Lift Pumps: What are they doing, anyway?

Stealth TDI

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Hello,

Stealth TDI said:
I'm not sure if the drop in pressure is related to time under load or if it correlates to rpm. I need to do more testing.
The drop in pressure is definitely related to RPM. Flogging it in 5th, pressure held at about 4-5 psi all the way to 90-mph. The same run in 4th resulted in the pressure gradually dropping as RPMs increase. I've updated my report above to reflect this. My next move is to check for restrictions in the sender.

Scott
 

Stealth TDI

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Hello,

I have more questions to help me (and others?) understand the FRB pumps:

1) Do other diesels (Cummins, Duramax, PS) return fuel to the fuel tank the same way we do? Or do they use what's at the IP without circulating it back? The FRB is designed to provide positive pressure to an injection pump. BUT...

2) What is a "vapor return line" on a carbureted engine? I haven't had a carb in 15 years! The FRB literature states "the electric fuel pump will not perform satisfactorily if used on a vehicle with a vapor return line." WHY is that?

What I'm wondering is this: If the FRB cannot be used on an engine with a vapor return line because fuel would feed back to the tank, and the pump is actually designed to provide pressure to an injection pump that doesn't flow fuel back to the tank, then one can see why this pump (or just one) is not ideal for the TDI.

Please correct me if I'm wrong. It's just a thought that hit me as I was rereading the literature. I eagerly await some schooling! :)

Scott
 

dvst8r

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Stealth TDI said:
1) Do other diesels (Cummins, Duramax, PS) return fuel to the fuel tank the same way we do? Or do they use what's at the IP without circulating it back? The FRB is designed to provide positive pressure to an injection pump.
Scott
No it is done the same. The extra fuel is used for cooling the pump in all apps, then returns to the tank.
 

Curious Chris

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Stealth TDI said:
2) What is a "vapor return line" on a carbureted engine? I haven't had a carb in 15 years! The FRB literature states "the electric fuel pump will not perform satisfactorily if used on a vehicle with a vapor return line." WHY is that?

What I'm wondering is this: If the FRB cannot be used on an engine with a vapor return line because fuel would feed back to the tank, and the pump is actually designed to provide pressure to an injection pump that doesn't flow fuel back to the tank, then one can see why this pump (or just one) is not ideal for the TDI.

Scott
Flow and pressure are not the same thing for sure. If the engine has a carburetor than the fuel is fed into the bowl which has a float and stops the flow of fuel when it is full. I know as my first car was a 1968 Ford Custom with a 302-2 barrel carburetor; diaphragm fuel pump that would just keep on trying to pump even if there was no fuel flow.

So FRB is saying "oh we can flow 43gph" but they are not saying at what pressure! A complete pump specification is flow at pressure and often it is expressed as a flow vs lift height, or flow vs pressure.I would push Walbro for this information. The dead head pressure means nothing when it comes to actually running other than the maximum pressure.
 

D_Bat

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It's the same with turbos. Pressure does not = more air. Pressure and CFM are not totally separate but are anything but the same. I've never seen a flow chart for the FRB> :(
 

Whitbread

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This is the flowchart for the A1000 I'm using. Overkill, but courtesy of e bay, it was cheaper than an oe pd pump.



FWIW - I tried to install a frb-11 on a customer's car with disasterous results. We mounted exactly in line with instructions and once the vehicle got below 1/4 tank, it wouldn't hold prime anymore and would cause the car to die at idle. Cracking injector lines in the middle of an intersection is not cool....

Over 1/4 tank, if worked just as it should and held 4-5 psi at idle. Don't know if we got a bad unit or what, but we pulled it off and put in a oe pd pump. Couldn't take anymore reliability chances.
 
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Whitbread

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Gearhead51 said:
A1000 is a MONSTER. I have one in my toolbox. I need to put it on something. First I need to find a dyno. What kind of regulator are you using?
Yeah, it's definitely a monster. When someone would ride in my car the first time, usually they ask what's growling in my trunk when I first turn the key on haha. You can't hear it going down the road though.

I'm using a Mallory 4309 bypass regulator using both factory lines as returns. I ran a new feed line to the regulator.
 
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Honeydew

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Whitbread said:
FWIW - I tried to install a frb-11 on a customer's car with disasterous results. We mounted exactly in line with instructions and once the vehicle got below 1/4 tank, it wouldn't hold prime anymore and would cause the car to die at idle. Cracking injector lines in the middle of an intersection is not cool....

