DaveySprocket
A2OC Donor
Okay thanks
1.4 Tdi Struggling to start..
- Thread starter DaveySprocket
- Start date
PlasticMac
Member
To have air in the return, when there is no air in the supply line, can only mean, (imo), air is getting in after the supply line joins the pump inlet.
Fuel after the actual pump, even within the pump body, is under pressure, and, (very), unlikely to vapourise, and form bubbles. But if it did, the bubbles are fuel vapour not air. Vapourised fuel would not get to the return line.
If their was a leak on the pressure side of the system, fuel would be leaking out. If that leak was within the injectors, then the leak would be into the combustion chamber, mixture too rich, smoke, etc.
If there was a leak anywhere else on the pressure side, air still cannot be drawn in while it's under pressure, (anything more than atmospheric). If pressure drops to zero, air can get in, but fuel must come out to make room for it, so it'd be visible.
We can see air in the return line, so there is a leak, which is allowing air to be drawn in. The leak is likely to be, (almost certainly imo), in the suction side of the pump.
Mac.
Fuel after the actual pump, even within the pump body, is under pressure, and, (very), unlikely to vapourise, and form bubbles. But if it did, the bubbles are fuel vapour not air. Vapourised fuel would not get to the return line.
If their was a leak on the pressure side of the system, fuel would be leaking out. If that leak was within the injectors, then the leak would be into the combustion chamber, mixture too rich, smoke, etc.
If there was a leak anywhere else on the pressure side, air still cannot be drawn in while it's under pressure, (anything more than atmospheric). If pressure drops to zero, air can get in, but fuel must come out to make room for it, so it'd be visible.
We can see air in the return line, so there is a leak, which is allowing air to be drawn in. The leak is likely to be, (almost certainly imo), in the suction side of the pump.
Mac.
DaveySprocket
A2OC Donor
Well I've ordered a new Elring gasket at least. Will see what happens when that arrives
DaveySprocket
A2OC Donor
I took the injectors out of my spare engine today, so I thought looking at them and where they go in the engine, might shed some light on how/if bad injector seals could let air into the fuel flow?
The hole near the top must be where fuel goes into the injector
In the head there are two holes, so I'm guessing one flow and one return.
I suppose if that top O ring wasn't perfectly sealed then air could get in there?
The hole near the top must be where fuel goes into the injector
In the head there are two holes, so I'm guessing one flow and one return.
I suppose if that top O ring wasn't perfectly sealed then air could get in there?
johnyfartbox
A2OC Donor
Any updates about the starting issues Davey?
The white one is still starting by the way.
The white one is still starting by the way.
DaveySprocket
A2OC Donor
Good to hear yours is still good!
Mine is still on the naughty step, I will get to it at the weekend hopefully. I'm just going to put the old Tandem Pump back on and see if that makes a difference.
DaveySprocket
A2OC Donor
Today I put the old pump back on with a new gasket (of course), bled everything through, and managed to get her started eventually, but she wasn't happy. As soon as the engine is stopped you can see air getting into the system from somewhere. I think I am done with this wee car, if anything I seem to be making the problem worse
I will put her in the classifieds and see if anyone wants to take her on..
I will put her in the classifieds and see if anyone wants to take her on..
johnyfartbox
A2OC Donor
Sorry to read that Davey.
Howey
Member
Did you ever fit the proper fuel filter bung from Depronman? I know you think you sealed it good but this sounds just like my old pug 306. I had replaced a fuel line from the filter to the pump secured with jubilee then a few days later the thing wouldn't start unless I popped the bonnet and pumped the fuel bleed bulb thingy, then it started straight up. For a few days I did this somewhat scratching my head as no leaks of fuel at all! Following morning whilst doing it I heard air hissing from the connection, ordered and fitted the correct pipe all sorted!
It's totally possible for the fuel system to drag air in without leaking a drop of fuel, this must be ruled out completely, if I was closer and didn't have too many already I would have bought this already!!
It's totally possible for the fuel system to drag air in without leaking a drop of fuel, this must be ruled out completely, if I was closer and didn't have too many already I would have bought this already!!
DaveySprocket
A2OC Donor
Yes I did get the Depronman one and fit it, also when I use a vacuum pump on the feed to the pump I get clean fuel through, no air at all.
I think the more I have messed about with all the different connections, the worse it has got, and it could still be the Injector seals, but nobody seems to quite understand how that would work. I just don't have the time as there are other things I have to get on with. I think a fresh appraoch to it would probably help as well, I'm just an amateur DIY mechanic
I think the more I have messed about with all the different connections, the worse it has got, and it could still be the Injector seals, but nobody seems to quite understand how that would work. I just don't have the time as there are other things I have to get on with. I think a fresh appraoch to it would probably help as well, I'm just an amateur DIY mechanic
Howey
Member
Blast! Is a fuel filter delete possible (short term only) this would rule it out as maybe there is a crack in the top half of the unit from potential overtightened previouslyYes I did get the Depronman one and fit it, also when I use a vacuum pump on the feed to the pump I get clean fuel through, no air at all.
I think the more I have messed about with all the different connections, the worse it has got, and it could still be the Injector seals, but nobody seems to quite understand how that would work. I just don't have the time as there are other things I have to get on with. I think a fresh appraoch to it would probably help as well, I'm just an amateur DIY mechanic
Howey
Member
That's not a bad idea at all although I would want to reinstall the cooler fuel can get hot on the pds especially with low fuel levels
johnyfartbox
A2OC Donor
I read that as well, thinking outside the box but a bit unsure about the cooler bypass, its there for a reason
audifan
A2OC Donor
The cooler is needed on these pd engines otherwise the plastic and rubber components will suffer heat damage and the last thing you want is to introduce further air sources.
Also Audi have designed the car to run at the temperature obtained using the cooler so fuel maps etc are all set.
Also Audi have designed the car to run at the temperature obtained using the cooler so fuel maps etc are all set.
johnyfartbox
A2OC Donor
That's interesting Graham.
So a question, if your car is mapped, will that alter the temperature resulting in problems?
So a question, if your car is mapped, will that alter the temperature resulting in problems?
audifan
A2OC Donor
A dodgy subject.. All depends on how radical the map and if the injectors are standard. But would GUESS that the "regular" maps would still be well within the cars capability.
As the map can not change the quantity of fuel supplied due to no control over the tandem then all they can do is changing the amount of fuel being burnt is to adjust the injector timings. This in turn will effect the return fuel but as around 70% ( not sure the exact figure ) in not burned and returned from each injector then I doubt that would be an issue. I would suspect the return fuel to be a bit hotter and the ECU will monitor that temperature using the fuel temp sensor in the return line.
As the map can not change the quantity of fuel supplied due to no control over the tandem then all they can do is changing the amount of fuel being burnt is to adjust the injector timings. This in turn will effect the return fuel but as around 70% ( not sure the exact figure ) in not burned and returned from each injector then I doubt that would be an issue. I would suspect the return fuel to be a bit hotter and the ECU will monitor that temperature using the fuel temp sensor in the return line.
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