Hi guys,

My 2003 sti JDM has developed a boost problem......

I was going onto the motorway and got the car up to about 4.5k rpm, under full chat. Car was boosting perfectly and then I felt it loose boost?

The car runs, drives and idles fine and there are no warning lights on the dash. I have checked all boost hoses and all other hoses, no leaks were found and everything was tightened. This made no difference. I changed the DV back to the standard item (from an HKS), still no difference. I've just cleaned the air filter and am waiting for it to dry (the filter was pretty minging).

The car is perfect, except not boosting properly (I would say it has lost about 70 - 80% boost, there is still a very small amount of boost, as if something is restricting it??)

Car has been mapped and has a full miltek with sports cat but has been running perfectly up until the point where it lost boost.

Any ideas guys?

 

are you sure its not the hot ambient temperatures, having had turbocharged petrol cars for some years now I noticed the hot weather seems to effect it quite a lot, especially as you have a top mount the heat soak can effect the boost.

 

No, in short. I see what you're saying, but there's no way that the car could lose so much power just through a bit of heat soak. I felt the car physically lose power in one swift go coming onto the motorway, and since then it hasn't been boosting properly.

 

prolly a boost leak or coil maybe

 

Does the engine management light work? If there's no boost leak then I would suggest a sensor. Might be worth getting it plugged in to a diagnostic scan tool.

 

Had a similar problem, actually it was 2 problems, one was the camshaft sensor the other was the NPS.
Best bet is getting it on a diagnostic machine/rolling road to see what it pulls up.

Tony

 

NPS?

 

Neutral position switch

 

Oh ok. Pardon the ignorance, but what does that do (or possibly not do in my case) x

 

The engine management light is not on mate. No other lights on the dash either (except the ones that shoud be on!). Everything looks normal.

 

A failing NPS switch can effect the use of the VVT Heads/CAMS. However, I'm not sure how that would reduce boost as you're suggesting.

 

If the boost just fell away it sounds like a pipe is off or split or maybe your actuator has come off the waste gate arm there's a load off vacume hosese are you sure you've checked them all

 

I had a failing NPS (MY04 JDM STI) and did not even know. It didn't affect anything in terms of how the car ran and I was even able to have the car mapped without it affecting things. It does sound like a split hose or something along them lines.

 

My nps played up when I had the l/c mapped I suppose if the car thinks its in neutral then it could take the boost out the equation but I'm guessing I don't know if the nps could do that didn't scooby clinc have a issue with a nps switch that troubled them cant remember what it was now.

 

I've just checked everything again, took the heat shield off, checked the actuator, all connections, nothing seems wrong (that I can see).

 

Had the same issue as this on my03 jdm cleaned the boost control solenoid and haven't had a issue since. Always worth a try.

 

Where is this located mate? (Pic??)

 

Drivers side front near strut

 

It might not be on but does it actually work? When I bought mine it had a running and boost issue but no engine management light was on. When I started investigating it the engine management light didn't actually work.

 

There are lots of things around that area dude, what does it look like? I'm no car expert lol!

 

Got a pic? There's a few things around that sot of area, I'm no car expert lol

 

It will have two vac pipes attached to it one going to the inlet trunk and one leading to the turbo/actuator on a T piece. Remove from drivers side strut tower remove vac pipes and clean with some brake cleaner.

 

Ok kl. I've removed it. It's just a case of getting some brake cleaner down the two holes that the vacuum pipes connect onto?

 

Yep that's it.

 

Any good?

 

No idea if this will be anything to do with your problem, but i found my lack of boost was due to the exaust been lose on the front section where it leaves the manifold

 

You mention 4.5k revs... Will it now not go past that?

If so, is your speedo also not working? Cause if not, it's a classic sign of gearbox sensor failure, IIRC.

 

Hi guys,

Ok, update for any one else who may have a 'mapped' JDM (no doubt applies to uk cars too!)

Firstly, thanks to Paul @ Xtreme Scoobies for sorting it!!

Ok, so, plugged the car into the diagnostics, took the map off and drove it up the road.....perfect drive with the standard map and, more importantly, boosted fine (although the overall power of the car was obviously down, but this is to be expected with the standard map).

The Powerstation map was then put back onto the car, test drove and was fine. It's suspected that the MAF may possibly be on the way out, but for now, its fine. When the MAF goes, it goes, no great drama, but until then, its back to normal!