Over 1/4 tank, if worked just as it should and held 4-5 psi at idle. Don't know if we got a bad unit or what, but we pulled it off and put in a oe pd pump. Couldn't take anymore reliability chances.
Not questioning this, just providing another data point: we atypically ran the wagon down into the red on the fuel gauge a 2-3 weeks ago, at 30 mile/day intervals. No issues then with prime loss on the frb-11, but after reading this post I'll probably repeat that test when I'm using the car since reliability is a bigger concern now that its the wife's DD. I've done the fuel sender mod on this car and still think that could be an issue when running an aftermarket lift pump with the stock sender vs. pd pump which replaces stock sender. Or at least there could be some unknown issue at the stock sender.
 

Stealth TDI

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Hey,

Whitbread said:
When someone would ride in my car the first time, usually they ask what's growling in my trunk when I first turn the key on haha.
Yup. One FRB gave off an audible tapping. A pair of them makes quite the symphony of racket back there. It's barely noticable at highway speeds. But a tad annoying around town. But hearing them makes me FEEL like I'm in a faster car, right? ;)

Honeydew said:
I've done the fuel sender mod on this car and still think that could be an issue when running an aftermarket lift pump with the stock sender vs. pd pump which replaces stock sender.
I considered the fuel sender mod. My searching found a post in which Lug Nut stated the A3 sender does not have the "rollover ball." I'll still pull the sender and check for a restriction. I DO know there's a little check valve on one of the fuel lines. I don't remember if its the supply or the return. If it's the supply, I suppose it COULD be a restriction. But is it wise to remove the check valve? It would seem that would allow fuel to run back into the tank when the engine is off, right?

Later,

Scott
 
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Jasengine

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I drilled out the check valve in the fuel line as it IS a restriction and it is on the line to the engine. Removing the restriction does give a bit more top end if a lift pump is not installed already.
Fuel does not run back to the tank unless you remove the pipe from the filter.
 

Stealth TDI

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Good to know. I suppose I can test it both ways. The check valve to which I refer is actually a small, separate component. So I can always put it back if I don't like it. :)
 

IndigoBlueWagon

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btcost asked me if I'd done a before and after lift pump dyno, and in truth I can't remember. It's been in there for about 4 years. I would suggest that his car's dyno and the remarkably flat curve is testimony to the benefits of the pump, along with a great front mount intercooler.

Jeff maintains that in modded TDIs at high revs the ECU's fuel request cannot be met by the rotary pump. And I'm not sure my car would be able to pull well to 5500+ RPM without the additional fuel flow the lift pump provided. But I don't have dyno data. I could get it in the Golf once it's running again, as the pump has a bypass and I can simply unplug it for comparison.

My otherwise stock A3 has a lift pump. If it includes a bypass (I forget) I could run it with and without the pump at the NE Dyno day. That might make for some interesting data.
 

Stealth TDI

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Hello,

I installed a PD lift pump tonight. It DOES hold pressure better than the pair of FRBs. It acts similarly to "Fix Until Broke." Here's what it does:

Pump: PD Lift Pump
Pressure sampled between the fuel filter and the IP
Pre-start: 8-psi
Idle: 6-psi
Acceleration: 4-psi
WOT at 5000 rpm: 2-psi

The only thing I don't like about this pump is the fuel gauge reading. My tank likely has less than two gallons in it; but it reads just under 5/8 full. What I don't know is whether it will go to full (better) or drop to empty (like my last PD lift pump) when I fill it up. I'll find out tomorrow after I tighten down the pump. I can work with the sender arm if the gauge moves in the correct direction. But, if it works backwards like the last one, then I guess I'll have to live with the inaccuracy if I want the mod.

The thing I really like about this pump is sort of cool. Unlike my stock sender which is basically a screen-protected suction point right in the tank, the PD lift pump suction point is inside of a "jar" of sorts. Fuel gets in, but doesn't come out unless it's sucked out. Better yet, the fuel returned to the tank is also put into this "jar" so it is constantly overflowing, even when the fuel level is low. This will come in really handy during autocross events (and good for road racers, too) since my stock sender would suffer from fuel starvation any time I'm at a 1/4-tank or less. With the PD lift pump, it would seem like I could run with very little fuel and still not starve it through the turns. :cool:

Scott
 

IndigoBlueWagon

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Lug_Nut, when driving my A3 during his B4V swap, got my lift pump sender to read right. I think it was a laborious process, including draining the tank, adding fuel a gallon or two at a time, and adjusting the sender throughout the process. I can say that my gauge reads as it should.
 

Stealth TDI

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BTW,

IndigoBlueWagon said:
Lug_Nut, when driving my A3 during his B4V swap, got my lift pump sender to read right. I think it was a laborious process, including draining the tank, adding fuel a gallon or two at a time, and adjusting the sender throughout the process. I can say that my gauge reads as it should.
I learned MrChill is fairly certain he swapped out the resistor board in that sender to get the sweep direction correct. LugNut got the sweep amplitude correct. Since I've broken one of those boards before (they're brittle), I'm going to just get a potentiometer and adjust the SWEEP to be "accurate" but backwards. I can live with that, especially if I pull the fuel warning lamp. ;)

For others reading this, this is only an issue with the older cars. MKIV and later are good to the best of my knowledge.

