel would be pushed down to the jet/lift pumps based on the restriction of the check valve.

I looked at that check valve when I built my system, and bought one, but chose to not install as its not e85 compatible. Instead i went from 8an to 10an for the filter and check valve to ensure flow.

Would be great to see a fuel pressure log example before and after your changes. I've noticed that my relative fuel pressure (relative to boost) jumps around up to .3 of a bar when I really stand on it. Initially it goes down slightly and then when I lift of quickly spike back up.

 

Hi John,

Does the motec fuel pump controller run as a standalone item or do you need a complete Motec system to run it? I am considering a fuel system upgrade sooner or later.

 

Hey Matt,
The MoTec fuel pump controller (Motec DHB) ties in with the Motec dash logger like I'm running or you need the Motec ECU. The DHB is fully programmable. We have it set up with a bunch of safeties to if there is any kind of a hick up in the system it automatically drives to pump to 100% output. It's also nice in that you can run the pump for testing without the engine running. The DHB is a sealed waterproof solid state controller with no internal wires. It's very small, only about 1.5x1.5x0.5" in size. It's unlike anything else on the market and like all the Motec stuff, its mil spec. You have to use a pump that can be controlled with PWM (pulse width modulation) which all the new generation pumps like the turbine Walbro 450 are.

http://www.motec.com/dhb/dhboverview/

The beauty of the Motec stuff is the on the fly flexibility. After every run last Friday, I would download the data and email it to Chris. He would look at it, tweak it and email me a new file within a few minutes which I would download back into the Motec dash. We did this 3 or 4 times until Chris was satisfied with the results. The dash logger is a very useful tool. With all the data available, Chris could analyze track data and make recommendations to shave a little bit of time in various segments of the course. If you are tracking your car, the Motec dash logger is an invaluable tool.

Regarding the fuel upgrades, there is a lot of aftermarket fuel stuff out there and most is largely untested and comes with drawbacks. As I said, there is more to it than just throwing a larger pump and lines in there. The ECU is pretty good at compensating so in most cases it works but is not optimal. In our case, being at a 5000' elevation in high ambient temps and not having a fuel cooler made the whole situation even worse. Basically the worst conditions to operate in. The fuel cooler was Porsche's "bandaid" to the fuel heating situation which resulted from the constant recirculation/reheating of the fuel. This was not needed on the GT3/Cup cars as the fuel pumps were of a lower output so the recirculation was less than that on the turbos. The 996 was the last car that used this relatively archaic set up. All the 997 and later stuff is return less.

 

Yes, the Aeromotive check valve uses a large spring loaded elastomer ball. It is not approved for straight E85.

Before and after logs were pretty clear. I could post them but you need the Motec program to display them. After getting rid of the restrictive check valve, basically, at idle, in off throttle or low load situations, the fuel pressure was needlessly high due to the high output of the fuel pump. There is only so much fuel the fpr can bypass even when fully open. The car will still run fine as the ECU can compensate but you are needlessly pushing tons of fuel through the system that is continuously getting heated as it recirculates back to the tank. Being able to reduce the output of the pump in low engine load situations drastically reduces the amount of fuel getting continually reheated, essentially you have an "on demand" fuel system. I can only imagine how much fuel would get pushed through if you were using multiple pumps running at 100% without any way to control them. When I ran the Walbro 450 last year, at my 5000' elevation and at high ambient temps, I was having fuel boiling issues. There was simply too much fuel recirculation with the pump running at a constant 100% output thus leading to the in tank fuel temperatures reaching the boiling point. Not good...

 

Hey John,
So you are running lower pressures through the FPR/entire system and when a parameter is reached it kicks up the duty cycle to deliver required fuel. Does the FPR then come into play or at the set base pressure where the pump was running at say normal PWM/voltage? Not sure if I asked this Saturday at HPR.

What about the DC of the injectors? When you lower the DC of the FP you are increasing the DC of the injectors right to match fuel requirements? I was curious about that...regarding tune, you have to increase the injector Time to compensate.

I looked at the Weldon PWM controller since we talked last time. It's something that I would do but not sure if it has the available trigger parameters that I would want like probably have...maybe I dunno. I need something with a map sensor OR maybe a Hobbs switch. Too bad Motec didn't offer it as a standalone component. Probably couldn't afford it anyways. �� ��

 

No, the idea is to allow the FPR to work as intended. What we are doing is scaling the output of the pump down to the point that you still have the required fuel pressure AND the FPR still has to remain slightly open to bypass some fuel. The idea is to have the FPR slightly open to bypass some fuel instead of wide open to bypass a bunch of fuel. Basically there is no need to feed the engine a ton of fuel when it doesn't need it. What we set up is an "on demand" type of fuel system with minimized fuel return.

