LS1TA385

iTrader: (1)

Just a little background on the setup:

408ci LS3 heads and intake
Front mount S475
M6 with 80#s and twin walbros

I have a good base tune in the car from a reputable tuner but the car would not make more than 1-2 psi during dyno tune. Since then i have went with a larger downpipe and "TR7" plugs and fixed a couple of boost leaks. I have noticed since the build that it lacks low end power but just recently is has been really bad to where it is popping through the exhaust until there is less load on the engine and then it pulls really hard in the upper rpms. Wideband is showing good when this happens and the only DTC is a P0103 which i figured is normal for an SD tune. I have been watching datastream while driving it this week and i have noticed the spark advance goes from 20sa to single digits and stays there under load and even as low as -2 under heavy load and lower rpms. There is no KR and no misfires but my map sensor data is not in sync with my boost/vacuum guage. Any ideas are really appreciated

BuffJoeyD

iTrader: (2)

Of course it doesn't knock. There isn't any timing in it. 1-2 lbs? What it supposed to be running at. If it built boost slow to your target boost then I would say make the tune more aggressive , but if your target boost isn't being reached then I would look for leaks everywhere.

Maybe I don't know, but you shouldn't have any reason for negative tuning in your power curve of your tune- timing table not set correctly.

LS1TA385

iTrader: (1)

Well I dont think it is a problem with the tune because it has just been recently that it started running very rough at low rpms and it is not a boost problem because the issue is primarily under vacuum and it starts building boost quickly under less of a load and into higher rpms. I just dont understand what could be pulling timing. According to datastream the MAP sensor is showing about 15in at idle and goes to 30-34in under load which is the complete opposite of my boost guage.

outkast6991

iTrader: (34)

If you feel the map is reading funny swap in a new one. Timing is based of map readings I believe

LS1TA385

iTrader: (1)

Yea the MAP data on my scan tool is way off but it is a 2 or 3 bar sensor so I wasnt sure how it would read. I will try a different scan tool to confirm the reading and then try a different sensor

soundengineer

iTrader: (16)

Timing is based off of dynamic cylinder air, which is a calculated value
MAF Airflow in g/sec * 15 / RPM

when in SD
DCA=GMVE*MAP/TEMP
where GMVE=VOL*VE/R
where VOL is a cylinder displacement, VE is the standard 0-100% volumetric efficiency, and R is a chemical constant for air


in SD(P0103 tells me that you are in SD), if your MAP sensor reads incorrect, or your IAT reads incorrect... its going to give you weird timing


is your tune a 2 bar or 3 bar OS?
is your MAP sensor a 2 bar or 3 bar MAP

base tune from a reputable tuner?... who is this tuner... a guy who does it for a living, or a guy who does it for a hobby.(not saying the tune is wrong... but you have to investigate everything)
a Simple check is to post the tune... we can very easily see if anything is "not right"

LS1TA385

iTrader: (1)

Ok I found out that my scan tool was misreading the 2 bar map sensor and showing 28in at KOEO so I changed units and is giving me a reading of 95kpa which is right at where it is supposed to be. But there is something still pulling the timing and causing really low power and popping under load. I still havent had a chance to look at datastream with my laptop scanner so as soon as I get some screenshots i will post them.