Annoying overboost

[boosh]

I've searched a bit on the forum, couldn't find anything that was similar to what I'm seeing.

I've got a 2000 ZD30. New motor, new turbo, new nearly everything except exhaust...

I have NADS all set up.

Issue: I have my dawes valve setup for 14PSI. I had my needle valve inside but it didn't seem to be working, I've put it under the bonnet.
I can't seem to get the needle vale right, it'll overboost, so I'll start turning it, but by the time I've got it down enough to stop overboosting, the spool up is way too slow and I start getting high EGT's just speeding up on flat...

It seems to be overboosting too easily though. I can be in 4th accelerating up a hill and it'll be doing 12-13PSI while I'm at 2700RPM, then overboost. It's even done it after I was past 3000RPM...

How is 12PSI @ 2700RPM overboosting?

Or am I missing something?

[critta11]

What's it doing when you "overboost" ?

[meh]

By overboost, do you mean its going into limp mode ?

[BillsGU]

The needle valve can't adjust for over boost. The Dawes valve does that. Just undo the Dawes valve lock nut and open the valve about one quarter turn (lengthen the Dawes valve). This will reduce the spring pressure on the ball valve and the boost will level out before it goes to over boost. Don't forget to re tighten the lock nut. All engines seem to go into over boost at slightly different pressures. 12 PSI seems a bit low but how accurate is your gauge? Don't worry too much about the actual numbers. Just get it going right first and fine tune from there.

[boosh]

The needle valve can't adjust for over boost. The Dawes valve does that. Just undo the Dawes valve lock nut and open the valve about one quarter turn (lengthen the Dawes valve). This will reduce the spring pressure on the ball valve and the boost will level out before it goes to over boost. Don't forget to re tighten the lock nut. All engines seem to go into over boost at slightly different pressures. 12 PSI seems a bit low but how accurate is your gauge? Don't worry too much about the actual numbers. Just get it going right first and fine tune from there.

Yeh I tested with another gauge cause I thought it was quite low.

The needle valve does prevent overboost partially... It controls how fast you spool up, so if it spools up mega fast, your gonna have too high boost in lower revs so it'll overboost... Slow it down with the needle valve and you won't get the overboost.

I've had the dawes valve out as far as it can go and it still overboosts. I can't set it any lower than 13PSI... (no the spring hasn't been stretched)

[boosh]

By overboost, do you mean its going into limp mode ?

Yeh, limp mode. I usually just take my foot off then give it a bit less throttle.

[mudski]

12psi at 2700rpm isn't overboosting. Is your boost going beyond your preset 14psi for starters? If so I eould start from the beginning. Open your needle valve right open, then set your boost level again. Ignore the sluggish feeling for now, just get the boost level set. Once that is done, wind your needle valve right in and start the car up. The rod on the turbo actuator should be sitting right up as far as it can go. Then start to unwind the valve until the rod drops about 1/4 of an inch. Take it for a spin and see how it feels and goes. The rule of thumb is 10psi at 100k's. Too low and the turbo will spool up very slow the car will still be sluggish and your egt's will be high. Too high and the boost will rise much too fast and it will bounce up past your max boost you have set on the dawes and then settle back down. Also having it too high you mid range boost level for 100k's will be higher too.

[boosh]

12psi at 2700rpm isn't overboosting. Is your boost going beyond your preset 14psi for starters? If so I eould start from the beginning. Open your needle valve right open, then set your boost level again. Ignore the sluggish feeling for now, just get the boost level set. Once that is done, wind your needle valve right in and start the car up. The rod on the turbo actuator should be sitting right up as far as it can go. Then start to unwind the valve until the rod drops about 1/4 of an inch. Take it for a spin and see how it feels and goes. The rule of thumb is 10psi at 100k's. Too low and the turbo will spool up very slow the car will still be sluggish and your egt's will be high. Too high and the boost will rise much too fast and it will bounce up past your max boost you have set on the dawes and then settle back down. Also having it too high you mid range boost level for 100k's will be higher too.

No it's not going over 14PSI. It doesn't get to 14 PSI, because it overboosts, i.e. limp mode, at 12 PSI! Sometimes if I'm on a decent hill it'll get to 14PSI and overboost, but it never jumps over 14.

I've started from the start a few times, trying to get it right but there doesn't seem to be any middle ground, because it goes into limp mode at such low PSI.

[mudski]

So if your hitting limp mode at or before 14psi you of MAF is faulty I reckon. Where are you located?
So its not overboosting as such. Your maf is giving the ecu incorrect voltages and then the ecu thinks its over boosting and then it kicks limp mode in.

[mudski]

Get some maf cleaner from supercheap. Remove the maf ans give it a good spray.
More oftern than not this doesn't help if the maf is beyond cleaning. But its only around 15bux a can and besides. You should clean the maf every service too. So you will need it anyhow.