Suddenly won't start after recent tandem pump change

allypug said:
same here when I splashed out on the same new Bosch pump.. was great for about a week then back to the starting issue again.......
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So thinking back what has changed, make a list of when, where the issues came about. Like easier starting when facing a certain way.
It might just give you a clue when you read back through it.
"There is never an issue until a change"
 
I havent read the whole thread as its huge, everyone wants to solve this one its very frustrating. How about cam shaft, crank shaft sensors, maybe one playing up and the poor start is the ecu recalulating the twin date fuel until it gets running?
 
Is there a injector rail pressure sensor on these engines, so that fuel pressure at the injectors can be monitored?
Mac.
 
CrispyEdd said:
I havent read the whole thread as its huge, everyone wants to solve this one its very frustrating. How about cam shaft, crank shaft sensors, maybe one playing up and the poor start is the ecu recalulating the twin date fuel until it gets running?
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Can't be that if the car starts fine pointing downhill, I'm thinking airleak or injector seals
 
Injector seals were shot on mine but it started OK, its Smokes if seals are shot as oil drops into cylinders for the first cold part. A real mystery. Maybe list out work done in simple way, and start again and some one will spot what's been missed.
 
I think that there is air being pulled into the system somewhere, even after changing the pump, the short length of clear fuel pipe still had tiny air bubbles in the fuel.
Thing is, I've no idea where else to look apart from the fuel filter housing.
 
I guess thats all you can check, all the pipe ends around the filter and the fuel cooler, although thats return part to tank I think? So maybe not that. I feel your frustration!
 
Apologies if this has been mentioned but if the cam sensor isn’t right starting will be poor. Is it possible that the wiring/ connector has been disturbed. The wiring runs along the front of the engine. It will show on a scan.
 
Risking embarrassment again, but I think the fuel gauge sender also acts as a "Swirl Pot" a mini tank that the pump draws fuel from. The idea is that the pot will contain fuel, when braking acceleration, etc, causes the level in the tank to vary widely. If that pot, or, more likely, the fuel line within it, leaks, the line will drain back and air will be drawn in, when the pd pump starts.
Mac.
 
PlasticMac said:
Risking embarrassment again, but I think the fuel gauge sender also acts as a "Swirl Pot" a mini tank that the pump draws fuel from. The idea is that the pot will contain fuel, when braking acceleration, etc, causes the level in the tank to vary widely. If that pot, or, more likely, the fuel line within it, leaks, the line will drain back and air will be drawn in, when the pd pump starts.
Mac.
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Edit: The fuel line to the pump is attached to the top of the Swirl Pot, and the other side of the the top, there's a line down to the bottom, where fuel is draw from.
That why the sender is large bec it's a sender
Mac. sender and Swirl Pot combined.
 
Haven't contributed to this for a while.

If you can confirm you have air in the fuel, perhaps by fitting a clear pipe on the fuel return and watching for bubbles (even tiny ones) after starting, then this is where the starting problems lie. The only question then is where the air is getting in. In my experience over 50% of the time the air is entering the system via hardened rubber fuel pipe connections. Since fuel pipe is relatively cheap it's the best thing to rule out first.

Trevor
 
When it comes to diesels the system MUST be air tight. As components age or are removed then those are the likely candidates. As John @johnyfartbox has reminded us the correct clamps are essential to ensure even clamping force is applied over all the diameter of the pipe.

Regrettably when replacing a major fuel component like the tandem is when air leaks are highlighted due to other components being disturbed i.e the fuel lines on the tandem. Very seldom can you walk up to the car and spot a puddle of diesel on the floor.

If it was a pressurised fuel system then diesel would eventually be forced out of the leaking area. As it is a vacuum type system the air is sucked in instead.
 
audifan said:
When it comes to diesels the system MUST be air tight. As components age or are removed then those are the likely candidates. As John @johnyfartbox has reminded us the correct clamps are essential to ensure even clamping force is applied over all the diameter of the pipe.

Regrettably when replacing a major fuel component like the tandem is when air leaks are highlighted due to other components being disturbed i.e the fuel lines on the tandem. Very seldom can you walk up to the car and spot a puddle of diesel on the floor.

If it was a pressurised fuel system then diesel would eventually be forced out of the leaking area. As it is a vacuum type system the air is sucked in instead.
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Interesting, so if the system could be pressurised????
 
VERY early AMf's had a lift pump in the tank as does the 1.2tdi.

The fuel runs hot in the diesels hence the fuel cooler. Does the lift pump make the fuel run hotter, is the pump effected by the heat, once the engine is off would you still have an air issue?? More questions than answers. All we know is Audi removed the lift pump and never fitted to the later BHC or ATL engines, nor was a check valve fitted.
 
PlasticMac said:
I don't think the fuel line from the tank/swirl pot can be pressurised, as the tank end is open, isn't it?
Mac.
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There are two potential leak points at the tank end, one where the line to the pump is joined at the outside of the sender/swirl pot, and another one on the inside.
As @audifan says, you're looking for an air leak into the line, not out, so there'll probably be no tell tale sign of diesel.
Mac.
 
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