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TDI Power Enhancements Discussions about increasing the power of your TDI engine. i.e. chips, injectors, powerboxes, clutches, etc. Handling, suspensions, wheels, type discussion should be put into the "Upgrades (non TDI Engine related)" forum. Non TDI vehicle related postings will be moved or removed. Please note the Performance Disclaimer.

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Old February 2nd, 2018, 04:20   #1
martin33100
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Default Tandem Pump pressure under load?

Hi guys, just wondered what kind of pressure a PD tandem pump should deliver under load, I have read somewhere it's around 7.5bar at 2000rpm.
I had my T5 2.5 dyno'd a week ago as I had fitted a new ex manifold and now the AFR is very lean.
At full load and higher RPM the fuel pressure drops to around 4bar but I never looked at it in detail when the AFR was fine so I don't know if this is low or not?.
One of my digital gauges picks up tandem pump fuel pressure but I may double check it with a gauge.
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Old February 2nd, 2018, 08:48   #2
[486]
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How is inlet pressure to the tandem pump? If it is going into vacuum you can't rightly blame the tandem pump itself. Might be time for a bigger in tank pump, filter and lines.

it should be around/above 100 psi rail pressure, yes. Otherwise you don't get good element filling and it stops making power.
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Old February 2nd, 2018, 23:13   #3
martin33100
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Quote:
Originally Posted by [486] View Post
How is inlet pressure to the tandem pump? If it is going into vacuum you can't rightly blame the tandem pump itself. Might be time for a bigger in tank pump, filter and lines.

it should be around/above 100 psi rail pressure, yes. Otherwise you don't get good element filling and it stops making power.
I will disconnect the tandem pump feed hose and force on the in tank lift pump via vagcom and measure what's comeing out.
I am guessing it should hold this pressure when under full load?, it holds 100psi when reved and when driving normally but it drops off when you are on full load.
I am going to put on a oil filled gauge to monitor the pressure, currently using one of the digital gauges on my dash but even though there is a snubber valve fitted the fuel pressure still changes very quickly.

Last edited by martin33100; February 2nd, 2018 at 23:15.
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Old February 3rd, 2018, 00:11   #4
Festa
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Quote:
Originally Posted by [486] View Post
Might be time for a bigger in tank pump, filter and lines.
What would you suggest? any recommendations?

The problem with this 5 pot engine is the restrictive nature of the port so they don't flow well It's also a fact that the single fitting of the injector to the head is a weak spot as the injector rocks in it's bore and so suffers from fuel in oil.
Have you sent away another oil sample for testing before looking else where Martin?
I know you have another tandum pump that you could try
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Old February 3rd, 2018, 02:24   #5
martin33100
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Originally Posted by Festa View Post
What would you suggest? any recommendations?

The problem with this 5 pot engine is the restrictive nature of the port so they don't flow well It's also a fact that the single fitting of the injector to the head is a weak spot as the injector rocks in it's bore and so suffers from fuel in oil.
Have you sent away another oil sample for testing before looking else where Martin?
I know you have another tandum pump that you could try
Yes I do have my original tandem pump but the current one that is fitted is the one I got from you.
The OE VW one is LUK but you can buy the Pierburg ones for around 270.
The fuel pressure under load may have always been slightly low but I honestly can't rember what it was, I only started looking at it recently after my van was dyno'd and had a very lean AFR, the only part that has been changed is a new ex manifold made of slightly thicker material.
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Old February 3rd, 2018, 09:23   #6
[486]
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Quote:
Originally Posted by Festa View Post
What would you suggest? any recommendations?
I'm talking out my ass, captain. Never worked on any PD motor.
Just trying to help along the diagnostic process, as the guy with his hands on the car's really the only one that can find his own issues.

