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MS3 w/ DSM CAS and LS2 Coils - Weird Timing Issue

drj434343

drj434343

Member
Joined
Feb 22, 2010
Location
Portland, OR
Everyone,

So I am working on getting my motor running with on MS3 and I am seeing some weird timing issues. My setup is below, but the main highlights is that it is a MS3 system w/ a DSM CAS for RPM/CAM sensing and 4 LS2 coils for spark. I have been able to get the CAS installed and I am seeing a nice strong RPM signal during cranking and with the engine running. However, I have had troubled getting the engine to idle and I have noticed a strange timing problem. At cranking speed and while running, the timing seen using the timing light is less than what the computer is commanding. It is easiest to see while cranking:

If I set the cranking RPM to 10 BTDC I get 10 BTDC (I twisted the CAS to obtain this)
If I set the cranking RPM to 20 BTDC I see about 15 BTDC with the timing light
If I set the cranking RPM to 30 BTDC I see about 20 BTDC with the timing light

I also see similar behavior while the engine is running. I have tripled check the CAS setting and they appear to match the "official" CAS information thread. I am at a bit of a loss as to I am getting this offset in timing...it appears the timing is about 2/3 what the computer is asking for. I am currently away from my home computer so I can't post the MSQ or Log yet, but I will do so tonight. I am looking for some ideas on things to check or software options to verify as I am at a bit of loss to what the source of this issue may be. Thanks in advance!

My Setup:
B230 Squirter block stroked to 2.5L
RSI Head
IPD Turbo cam
NIW Intake/fuel rail
MS3-Pro running recent (last 2 months) firmware
750 CC low-impedance injectors (running resistors)
DSM CAS w/ Yoshifab Hi-res Disk
4 LS2 coils running in sequential Coil-Near-Plug configuration
 
So it turns out this was a dwell issue. I did some searching on the MS forums about those LS2 coils and my dwell + battery correction was too low and apparently the LS2 coils don't like having too low of dwell. Once I upped the dwell and adjusted the timing, everything runs great now!

Brian
 
What was your battery correction? I'm running the default correction table and currently I use the dwell table and under cruise I run like 2.5ms and under power I ramp to 3.8
 
Nathan,

I stole the table from a post on the MSextra forums...the guy indicated he had pulled it from a GM car that originally ran the LS2 coils.
https://drive.google.com/open?id=0B9TBGLcBM4-OVDlUb3ZlV2RMTUk&authuser=0

I think most of my problem was that I was setting timing while cranking (so low voltage) with a low cranking dwell and relatively low battery correction table. These probably compounded to give me issues while cranking and so the timing I set while cranking was not right once the engine was running. If I had just set the timing once the engine was running I probably would have been fine :)

I was looking to run a dwell table as well, but that option doesn't seem to appear in the latest MS3 firmware...there is only a nominal dwell and battery correction curve. The "Use dwell vs. RPM curve" is greyed out for my when doing "standard dwell".

Brian
 
Ah yes. My cranking dwell is like 5.5

The table should be there. You activate in the ignition decoder page, and then the table comes live
 
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