Boost suddenly drops midway through run - seen this??

[PL]

If you have, then you're not alone. I've just got off the phone from another tuner describing what seems like some sort of boost cut - only to find that it's not a tuning or electrical issue. It's the pipework between the AFM/air filter and the turbo sucking in and cutting off airflow!!

I've been done by this one twice myself - and heard from other guys battling with the same problem. So I thought I'd post something up here so hopefully other people don't get caught.

It's usually cars with light modifications - your typical FMIC, exhaust and pod filter guy. The cars with the more serious mods usually have the inlet piping replaced with a hard-pipe. Nissan usually fit a spring inside the nasty convaluted rubber pipe to help it keep its shape. But I've heard that some cars didn't get them! I'm sure some owners remove the spring in an effort to free up airflow too. I'd replace the OEM rubber pipe anyway - anything so nasty on the inside can't possibly be good for smooth airflow.

The bit that gets you is that everything seems fine at first. Cool - easy tune. And the owner has probably been driving it around like this for ages. But then you turn that boost up a tad more and everything turns baaad! WTF? Exhaust restriction? Baffle in the muffler loose? Some sort of funky wastegate actuator problem? You start to come up with all sorts of creative reasons to explain where the boost has gone! It's only when you have somebody watching under the bonnet that you'll pick it.

It tends to get worse as heat soak warms up the rubber too. To really confuse things - if you give up and come back in the morning you might get a couple good runs in before the rubber heats up and collapses again!

I hope somebody reads this and it saves them the frustration of tracking down this nasty problem!!!!

PL

[bachig24u]

The rubber pipe isn't the problem!!

[nissangts]

Yeah? So what is the problem then?

The rubber pipe isn't the problem!!