Boost leak time from 100Kpa to 0Kpa

[orsum]

My S2 seems to have developed a boost leak.

I did a boost/leak test (as per the sticky) from the MAF (A1) with the crankcase hose blocked (A3) and the crankcase cover pipe open. After a bit of soapy water I found a leak on the MAF outlet hose (A3) that goes to the crankcase. I fixed that.

I then did the same pressure test and I was able to get the pressure to 1.1 = 110Kpa bar which it held for about 15 to 20 second before it reached 0 bar 0 Kpa. Does that sound right? I could not find any other leaks. And I had no faults using the Ross Tech diagnostic software.

Anyway I put everything back together and took the car for a test drive. The car felt a bit better but the misfire/spluttering issue was still present. Clearly I have not found the actual fault.

As a pointer how long should a good turbo system hold its pressure during the boost leak test I did assuming the system has no leaks other than that of a car in top condition.

Going to have another go at finding the issue on Wed.

Any pointers?

[orsum]

Just found this video of an S2 pressure test. Mine drops much faster. https://www.youtube.com/watch?v=wdFJMT0urH4

So I do have a second leak

Hope this video helps others.

[newsh]

Pull the breather pipe out of the MAF hose and block the hole in the MAF hose. Test again.
There’s no point pressurising the PCV system too much as it only ever sees vacuum. If you get air coming out the open end of the breather at the MAF hose then there’s a little one way valve under the IM which may be leaking. This should open when the IM is in vacuum to purge the PCV and close when there’s boost. They can split or get dirty and stick open.

Pay attention to the injector seals at the inlet manifold.



I believe you’ve already replaced all your small bore vac tubes with new? If not then I recommend you do so.

Pull the vac tube off the front of the inlet manifold and cover the nipple with your finger.
If you get air escaping from the vac hose your DV diaphragm is leaking/split.

Also listen carefully inside the car that you don’t have a leak in the line to the ECU or under the back seat where the difflock vacuum hose goes.

Small leaks are hard to find!

[Rikki Kitto]

I hate boost leaks

[orsum]

If you get air coming out the open end of the breather at the MAF hose then there’s a little one way valve under the IM which may be leaking. This should open when the IM is in vacuum to purge the PCV and close when there’s boost.

Lucky for me I have a spare. I did check that one way valve but I will check it again.

I hate boost leaks

[orsum]

The valve was leaking a little so I changed it. Still got the same problem the search goes on

[fish]

Have you checked the O-ring on the intercooler?

[orsum]

Hi fish yet it has been checked. There is no leak from the MAF to the throttle body holds 100Kpa.

The leak is from the pipe that is connected to the throttle body and idle stabilization valve onward. Now battling to get to 40Kpa and it is dropping quite fast when I take the air line off.

I hate boost leaks

[Bowie69]

Can you get some smoke in there?

[orsum]

I could if I had or get hold of a smoker. Phone lots of people asking if anyone has one and so far no luck.

Looks like I need to search google on how to make one.

[Tractor Dave]

Have you tried spraying everything with a washing up liquid solution? You should see bubbles.

[orsum]

I have checked the engine bay and there was no bubbles that I could see.

Tomorrow I will be going inside the car to check the ECU and the diff lock piping.

[orsum]

Update.

Managed to get the car to a friends place who has a good compressor that can give me a continuous 1 bar. I found two leaks. The first was on the ISV N71. The second was on the clips on the petrol pressure regulator. The hose was an easy fix and it has solved some of the boost/performance issue.

As soon as I can get to it the N71 leak will be fixed with a good clean and Epoxy the end which is leaking.

[orsum]

The ECU and Diff lock piping have no leaks.

[Rikki Kitto]

I hate chasing boost leaks thanks for posting it will so eone else for sure, its amazing where they can turn up. I had one behind a jubilee clip