Annoying overboost

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?

What's it doing when you "overboost" ?

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

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.

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Originally Posted by 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.

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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)

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Originally Posted by meh

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

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

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.

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Originally Posted by 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.

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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.

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.

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.

It's got a brand new genuine maf. Only about 2000k's since I put it in.

How much does the exhaust factor in? It's the stock exhaust but it's in pretty bad shape.

When I know it's about to overboost, if I really put my foot into it and max out the dawes valve, it doesn't overboost, or at least takes longer. Taking this into account, I've just gone for a drive where I closed the dawes slightly and opened the needle a bit. I got slightly higher EGTs but they settled quite quickly... I didn't have any limp mode issues, maybe it was just a lucky day, maybe I'm on to something. :1087:

I think it's just going to take me a while to get it right. Like I said, it's a new motor with new turbo and a few other things and it's just slightly different than the previous motor so it's taking a while for me to get used to it...

I think you may have your terminology mixed. Overboost suggests (for example), if you have your dawes set at 14psi, when you accelerate you 'overboost' and hit 16/18 psi before it settles at 14. When limp mode happens you will have max 10psi with virtually no acceleration until you lift off the throttle then power will return.

Limp mode in my experience is a combination of too high MAF voltage and/or too high boost. If you have ECUtalk its easy to see it happen.

Overboost on the other hand is fine tuning dawes and needle. I still get a slight overboost on mine but I like the quicker spool-up rate :D With my setup I will 'overboost' to 19/20 under WOT then settle to 17psi.

The car could have collapsed causing back pressure and stuffing everything up.

^^^^ Eh?

Also the MAF still could be faulty. Unlikely but it does happen. I have sold around 100 OEM MAFs in the last 12months and only have had one faulty one. So while its not common, it does happen. You don't have your old MAF to try? Just for the sake of trying...

I think Critta may mean 'cat', which is entirely possible and a great excuse for a shiny new exhaust ;)

Boosh, is your EGR blocked?

Lol yeah.:1087:

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Originally Posted by Mud Gecko

I think Critta may mean 'cat', which is entirely possible and a great excuse for a shiny new exhaust ;)

Boosh, is your EGR blocked?

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Yeh my EGR is blocked.

That's an interesting thought about the cat... The previous owner fixed/welded it up at some stage. I do plan on a new exhaust, just don't have the funds yet. Is there a way I can check that?

I might put the old maf in to test it mudski.

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Originally Posted by mudski

^^^^ Eh?

Also the MAF still could be faulty. Unlikely but it does happen. I have sold around 100 OEM MAFs in the last 12months and only have had one faulty one. So while its not common, it does happen. You don't have your old MAF to try? Just for the sake of trying...

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Yeh I did mean CAT haha my bad