Timing

[adamuise]

So, ive been chasing a interesting problem for the last couple days. In my tune i have commanded between 4-5 degrees of Main Timing in the 1300 rpm range at light throttle (less than 30mm3). Yet i can hear chatter and can see in the log it goes up to around 10 degrees which i feel is way too much. Ive tried zeroing the correction tables on the ECT, IAT, Baro and Boost without any change.
Where is the extra 5-6 degrees coming from?

[Jim P]

Both transient and steady state maps are the same? With a quick check I didn?t see anything other correction factors in the system other than what you listed that might be causing it but I didn?t go through everything to see, just the main SOI. Maybe something within combustion management parameters?

[adamuise]

Both transient and steady state maps are the same? With a quick check I didn?t see anything other correction factors in the system other than what you listed that might be causing it but I didn?t go through everything to see, just the main SOI. Maybe something within combustion management parameters?

Ill double check when i get home but im 99% sure that both the LAD and Transient main sointables are the same.

[paulb]

My guess it's picking up a misfire and applying the misfire timing. Change the misfire timing and see if the logged timing follows.

Paul

[adamuise]

My guess it's picking up a misfire and applying the misfire timing. Change the misfire timing and see if the logged timing follows.

Paul

I compared the LAD and Transient maps, they are the same. I will try disabling the misfire timing and see what happens later tonight or tomorrow. Any pros-cons to leaving it disabled?

I figured i missed "something" and after having a look at the log and the misfire map, im starting to think that might be it.

Will let you guys know what i come up with

Thanks

[adamuise]

Disabling the misfire cured it. Thanks Paul

Next question is, "detecting a misfire" and applying the map. What would be an example of the cause of that? I am taking the truck into the city tomorrow to drop off some rods for a friend so i will see how it runs but from the quick fire up and test hit, it feels fine.

[Jim P]

Misfires are measured with vibration sensors but since the Cummins has none I?d imagine some algorithm is in place using real runtime values and expected values after calculations, maybe rpm? An unignited cylinder causing a drop in rpm outside of the expected rpm for that cylinder if it did fire?

[adamuise]

Interesting it would be beneficial to know precisely how that map works. For trouble shooting purposes i have deactivated the misfire timing map and (as far as i can tell) so far the truck is responding and acting fine.

Can someone help me wrap my head around how the IAT, ECT, BARO and BOOST "correction" and "multipliers" actually work in conjunction with the main maps? Unfortunately for me it is difficult to understand exactly how they work. I understand what they base themselves off but get lost in figuring out how they work together and with the main map. (i wish they had a "dumb it down" button for the descriptions lmao)

X+Y+Main= timing....?

[Jim P]

I haven?t fully understood the correction factors and multipliers on how/when they work either. It?s like sometimes they are used and sometimes they aren?t. I?ve seen them have a larger affect on pilot than the main

[adamuise]

I dont mess with them too much, but in an effort to be a better tuner i'd like to try and understand as much of this program as possible. I have the basics covered (to an extent) but its always the finer details that tend to be the most important.

[JaegerWrenching]

If they are multipliers then yes, say your base timing is 4* @800RPM, and your truck is at 30F while you're idling. If your ECT table is set to -2* @30F @800rpm, that table is now in effect so 4*-2*=2* total timing. Also any of those other tables will stack on top of that as well so if you think you're having an issue with them 0 them out and see if your timing matches your main table.

Also misfires are usually detected by cylinder contribution in gas engines. The PCM can see how much each cylinder contributes to moving the crank per ignition cycle. Now i'm a gas guy who's looking for diesel knowledge, so that being said IDK if diesels's are the same. i would assume so.... but you never know lol!

[Jim P]

My testing with multipliers on the main injection it didn?t quite work as you describe