1.4 Tdi Struggling to start..

PlasticMac said:
Given the volume of white stuff, it must be coming from the tank, or, at least the line to it. Maybe the filter? Looks almost like an emulsion.
Mac.
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The clear line I have on the tank was not showing any air bubbles, so I wouldn't think so. It looks like I am going to have to start from scratch again and follow the circuit around to see what is going on.
 
depronman said:
My understanding of the 1.9/2.0 pd engine setup is that there is a in tank mounted fuel pump to proved fuel to the injectors
Therefore the pump on the end of the cylinder head is a vacuum pump for the brakes and not a tandem pump
Tandem pump as fitted to the 1.4pd engines is a fuel pump and a vacuum pump hence the name tandem

Like I said earlier. May be wrong and the 1.9/2.0 engines may have had a in tank pump and a tandem pump but this was not my understanding

Indeed a meme we on here brought me a pump that he had bought for the 1.4pd engine (ATL) which was mis sold to him as it was for a 1.9pd and from memory it only had the vacuum pipe on it

This is why I think the pump in the earlier picture may actually fit the 1.4pd because it as 3 pipes. Assumed to be fuel in, excess fuel return to tank and vacuum to brakes BUT what spooked me was the 1.9/2.0

Paul


Sent from my iPhone using Tapatalk
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I had an A3 tdi Quattro Sport with a 130 PD engine. I changed the tandem pump on that and I am 99% sure it’s identical to the 3 cyl version having changed both.
 
DaveySprocket said:
Sorry Mac, I should have been clearer, it's within the sender unit itself. The return connection on the sender is a plastic tube that goes back into the swirl pot, and the non return valve is in that pipe.
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So the return discharge is below the fuel level, in the swill pot. That means air isn't being drawn in that way, even if the non return valve fails. I think.
Mac.
 
DaveySprocket said:
I just dropped mine off the blocks and then started it, she fired on the button.

So I put some clear pipe in the return line and started her again. There was a whoosh of air bubbles through the pipe and then she ran clear, with the occasional tiny bubble passing through. Just as I thought that she was going to stay clear, suddenly the fuel in the return line turned white and stayed like that until I shut the engine off. Then it settled back to clear fuel.View attachment 122068
I've put the front end up on ramps now, so will wait for a while and see how she starts like that.. 🤔
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This white fuel in the return is millions of microscopic air bubbles being bled out and is a sure sign there is still air in the feed fuel.

I'm not convinced that having the front or back of the car elevated actually tells you much about where the air is getting in. Obviously with the front raised you are increasing the suction required to draw the fuel therefore exacerbating the air in leak wherever it is.....and the opposite with the rear raised.

Suppose the leak is at the sender: After bleed starting, air is drawn in at the sender and travels along the feed pipe. The air is bled out by the tandem pump while the engine is running. After stopping the engine, you still have air in the feed pipe at the pump, so it doesn't start.

Suppose the leak is at the pump: After bleed starting, the air drawn through the leak is bled out by the tandem pump while the engine is running. After stopping, the fuel in the feed pipe is allowed to fall back to the tank by the leak creating an air pocket at the tandem pump so it doesn't start.

Just theorising that an easier start with the rear raised might only tell you that the leak only occurs at a certain level of suction.....and not much more.
 
Regarding nose up and arse up and suction that you mentioned, in my limited mind, gravity must be a contributing factor how a fluid acts.
That's just my thoughts by the way.
A little like a closed central heating system in the house, leak on a downstairs radiator if you have a boiler in the loft.
Disregard my ramblings, I'm no plumber but it seems to make sense to me.
Regards.
John
 
