Lift Pumps: What are they doing, anyway?

Stealth TDI

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2017 GTI APR Stage 3 (395 hp/376 lb-ft)
Hello,

Some of you may have read my "Dyno Letdown" topic in which I questioned the operation of my Walbro FRB-11. My troubleshooting compelled me to install a fuel pressure gauge so I could see what the pump was actually doing. It is specified to flow 43-gph at 6-8 psi. After installing the fuel pressure gauge, I learned the pump was pressurizing the fuel line to 6 psi when I first turn on the key (N109 cycle). Once the car is started, pressure hangs out around 3 psi at idle. It's about 2 psi at 50 mph cruise and 1 psi at 80 mph. It drops to ZERO under anything more than casual acceleration. I thought it was safe to say the pump was not delivering enough fuel to keep the feed pressurized under all conditions.

Tonight, I installed a brand new FRB-5. It's specified to flow 45-gph at 8-11 psi. They seem to be a popular upgrade (add-on?) for the Duramax folks. I got everything installed and hooked up. When the key is turned, the pressure jumps to about 5-psi and slowly climbs to 7-psi. Pressure drops to 3-psi at idle. In short, the pump behaves quite similarly to the FRB-11. The good news is my FRB-11 is fine. The bad news is either these pumps don't do what they're supposed to or I don't understand the external influences on these pumps (likely the latter).

I've been told, "get a PD lift pump," "get a Carter," "your pump is bad..." I suspect the majority of us read the specs of a given pump and accept that is what the pump is doing. But I'd like to request something a bit more scientific:

I'd like the input of those who actually have a fuel pressure gauge installed. Please post what lift pump you use, where your pressure is sampled, and what your pressure is just prior to start-up, at idle, and under acceleration. Perhaps a format like my example here:

Pump: FRB-5
Pressure sampled between the fuel filter and the IP
Pre-start: 6-psi
Idle: 3-psi
Acceleration: 0-psi (unknown if this is "zero" or vacuum since there is a mechanical stop... but IP timing is fine)

I don't mind a few theories of how pumps work and why my pressure reads what it reads. But please don't jump to the conclusion that I have the "wrong pump" or another "bad one" off the shelf unless you have a lift pump which maintains its specified pressure under all conditions and you have a fuel pressure gauge installed to prove it (meaning you understand how lift pumps behave in our application with fuel returning to the tank).

While I understand my topic is diagnostic in nature, I opted to post it in the Power Enhancements section due to the fact lift pumps are a popular power enhancement and my goal is to learn what the lift pump is actually doing (is it really providing "pressure" to the IP, or just ensuring there's not vacuum?). Others stand to learn something as well since I'm sure the vast majority of drivers do not have a fuel pressure gauge installed. Of course, moderators are welcome to move this at their discretion.

Thanks,

Scott
 

Whitbread

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Woops, looks like i'm a minute too late. I just posted in your other thread haha. But anyway,

Pump: Aeromotive A1000 and Mallory 4309 bypass regulator
Pressure sampled between the fuel filter and the IP
Pre-start: 24psi
Idle: 24psi
Acceleration: WOT@5.5K 12-13psi.
 

Fix_Until_Broke

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I've got a PD in-tank lift pump, cat 2u filter and 11mm IP.

I can hook up my pressure sensors and take data similar to my EMP/IMP measurements while taking a VagLog of Channel 1 (RPM, IQ, Collar Position and Coolant Temp).

Then we can compare fuel pressue and delivery vs RPM or whatever else you want me to measure.

Actually on the quick and dirty - I've got a 30"Hg-15psi analog gauge that I could hook up and just visually see what happens when driving around. What's another gauge on the dash - I've already got 4 extra ones :)

If someone can point me to where I can measure the case pressure I can record that as well (runs at ~80 psi I think right?)

To dig into the theory a little bit (until I can take some data).

The pumps you're using flow 45 gallons/hour or ~0.75 gallons/minute. The vane pump in the injection pump is a fixed positive displacement pump so for an easy test, we can remove the return line from the IP and run it into a bucket and measure the volume that comes out at idle (~903 RPM) for a 20/30/60 second time period and calculate the flow rate.

I did this once when I first bought my car (don't even remember why) and I seem to recall that I got ~1/2 gallon/minute at idle but can't be sure of that.

Anyway, being that it's a fixed positive displacement pump, we should get double the flow at 1806 RPM, triple the flow at 2709 RPM, etc. With this information we should be able to then at least get in the ballpark selecting a lift pump on specifications (I suspect that 45 gallons/hour is not enough).

