Lift Pumps: What are they doing, anyway?

dieseljunkie said:

...Recirprocating sounds to me it's a solenoid pump with no motor. Solenoid pumps are puny pumps in general, pressure wise. The 6 to 8 psi spec is met only when deadheaded. Furthermore, the FRB-11 is pumping into the inlet of the VE pump which is under vacuum because of its internal transfer pump. This vacuum subtracts from the pressure generated by the FRB-11, that is why you are not seeing 6-8 psi. If you want to maintain a certain fuel pressure, you need a positive displacement pump with a fuel pressure regulator (to protect the VE pump).

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I would have to say this summarizes my experience w/my puny Facet lift pump. I don't think it stands a chance of keeping up w/the demands of the low pressure side of my IP. To keep positive pressure on the IP inlet under all conditions, I suspect it takes one heck of a pump. One would have to balance that with the reports here of significant high-RPM gains after adding the PD lift pump. By way of comparison, does anyone have the specs for the OEM PD pump? Is it much greater than the Walbro, or even the Facet pumps?

Knowing that the FRB-11 does nothing with top-end performance I want to install a pd lift pump.

Does anyone know if the FRB-11 would be a restriction in flow/pressure with a pd lift pump installed?

I like the function of the FRB-11 in priming/filling the fuel filter when changing the filter. And would like to leave it in place if it doesn't impede what the pd pump is doing.

Why not just let the in-tank PD lift pump (ITLP) do your priming? Whatever wires/relays are powering your FRB-11 will surely do the same for the ITLP. I have a bypass switch that allows me to energize my ITLP to either prime the fuel filter or, if I'm racing with Syndiesel or B100, pump the tank completely dry so I can ensure I fill up with 100% of my choice fuel with the precise amount I want. Yeah, it's a bit neurotic. But it works.

I have my FRB-11 still intact for the same reasons as roadlust. Makes priming when doing a fuel filter or any type of fuel related work.

Thanks Scott, really wasn't thinking on this one. Of course they do the same thing....Duh!

After briefly reading thru this thread, seems like the lift pump has no evidence of provding additional power.

Not true. I don't think anyone here has a direct before and after dyno with no other changes to the car, but Jeff Robertson has repeated said that with big fuel and an aggressive tune you can see where the IP cannot meet the ECU's fuel request at high revs. The pump helps the IP meet that fuel request and therefore can provide better top end power.

The pump in my Golf has a bypass. Next time I dyno it I'll do a pull with the pump unplugged so folks can see the difference.

Pcar993 said:

After briefly reading thru this thread, seems like the lift pump has no evidence of provding additional power.

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I am assuming you are referring to the Walbro lift pumps and not the PD lift pump.

The Walbro seems in my case to have made my fueling more stable at higher rpm's than without it. Whether or not it made any additional power, I do not think so. I have heard success stories though with the PD lift pump mod.

what happens if you hit the back side of a IP with ~43 PSI (3bar).

so if someone were to use a gas fuel pump (high volume, high pressure) Vs a low pressure high volume pump

keaton said:

what happens if you hit the back side of a IP with ~43 PSI (3bar).

so if someone were to use a gas fuel pump (high volume, high pressure) Vs a low pressure high volume pump

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on an ALH engine you will simply blow off all you fuel return lines. and make a big mess

btcost said:

on an ALH engine you will simply blow off all you fuel return lines. and make a big mess

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assuming you put the right clams on to keep the lines on, hard lines with steel braided NPT threaded lines, then what happens? damage to the ip? over fueling?

For my setup.....doing logs with Jeff(great guy) from Rocketchip he mentioned that a lift pump would help my low case pressure at high rpms(pump is rebuilt)

BUT a PD lift pump wouldn't fit in my B4.

If money were of no concern which inline lift pump would be best? The options for Cummins guys seem to have to much pressure for us. A pressure activated pump would be great; once it reads low pressure it would kick on.

