Thread: Suspect it's slow...

Originally Posted by sierrafery

Make a test, clamp the pipe which goes from the WGM to the valve, this way you can see at what rpm goes to overboost... if it revs above 3000 and no overboost it's not about wastegate adjustment but about low boost which can be due to worn turbo, boost leak, clogged intercooler or bad fuelling... the real test would be to connect a boost gauge and compare the real boost with the MAP reading using the following formula: Boost = MAP - AAP

btw, did you clean the MAP sensor after the EGR bypass... if not do that ASAP and concentrate to free up the small hole in it near the protuberant element cos there's the boost reading

Can just unplug it from the actuator? Or needs to be clamped?


I cleaned the MAP about 4 months ago when I first got the car (and the MAP was filthy!) I'll clean it again now anyhow.

Fuelling is a possibility too - the MAF won't get above 550 at full noise. Though unplugging doesn't change things, so maybe MAF is ok. I've nights second hand on to try at any rate.

If you unplug the pipe from the actuator without clamping it there will be a slight boost leak to the air there when the modulator opens, the test is better with it clamped. Is your air filter new and good brand?

Originally Posted by sierrafery

If you unplug the pipe from the actuator without clamping it there will be a slight boost leak to the air there when the modulator opens, the test is better with it clamped. Is your air filter new and good brand?

Ah, good point.

At any rate I've already tried it by just unplugging it and sure enough it went into overboost quickly, maybe 2750 or so (and given what you've mentioned re boost leak it might have been quicker with the hose clamped). The corresponded to a reading about 235 or so from the MAP (AAP - 94, which the MAP was consistent with the MAP reading at idle).

So I am thinking this suggests the boost is being limited by the wastegate opening early... Might shorten it again a couple of turns and see how it goes.

OK then , it seems that at least the engine is producing boost and that's good, if everything is OK with the wastegate you should get normal boost around 1.3 bar with 13 threads left on the actuator rod and go to overboost at 9 threads left so if it's shorter than that and still low boost it might be a problem at the wastegate port... when my turbo was opened to fit the uprated billet core there were some carbon deposits under the flap which could have let some boost out there, the mechanic cleaned it well with abrasive paper to make sure it fully closes