Tuning for a big cam - 'desensitizing' the misfire table

[Turbo6TA]

For anyone that has installed a bigger cam in there LS (Gen 4) engine and running the E38 ECM:

I read the following and was wondering which table in the tune could be modified to 'desensitize' the misfires which can come from a bigger cam install:

"Normally when you tune a car for an aftermarket cam, you will re-calibrate the misfire table in the tune which will keep the PCM from interpreting the rougher aftermarket cam idle as misfires".
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Is there any truth to this and if this can be done, what table in the tune could be modified with HP Tuners.

Thanks,
Ron

[Turbo6TA]

BTW ... With the cam I have installed, I will get maybe 30-40 total misfires during first cold start-up ... After a short period of time and the engine gets up to temp, I get no misfires.

[smokeshow]

Yes that is true. A bigger cam will exhibit partial misfires that are counted by the monitors. If the apparent misfires go away when warm, you won't need much adjustment. There are long official methods to doing it, but you'll be fine just increasing values by maybe 10% to start.

[Turbo6TA]

smokeshow ...

Thanks for the info.

I am looking at the tune right now on table Engine Diagnostics / Misfire

1. Detection . (Misfire RPM Test)
2. Revolution Mode . (Normal)
3. Cylinder Mode . (Idle not Moving, Normal, Normal 2)
4. SCD Mode . (Idle, Off Idle, Idle 2, Off Idle 2)

I just don't know which one of these to increase the value by 10%

[Turbo6TA]

Well, I multiplied all the various numbers that are found in Engine Diagnostics / Misfire area (that were not 32,767) by 1.3

Be advised that any numbers that are originally set to 32,767 cannot be increased ... so I left those numbers alone.
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We shall see how this works out ... If it don't, I can always go back to the original numbers. (nothing lost / nothing gained)

[Alvin]

I normally just max them out. Someone chimed in on one of my post to say he takes time to find the value that will keep the ECM happy but that seems like a lot of work for very little payoff.


I've seen misfire diagnostics failing to find misfires on too many completely stock cars to care to get it working on a heavily modified one.

[Turbo6TA]

Well, increasing all the numbers that were not 32,767 by 1.3 times wasn't enough.

However, increasing the numbers 1.5 times fixed the problem.

The misfire detection system is still working because on the first cold start, I will see somewhere around 7 or 8 misfires (but not 25+ like before).

Once the engine has run for a minute or two, I see no misfires at idle, cruise, part throttle or WOT ... So it looks like my 'desensitizing' pretty much worked (without completely turning the misfire detection off)

[garrison]

how would you unlock the tables to edit?

[Alvin]

Well, increasing all the numbers that were not 32,767 by 1.3 times wasn't enough.

However, increasing the numbers 1.5 times fixed the problem.

The misfire detection system is still working because on the first cold start, I will see somewhere around 7 or 8 misfires (but not 25+ like before).

Once the engine has run for a minute or two, I see no misfires at idle, cruise, part throttle or WOT ... So it looks like my '[COLOR=#3E3E3E]desensitizing' pretty much worked (without completely turning the misfire detection off)

One way to find out for sure.. pull a plug wire and see if the diagnostics can figure it out

[Turbo6TA]

Alvin ... I am going to do that

Thanks