3rd Gen Fuel Filter and Low Pressure Pump System

Ok guys, so I'm looking for some information/validation on the 3rd gen Tacoma's Low Pressure fuel system. This is in part related to modifying the fuel system for a turbocharger, but may apply if anyone feels the need to replace the fuel filter with an external (like some have done with the 2nd gen).

This system is similar to the 2nd gen in some aspects but is different in a few key areas. First off, the 3rd Gen Tacoma has a "Returnless Fuel System". Meaning there is only 1 fuel line coming from the fuel tank. No return line at all. The single fuel line has a Tee shortly after it leaves the tank, but this is not for fuel return.

There are 2 fuel pumps in this truck as well. There is a Low Pressure pump in the tank, and there is a High Pressure pump in the engine bay. I'm only talking about the in-tank Low Pressure pump here.

The purpose of the Low Pressure pump is to feed fuel to the Port injectors as well as the high pressure pump (which feeds the direct injectors).

I was confused by the returnless system at first (or lack of a return line), but after looking at the diagrams below, it makes a little more sense. The Tee after the tank is where fuel diverts between the port injectors and the high pressure assembly.

According to Toyota, the returnless system is accomplished by integrating the fuel pump assembly, the fuel filter (the canister, not the sock), and fuel pressure regulator assembly. These are used to prevent temperature rise in the tank.

Fuel pressure regulators: again there are two. One is inside the high pressure pump up front (called a spill control valve). The other is inside the fuel tank. Now here is where this thread is going.

Picture 1 below is of the two valves inside the fuel pump assembly. One is labeled as the Fuel Pressure Regulator Assembly (Relief Valve) and the other as the Fuel Main Valve Assembly. These valves are integrated into the Fuel Filter Assembly inside the pump housing. Picture 2 below shows the Fuel Filter Assembly. To be clear, there is a sock on the bottom of the pump which purpose is to help with fuel pickup, and then there is a stupid media filter (which I don't know how to describe) inside the housing around the pump. That filter is known throughout other threads as being easy to clog and a pain to service. This filter is why 2nd gens put an external serviceable filter on their trucks.

Now I'm no engineer, but looking at this assembly it looks as though these two valves are pressure valves (spring activated) that are used to relieve pressure in the fuel system instead of allowing unneeded fuel to return. Because they are both after the filter and not inline, they act as relief valves. Pressure buildup equals heat, so by relieving pressure you prevent heat buildup.

That being said, it seems as though these two valves are detrimental in the operation of the returnless system.

So let's look at the external filter mod. Some of us turbocharging our 3rd gens want to remove this crap filter and go to an external filter. That would require removing the filter assembly and these two valves, but it doesn't seem prudent given the returnless setup. I've considered removing the media from the housing and putting the housing and valves back...but the housing is pretty permanently sealed.

Any ideas? Anyone removed these and not had any issues? Any engineers have a workaround?

 

@MESO ; @Torspd ; @Shellshock ; @TheTacoChrist ; @Speedwaytacotuesday

 

All fuel systems have FPRs. They are needed to raise the pressure of the system for it to work. You do not want to remove the FPRs. In fact, some mods on some vehicles require a higher pressure FPR, or a rising rate FPR.

Going external on the filter would be nice though.

 

So yes, this one has 2. The primary one is for the high pressure system up front. The ECM reads pressure to the high pressure pump (via the direct injector rail) and opens/closes the spill control valve to regulate high pressure.

The low pressure is different. The ECM reads low pressure on the port injector rail and sends a signal to the fuel control ECU (a little box on the frame near the tank) which then varies voltage to the low pressure pump to increase/decrease pressure. That being said, the FPR valve in the tank...it's not electronic. It's a spring driven valve that opens when it reaches a certain threshold. So it doesn't raise FPR, it limits it to prevent overpressure.

Low pressure FPR is controlled via the pump, not the valve.

 

Yes. The FPRs are mechanical. Some folks, when modding, will hammer a dent in the bottom of the FPR to raise the system pressure.

Also, I believe in typical LPFPs, there is another internal bypass at something like 5bar?

As OVT noted, like you said, our LPFPs have three different ECU controlled modes. Interestingly on Meso's install of the OVT pump, the three wire Stock connection was ganged together on the new two wire pump. I am assuming that he is also using OVT's new pump controller. The cost there is not for the causal mod and makes that leap to 8psi+ a very costly one.

For the Stock LPFP, I do not recall the three voltages delivered or if they were even noted. If two are lower than 13.7v, then the FPR is probably not operating until that final mode is triggered.


In the end, I suppose that I am saying that the system appears to work good enough for NA and may need help depending how deep folks go into FI. My PoS 1996 Dodge had a returnless system with an external filter. It had no issues over the short life of the vehicle (140k). So in my mind, going with an external filter would be a good idea, but I don't think messing with the FPRs would be advisable.

 

I'm guessing the reason OVT's fuel controller puts all 3 wires together is because instead of 3 different fixed signals, it's just variably raising and lowering voltage at a dynamic rate. With his kit you add a higher flow aftermarket pump and a far more dynamic fuel control. All just guessing since I don't know how he made it. His controller should have far more precise control. This will be hugely beneficial with a turbocharger. Tighter controlled AFRs and better fuel efficiency.