I'd ditch the tandem pump and run an EFI pump in the tank from a gas motor golf/jetta run into a bosch 044 to bump the pressure up, like fords used to do.
External pressure regulator holding 100-150 psi in the rail, if one isn't already integrated into the return.
but that's my woefully uneducated solution to a problem he may well not even be having
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Old February 3rd, 2018, 11:26   #7
martin33100
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Quote:
Originally Posted by [486] View Post
I'm talking out my ass, captain. Never worked on any PD motor.
Just trying to help along the diagnostic process, as the guy with his hands on the car's really the only one that can find his own issues.
I'd ditch the tandem pump and run an EFI pump in the tank from a gas motor golf/jetta run into a bosch 044 to bump the pressure up, like fords used to do.
External pressure regulator holding 100-150 psi in the rail, if one isn't already integrated into the return.
but that's my woefully uneducated solution to a problem he may well not even be having
I ran a Bosch 044 on my Westfield track car but the fuel pressure was only 4bar, also a tandem pump is required to run the vacuum system for the brake servo and turbo boost control.
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Old February 3rd, 2018, 12:11   #8
martin33100
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Did a little video of the fuel pressure dropping when on full load.
https://m.youtube.com/watch?v=DBONOzso09Y
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Old February 3rd, 2018, 23:53   #9
[486]
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Quote:
Originally Posted by martin33100 View Post
I ran a Bosch 044 on my Westfield track car but the fuel pressure was only 4bar, also a tandem pump is required to run the vacuum system for the brake servo and turbo boost control.
My thought is feed the 044 with another pump in the tank.

All the 044 sees is inlet and outlet pressure, no atmospheric reference, so it's gotta just add that 4 bar or thereabouts atop what you feed it.
Electric vacuum pumps are easy to find in the junkyard. Heck, some mk4's even came with them mounted down by the steering rack.
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Old February 5th, 2018, 01:02   #10
Rub87
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sure but they are not meant for 100% duty cycle.
__________________
'99 Black Ibiza GT90: 2260v, ARL bottomend, rosten rods 81mm slugs, 17:1 CR, 35/38mm exh/in valves, 02M, 305mm discs with Brembo calipers, OZ Superturismo 16"x7.5J, .............
Dyno'd area, Old VNT20 setup dyno'd 192whp
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Old February 5th, 2018, 05:51   #11
martin33100
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If the fuel system is working correctly then the Tandem pump should have no issues in supplying a good fuel pressure under load.
When my van was first mapped 15 months ago by Bobby the AFR was spot on, now it is very lean and all I have changed is my exhaust manifold for one made of thicker material but the ID may have gone up by 1mm.
I am sure my van held better fuel pressure under load before but I can't be sure what it was.
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Old February 5th, 2018, 13:25   #12
Festa
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Quote:
Originally Posted by martin33100 View Post
If the fuel system is working correctly then the Tandem pump should have no issues in supplying a good fuel pressure under load.
When my van was first mapped 15 months ago by Bobby the AFR was spot on, now it is very lean and all I have changed is my exhaust manifold for one made of thicker material but the ID may have gone up by 1mm.
I am sure my van held better fuel pressure under load before but I can't be sure what it was.
When was the last time you changed the filter? the fuel isn't as good as it used to be it could just be blocking up and restricting flow
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Old February 5th, 2018, 17:29   #13
martin33100
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Quote:
Originally Posted by Festa View Post
When was the last time you changed the filter? the fuel isn't as good as it used to be it could just be blocking up and restricting flow
The fuel filter was changed Jan 2017, I will check the flow over the next few days.
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Old February 5th, 2018, 18:38   #14
[486]
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Quote:
Originally Posted by martin33100 View Post
If the fuel system is working correctly then the Tandem pump should have no issues in supplying a good fuel pressure under load.
When my van was first mapped 15 months ago by Bobby the AFR was spot on, now it is very lean and all I have changed is my exhaust manifold for one made of thicker material but the ID may have gone up by 1mm.
I am sure my van held better fuel pressure under load before but I can't be sure what it was.
there you go, as said, you're the only one that can do the diag

stick a pressure gauge on the tandem pump inlet
go for a rip
no inlet pressure when loaded means supply issue (filter, the inlet sock in the tank, lift pump, gelled fuel, etc...)
small pressure drop when loaded means issue is elsewhere
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Old February 8th, 2018, 04:21   #15
martin33100
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I have done a quick flow test before and after the filter and it looks like the filter could be causing the issue, the filter was replaced 13 or 14 months ago.

After filter:-
https://m.youtube.com/watch?v=

Before filter:-
https://m.youtube.com/watch?v=HWoSL6T7KqE
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