Naturally at low engine power settings and especially at idle, the engine consumes very little fuel and with the pump running at 100% basically all the fuel is bypassed through the FPR and returned back to the fuel tank, albeit slightly warmer as it has to circulate around the engine. In my case, with the 450, idle fuel pressure was 4.3 bar which indicated that the FPR was wide open and could not handle the amount of fuel that was being shoved through it. We began to reduce the output of the pump and pressure began to fall down to the base 3.3 bar. As pump output is reduced further the FPR begins to close to maintain base pressure. When we continued to reduce the output further we got to a point that the FPR was fully closed (to maintain pressure) and fuel pressure would then begin to fall below 3.3 bar. This was the lower limit. We bumped it up a little from there to get to 3.3 plus a small margin. We then gradually scale up the pump output from 55% at idle to reach 100% by 4000rpm. Motec also looks at throttle position and also boost, ramping up the output of the pump with increasing boost reaching 100% output by 0.4 bar. We may fine tune it further by tying it to air mass when we have more time. That's it in a nutshell.

 

Did something similar with a Supra running dual 255lph pumps and a stock return. All was fine when first installed but within a month I had all sorts of idle issues and the car ran rich. Long story short, the pumps broke in and were overwhelming the stock return line at idle. Staging the pumps solved it! I'm hoping my new fuel system won't have issues, my ecu can now apparently pickup fuel temp from the E85 sensor so I have hopes of being able to monitor for an issue at least.

Sean at SRM has a control board he's designed for PWM pumps, it might work with Walbro. I've heard of several Walbro pumps working fine from PWM input but I'm not sure which ones. Interfacing PWM with a stock ecu is an issue, Sean's board can do it and is programmed standalone so if a pump can be identified and IF he's willing to sell boards that could be a solution.

 

I checked with Ti Automotive (manufacturer of the 450, they are no longer Walbro) and the tech guys assured me that the pump is designed for PWM. I would imagine all the newer generation pumps are but would recommend checking with the respective manufacturer.

Staging pumps works but ideally you wanna be able to smoothly ramp up the output of the pumps as opposed to simply turning it ON/OFF.

In my case we are not interfacing the fuel controller with the ECU but rather with the Motec dash which gets all of its data directly from CAN bus and other external sensors.

 

Got it John! Thanks for the clarification!!!

 

good finds John, i had a similar situation replacing and fixing the fuel system on my turbo dune buggy with standalone, suddenly had so much fuel pressure it would kill the motor from being so rich.

 

The problem is that hardly anyone that puts aftermarket fuel stuff on these cars really researches the effects that big pumps and lines have on operation where the demand for fuel is low, i.e. idle or low power mid throttle operations. Who actively logs and looks at fuel pressures during the course of aftermarket system fuel development and installation?? My guess is no one as pretty everyone is concerned with feeding their engine with a garden hose hose designed to provide the fuel requirements for 1500+ hp, but what happens when you only need a small fraction of that? That's never really addressed or though of. After all, for street driven cars, 95%+ of your engine operation is conducted at low power settings while cruising or sitting in traffic with only the occasional high power "pull".

I've driven a number of the 1000 hp monster cars and they all sucked at mid/part throttle. Granted, they were all Mafless but my bet is that they all had a huge surplus of fuel at low/part throttle which put it outside the envelope where the ECU could compensate thus making the mid range transition too rich. Nobody really tunes these cars for low/mid throttle operations. Cars are put on a dyno and all tuned at the top end where all the chest thumping happens. The more you stray from OEM stuff, the more carefully you have to look at the all around effects of your upgrades in the big scheme of things if you are concerned with OEM reliability and drivability.

The more we have researched this and looked at the effects of running just one large fuel pump, the more I'm convinced that to do this right you must have a way to control pump output in a linear fashion mirroring fuel demand, especially if you are running multiple large pumps. Then there is the factory fuel cooler no one really talks about. That in itself is a very restrictive item that should be removed to free up flow in high HP applications. Granted, it's on the return line but becomes a bottle neck if you don't have a way to reduce pump output at low power settings where fuel return is the greatest. If you remove the cooler however, you will make fuel overheating/boiling and vapor lock a real issue especially in warm climates. At high altitudes things become even worse as your boiling point is reduced. Been there, done that. All food for thought...