1.9 16v decatting and got big overboost - Alfa Romeo Forum
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(Post Link) post #1 of 8 Old 20-01-14 Thread Starter
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'03 Stilo JTD115

1.9 16v decatting and got big overboost

My turbo was almost dead, so i've got a replacement from scrap yard.
The same - 1749.
While installing it , i've removed the catalyst from the downpipe and the second catalyst too.
View image: 2014 01 11 17

After assembling everything , took a ride test.
And i've got an overboost.

With downpipe and old turbo - 4th gear - View image: screenshot 51
W/o catalyst in downpipe, "new" turbo with cleaned vanes from the old turbo and old actuator - View image: screenshot 52 4th gear again

Should i continue with editing N75 map or there is something mechanical I'm missing ?
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Is there any extra fueling from std mapped or tuning box.
Doesnt look massive overboost and only later up revs.
To be expected a bit with decat.
Can you check against vnt% unless its 19.99%
If your already mapping vnt% where overboosting take 5% at a time less and relog.
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(Post Link) post #3 of 8 Old 20-01-14 Thread Starter
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Yes there is extra fuel.
But with stock file, overboost is the same.
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(Post Link) post #4 of 8 Old 22-01-14 Thread Starter
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Think I'm on the right track, after messing with the N75 map

http://s29.postimg.org/cwzulq5yf/screenshot_263.png
emzo is offline  
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looks nicer well done, stll a touch at spool up.
can I ask why you are keeping standard boost map if you already have extra fuel ?
your already adjusting vnt% in the ecu maps why not add an extra 50-100mbar of boost at max IQ, and this should move you away from the 20% vnt mark nearer the 30%vnt.
do you currently see smoke , whats your afr(logging act maf mg/I and act IQ)
Is yours jtd 16v or jtdm 16v as there is a small difference in the turbos ?
either way search on here for max boost im sure 2400-2450mbar is not pushing the envelope.
how is the extra fuel delivered map or box ? as when I had tuning box and had fully decatted the car ,I had similar overboost and 19.99%vnt due to extra fuel without any soi advance that leads to extra injection after tdc causing quite high egt and overspooling turbo quite a bit( worse Id seen was close to 2600mbar and 850deg c egt)
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(Post Link) post #6 of 8 Old 22-01-14 Thread Starter
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'03 Stilo JTD115

16v jtd 140bhp

The graph above is on stock condition.
Just needed to be sure if overboost is caused by decatting and not by the turbo, cause it was from a scrapyard.
Geometry clean was necessary - http://s29.postimg.org/oshjcs61z/2014_01_17_10.jpg
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im guessing the vnt actuator was removed to split the housing, I remember being told to check that the actuator was pushed towards the internal stop pin inside the housing with the locating bolts slackened off and then tighten up holding against that pin.
there is a mm or 2 slack on the mounting holes and every mm helps.
also disconnect linkage to vnt arm and push arm to pin if arm cant be reconnected the linkage may need legthening to be sure its resting on internal stop
on the car probably quite hard to get to.
I think it was described as being equall to around 5% vnt difference
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The 8v variants are more prone to heavy over boost when decated but I've seen it on the 16v many times and only managed to combat it by reducing peak fueling around 2000-2750rpm and forcing vnt duty down .
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