johnyfartbox said:
Regarding nose up and arse up and suction that you mentioned, in my limited mind, gravity must be a contributing factor how a fluid acts.
That's just my thoughts by the way.
A little like a closed central heating system in the house, leak on a downstairs radiator if you have a boiler in the loft.
Disregard my ramblings, I'm no plumber but it seems to make sense to me.
Regards.
John
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Your completely right in your thoughts but there is a but. Diesel is an incompressible fluid, well almost but suppose it is. If you block the output from your tandem pump and drive it will lock up to the point it lifts the veins and diesel flows back. Actually there is a relief valve that protects it but ignore that for this discussion. The pump will remained locked. Release the pressure and the pump goes nowhere; nothing to compress, nothing to release. Pressure comes and goes with input mechanical pressure.
So the pump draws fuel from the tank and the pressure at the inlet to the pump is negative. Switch off and it is still negative so it could suck air in via a leak to flow back; only if you have a leak. No leak no flow back; incompressible fluid. Think about it like this, stand on a brick, does it go anywhere, no but it is under pressure. Step of it and it is not under pressure. Does it go anywhere no. Take a brick between two hands and stretch it, negative pressure, does it go anywhere, no. Diesel is the same unless there is a leak.
Switch off and you have negative pressure at the pump and unfortunately a leak.
Car arse up less negative pressure and less air gets in.
Car arse down more negative pressure and more air gets in.
All of that said I was resisting this post before I had checked for;
Return valves in the return feed at the fuel sender
Capillary drain at the tandem pump return
Mixing of return and fresh fuel in the fuel filter.
Other things to understand too but I hope this is not disrespectful nor wrong and helps.
 
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I am thinking that my car started up okay and ran without air leaks for a little while on the ramps, until the extra effort required to suck the fuel uphill caused my very sketchy temporary connection to leak.
IMG_20240407_111509_HDR.jpg
The conical rubber piece connected into the nylon pipe will be causing quite a restriction to flow, and the clear pipe is not clamped at all, so it would not be at all surprising that it leaked eventually. I've ordered a load of Mikalors spring clamps of various sizes, so when they arrive I will try to find a better way of making this connection.
IMG_20240409_195550.jpg
These connectors were on the kitchen table the other day when a mate came around, he immediately said "Those things are a pain in the bum, they let air in" He'd had a nightmare with a JCB that lot's of these connectors and they had all started letting air into the fuel system, so that was interesting and telling.

It may all be wishfull thinking, but I'm hoping that by the time the connectors arrive, the ground will have dried out a bit, and I can get it hooked up properly and I might be back on track.. :rolleyes:
 
johnyfartbox said:
Interesting theory about the those conectors,
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I think left undisturbed they would probably be okay, it's once you start removing and replacing them the rubber suffers. That's why I was a bit worried about you experimenting with your good cars. Some silicon grease on them can help, but at the end of the day it's 20 year old rubber, so it's not going to last forever.
 
What I cant belive is that you two guys are the only ones that have this issue and that no one else has had it and solved it!
I feel sorry for you guys with a nice car that won't start due to a small air leak in one little pipe or clip somewhere. I really feel the pain! It's ridiculous.
 
Another update, the car has been on the ramps overnight facing uphill and only 10 minutes ago it started

So fingers crossed, it's now ok.

I shouldn't have said that should I ??
 
One thought, most tdi don't have this problem, most tdi have the shield over fuel filter. You car hasn't got the shield so I reckon the problem will be there in the bundle of knackered hoses and rusty clips.
 
johnyfartbox said:
Another update, the car has been on the ramps overnight facing uphill and only 10 minutes ago it started

So fingers crossed, it's now ok.

I shouldn't have said that should I ??
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It’s the hope that kills you in the end 😂

I think you concluded that there was never actually anything wrong with your original tandem pump right? It would be a bold move, but considering the price and availability of Bosch pumps, I might be tempted to switch back and sell the Bosch one.. 🤔

So that also raises the question, what was the original fault?
 
The original problem was hard start, firstly facing uphill when ever I parked it, then it went worse, even on the flat.
That's when I started asking for advice and digging around.
The conclusion was the pump, it wasn't leaking any fuel, everything was dry around the pump so the thought was it was leaking in air inside the pump itself.
Hence the change to a new pump.
 
johnyfartbox said:
The original problem was hard start, firstly facing uphill when ever I parked it, then it went worse, even on the flat.
That's when I started asking for advice and digging around.
The conclusion was the pump, it wasn't leaking any fuel, everything was dry around the pump so the thought was it was leaking in air inside the pump itself.
Hence the change to a new pump.
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Yes but if it is fixed, and it wasn't the pump, then what was it? 🤔
 
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