Late Model Toyota Non Return Fuel Rails and Their Associated Pumps and Plumbing

[timbosaurus]

There are three common fuel systems used in the last 10 years.

Mechanical return:
This has an intank pump, line to the rail, regulator on the rail, and line back to tank.

Mechanical returnless:
This has an intank pump, regulator at the pump output, line to the rail and no line back to tank. The regulator is set to a constant pressure (like the returned system above), around 400kpa is common.

Electronic returnless:
Similar to above, but the pump is no longer constant DC, it is PWM controlled by the ECM from about 5V to 12V. The lower voltage uses less power (slightly better economy) and doesn't circulate the fuel as much. The ECU can also adjust FP to suit conditions (400kpa WOT, 300kpa cruise, etc) and give wider dynamic range of the injectors. The regulator after the pump is still there, but is set MUCH higher (600kpa) and used as a safety relief in case the pump goes flat-out more than anything else. The ECU cant drive a 10 Amp pump itself, and relays don't like long-term PWM, so there is usually a FET style driver near the pump.

These are all independant of the engine itself, so there's not reason why you can't swap them around.

If you don't want to transplant the whole 3S fuel pump/sendor assembly, just find out what FP it runs standard, and use an adjustable FPR and the returned system of a FWD 3S as Huy suggested.

Returnless systems suck for FI, because you need a MAP referenced FPR. I don't fancy running a vacuum line from my manifold all the way back to the FPR in the tank

[oldcorollas]

Timbo, is the fuel pressure a closed loop, with a pressure sensor? or the ECU just hopes the FP is still up to the job and that a certain PWM = certain pressure?

[Joshstix]

return systems have a fixed fuel pressure differential across the injectors.
for example. a diferential of 40psi means that the real fuel pressure minus the manifold pressure, is always 40psi. this makes it easier to work out fueling, and has the benefit of letting the pump work less for 95% of the time when you are not on throttle.
to maintain the pressure differential, the regulator needs to be MAP referenced.

This also makes it easier to have a nicely idling engine with decent sized injectors. At Idle there will be significant vacuum and if the fuel feed pressure is not reduced in that situation the injector will flow mroe fuel per unit of time meaning the pulse width would need to be very short. When the pressure is reduced by refferencing it from the manifold pressure we can have a longer injector pulse which really helps when you have big injectors that are getting down to having a pulse width very close to the injectors open time, ie we are barely driving it hard enough to ensure the injector actually opens.

However this is more just a bonus of the manifold refferenced design rather than being an original design aim.

[RA35GT]

Timbo, is the fuel pressure a closed loop, with a pressure sensor? or the ECU just hopes the FP is still up to the job and that a certain PWM = certain pressure?

(I think it would be more like, certain PWM on fuel pump and certain Inj Duty on injectors = certain pressure and assume there is actually fuel in the rail)

I have read of engines which incorporate a fuel pressure sensor in them. Probably the best way to go I would think.

[timbosaurus]

Timbo, is the fuel pressure a closed loop, with a pressure sensor? or the ECU just hopes the FP is still up to the job and that a certain PWM = certain pressure?

actually, both. But I'm not certain how much I'm really allowed to share here, so I'll be very general.

Calibratable map, essentially inj duty cycle vs PWM%, can be used as open loop. But this does not compensate for component wear, so you need a line pressure sensor as well for closed loop. You compare the actual line pressure to what you'd expect from the open loop table to generate a correction factor which you apply on top of the open loop table. This means you're sort of running open loop, but using a pressure sensor to correct. Added bonus is that when the correction value gets to high, the ECU can set a fault code for "about to fail fuel pump"

ELECTRONIC return-less has only really come in over the last few years - stringent emmision and diagnostic requirements, and tightarse customers wanting every last km out of there litre of fuel were the driving factors. So I wouldn't expect many pre-2004ish cars to use it.

[oldcorollas]

that sounds more sensible than trying to drive the pump harder and harder...

[timbosaurus]

Well, you essentially do drive it harder and harder as it wears out. But after a predefined correction level eg: 10% extra D/C, ECU goes "Fuel pump says nooooo... cough". And tells you to see a dealer

[Major Clod]

Might be chiming in a bit late, but I might as well share my experiences with the Altezza 3SGE Beams engine in my RA23.

The 3SGE rail has two bungs in the end, with a banjo at the top for the fuel entry. The bungs are an odd thread 12mm x 1.25. In the end I managed to get an AN type fitting that screwed in place of the bung, and then another fitting from the AN to a standard 5/16 barbed fitting. I'm sure you could re-tap etc, but I opted for the bolt up way.

I hooked up the Altezza fuel pump and got a pressure reading on a fuel gauge at the rail. With this returnless it's always a constant pressure, regardless of rev's. I believe its along the lines of 62psi for the Blacktop, as mentioned on Billzillas website.

I then hooked up my existing return fuel system from my RA23 with a Sard FPR sitting just after the rail. Turned on my pump and adjusted the FPR until the pressure matched the original pump. Don't hook the FPR up to vacuum and it should maintain this pressure.

So far so good, finally drove the car the other day and it pulls hard all the way to 8000rpm, so no issues. I don't believe the Altezza pump has any sort of special controlled flow, its just using a built in regulator.

Only thing I need to do is find a pump that can handle this, as my old crappy VL external seems to have spat the dummy just today. I can't imagine 62psi constant would have been any good for it anyway!

[oldeskewltoy]

If we can formulate coherent questions..... I have worked with a Walbro engineer in the past, and can email him questions.... but since our relationship is not a business one anymore, I'd like to be concise and coherent with the questions as to limit his time needed to find an answer.


Here is the flow chart for a GSS342