Are you certain a PD lift pump won't fit? Check with IndigoBlueWagon on that since it seems he has one of each generation TDI at least. If the fuel senders for the A3 and B4 are the same, then it would seem it'll fit, abiet tight with the gasket. The fuel gauge will be off, though.

I have a lift pump in my A3. I believe mrchill swapped the fuel level indicator from the original sender to the lift pump. And Lug_Nut calibrated the gauge. You could probably do the same on a B4, but it would take some effort.

Id like to do this for track/autocross use myself soon.. I swear I could feel power loss in the upper rpms around some longer corners

Turbo is still doing good at 18 psi thanks IndigoBlueWagon

I've done a compromise with my cheapo walbro, after I saw how it ran better without it. With this compromise, I don't lose timing like I did with the walbro.

You make a fuel loop, but also have a limited return, as our cheap pumps can make pressure but not flow.
Fuel temps stay low even without the fuel cooler (my winter setup) because some fuel returns to the tank.
In from tank ----> to TEE -----> 1)to fuel filter 2) return line from IP
Use smaller tee to connect the injector line return and the small return line from IP (by banjo fitting) to a reducer that goes into the return to tank (or fuel filter port for return). So the fuel pump is basically flowing only the fuel returned to the tank which comes from the tiny lines- a restriction to keep pressure on the fuel pump.

has anyone tried a fuel pressure regulator on the return line between the IP and the fuel filter?.. or maybe on the return line after the filter?

maybe this would help the weaker lift pumps keep more consistent psi.. maybe?

Why would you need a FPR?

shwagondawheels said:

maybe this would help the weaker lift pumps keep more consistent psi.. maybe?

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maybe

shwagondawheels said:

has anyone tried a fuel pressure regulator on the return line between the IP and the fuel filter?.. or maybe on the return line after the filter?

maybe this would help the weaker lift pumps keep more consistent psi.. maybe?

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I don't think that would be a good idea because you don't want to restrict the return as it would be fighting against the IP's internal vane pump because it will restrict the flow through the vane pump at higher RPM. I would think that we don't want to restrict flow through the IP at all.

In my loop with limited return, yes a FPR may help, but I'm using a check valve on the return that requires some pressure to open, which regulates pressure to 1-2 PSI depending on viscosity of fuel.

Why did I do a partial return with a loop? My carter fuel pump can do 8 PSI but cannot flow enough to feed the vane pump at higher RPM (the pressure drops to a vacuum- like running without a lift pump). So with a limited return, the fuel pump can flow enough fuel, as most of the fuel exiting the IP is being fed back into the fuel filter. Even without the heat exchanger hooked up in the loop, the fuel filter doesn't get very hot, because some fresh fuel does come in (to replace the amount that leaves the limited return).

keaton said:

what happens if you hit the back side of a IP with ~43 PSI (3bar).

so if someone were to use a gas fuel pump (high volume, high pressure) Vs a low pressure high volume pump

Click to expand...

Necro-bump because I can't find an answer to this ^^

The only decent pumps I can find in the UK that will fit under my A6 Quattro are gas ones which will do 200+ lph but are intended to run at 3 bar in to EFI systems. i can't run a PD pump in the tank as it already has an internal pump to balance the sides of the tank and there is no more room.

Since the IP seems to offer little resistance to smaller pumps, I'm not entirely sure the pump I'm looking at will even make 40psi, especially since it has an 8mm return. I'm not too concerned about blowing lines off - they're all clamped down anyway, apart from the spill pipes.

Thoughts please?

You'd probably blow out the shaft seal.
There is an orifice in the 8mm return to allow it to hold 100psi case pressure(generated by the vane pump)

Thanks Jon. I had a look at the return union earlier and I see what you mean.

I'll have to run a regulator in line then I think.

too much pressure kills the shaft seal very quickly! 7-10psi is plenty!!

what are the pressures on a PD? do i even need to worry about under fueling issues.

