Where's all this fuel coming from?

[Jack Alltrades]

Still on a steep learning curve as far as tuning goes, please be patient.

Logged my truck and at 25% throttle @ 1800RPM total fuel qty was 56.2mm3. When I go back and look at the pedal map, either steady state or transient, is says base fueling is 13mm3. For some background, it has 60% over injectors and I'm thinking the guy who developed this tune may have cut back the base fueling to reduce smoke? The stock pedal mad shows 35mm3. Pilot qty says it should be around 3mm3. So where is all the extra fuel coming from? Admittedly I do not have a good handle on all of the pilot corrections.

[Jim P 2.0]

Pedal table is driver demand fuel but you also have other tables like friction fuel tables that are part of the equation of the ecm deciding fuel quantity to inject. The ecm uses all sorts of inputs and tables to determine total fueling and splits it between pilot, main and post, depending on how those tables are setup, if you zero out post fueling you’ll see that fuel shift over to the main fueling. The so called correction tables and multiplier tables are not always in play. They are conditional tables, where under certain conditions, they become the table used rather than the ecm using the base and normal air density based tables

[Jack Alltrades]

So when it says 'No Throttle Fueling' for ECT, Friction, Fan and AC Comp, that means independent of throttle and not necessarily 0% throttle? Clearly the tables have values at the full range of RPMs...probably just answered my own question.

Please correct me if any of the following is false: If the post qty is zeroed out, then all commanded fuel would go into pilot and main injection. If there IS a post qty it would be in addition to main injection qty. Everything in the Main Injection Limits and Governors tabs are reductions/caps to fueling (not gaining any fuel here). 'Adder' corrections to pilot and post injections could drive up total fuel qty.

If post injection tables are zeroed out (modes 0-4), could adders still result in some post fuel being injected if they are not also zeroed?


"The ecm uses all sorts of inputs and tables to determine total fueling and splits it between pilot, main and post, depending on how those tables are setup" If I understand what think I know, total fuel is determined, then the pilot and post qtys are subtracted out to go in at their respective times and the balance goes into main injection?

[Jim P 2.0]

If I understand what think I know, total fuel is determined, then the pilot and post qtys are subtracted out to go in at their respective times and the balance goes into main injection?

Correct. Like said with the correction tables/adder tables, those are conditional, they only come into play under certain conditions and when they come into play, the mode 0 - 4 tables are ignored and only the so called correction table is used. As an example, pilot timing, it is minimum wins, the pilot timing coolant temp correction table has the lowest timing, when the engine is cold you will see that table will be used, all other pilot timing tables will be ignored.

[Jack Alltrades]

Thanks for the confirmation/correction.

With what I know at this point the total fuel makeup is this: 13mm3 base fuel from pedal map + 0.5mm3 for coolant temp (ECT was 142* at the point in time I chose) + 9.9mm3 for friction + 3mm3 for cooling fan (not 100% positive about this number but 5.3 is the max at this rpm) + 0mm3 A/C off, for a grand total of 26.4mm3. Logged total fuel was 56.2mm3 judging from the main injection PW at that time, about 50mm3 went into main injection, leaving 6.2 for pilot which seems to jive with the pilot tables. I wasn't logging pilot qty or PW on this run, will correct that oversight next go round.

So I'm left with almost 30mm3 of mystery fuel. How does engine load play in if at all?