Suddenly won't start after recent tandem pump change

Well over the last few days it's been starting much much better. There's still a little stuttter on actually starting,its not instant like the other two so I'm thinking there is still a fuel drain back but it's no where near as bad as it was.
Thanks for asking.
 
Don't think it is drain back but still air leak. Have a good look at the filter and the pipes in that area.
 
audifan said:
Don't think it is drain back but still air leak. Have a good look at the filter and the pipes in that area.
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Two sides of the same coin. Air in, fuel out. If there's air getting in, the line will drain back.
Fitting a one way valve, can make things worse, unless the line has a thermal relief valve, as fuel expands as it warms up. If no relief path, the line will be over pressurised, and a leak may result. No idea if such a relief valve is fitted, but if no check valve was fitted originally, then probably not. The check valve must not be spring loaded, as the pump load will be increased, overcoming the spring as well as gravity.
Mac.
 
Drain back is a different issue. That is when the pump is unable to maintain the fuel line full of fuel. Air in is normally from a bad pipe, joint or filter. The difference is with drain back and the clear fuel tube at the tandem the level can be seen to drop back down the pipe. Air leak is shown as bubbles in the fuel travelling towards the pump.

The fuel in the diesels gets very hot hence the fuel cooler fitted to the cars. This hot fuel is cycled through the system as much more fuel comes back down the return line than consumed by the engine.

There is a vacuum in the feed line and the pump increases the pressure for the injectors to increase much more as it is injected into the cylinders.

Audi designed the 1.4 diesels with no check valves so do not fit one as you will only mask the issue and possibly cause more.

Please do not confuse petrol fuel systems with the diesels.
 
There's no obvious leak around the fuel filter housing, but have just ordered a new filter to fit and have a proper look next time. Also had the issue a few years back, and the car was fine when parked nose down. This was when a check valve was fitted in the line, but made no difference, so think I'll remove it upon the advice here!
 
audifan said:
Drain back is a different issue. That is when the pump is unable to maintain the fuel line full of fuel. Air in is normally from a bad pipe, joint or filter. The difference is with drain back and the clear fuel tube at the tandem the level can be seen to drop back down the pipe. Air leak is shown as bubbles in the fuel travelling towards the pump.

The fuel in the diesels gets very hot hence the fuel cooler fitted to the cars. This hot fuel is cycled through the system as much more fuel comes back down the return line than consumed by the engine.

There is a vacuum in the feed line and the pump increases the pressure for the injectors to increase much more as it is injected into the cylinders.

Audi designed the 1.4 diesels with no check valves so do not fit one as you will only mask the issue and possibly cause more.

Please do not confuse petrol fuel systems with the diesels.
Click to expand...
The term "drain back" does not apply, when the pump is running, but is unable to maintain fuel in the line.
It does apply when fuel drains out of the line, with the ignition off.
With the ignition off, the fuel line is still open at one end, but closed at the pump.
The line, (should), remain full of fuel, because the weight, (negative head), of the fuel in the line creates a vacuum. As long as a vacuum is present, the line remains full.
If air enters, the vacuum, is lost, causing the line to "drain back"
Mac.
 
allypug said:
There's no obvious leak around the fuel filter housing, but have just ordered a new filter to fit and have a proper look next time. Also had the issue a few years back, and the car was fine when parked nose down. This was when a check valve was fitted in the line, but made no difference, so think I'll remove it upon the advice here!
Click to expand...
I'm curious as to how you can physically check the fuel filter housing
 
Hi Graham.
Kind of but still a bit iffy so in a word, no.
I'm doing some work on the silver one at the moment and then the mother in law decided to curl her toes up last weekend so haven't done anything.
Now that the weather is slightly improving ie getting warmer, I'll plod on with them both
 
Getting back trying to sort the same starting issue, changed the fuel filter which was full of muck, also replaced the filter housing screw on cover as mine was bodged.. the bleed screw hole had been drilled and helicoiled.. badly! so would probably let air in.
Left overnight and started first thing, hasn't done that for a very long time. Hope thats it sorted... again!
 
I give up... the hard starting is still there!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
Only just jumping onto this so no sure if someone has already suggested it, but perhaps the injector seals have had it?
 
Yes, been doing a lot of reading up loads of forums about possible causes, and the thing about it starting fine when pointing downhill, not so when facing uphill. Is changing injector seals a big/expensive job?
 
allypug said:
Yes, been doing a lot of reading up loads of forums about possible causes, and the thing about it starting fine when pointing downhill, not so when facing uphill. Is changing injector seals a big/expensive job?
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I'm not the expert on this but I have seen mentioned a few time that Darwen diesels (Lancashire) is one of the best for checks and refurbished injectors. I'm sure others with more experience of using them can help you out.
I know it's frustrating but don't give up, you'll get there in the end. 👍
 
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