Suddenly won't start after recent tandem pump change

The other test we can do is run the engine for another 30 minutes from the a jar and see if the bubbles reduce.
And I think from distant memory when I did a diesel purge using the same method as yourself @johnyfartbox there were no bubbles in the return line. (solid fuel)
Perhaps if someone else has carried out the same job recently they could give us their findings?

Are you sure the o-ring in the diesel temperature sensor housing is 100%?

Or did I miss where you connected the clear tubes at? I'll check.
Checked, the fuel temp sensor is still part of the diesel purge rig.👍
 
Last edited by a moderator:
1000008382.jpg

Brand new.
I'm beginning to think that the old pump was ok after all, I kept it just in case, I hate chucking stuff like that away.
 

Attachments

  • 1000008383.jpg
    1000008383.jpg
    3.3 MB · Views: 15
I did think about the temperature sensor in the return line and yesterday I checked on another A2 that the green clip was fully home, I noticed that the clip on the other A2 was slightly further up, so went back to the white one and managed to click it up properly.
 
Good stuff, thank you for answering what may have seemed like daft questions.

We would be seeing fuel dribbling from most these items and not air being drawn into the system.
You have a new pump and new gasket.
Which would also be seen as a leak around the engine and it would be unlikely to draw in air to the lines when the car is running.

It looks like everything on the outside of the engine from the purge jar and back is in tip top condition.

Therefore we may be dealing with what @PlasticMac said about residual bubbles in the system.

It could be injector seals or highly unlikely an internal seal failure in the new pump between the vacuum and fuel sections.

If the car is running fine in this state with bubbles in the line. I would leave well alone and make a note if it incase the car starts to go wrong in the future.

When you have worked as had as you tracking down a fault like this you keep second guessing your work.

From what you have said in your replies I can say with a good degree of confidance you have done a great job and the bubbles may clear after the car has been out for a test run.
 
Last edited by a moderator:
johnyfartbox said:
Ok peeps.
Update time.
I've just done a diesel purge on the car, white one, the one in this thread.
I hope I've done this right, I followed instructions so I think so.
When I connected the two clear pipes to the feed and return pipes submerging them into a glass jar almost full of the purge making sure that they were on the bottom so no air could get in I started the engine, cracked first time and then laboured for a couple of seconds then ticked over fine . I began to increase the revs slowly up to around 3000 RPM then back down, repeat and rinse for around 30 minutes, keeping an eye on the level.
The return fuel started to get warm obviously and then decided that would have put enough through to do a clean of the jets and whatever else it does.
The thing I did notice though, there was a constant stream of bubbles going through the return pipe back into the jar, the feed pipe was solid fuel, no bubbles whatsoever.
Thoughts?
View attachment 122010
Top pipe feed.
Bottom pipe return to the jar
Click to expand...
I am trying to visualise how you connected the hoses but not 100% sure. Can you confirm that one of the clear hoses is connected directly at feed inlet of the pump, and the other directly at the return outlet of the pump?
If so, and if you are observing constantly new bubbles in the outlet hose this means that new bubbles will all the time be added to the fuel system and will not disappear with time.
And if the hose connections are as I think, see above, then it can hardly be snything else than a problem of the injector seals or pump seal. Assuming your hoses are tightly mounted!
Does this sound reasonable ?
 
rotifer said:
Good stuff, thank you for answering what may have seemed like daft questions.

We would be seeing fuel dribbling from most these items and not air being drawn into the system.
You have a new pump and new gasket.
Which would also be seen as a leak around the engine and it would be unlikely to draw in air to the lines when the car is running.

It looks like everything on the outside of the engine from the purge jar and back is in tip top condition.

Therefore we may be dealing with what @PlasticMac said about residual bubbles in the system.

It could be injector seals or highly unlikely an internal seal failure in the new pump between the vacuum and fuel sections.

If the car is running fine in this state with bubbles in the line. I would leave well alone and make a note if it incase the car starts to go wrong in the future.

When you have worked as had as you tracking down a fault like this you keep second guessing your work.

From what you have said in your replies I can say with a good degree of confidance you have done a great job and the bubbles may clear after the car has been out for a test run.
Click to expand...
Thanks for the respectful and welcome praise rotifer.
To be honest, I have driven it around the estate I live on to keep off the main roads because its on SORN, so no tax or insurance , I know its still a risk incase someone hits me or vice versa.....................up to now it drives absolutely perfect, it pulls well and never misses a beat.
I only noticed today that I have done almost 13 miles over the last few weeks driving around the small estate I live on.

It was only a few weeks ago that I changed a snapped wishbone on it, that was fun, (not) even though I've done two wishbones on my other A2.
Tomorrow I will check the temp sensor O ring, how I do that im not sure yet, I can also swap out my other sender that I know is fine and see what happens .