I know i have a in tank lift pump ---> Filter --- tandem pump on the head --> injectors -- > fuel tank

Must subscribe to this. I just ordered the Facet FEP87SV lift pump and will be installing it hopefully next weekend.

Here is what I just installed. The tank and sending unit are out of a 97 Jetta TDI, in order to get my Passat cluster reading properly. The pump I used was a Facet FEP87SV. It is rated for 1-8 psi @ 45 gph. All lines are new 5/16 ID line.

Here are the readings I got with a vaccum/pressure gauge on the feed line, teed in before the 100 micron prefilter.

With pump off:
At idle - 1" vaccum
Full Throttle at about 3500 RPM - 10-12" vaccum

With pump on:
Key on, engine off - 4 psi
Engine idling - 3 psi
Full throttle about 3500 rpm - .5-1.5 psi

Edit: One piece of information that may be key. I have Bosio PP520 injector nozzles and a stage 3 malone tune for 18 psi of boost.

As far as power goes, I didn't necessarily notice any more power, but what I did notice is consistent with the timing logging somebody did a couple pages back. The power delivery feels smoother, and a bit more responsive.

I wired a relay to power the pump with a 12v ignition source and the relay is ground triggered by the oil pressure switch (on the filter housing) so the pump only runs when the engine is running. The relay is easily accessible so I can jump it out to bypass the oil pressure shutoff if I want.

One interesting thing I found was once the motor warms up to OT, the oil pressure switch (brand new) stops sending ground at idle due to lower oil pressure. This basically makes it so the fuel pump I installed only runs when the motor is above idle once its warm. At first I thought this was an issue, but it should work to my advantage because the pump will only be working when there is a demand for fuel. This should prolong pump life.

I have an oil temp and pressure gauge in the car, and once the oil temp gets to around 200 degrees, it runs about 5-10 psi at idle. I do not have an oil pressure light on on the dash(yes it works), so I figure its operating as it should.


Under hood pic of my new prefilter and new lines running from the filter to the IP.



Under car pic of lift pump. I made a bracket (hard to see in pic) that utilized the factory studs under the car that the CIS pump was mounted on. I also used the factory CIS pump wiring to get my +12v from the relay at the fuse box to the pump in the back.

Bassman, what are the ratings of the facet... particularly GPM?

Seeing it drop to 0.5-1.5 psi at 3500 makes me wonder... how is it at 4500 rpm?

If anything you can try a partial return like I have done in post 76:
http://forums.tdiclub.com/showpost.php?p=3767008&postcount=76

It's just the fuel that comes out of the small lines that goes back to the tank, and the big line from the IP recirculates to the input of the fuel filter.

My solenoid based (instead of louder vane based pumps) carter lift pump had a low gpm rating, dropping pressure at rpm. Instead of getting a PD lift pump or something else, I tried this and it fixed my timing issue at high rpm.

When I had a gauge to test, the pressure was the lowest at 5500 at 5 psi (the output of the carter is 7 psi).

Before then, I was pulling MORE vac at high rpm with the carter, than without, lol.

Just took it for a quick highway drive and it is running great. I tried to log with vagcom but my laptop died. :banghead:

Like I said, power delivery was much smoother and another thing I noticed was it can really dump some soot in high load and high rpm situations, a bit more than before. I am not home right now so I can't really type much, but when I get home I will respond more fully. The GPH rating is mentioned in the beginning of my post. 45 GPH.

Sent from my Bosch ECU via VAG COM

Thanks
Yeah I see now, the images made the page so wide that I couldn't see on my screen, lol.

If you log group 04, you can see timing req, timing actual, and n18 duty cycle. If they don't match and the n18 duty cycle is way high, that means the pump is either losing pressure, static timing too low, or the case relief valve might have a problem.

Also interested to see what you get at higher rpm. Even without load is a good test with the pressure/vac gauge because the IP vane pump flow is directly related to RPM, not fueling. Internal pressure is regulated by the case relief valve.