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Tuning for Startup Flooding and Bogging

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Dec. 19, 2014

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Do you have an issue with your startup fueling being too rich and flooding or bogging? This is specifically seen with aftermarket intake manifolds used with factory tuning settings. For example, with the marine intake on an L31 engine, there is some flooding caused by fuel pooling in the runners when using the stock L31 tune settings. This is due to the different injector aiming and airflow differences between the manifolds.  The intake really doesn’t need much extra fuel to kick things off and get it running, and what is needed is typically covered in a few different ways such as initial batch firing.  So to address the issue we have with our startup being too rich, we are going to modify these tables in the following way:

B3666 – Additional After-Start Decay Rate
Set to zero to disable.

B3667 – Additional After-Start Decay Amount
Set to 0.000

B3668 – Additional Enrichment Enable
Set to Disable

Now we are going to disable the tables associated with the cells we mentioned above, but why?  That’s a question that comes up a lot.  Basically, because even though we have disabled the use of those tables in a few specific cells, they may still be used elsewhere in the Computer or operating system and cause modifications to the fueling of the computer in unforeseen ways.  Realistically, it’s a hack that we’re able to modify the computers the way we do.  That being said this is basically a failsafe measure to make sure that you get the results you asking for.

B3663 – Additional After- Start Enrichment
Zero this table

B3664 – Additional After- Start Enrichment Delay
Zero this table

B3665 – Additional After-Start Enrichment Active
Zero this table

Now we want to see what effect this has on startup.  Prep your wide band and start the engine while watching your AFR readings.

Did you see the desired AFR you’re after?  If not then we should adjust B3632, which enriches the startup based on engine coolant temperature and we have direct control over the extra fuel here without guessing. Want it richer or leaner? Simply adjust this table.


Another way to improve your startup quality, especially useful for when it gets cold outside, is adjusting the table pertaining to startup air friction. Changing this table helps give an extra burst from the IAC valve when starting to help crank over a cammed or modified engine.

B4343, You can increase Start-up Friction Airflow Correction table to help with easier starting. This table is based around coolant temperature, You can add and remove based on how your car/truck acts at different temperatures. Sometimes cams do not start-up well in the cold or handle restarting well. If your engine stumbles or struggles right after startup, it may be because there is not enough initial airflow. Adding air in here is a good, temporary way to add in the airflow, which will be decayed out after the first 30 seconds or so.

Im running an LS style throttle body and have opened up a second hole in the throttle blade, and the additional air helped solved alot of my idle problems. However sometimes I still have trouble starting and restarting, butmodifications to this table have seemed to help that.

Now that we’ve addressed this startup issue, and you’ve read this far, it is likely you are probably having issues with your Park to Drive fueling enrichment as well. Please see our upcoming article for details on tuning the park to drive settings for info on how to correct that as well.