The other thing is that the timing piston can consume/expel siginificant ammounts of fuel in very short times if there's very quick timing changes. This could cause momentary dips/rises in fuel pressure as the piston extends/retracts to adjust the timing. Not too big of a deal if there's sufficient supply pressure there to feed it, but something to think about (secondary)
 

Fix_Until_Broke

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Had a moment of motivation and went and spliced in my -30"Hg to +30 PSI gauge in between my fuel filter and injection pump and went for a trip around my "off road" course.

Key on engine off: 7 psi
Key on engine running at idle: 7 psi
Neutral rev to 5000 RPM: 6 psi
Normal driving around 25-40 MPH at all kinds of throttle positions and RPM's: 5-7 PSI
Full throttle 5500 RPM 3rd gear pull: 3-4 psi minimum at high RPM: ~5 psi typical
3000 RPM overrun (foot off of throttle) turn key off - goes from 7 psi to ~10inHg

I made a Channel 4 Timing log last week (RC5 ALH) and it holds pretty well
[/IMG]

Apparently the PD lift pump keeps up pretty well?

Let me know if you still want Vag logs vs case or inlet pressure.

Hope this helps you out.
 

oldpoopie

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SERIOUSLY THE MOST INTERESTING THREAD IN MONTHS!!!!!!!!!!!!!!
BRAVO!!!!!!!!!!!

If I have some time this weekend I'll hook up a gauge as well.
 

D_Bat

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I haven't installed my FRB-11 yet but it did say that it had to be oriented a certain way and that it couldn't be turned a certain way. I forget but it was on the install instructions that came with it. Just something I'd like to quickly mention.
 

Jasengine

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Yes your correct on that, it has to be installed vertically.

I have the FRB-11, which I installed as I have fuel stavation when pulling hard in 4th or 5th gear. Once I installed this, the 'surging' had almost disapeared. I took logs before and after lift pump install so I will post them up later.
 

Gearhead51

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I know there was debate on some IDI forums to a lift pump's abilities to skew timing. The timing actuator in those is pressure based. I guess this is not an issue on the TDI pump, though. I know the fuel return line is a busy place to be at high RPMs, so you'd have to have a heck of a pump to keep pressure on the inlet in these circumstances.

I measured case pressure on my IDI once by putting a gauge in a standoff between the return port in the pump and the banjo fitting. The return port on IDIs had a restriction orifice in the bolt.
 

MethylEster

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I'm still waiting for dyno numbers with and without the lift pump to see what, if any, additional performance you get. Unless I've missed something recently nobody has yet to do that. Again I don't want subjective seat of the pants feelings. I am looking for hard facts.
 

Stealth TDI

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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... ???
 

Jasengine

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Here are my results for the timing before and after lift pump install:



 

dvst8r

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Airdrie, AB
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'03 Wagon
Old setup.

Small Holley Red 67gph
KOEO: Never really paid attention
Idle: 7psi
WOT: under load 4-5psi.

New setup:
Bosch044: -6an feed on an areomotive bypass after CAT filter, -8an after the bypass (helps dampen pump pulses)
Idle: 25psi
WOT: Under load 24-25psi

I am quite certain that I could push this setup to 60psi+, but I know what happens at that point, and I don't feel like getting this pump machined for the retaining ring yet, as it is just a daily driver, nothing fancy.
 
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shizzler

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Good thread Scott.

I too would like to see a before/after dyno. But there are several documented instances like the one above where injection timing better matches requested after installation of a lift pump. I wonder if actual timing slipping from requested as an indicator of fuel starvation also implies that actual vs. requested injection quantity would suffer too? Has anyone logged that data?

This thread is quite timely as I was thinking about purchasing a walbro or carter pump, but then went with a PD in-tank pump when Aaron ran his killer October special. Hopefully it'll keep my "light haze" from disappearing over 3500 rpm....
 

hatemi

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Audi A6 4F 3.0TDI
Nothing real info about the benefits but a plot of how mine behave with Facet crappy ass lift pump and tapped relief valve on the pump. It was running some serious case preasure I found out just recently but it was working better than any pump I know of. At idle and low load and RPM it was above requested but at high it followed it pretty well.

 

Stealth TDI

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2017 GTI APR Stage 3 (395 hp/376 lb-ft)
Does anyone else have a fuel pressure gauge installed who can provide data? I'm interested in seeing more FRB and PD lift pump comparisons.
 

hatemi

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Mate did the measurements since he has the pump in his twin turbo quattro now. So I'm not 100% sure if I remember the numbers right but it was something like 7bar at idle and over 11bar at 2000rpm.
 

