DaveySprocket
A2OC Donor
Sometimes you just have to let the mystery beThat, we may never know.
Sometimes you just have to let the mystery beThat, we may never know.
For mere observers, like me, it's been an interesting, and informative journey. Thanks to all who posted.Sometimes you just have to let the mystery be
Was it not eventually proved to be air entering the fuel feed line somewhere as evidenced by air bleeding out of the return line? For the benefit of future readers, would it be possible to now establish there is no longer air being bled out in the return line?Yes but if it is fixed, and it wasn't the pump, then what was it?
Iām still puzzled by the air in the return line during the diesel purge??Was it not eventually proved to be air entering the fuel feed line somewhere as evidenced by air bleeding out of the return line? For the benefit of future readers, would it be possible to now establish there is no longer air being bled out in the return line?
Maybe I've misunderstood, please correct me.
FYI, I fitted a used one of these today, straight swap.Hello.
I can only assume that the tandem pump has failed internally as the reason for your fuel tank to be black inside. It has to be engine oil. This design of pump is rather weak in terms of the seal arrangement and the cover plate flexing/distorting. Often they leak fuel or oil externally too, I have replaced many on A4's that I have owned in the past. On the A4, from 2004 they got a different pump design which is a direct replacement and has a cast alloy cover rather than the shabby steel plate on our ones. The updated pump will fit perfectly on any 1.9 or 1.4 PD engine as far as I am aware.
My new A2 is running ok but the tandem pump is leaking so I will be replacing it with a used one of the newer style pretty soon.
For example, I'll be buying one on ebay part no 038 145 209 Q, it looks like this
View attachment 120607
Note that the cover is completely different when searching for one, I expect that the Q at the end is the key but there will likely be other letters for this style so the part number above is not definitive.
IIRC correctly, oil can also get into the fuel system from the injector seals but I think we should cross that bridge if it comes to it! Tandem pump is no1 suspect at this point.
Apologies if I have covered old ground here, all the best...Dan
Interested in how air get into the return line from the injectors? Where does the injector seals fit between, the injector body and cylinder head?I was working on mine at the weekend, I made good the connection on the sender.
View attachment 122561
With that set up I was bleeding clean fuel through the feed pipe in the engine bay, yet it still didn't want to start. When I did eventually get it to start, there was tons of air coming out the return pipe. So I put some clear pipe in the feed line to see if there was air there too, and ther was air bubbles coming though.
View attachment 122560
The problem is, with the return line feeding back into the filter, it is hard to know for sure where the air is coming from, so I figured the only way to be totally sure is to run it from a fuel can and into another empty can.
View attachment 122558
So today I ran it like this and it still didn't want to start, and when I got it started there was tons of air in the return line. I realised that there was still a chance it could be the temp sensor and the pipes to the pump causing the problem, so I hooked up my pipes direct to the pump itself as a final test.
View attachment 122556
Like this I still got loads of air coming out of the return pipe. Given that this is a replacement pump, with a new gasket, then it would seem that the problem has to be the injector seals?
When @johnyfartbox did his diesel purge, he also had air coming out the return pipe. He has a new Bosch pump fitted, so I would say he has the same problem, although last we heard from him the car was starting okay?
Given the lack of space above the engine in the engine bay, it looks like it would be a bit of a nightmare job to be delving into. I'm starting to wonder how much trouble I am willing to go to to keep this old A2 alive. I'm very reluctant to scrap it, but have to wonder if the time hasn't come. What to do?
You are doing all the right things. You seem to have it narrowed down to only a couple of possibilities.I was working on mine at the weekend, I made good the connection on the sender.
View attachment 122561
With that set up I was bleeding clean fuel through the feed pipe in the engine bay, yet it still didn't want to start. When I did eventually get it to start, there was tons of air coming out the return pipe. So I put some clear pipe in the feed line to see if there was air there too, and ther was air bubbles coming though.
View attachment 122560
The problem is, with the return line feeding back into the filter, it is hard to know for sure where the air is coming from, so I figured the only way to be totally sure is to run it from a fuel can and into another empty can.
View attachment 122558
So today I ran it like this and it still didn't want to start, and when I got it started there was tons of air in the return line. I realised that there was still a chance it could be the temp sensor and the pipes to the pump causing the problem, so I hooked up my pipes direct to the pump itself as a final test.
View attachment 122556
Like this I still got loads of air coming out of the return pipe. Given that this is a replacement pump, with a new gasket, then it would seem that the problem has to be the injector seals?
When @johnyfartbox did his diesel purge, he also had air coming out the return pipe. He has a new Bosch pump fitted, so I would say he has the same problem, although last we heard from him the car was starting okay?
Given the lack of space above the engine in the engine bay, it looks like it would be a bit of a nightmare job to be delving into. I'm starting to wonder how much trouble I am willing to go to to keep this old A2 alive. I'm very reluctant to scrap it, but have to wonder if the time hasn't come. What to do?
I think this is unlikely too. Mainly because the fuel feed after the tandem pump is at about 3 - 7.5 bar and the fuel in the return is at 1 bar. Remember 1 bar is about 10m head. So surely there would be an awful lot of diesel coming out and not much air going in. The only possibility I can think of is combustion gasses but I've never personally experienced this as a mode of failure.Interested in how air get into the return line from the injectors? Where does the injector seals fit between, the injector body and cylinder head?
Mac.
Given the above, with fuel fed straight into the pump from a 5 litre can, using a clear pipe, and the return (clear pipe) also connnected directly to the pump, what would be your best guess for air getting into the return?The VAST majority of air leaks are from the filter / drain screw or pipe connections. Remember every time a pipe is disturbed you greatly increase the chance of it leaking air. The more you disturb the more you have to rule out.
From SSP 233
The fuel return line in the unit injector has the
following tasks:
Cooling the unit injector. For this purpose,
fuel is flushed from the fuel supply line through
the ducts of the unit injector and into the fuel
return line.
Discharge of the leaking fuel from the
pump piston.
Separation of vapour bubbles from the fuel
supply via the restrictor into the fuel return
line.