Starting problem bhc diesel

spike

Member
My fuel tank sender unit arrived from Kaz. Gave it a quick clean and did a couple of tests to try and understand how it works.
A youtube video on golf starting from cold problems suggested it was not uncommon for the unit to contribute to fuel delivery problems so I was intrigued to know how.
First thing I found was a one way valve in the fuel return connection. This is no doubt to stop fuel draining back from the tandem pump when the car is stood for a while. The valve seemed to be working correctly on this unit.
Next step was to remove the plastic strainer on the bottom of the unit. It's located on two pegs and just prises off. Could not believe the amount of hardened grease like lumps which came out. Certainly enough to block the fuel supply port.
It's quite labour intensive to strip, clean and re-assemble the unit, so with no internal parts available if anything breaks, I can see why the youtube garage just fits a new assembly

More pics to follow

Cheers Spike
 

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Well done on that research on this item spike ....Can the fuel tank sender unit be accessed for removal from inside car or is it a tank drop ??
 

depronman

Member
No need to drop the tank I’m sure there is access from inside the car under the rear drivers side seat (but I may be mixing up my cars)


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AndyP

Member
I think I'm going to take a look at this as I'm 90% sure the problem is something to do with fuel delivery.
 

spike

Member
The tank sender unit can be stripped down fairly easily for cleaning.
The 2 sender wires are removed by using a small screwdriver to press in and release the 'barb' on each connector and the wires will just pull out.
Sender mini circuit board and float arm unclip and slide out of the slot on the housing.
Release the three tabs on the top edge of the main chamber and remove the top cover with supply and return tubes
Slide out the inner chamber
On the bottom of the unit there is a float and pivot arm which I did not remove. Attached to the arm is a dual purpose 'flap valve' The rectangular plate looks like it's open most of the time so fuel is continually drawn into the chamber and on its way to the tandem pump but seals the reservoir when the main fuel tank level gets very low and the float drops. The smaller round flap valve seems to work on the return line and possibly stops fuel returning to the main tank when the level is very low - working like a mini reservoir for the fuel supply
This flap valve just unclips from the bottom float arm and can be pushed into the chamber and removed

Cheers Spike
 

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spike

Member
Forgot to mention a basic test which could be done without removing the tank sender unit.

The fuel check valve in the return pipe within the unit needs to function correctly to prevent fuel drain back when the car is standing for long periods.
For access follow the steps in post 26. The manual indicates the return line to the tank is blue and connects to the port marked with an 'R'
Press in the locking tab and remove the quick connector. I found the connectors were reluctant to release if dirty. A quick blast of carb cleaner really helped.
Fit a long piece of tube to the stub end on the sender unit and you should be able to blow into the tank but not suck. Be CAREFUL not to get a mouth full of fuel if the check valve has failed

Cheers Spike
 

spike

Member
Missed this post first time around but there seems to be a trend building

Cheers Spike
 

spike

Member
Tips on removing the tank sender unit (another post I missed)


Cheers Spike
 

CD17

Member
My starting problem has turned out to be a leaking fuel filter, this is the 2nd time this has happened to my car, although I have had it nine years now. I noticed a diesel patch under my car the other day. It's been repaired for now but I'm going to look at getting a replacement bolt made.
 

audifan

A2OC Donor
@CD17 check the filter housing itself isn't split and the seal on the cover also is good. Then contact Paul @depronman for a replacement drain plug that is far superior to the Audi original. If you already working on the housing I would recommend you replace the filter at the same time and all new seals and Pauls drain plug.
 
When I did my lads fuel filter I was told that the fuel lines have to be clamped to stop fuel running out of the filter housing,
 

audifan

A2OC Donor
That is correct you will drain the contents of the tank through the open filter housing unless the lines are clamped.
 
That is correct you will drain the contents of the tank through the open filter housing unless the lines are clamped.

It drains out relatively slowly but it does drain out and even a little diesel is a pain. You can get clamps for £5 so worth it.

It’s a useful beside the road emergency option if you accidentally misfuel. Unscrew the little bolt (old can filters also have a little screw). Ask me how I know...




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audifan

A2OC Donor
That is why I left it as drain the contents, didn't want to give you flash backs. How many hours was it to drain?
 
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