But again, FPR is accomplished via the pump. This valve I think should be more aptly called a Fuel Pressure Limiter. I think removing them would result in higher overall pressures and more work on the part of the pump to compensate.

According to Toyota the Fuel Pump assembly varies fuel pressure between 300 and 530 kPA (44-77 psi). So I'm thinking these valves keep the lines from being pushed over a threshold. Either they are a redundant safety feature, or they are necessary to ensure lines/fittings don't burst and tank temperature doesn't rise.

The question is, how do we remove the internal crap filter without upsetting the system. Adding an external without removing the internal would be pointless.

 

Well shit.. I pulled that whole apparatus out

 

Yes. I do believe that OVT nailed it and eliminated some big problems with his design. I am looking forward to more details about it, the TT system, and the rest of the 2.0 info. Just experiencing 2.0 and messing around a bit in vF, it is amazing how much OVT knows and can do.

Good info on the pressures. 3bar / 44psi is the typical fuel pressure for multi-port systems. 77psi (5bar) would be near the internal bypass of typical pumps.

Yes. You can control pressure with a pump where the injectors would regulate the flow, but with changing demand, esp with a sharp increase in demand, the lack of an FPR keeping the system at some min pressure, you will have a momentary extremely lean condition until the pressure rises. The inertia of the pump and fuel mass, however small, has a significant effect.

 

The FPRs are gone with OVT's kit?

 

I'm thinking there may be a way to add in some relief valves without using the originals. Figure out exactly what those two valves are doing, and find an equivalent to throw inline with some Tees.

So check this out, there are two inline check valves in that fuel filter assembly. These are likely keeping the lines pressurized. You can easily throw a 6AN inline check valve on the external filter. I already ordered one anticipating this.

These two regulator valves though, one looks like a filter bypass so the direct injection system's high pressure pump can still pull unfiltered fuel if necessary. The other is the Fuel Main Valve, which I'm thinking is what keeps the pressure in check overall since it vents before everything.

 

I took it upon myself to remove it..I thought it was a fuel filter. As of now, there are no instructions for OV tune's fuel pump install... I'm kinda winging it. No clue if removing it will cause any issues... guess we will find out because I already reinstalled it
maybe @OVTune can chime in with his experiences. I know fuel pumps for 3rd gens is uncharted territory.

 

I would say at a minimum throw a 1 way check valve in the system. That will help keep a minimum pressure to a point. It'll keep the system pressurized when the engine is off too. I got one of these:

https://www.deatschwerks.com/6-02-0723

I can put it right inline on the filter line. But like I said before, the filter needs to incorporate both lines to filter everything. So either move the filter to the single line side of the tee (not sure how to do that with the type of fitting on the tank), or you need to run each line through the external filter's 2 ports and add two check valves.

On the plus side, this is all for the Port injection system which is a supplemental to the direct injection system, so this may not be all that detrimental to port injection operation. I would be willing to bet the whole purpose of these valves is to enable the returnless system. So you may see increased temps in the tank or overall rampant pressure in the lines. Hard to say.

 

Ah!

Yes. For as much as we are Gen 2.5, there are some really significant differences.

I think that will certainly answer @JamesT 's questions.

I am looking forward to you TT experience. How much longer do you think until you're rolling?

 

The one thing with check valves is that they have to potential to reduce flow. This is why FPRs are on the return side of a typical fuel system. So, just be sure that the check valve can flow at the required rate in the noted pressure range.

 

It appears that the FMVA is for overpressure protection past check valve in the LP line, and FPRA is for pump overpressure protection. Without knowing what the lift points are I don’t see why you want to keep them in with a new pump thats rated higher than stock both in flow and pressure. The actual fuel pressure working in conjunction with the new pump pressure set point is the overpressure protection for both cases with the OV setup.

I wonder if the new pump has an internal relief valve? If it doesn’t, there’s probably a recommendation from them on what to use.

 

Valid point. I am going to look into that. That's why I went with a fuel type check valve versus a general one. Unfortunately there really isn't a return side in this system.

I agree with what those two valves are doing. With OV's controller it may be all ok, but then again I think they work less for the pump then they do for the function of allowing a returnless fuel system. So if you remove them altogether and don't have a return fuel line then you may be causing pressure problems with the entire system.

I don't think the new pump has an internal relief valve. It looks like the same design as the factory pump. 1 in, 1 out.

 

According to DW, the pump has a PRV (pressure release valve). It's an integrated safety that significantly decreases pump output on activation. It requires that working pressure is kept below that activation point.

Question is, will fuel control keep it below that activation point or does it need that valve. PRV is at 105 (LPH?) at 16 volts and 95 at 18 volts.

 

That’s what I just found as well, PRV lift @ 100 psi. With that, I would not keep either OEM PRVs in place and use an external fuel filter. Just like MESO did. A check valve isn’t necessary in my opinion, will only impede flow.

Edit: Looking back at OVs fuel pressure log, it stays well within the operating range. He should have incorporated some sort of high pressure scenario in the FP control logic though. He knows his stuff.

 

Yeah I actually just saw that the pump has an internal check valve so it should keep the lines pressurized itself.

 

I guess I'll be the guinea pig