DaveySprocket
A2OC Donor
Sometimes you just have to let the mystery be
1.4 Tdi Struggling to start..
- Thread starter DaveySprocket
- Start date
PlasticMac
Member
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
Mac.
johnyfartbox
A2OC Donor
Not a problem.
Surprised that there's not more on the subject within the forum.
Surprised that there's not more on the subject within the forum.
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?
Maybe I've misunderstood, please correct me.
DaveySprocket
A2OC Donor
Iām still puzzled by the air in the return line during the diesel purge??
johnyfartbox
A2OC Donor
At the moment I think it was probably a fuel pipe under the bonnet, which one I don't know.
Having cut off the first half inch from the return pipe and reclamped them and also taking out the returning fuel temperature sensor and putting a very small amount of HYLOMAR Blue sealant on the end of the sensor where it squashes onto the O ring and pushing fully home and making sure that the green horseshoe clamp is firmly in place.
I also nipped up the bolts on the tandem pump, my new torque wrench set to the correct NM did slightly move the bolts, not by a lot but all the same.
The only other pipe I changed was the input pipe on the cooler, it looked like someone had been there before so changed it and used proper clamps.
The filter bottom screw housing is now completely sealed where the small bleed screw is, yes it's a bodge and I will sort that out, I just wanted to illiminate any slight air leak from that area.
It's still got its original sender unit but it's been cleaned within an inch of it's life.
So basically I can't pinpoint where in the system was the culprit.
One thing I do regret is changing the pump.
It would have been better if I had fully checked the fuel lines first.
It's been up in the air now for a good while, and it's in that position where it would always either struggle to start or not start at all.
Cross fingers, it's still up in the air and is starting no problem.
In fact, I'm tempted to refit the other pump and see what happens.
I will keep this going and update.
Oh, I've just restarted it to move it to get the bins out and it started.
Having cut off the first half inch from the return pipe and reclamped them and also taking out the returning fuel temperature sensor and putting a very small amount of HYLOMAR Blue sealant on the end of the sensor where it squashes onto the O ring and pushing fully home and making sure that the green horseshoe clamp is firmly in place.
I also nipped up the bolts on the tandem pump, my new torque wrench set to the correct NM did slightly move the bolts, not by a lot but all the same.
The only other pipe I changed was the input pipe on the cooler, it looked like someone had been there before so changed it and used proper clamps.
The filter bottom screw housing is now completely sealed where the small bleed screw is, yes it's a bodge and I will sort that out, I just wanted to illiminate any slight air leak from that area.
It's still got its original sender unit but it's been cleaned within an inch of it's life.
So basically I can't pinpoint where in the system was the culprit.
One thing I do regret is changing the pump.
It would have been better if I had fully checked the fuel lines first.
It's been up in the air now for a good while, and it's in that position where it would always either struggle to start or not start at all.
Cross fingers, it's still up in the air and is starting no problem.
In fact, I'm tempted to refit the other pump and see what happens.
I will keep this going and update.
Oh, I've just restarted it to move it to get the bins out and it started.
FYI, I fitted a used one of these today, straight swap.
DaveySprocket
A2OC Donor
I was working on mine at the weekend, I made good the connection on the sender.
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.
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.
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.
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?
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.
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.
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.
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?
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johnyfartbox
A2OC Donor
Hi Davey.
Yes, she seems to be ok at the moment.
There's still a very slight hesitation on the turn of the key, I think there is probably air in the system but nowhere near as much as before.
So that says to me that fuel is no longer running back to the extent it once did.
Yes, she seems to be ok at the moment.
There's still a very slight hesitation on the turn of the key, I think there is probably air in the system but nowhere near as much as before.
So that says to me that fuel is no longer running back to the extent it once did.
PlasticMac
Member
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.
You are doing all the right things. You seem to have it narrowed down to only a couple of possibilities.
I have in the past fitted a tandem pump and had the new (cheap) gasket fail instantly. They are one use only items. If the bolts are tightened, loosened and tightened again, this can be enough to make them leak. They seal by deforming the risen parts of the metal gasket. There are many cheap gaskets out there that can be troublesome. If you haven't already, then I would buy an Elring gasket and tighten the bolt very progressively before venturing into injector seals.
If it comes to it I don't think injector seals are especially difficult to change. Might have to undo the dog bone and disconnect a few bits to lean the engine forward a bit. The seals are about Ā£10 per injector. Might need slide hammer to remove injectors.
I think these are the only two remaining possibilities and my money's on the gasket.
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.
I would have to admit that a leaking gasket normally shows as a diesel out leak also due to the above.
DaveySprocket
A2OC Donor
I did use an Elring gasket, so I would hope that is not an issue, although I wouldn't rule it out completely..
A few people have mentioned that leaking injector seals create exactly the same symptoms as I am having, but I have no idea if leaking seals would actually cause the air in the return pipe.
As mentioned before, when Johnyfartbox did his diesel purge (new Bosch pump/Elring Gasket) he was getting air in the return pipe, so I am wondering do we know for sure that this not normal?
Mine has run clear for short periods of time, but always reverts to what looks like foam.
A few people have mentioned that leaking injector seals create exactly the same symptoms as I am having, but I have no idea if leaking seals would actually cause the air in the return pipe.
As mentioned before, when Johnyfartbox did his diesel purge (new Bosch pump/Elring Gasket) he was getting air in the return pipe, so I am wondering do we know for sure that this not normal?
Mine has run clear for short periods of time, but always reverts to what looks like foam.
I can categorically guarantee that there should be absolutely no air in the fuel lines....feed or return. Sometimes it can take 10 minutes or so ticking over for the air to be fully bled out but after a 20 minute drive it should be air free.
If you are confident in your gasket (maybe by trying another one and experiencing no change) and your pipe connections when you fed the tandem pump directly (ie no air in at connections) then that really does only leave the injector seals. As unlikely as that feels to me, logically I can see no alternative.
If you are confident in your gasket (maybe by trying another one and experiencing no change) and your pipe connections when you fed the tandem pump directly (ie no air in at connections) then that really does only leave the injector seals. As unlikely as that feels to me, logically I can see no alternative.
As much as you wouldn't want to read it, I suppose we also have to entertain the possibility that the new tandem pump could also be the cause. I wouldn't normally suggest this sort of thing but when you are down to so few possibilities, all of which are unlikely, even the most unlikely should be considered.
DaveySprocket
A2OC Donor
I'm fairly confident in all that I have done, but don't have a huge amount of experience.. The 2nd pump was a s/h one, not new.
As you say, I wouldn't rule anything out. I think I'll just leave it for a bit and ponder options going forward.
It's not the most exciting A2, no nice options, just a Dolphin Grey car with black cloth interior, but still a shame if it has come to the end of it's road.
Thanks for taking the trouble to share your considerable experience in these matters, it is very helpful! Cheers
As you say, I wouldn't rule anything out. I think I'll just leave it for a bit and ponder options going forward.
It's not the most exciting A2, no nice options, just a Dolphin Grey car with black cloth interior, but still a shame if it has come to the end of it's road.
Thanks for taking the trouble to share your considerable experience in these matters, it is very helpful! Cheers
audifan
A2OC Donor
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.
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.
DaveySprocket
A2OC Donor
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?
audifan
A2OC Donor
That I could not say, could be injector wear causing excessive foaming of the fuel or indeed a normal function for the return line due to the fuel being hotter and the possible action of the solenoid valve dumping pressure up to 2000 Bar into the port.
Perhaps even a remap could influence the return fuel.
Perhaps even a remap could influence the return fuel.