Lord_Verminaard

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Columbus, OH
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2005 NB TDI
I wish I had a fuel pressure gauge to test the pump on my wife's IDI. I know it took no time at all to fill the (dry) fuel filter and the pump. Upon initial start of the engine, it was a very short time of cranking to get the air out of the lines.

It's an Airtex E8012S, specified 5-9 psi at 30 GPH.





If I find a cheap fuel pressure gauge somewhere, I'll get it just to see what it's doing, sorry I don't have any actual numbers for you.

Brendan
 

Stealth TDI

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2017 GTI APR Stage 3 (395 hp/376 lb-ft)
Questions:

1) What are the flow characteristics of the PD lift pump that would allow it to maintain pressure at WOT where a 45-gph Walbro pump cannot? Is it possible the fuel return port has a built-in restriction to let pressure stay up?

2) Someone in my other topic is advocating the capping of the fuel return line. I imagine the reason the Walbro's are not maintaining pressure is because fuel is being returned to the tank as fast as the pump can deliver it. The user advocates a path which fuel goes from the tank to the filter to the cooler to the IP. The return line from the IP is tee'd to just before the filter (which is pressurized). Capping the return would certainly allow pressure to build. But is it a good thing?

3) In addition to wondering if the PD lift pump may have a restriction, it dawned on me that I didn't consider the possibility that those who posted numbers MAY still have the factory fuel filter tee. The tee COULD provide just enough restriction to allow pressure to build on the IP side, no? Can you please comment on the presence of your tees? I do not have a tee.

Thanks,

Scott
 

dvst8r

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hatemi said:
Mate did the measurements since he has the pump in his twin turbo quattro now. So I'm not 100% sure if I remember the numbers right but it was something like 7bar at idle and over 11bar at 2000rpm.
Sounds about the same as I found. I think we were a little lower at idle about 80-90psi, and were about 150-160psi wot. We could influence that with input pressure, to a point, the pump guys could change it drastically with playing with something inside.

When we were screwing around, we tried about 70psi inlet pressure, and some internal pump tweaks (sorry I'm not really a pump guy so I couldn't tell you what they played with) and we saw over 350psi!!! :eek: Needless to say I shut it down right away.

Scott capping the return would be a bad idea. I have a feeling the same thing as the above scenario would happen. If you do decide to try this please use a case pressure gauge and let us know, the results.

The pd lift pump may very well have been a restriction. You should try running them both. Just for information sake.

I can't say anything about the T, as my fuel system is all new line now.
 

Fix_Until_Broke

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Stealth TDI said:
Questions:

1) What are the flow characteristics of the PD lift pump that would allow it to maintain pressure at WOT where a 45-gph Walbro pump cannot? Is it possible the fuel return port has a built-in restriction to let pressure stay up?

2) Someone in my other topic is advocating the capping of the fuel return line. I imagine the reason the Walbro's are not maintaining pressure is because fuel is being returned to the tank as fast as the pump can deliver it. The user advocates a path which fuel goes from the tank to the filter to the cooler to the IP. The return line from the IP is tee'd to just before the filter (which is pressurized). Capping the return would certainly allow pressure to build. But is it a good thing?

3) In addition to wondering if the PD lift pump may have a restriction, it dawned on me that I didn't consider the possibility that those who posted numbers MAY still have the factory fuel filter tee. The tee COULD provide just enough restriction to allow pressure to build on the IP side, no? Can you please comment on the presence of your tees? I do not have a tee.

Thanks,

Scott
1) I'll check this tomorrow - I'm not running the fuel through the thermostatic tee - just straight back to the tank so it'll be really easy to check.

2) This idea is probably best for fuel filtration since 99% of the fuel goes around again to get filtered and only 1% of the fuel in the filtration loop is new from the tank. For the same reasons, I think a cooler would be required in this loop else the fuel will get very hot. From a performance standpoint I'm not sure, from a longevity standpoint it would put extra stress on the external seals of the injection pump - may or may not be a real problem. We've got enough people making up solutions to made up problems...:rolleyes:.

3) No thermostatic tee for me.

To continue the thought train here - the OEM fuel system with a thermostatic tee behaves (I would think?) just like the proposed system in #2 when the fuel is "cold" It has to if it actually recirculates fuel right? I would think that this would validate that it's "OK" to do this sometimes, but not sure of the long term effects of it or the benefit of running a system this way. I guess it may allow a wider variety of lift pumps to be used - but requires the use of a fuel cooler.

????
 

