Enrichment tables, how do they work?

[mrQQ]

Hi,

the Enrichment table - is that a percentage? Does it get added to target AFR for any rpm/load combo? Or when does it get added?

Also, decrement - how does that work? How often does it decrement? Is this a percentage? Or number taken away from enrichment table value?

Also, why does it show enrichment even up to 80c?

[Steve @ VersaTune]

These are percentages that get added to the final trim.

The decrement value reduces the value from the main table until it is zero. It gets decremented every time the ECU runs that sub. It's not on a specific time cycle.

There is always afterstart enrichment, even at 80C ECT. It is there to help get the AFR right until the combustion chambers get up to operating temperature.

Basically, you have two slopes. The cranking slope is taller and steeper than the warmup slope. Both values are calculated and the ECU uses the larger of the two. As the cranking/afterstart enrichment decays rapidly, it's value will drop below that of the warmup enrichment. At that point, the warmup enrichment will take over at a lower decay rate. Neither is active all that long.

[mrQQ]

Thanks!

What's the average interval for the decrement, or is that unknown? I wonder how is it in effect.

Also, when you say "trim", what do you mean by that? If the value is "40", and you're idling, what happens?

By the way, is there any table in the ECU logic which raises neutral speed when coasting? I've noticed it runs higher than idle rpm when coasting in neutral.

[Steve @ VersaTune]

Fuel trims are a percentage that is applied to the base fuel calculation. These afterstart trims are applied with the LTFT and STFT in the same manner.

[mrQQ]

So they cannot be seen in STFT/LTFT logging, and would result in richer and stoich AFRs?

[Steve @ VersaTune]

They are all a part of the final trim. There is no PID for the warmup trim component or the final trim.

[mrQQ]

What I don't understand is that if normal LTFT+STFT targets stoich afr, and then some more fuel is added to that, we should see richer than stoich AFR while enrichmenent is active?

Or am I missing something?

[Steve @ VersaTune]

I think these after start enrichments fade out before the STFTs start. The STFTs wait for the WBO2 to come up to temp.

[mrQQ]

I'll check it out, but I think when logging trims are active pretty instantly?

[mituc]

They are, the already "learned" trims + whatever trims the ECU logic adds (like the ones corresponding to the enrichment tables).