Finding Boost Air Leak

Tom B

Über Member
Okay my Ford Focus 1.6TDCI has an air leak.

In July when I was on my hols with a fully loaded car i noticed it was down on power and hissing a bit the mpg took a bit of a hit too.
I easily found an air leak on the post intercooler pipe that was blasting oily air over the washer bottle area.
Gorrilla tape and agricultural cable ties kept it under control for the holiday and 500mile drive home.

Pipe was duely replaced in August - getting the right pipe was a faff.

All was well, until a few weeks after I noticed a further hiss, this time much quieter and only really noticeable when on boost and accelerating hard or getting out of the throttle after acceleration. However I cant seem to find the leak! I decided to leave it an let it develop initially hoping the usual oily stain /spray would give it away.
Its not present on tick over and revving it in neutral doesnt create enough boost to hear it.

I have now done 1000miles in it since Aug incl 300 last Wednesday, it is perhaps a little worse (but perhaps i can just hear it having fixed the antiroll knock) but still no tell tale and no clues.
Fuel economy is standing firm at about 51mph (probably still on summer diesel).
It is throwing up error code p0428 which suggests an air leak.

I have had a feel over the pipes i can see and all seem good, there is a steel pipe section that is a bit scabby but seems fine, intercooler looks good.
There is a bit of oil sitting on top of the turbo actuator possibly leaked from the turbo itself, but I cant really see how this woudl create my hiss.

I'm considering filling a garden sprayer with soapy water and trying to spray the hoses.

Does anyone have any other ideas - other than leaving it and turning the radio up?


Legendary Member
Some pipes are vacuum rather than pressure, so the soapy water would not tell a leak.
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