Stealth TDI

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2017 GTI APR Stage 3 (395 hp/376 lb-ft)
Hello,

Jasengine said:
Yes your correct on that, it has to be installed vertically. I have the FRB-11, which I installed as I have fuel stavation when pulling hard in 4th or 5th gear.
I forgot to address this. The directions state to mount as close to the tank as possible and to mount it with the output pointed upward. Accomplishing BOTH of these feats is not easy in the MKIII (the pump becomes a low point under the car). A small consensus in the FRB-11 thread seemed to think orientation wasn't as important as "close to the tank."

I'll not make a total repost of what I just typed in my "Dyno Letdown" topic. So I'll cut to the chase and share that I took the first FRB (which I thought was bad) and put it in tandem with my second FRB. I have pressure NOW! :D

In short:

Pump: FRB-5 and FRB-11 in tandem
Pressure sampled between the fuel filter and the IP
Pre-start: 12-psi
Idle: 7-psi
Acceleration: Starts at 7-psi and slowly decreases to 0-psi at 4500 rpm.

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. I'm also going to check into any restrictions in the fuel sender.

Jasengine - Have you considered a fuel pressure gauge? I'd love to see what a properly installed FRB does in another car. But I don't think anyone has posted who has an FRB AND a fuel pressure gauge. :eek: For all, I like the Autometer electronic fuel gauge I purchased at egauges.com. Installation was a snap!

Take Care,

Scott
 
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Fix_Until_Broke

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Fix_Until_Broke said:
1) I'll check this tomorrow - I'm not running the fuel through the thermostatic tee - just straight back to the tank so it'll be really easy to check.........
Well - tomorrow came and went, but I was able to get some data today.

Basically no matter what I did I couldn't get more than 1.5 psi in the return line and that was 30F startup. Once warmed up I couldn't get more than 1.0 psi and typically it ran ~0.75 psi.

There must be a light check valve somewhere in the return line (I think Franko6 mentioned this a couple weeks ago) that modulates to maintiain a ~constant pressure. If the 1 psi at idle is caused by the diameter and length of the tubing back to the tank, then there should be much more than 1 psi at 5000 RPM and 5x the flow.

Scott - I like your idea of using both pumps since you already have them.

Looks like it works more/less the same as the PD in-tank one.

When you say tandem do you mean seires or parallel?
 

Stealth TDI

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FUB,

Fix_Until_Broke said:
Scott - I like your idea of using both pumps since you already have them. Looks like it works more/less the same as the PD in-tank one. When you say tandem do you mean seires or parallel?
Thanks! The pumps are in series. I didn't have the hardware to run them in parallel (proper "T" connection... although a "Y" could be better). I thought "compound turbos" and hoped one pump would increase the pressure of the first. I might have that wrong. But something appears to have worked since each pump flowed 3-psi at idle and now I have 7-psi. The two in parallel might have accomplished the same... maybe even run cooler?

I may test them in parallel in time. For now I'm just glad I can stay out of the garage for a while and drive. I'm heading to SC tomorrow for a few days.

Scott
 

Stealth TDI

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2017 GTI APR Stage 3 (395 hp/376 lb-ft)
BTW, here's a photo:



I'll eventually fix the mix of hose clamps and do a proper wiring job.
 

btcost

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I think that a few years ago IndigoBlueWagon (Peter Noble) did a before and after dyno on his OEM lift pump.

I believe that there was not any real increase in HP, just a slight shift in the curve.

For example: his car was making 148HP pre lift-pump, peak HP came at say 3200rpm and was gone before 4000.

then he dynoed with the pump and he made 149HP which again came on at 3200 but this time lasted until 4500.

I made these #'s up. . but that is the trend I recall seeing. It was a few years ago. . .
 

Jasengine

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Stealth TDI said:
Hello,


Jasengine - Have you considered a fuel pressure gauge? I'd love to see what a properly installed FRB does in another car. But I don't think anyone has posted who has an FRB AND a fuel pressure gauge. :eek: For all, I like the Autometer electronic fuel gauge I purchased at egauges.com. Installation was a snap!

Take Care,

Scott
I haven't thought of installing a pressure gauge really as the fuel starvation issue I had has gone since I installed the pump. I have also had a remap to take advantage of the extra fuel and it goes like a rocket! But I'm not pushing the rpm's over 4800, unlike you guys going over 5k. IMO I think that as long as the IP is not creating a vacuume in the line, there should be enough fuel. But then again the IP are not designed to run at these high speeds(?) has anyone solved this issue at high revs? Maybe I have missed something :confused:
 
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