Diesel purge 101

dj_efk

dj_efk

A2OC Donor
United-Kingdom
So this is the last job left to do on the list of items to improve Audrey’s fuel consumption. I’m borrowing the car for a long trip this Saturday and while I have it, I want to do a purge during the day.

According to THIS THREAD it’s well worth it, so for an ATL TDi90, can anyone show a picture of which hoses I should disconnect (I’m assuming the two metal ones at the front of the engine as shown in this pic?), which is the supply and which is the return - also which pipe I should put an in-line filter on - I assume the supply that’s drawing the cleaner into the pump?
1616519875186.png


Alternatively, as time on the day will be precious and I have bought 5l of Liqui Moly diesel purge, I COULD just run the fuel down to 0 miles on DIS (I understand from other threads on tank capacity that there would still be a couple of litres of fuel left at that point) then just chuck the whole 5 litres in the tank and drive it 50-60 miles on that, then fill up - I assume any gunge that the cleaner pulls out of the fue system would then be sent to the tank and eventually trapped by the fuel filter - thoughts?

@depronman I think I am correct in assuming you’re the authority here and would welcome your input / guidance - also that of anyone else with direct experience too.
 
Last edited:
Try here.

Diesel purge 101

So this is the last job left to do on the list of items to improve Audrey’s fuel consumption. I’m borrowing the car for a long trip this Saturday and while I have it, I want to do a purge during the day. According to THIS THREAD it’s well worth it, so for an ATL TDi90, can anyone show a picture...
www.a2oc.net

I have done this a few times with my 1.9 TDI on both a Skoda Fabia estate and Audi A6 & Audi A4 Avant.
The filter certainly changes colour by using the loop method.
I used Liquid Moly.
Ran smoother afterwards with slightly better fuel mpg. Fabia AVE 56 mpg throughout the year even at 100K+
 
Ok so this is what I do

Purchase a litre of purge
Run car down to low fuel warning then zero trip
Have a 5l can of diesel in the boot
Drive a further 80 miles, 59 miles or so the needle will be on empty and a further 39 miles because the tank is not empty when the gauge says it is
Engine hot
Then remove and plug both rubber pipes from the drivers side of the engine as they joint to the steel pipes that run across the front of the engine
Attach a length of clear plastic pipe 8mm bore to each steel pipe
One poses into the bottom of a litre container the other as a fuel filter as used on old petrol cars in the line then the other end goes into the top of the litre container
I can’t recall which line is in and out of the random pump but the in line goes to the bottom of the litre container
Empty the litre of purge into the container and start the car. Keep the revs high >3000 until the engine splutters as it hits the air in the pipe before it starts to use the purge
Run the engine at various revs for 1 min. Vary from Tick over in 500rpm increments to 3500
Repeat until ½ of the purge is used up
Remove the temp 1litre tank and connect tank feed and return pipes
Start engine and hold at >3000 until engine splutters as it hits the air and starts to run on diesel again
Allow to tick over and empty the remains of the purge into the fuel tank
If you have some extra ie the remaining 4 litres then add maybe a total of 1.5 litres of purge to the fuel tank
Take the car for a spirited drive. Exercise the entire Rev range over say 20 miles
This is now flushing the purge diesel mix around the tank, pipes, fuel cooler and tandem pump/ injectors
After the 20 miles change the fuel filter for a new one. You do have one of my machined ally drain screws don’t you!!!!
One changed start car and hold at >3000 revs until the engine as spluttered then take it for a drink to the shell station and fill up with premium diesel

Your now all set for the next 60000miles
Run good quality fuel and it should keep itself clean
The purge is great for removing the built up crude in the injectors
Running it on neat purge does a good job on the injectors and tandem pump and the lower but still strong concentration for the 20 miles hits the remainder of the fuel system
Once you fill up the purge is very diluted but is still there for a couple of tank fully and will work it’s magic
I found changing the filter was needed as the amount of crude the purge releases was blocking a filter which was only a few months old

I did drop the filter again after 3 months but is was spotless so refitted said filter
Come to think of it it’s on the service plan for this year to change it again though only done about 10k miles with lockdown

Cheers. Paul
Ps there was at least 5 litres in my tank when the gauge hit empty. Some 60 miles after the warning chimes so don’t be afraid to get the tank as empty as possible as the purge is then running at max concentration


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Stan H said:
Try here.

Diesel purge 101

So this is the last job left to do on the list of items to improve Audrey’s fuel consumption. I’m borrowing the car for a long trip this Saturday and while I have it, I want to do a purge during the day. According to THIS THREAD it’s well worth it, so for an ATL TDi90, can anyone show a picture...
www.a2oc.net

I have done this a few times with my 1.9 TDI on both a Skoda Fabia estate and Audi A6 & Audi A4 Avant.
The filter certainly changes colour by using the loop method.
I used Liquid Moly.
Ran smoother afterwards with slightly better fuel mpg. Fabia AVE 56 mpg throughout the year even at 100K+
Click to expand...
Yes I have a friend with an A4 1.9 PD (so essentially a very similar engine but in 4 cylinder guise) - he did it to his and was surprised by how much it improved his car all round, ran better (not that it ran badly previously) and used less fuel.

