Fuel Pumps

[Shoppinit]

That sounds encouraging. Just got to find the leak now. If you try to blow into it can you push any air through with your mouth? If so, find a smoker and get them to blow some smoke into the system. Not sure if you'll find a smoker in Paris though.

Hold on, blow hot air into the inlet and use your magic thermal camera!

[Shoppinit]

In the past I've found noises like that by using an improvised stethoscope. Bit of 6mm compressed air tubing or similar. Stick one end in your ear and explore with the other end.

[Shoppinit]

Also, if you are blowing smoke into the engine with a tube sticking out of your ear in a street in Paris then I absolutely need to see a photo of it.

[Classik]

That sounds encouraging. Just got to find the leak now.

Yes, thanks for the encouragement and the good vibes again! I just hope this is not something too serious & expensive to fix..

If you try to blow into it can you push any air through with your mouth? If so, find a smoker and get them to blow some smoke into the system. Not sure if you'll find a smoker in Paris though.
Hold on, blow hot air into the inlet and use your magic thermal camera!

Good tricks! However none of the above would do I'm afraid as there is some sort of 'valve' effect, like the leak doesn't appear until air reaches a certain pressure (0.2 bar or something?), so I guess the smoker will loose its lungs sooner than expected if he needs to hold that pressure whilst sending enough smoke in the system..

In the past I've found noises like that by using an improvised stethoscope. Bit of 6mm compressed air tubing or similar. Stick one end in your ear and explore with the other end.

That's a good one too!

[Classik]

Also, if you are blowing smoke into the engine with a tube sticking out of your ear in a street in Paris then I absolutely need to see a photo of it.

Count on it! LOLOL

[Shoppinit]

I guess the smoker will loose its lungs sooner than expected if he needs to hold that pressure whilst sending enough smoke in the system..

Maybe you can find a smoker who's good at blowing in rue Saint Denis?

[Classik]

Ooops, you seem to know quite a few things about Paris...

[Shoppinit]

Where are you at with this?

[Classik]

Hi Shoppinit,
Thanks for the continued interest! Other priorities have taken over (family and make a living to name a few) but I'm on it, definitely. If time permits I'll have more news before the end of the week. I just cross fingers this air leak will be easy / cheap to fix...

Since you're asking I have another question for which I may need some help . I bought new oem MAFs connectors with their protection (grommets) but the pins need to be reused as they are attached to the harness. What would be the best way to take them out of the old connectors without breaking anything in the process? Also, the black plastic hose surrounding the wires has broken due to heat and age. Any suggestions to replace it with something equivalent that will stand the heat? Initially I though I could use some heat-shrinkable sheath that I use for standard electrical duties, but I don't think they could endure both the temperature and possible chemical (oil, coolant) aggression.

Many thanks!

[Shoppinit]

Something like this could help:

https://www.amazon.co.uk/QISF-Terminals ... B07JZ39JTG

You can get a new connector and boot from Audi. Probably I’d use heat shrink. Can always be replaced if necessary.

You could also get new pins if you want. I think there’s a list of pins in the FAQ.

[Classik]

Spot on, many thanks!

[Classik]

Hi Shopp & all,

As promised here's a report about what ve've done with my mechanic today.

1/ throttle valve adapter : I grabbed a second hand one on German eBay to replace mine which was doing strange noises (like those 56k modem ) and changed the related seal + O ring. It appeared like the throttle body adapter wasn't tightly attached to the intake manifold so I guess a potential air leak has been corrected in the process. I had great hopes on that one but unfortunately it didn't change a thing with regards to the MAFs reading discrepancies.

2/ Air leak tests: we did 2 tests but both of them led to leaks. So I certainly need some guidance as how to organize those air leak test.
- Test 1: blocked both intake air ducts (077133354) and injected air through one of these ducts (that's the first test I did earlier in this thread) : leak but we couldn't find where it goes out
- Test 2: blocked the output of one intercooler and injected air through the related air duct : leak through the pressure relief valves (034129101C). It seems the right side valve (Bank 2) is snoring (for lack of a better word) more than the left one

I'd love an expert eye on the above, but my naive interpretation is that those tests above won't lead to specific conclusions. Take test 2 for instance: when I push air through the air duct I suppose it's quite normal for the air to go backwards in the dump valves exhaust then to find its way back to the pressure relief valves, or?

This thing is really driving me nut.

[Shoppinit]

Quite a good guide here:

https://www.bimmerforums.com/forum/show ... ow-and-Why



You might be leaking air out through the exhaust. You might have to block the throttle body but then you won’t be testing the inlet manifold.

Or you could try moving the crank so that the valves are closed. Maybe with a V8 that’s going to be tricky.

[Shoppinit]

The PCV valves are designed so that when there is depression in the manifold, crankcase vapours are sucked into the intake manifold. However, when boosting, the diaphragm inside moves and it then diverts the blow-by to the air intake upstream of the turbo.

When you are pressure testing, you are pressuring the intake manifold (assuming the throttle butterfly and cylinder head valves allow some pressure to build up). Depending on the air flow / pressure you are able to achieve with your test, if the PCV valves don't actuate you could just be pumping air into the crankcase. If the pressure is sufficient to close the PCV valves then they should be communicating with the inlet, upstream of the turbos (where you are pressurising). This should be a closed system and pressure should build up. Again, depending on how much air is escaping down the exhaust.

You might need to block of the PCV valves / tubes to properly test the pressure in the rest of the system.

Also, the PCV valves are connected together and could potentially allow a transfer of pressure from one bank to another. I wonder if the valves could be affecting your MAF reading. I suspect they are not very expensive. Might be worth replacing as a preventive measure, even if that doesn't cure the problem.

[Shoppinit]

Also, now I'm wondering about wastegates. Have you checked the condition of the hoses going to the wastegates? I wonder if you've got a weak spring in one of the wastegates or something, although I wouldn't expect that to account for your MAF discrepancies at idle.

/Or maybe it would have a slight effect, even at idle. I wonder how fast the turbos are spinning at idle. There's still 4.2 litres being displaced 500 times a minute. That's 35 litres a second, even before you account for the expansion of the combustion product and the fuel mass going through. Maybe that's going to spin up one of the turbos a bit if the wastegate isn't working properly.