OH - The intake OEM pump is MUCH quieter than the FRBs which were beneath the rear seat. All I hear is a little "whoosh" before I start. So far so good. :)

Later,

Scott
 

IndigoBlueWagon

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I think Chill misremembers. We did try swapping out a resistor board but were unsuccessful, and I think we finally swapped in another pump. But I could be mistaken. I had conveniently forgotten about a lot of that process.
 

LNXGUY

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Still racking my brain to see if there is a better option then the PD liftpump.

I think I might just have to bite the bullet and be a gineau pig myself, lol
 

Honeydew

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LNXGUY said:
Still racking my brain to see if there is a better option then the PD liftpump.

I think I might just have to bite the bullet and be a gineau pig myself, lol
Kennedy Diesel pumps maybe? Some people run them on the Liberty CRDs which use the same pressure as the TDI does.
 

LNXGUY

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Honeydew said:
Kennedy Diesel pumps maybe? Some people run them on the Liberty CRDs which use the same pressure as the TDI does.
Thanks, I'll look them up.

I'm also looking at the Facet Duralift pump... Looks like quite a few guys use them in marine applications along with the big diesel trucks.
 

Stealth TDI

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Bill,

Not sure how you think you'll be a gineau pig. The PD lift pump drops right into the A4 with no fuel gauge issues. Do the failsafe mod and you'll always make it home even if the pump fails. The only thing left from there is the wiring which you'd have to do with any lift pump. This is a tried and true upgrade to the A4.

Have Fun,

Scott
 

LNXGUY

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Hey Scott,

I know the PD liftpump works just fine, I just have a hard time swallowing the $200+ pricetag.

Looking for other alternatives besides the OEM one :)
 

dieseljunkie

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Stealth TDI said:
My recent dyno testing showed just 2-hp difference with the FRB-11. It appears that's because there's no pressure at higher RPMs. But a lift pump that can actually pressurize the feed at all RPMs... ???
I looked up the specs for the Walbro FRB-11:

FRB-11 Reciprocating Fuel Pump

Performance
Voltage: 12 Volt (9.0 min – 16.0 vdc max)
Minimum Flow Rate: 162 liters per hour (43 gph)
Deadhead Pressure: 42 to 56 kPa (6.0 to 8.0 psi)
Maximum Current Draw: 2.3 amps
Life: >18,000 hours
Dry Lift: 48 inches (120 with optional outlet check valve)
Compatible Fuels: No-lead regular gasoline, premium gasoline, gasoline-alcohol blends, diesel and biodiesel fuels (20% and 100%), and E85
Corrosion Resistance: 96 hour salt spray test (ASTM B-117)
Operating Temperature Range: -40ºF to 155ºF (-40ºC to 68.3ºC)


Electrical
Reverse Voltage Protected
Transient Voltage Protection
Ground: Neutral Ground: Circuit Boardis Not Internally Grounded to Pump Body
Electrical Connection: Flying lead (1); No connector
Fuse: 5 amp recommended


Mechanical
Inlet & Outlet Size: 1/4-18 NPSF
Inlet Filter Screen: 70 micron
Magnetic Trap: Yes
Outlet Check Valve: None

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).
 

SheeB

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I noticed not long after installing the Walbro that my injection pump is leaking in the upper and lower seals. Could this be the culprit of the Walbro?
 

The Shootist

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The case pressure spec on a rotary pump is around 100psi. I doubt that an electric pump is going to be much of a problem pressure wise.
 

diesel-dave

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IndigoBlueWagon said:
Lug_Nut, when driving my A3 during his B4V swap, got my lift pump sender to read right. I think it was a laborious process, including draining the tank, adding fuel a gallon or two at a time, and adjusting the sender throughout the process. I can say that my gauge reads as it should.

wow, what a pain!!

planning on swapping my lift pump and tdi parts wiring kit from my wrecked sedan to my wagon, cant wait!:rolleyes:
 

Whitbread

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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).
Yup, a positive displacement pump is the only thing that will keep up with a ve pump's volume at full song and maintain positive inlet pressure. Even my A1000 will drop a few psi at 4+K. And that's silly overkill of a lift pump.
 

SheeB

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The Shootist said:
The case pressure spec on a rotary pump is around 100psi. I doubt that an electric pump is going to be much of a problem pressure wise.
Ok. Can't blame this repair on a mod :p
 
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