Oh , heres the DP before and after purge.
PXL_20240407_135946247.jpg

Obvs used on the left, not as bad as I thought it would be
 
I am the same, I have a 'test run' circuit. I choose a quiet time to do a test, think it got up to 7 miles on the red car before it went for the MOT.
👍
Diesel purge is a good idea for all cars with high miles and original injectors. Should improve MPG but for a short while the MPG may go down as I tend to used that new performance provided by a clean injector. 😁
 
Joga said:
I am trying to visualise how you connected the hoses but not 100% sure. Can you confirm that one of the clear hoses is connected directly at feed inlet of the pump, and the other directly at the return outlet of the pump?
If so, and if you are observing constantly new bubbles in the outlet hose this means that new bubbles will all the time be added to the fuel system and will not disappear with time.
And if the hose connections are as I think, see above, then it can hardly be snything else than a problem of the injector seals or pump seal. Assuming your hoses are tightly mounted!
Does this sound reasonable ?
Click to expand...
1. one of the clear hoses is connected directly at feed inlet of the pump, Yes, to the metal pipe on the left of the engine.
2. the other directly at the return outlet of the pump. Yes, to the metal pipe on the left of the engine. as you look at the engine from the front.
That was the easy way to connect the clear hoses to the pump.
No, I didn't use a clamp for the hoses but they were quite hard to push on but flexible if you know what I mean.
And it does sound reasonable yes.
 
Joga said:
I am trying to visualise how you connected the hoses but not 100% sure. Can you confirm that one of the clear hoses is connected directly at feed inlet of the pump, and the other directly at the return outlet of the pump?
If so, and if you are observing constantly new bubbles in the outlet hose this means that new bubbles will all the time be added to the fuel system and will not disappear with time.
And if the hose connections are as I think, see above, then it can hardly be snything else than a problem of the injector seals or pump seal. Assuming your hoses are tightly mounted!
Does this sound reasonable ?
Click to expand...
I'm not convinced that the bubbles in the return line, into the jar of diesel, will be drawn back into the supply to the pump.
Need convincing ...
Mac.
 
it looks like the bubbles are going upwards near the end of the vid, where you can see the tube connected to the out feed pipe in the background, strange but didn't happen .
I suppose I could do it again tomorrow and clamp the clear pipes properly and test again.
 
Bet everyone is getting fed up with this now, I am.
Been facing uphill on the ramps for an hour and a half so thought I'd try it, nothing, nada, cranking strong but not firing.
That's proof of fuel run back without a doubt.
Time for a beer or should I make it a few beers.
 
PlasticMac said:
I'm not convinced that the bubbles in the return line, into the jar of diesel, will be drawn back into the supply to the pump.
Need convincing ...
Mac.
Click to expand...
I dont think so either. But when the system is returned to its org state (without the jar) the source of the bubbles seen in the jar test case will keep on producing new bubbles all time into the fuel system I think.
 
Joga said:
I dont think so either. But when the system is returned to its org state (without the jar) the source of the bubbles seen in the jar test case will keep on producing new bubbles all time into the fuel system I think.
Click to expand...
I just can't see where, in the jar setup, air is entering the feed to the pump. That's why I was hunk
johnyfartbox said:
Bet everyone is getting fed up with this now, I am.
Been facing uphill on the ramps for an hour and a half so thought I'd try it, nothing, nada, cranking strong but not firing.
That's proof of fuel run back without a doubt.
Time for a beer or should I make it a few beers.
Click to expand...
So, is that everything back to as built?
Mac.
 
@Joga is right because instead of the return going to the tank it goes to the fuel filter housing.
A bubble feedback loop.
 
Good starting from the jar of diesel would seem to suggest that the pump is okay.

If the air in the return line is being caused by injector seals, then maybe the air can travel back down the return line to the filter, and mix in with the fuel feed again? I guess trying it with the return run into a bucket may be a way to check that theory?

Personally I would check the fuel feed for air again, see if air is present in the lines in the engine bay, and then work back from there. Are you confident that the air that you saw being drawn up from the sender is no longer a problem?

If there is no air in the feed lines without the engine running, then maybe try running it with the return into a bucket, to see if the air is working back into the system?
 
For the line to the pump to be empty, air has to get in.
If this only happens with the car facing uphill, the air entry point is below the fuel level, when the car is level, but above the fuel level when it's facing uphill.
I think you've proved the problem is in the sender assembly. That is, as long as you're sure that when facing up hill, the fuel level is high enough to fill the swill pot, and that the swill pot float valve is working as a one way valve, keeping the swill pot full, but not allowing it to empty.
If the swill pot is not full, the pump will draw air.
An empty line is the same wether you call it drain back, or leak.
Two beers I reckon.
Mac.
 
You must log in or register to reply here.
Back
Top