I’m hoping for the same results as him and you
.
 
depronman said:
Ok so this is what I do

Purchase a litre of purge
Run car down to low fuel warning then zero trip
Have a 5l can of diesel in the boot
Drive a further 80 miles, 59 miles or so the needle will be on empty and a further 39 miles because the tank is not empty when the gauge says it is
Engine hot
Then remove and plug both rubber pipes from the drivers side of the engine as they joint to the steel pipes that run across the front of the engine
Attach a length of clear plastic pipe 8mm bore to each steel pipe
One poses into the bottom of a litre container the other as a fuel filter as used on old petrol cars in the line then the other end goes into the top of the litre container
I can’t recall which line is in and out of the random pump but the in line goes to the bottom of the litre container
Empty the litre of purge into the container and start the car. Keep the revs high >3000 until the engine splutters as it hits the air in the pipe before it starts to use the purge
Run the engine at various revs for 1 min. Vary from Tick over in 500rpm increments to 3500
Repeat until ½ of the purge is used up
Remove the temp 1litre tank and connect tank feed and return pipes
Start engine and hold at >3000 until engine splutters as it hits the air and starts to run on diesel again
Allow to tick over and empty the remains of the purge into the fuel tank
If you have some extra ie the remaining 4 litres then add maybe a total of 1.5 litres of purge to the fuel tank
Take the car for a spirited drive. Exercise the entire Rev range over say 20 miles
This is now flushing the purge diesel mix around the tank, pipes, fuel cooler and tandem pump/ injectors
After the 20 miles change the fuel filter for a new one. You do have one of my machined ally drain screws don’t you!!!!
One changed start car and hold at >3000 revs until the engine as spluttered then take it for a drink to the shell station and fill up with premium diesel

Your now all set for the next 60000miles
Run good quality fuel and it should keep itself clean
The purge is great for removing the built up crude in the injectors
Running it on neat purge does a good job on the injectors and tandem pump and the lower but still strong concentration for the 20 miles hits the remainder of the fuel system
Once you fill up the purge is very diluted but is still there for a couple of tank fully and will work it’s magic
I found changing the filter was needed as the amount of crude the purge releases was blocking a filter which was only a few months old

I did drop the filter again after 3 months but is was spotless so refitted said filter
Come to think of it it’s on the service plan for this year to change it again though only done about 10k miles with lockdown

Cheers. Paul
Ps there was at least 5 litres in my tank when the gauge hit empty. Some 60 miles after the warning chimes so don’t be afraid to get the tank as empty as possible as the purge is then running at max concentration


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Click to expand...

Wow, that’s some write-up! Really clear and concise instructions! Certainly a contender for a sticky I would think.

So you think a fuel filter change is going to be a must after having done all this?

Does anyone know which fuel pipe is the inlet and outlet from the pump?
 
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One thing I should have mentioned is to NOT do the initial run on purge with the car on a drive that you wish to remain clean
Please don’t ask me how I learned this gem of wisdom - let’s just say that mrs whittle was not overly pleased with me and leave it at that

Paul


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Paul, I have a question around tank capacity:

depronman said:
Drive a further 80 miles, 50 miles or so the needle will be on empty and a further 30 miles because the tank is not empty when the gauge says it is



Ps there was at least 5 litres in my tank when the gauge hit empty. Some 60 miles after the warning chimes so don’t be afraid to get the tank as empty as possible as the purge is then running at max concentration


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Click to expand...

So are you saying that 80 miles after the low fuel warning went off there was still about 5 litres left in the tank? Did I read that right?

As I said above, I was considering running it down to 0 miles of range indicated on the DIS, safe in the knowledge that there would be at least a couple of litres left - how does that compare with your method (80 miles after the low fuel warning) - which I assume you do as you don’t have DIS?
 
Yes
When I filled up after the ½ litre of purge and 20 miles run I got 29.5 litres in to the tank
Mine is a 34 litre tank
All I can say is that Audi did not want anyone running out of fuel

Paul


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dj_efk said:
According to THIS THREAD it’s well worth it, so for an ATL TDi90, can anyone show a picture of which hoses I should disconnect (I’m assuming the two metal ones at the front of the engine as shown in this pic?), which is the supply and which is the return - also which pipe I should put an in-line filter on - I assume the supply that’s drawing the cleaner into the pump?
View attachment 77958
Click to expand...

From the service manual, the upper metal hose in this picture is the supply, following it from left to right it goes into the tandem pump, the return line is the one that comes out from lower down https://workshop-manuals.com/audi/a...dem_pump/removing_and_installing_tandem_pump/
 
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Look what turned up today ready for Saturday...

38A98207-83BE-4169-9722-9744AF33C5D2.jpeg


I’m strangely looking forward to seeing what muck comes out of Audrey’s high pressure fuel system - call it morbid curiosity.

I’m (perhaps somewhat wistfully) hoping that I’m going to see a good 5-10% improvement on DIS reported fuel consumption afterwards: The only way that’s going to happen is if there’s a enough gunge in there to turn the temporary bottle of purge the engine will be running on completely black!

What I’m not looking forward to is running the car down to 0 miles on DIS .... and then the further 50-100 miles beyond that! I’m pretty sure I’m going to bottle it early and put the purge in the tank earlier (but as the car has over 3/4 of a tank in it now and I have a 400 mile round trip I may have to anyway before giving it back to my brother-in-law, as naturally I can’t give it back running on (purge) fumes! Either way I will be ensuring I have my breakdown details with me just in case!

As I understand it, if it does run dry then at least putting fuel in will be enough to eventually prime it with enough cranking with no further dismantling, is that right?
 
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Yes that’s right but there is a LOT of cranking to do
The battery often gives up before the fuel is pulled through
However as you go around bends it will cough a few times as a warning before running dry
I was amazed that at low fuel I then ran a further 80 miles local running around then put ½ litre of purge in the tank ran a further 20 miles actually more like 23 if I account for the trip to the petrol station and after all that could only get 29.5 litres into the tank
It certainly means that I now run to low fuel warning and don’t panic about finding a shell fuel station

Have 5lt of diesel in a can in the boot you’ll be fine

Paul


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Luckily I have a known good / strong battery as @Special edition replaced it a few years ago during his tenure with the car.

If it does run out (which it won’t unless my gauge is much more accurately calibrated than most - from what I’ve read they all have a massive safety reserve designed in) - then I’ll tip the rest of the 5l can of purge in so as to get me to the nearest petrol station, at least I know it will definitely clean everything out I’m the fue system completely then!!
 
audifan said:
Rather than kill your battery I would vacuum the fuel up to the tandem with a manual pump, reconnect the line then go for a start.
Click to expand...
I think from what Paul says it wont come to that, as it will give fair warning it’s running out before it actually runs completely out. I will just be listening & “feeling” for that cough from around 100 miles after the low fuel warning goes off ?

Like I say, I’m sure I’m going to bottle it before then so I’m not worried!
 
dj_efk said:
Yes I have a friend with an A4 1.9 PD (so essentially a very similar engine but in 4 cylinder guise) - he did it to his and was surprised by how much it improved his car all round, ran better (not that it ran badly previously) and used less fuel.

I’m hoping for the same results as him and you
.
Click to expand...
 
dj_efk said:
The car will win!!!
Click to expand...

Ha ha I know what you mean
If you bottle it and have more fuel in the tank then just add a little more purge to the tank
It’s all about concentration of the purge
Hence you run it neat on the injectors and tandem pump first
You will be amazed how quickly the litre of purge turns near black

Paul


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I'm surprised to hear that anyone would want to run their fuel down to the dregs. The reason being that the A2 is not a new vehicle so there is years of all kinds of build up in a tank. I used to work for an independent fuel & oil supplier and we would pick up fuels from Manchester Fuel Terminal (MFT) and Shell Stanlow, Cheshire. There would be Shell tankers before and after our vehicle and the notion of the fuel being different could not be further from the truth, we also loaded up alongside the major supermarket tankers. So again everyone was taking the same fuel to the same specifications.
Shell were a bit naughty as their fuel came out warm from the refinery and cooled overnight. Some fuel stations complained that they we're loosing up to £30K / year due to the specific gravity when sold ment that the temp difference ended up with the load being short.
In winter 200 LTRs of Kerosene would be added to 17,800 LTRs of diesel or as the owners said Winter fuel.
We also stored fuel at our site in silos, but in summer when quiet the silo would be run down and the service plate opened, and here's why you should not run your fuel down to the dregs. You would have to shovel out the algae that had grown in-between the fuel (oil) and water. The water is there from condensation and most A2's have had15-20 years for it to build up in the tank. There was other debris that had got past filters as well another reason not to find down the fuel to nothing.
On the oil side that was similar in that the oil is made to a specification so as long as you go for the same spec you should be OK. I have been using oil from Westway Lubricants in the Midlands and just bout 20 LTRs of the correct spec for one of the cars for £65.
A bit of a story but that's what happened.

Take some photos of before and after of the inline fuel filter when you have done your diesel purge.
 
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