LT5 ECM Tuning thread

[tpepmeie]

Tyler,
It is a multiplier used to cut the fuel pulsewidth in half when the second set of injectors is active. For example, say you have an base pulsewidth of 10 milliseconds when the engine is running on only the 8 primary injectors. When the ECM commands the secondary throttles open, there is a very slight delay (0.3 sec) then the secondary injectors are energized, and the NEW pulsewidth is now 10ms x 0.51 = 5.1ms. Of course, since it is being delivered with twice the number of injectors, the overall fuel injected is the same as before the port throttles opened.

Increasing this multiplier would have the effect of adding fuel when the secondary injectors are energized. If it were, say, .75, then you would end up with 2 injectors x 10ms x .75 multiplier = 15ms total fuel delivered. This could be used as a band-aid to increase fueling if the injectors are too small or the VE table is not correct. However, I would think the transition would be terrible, and you'd end up with a surge due to the sudden enrichment.

just my $0.02.

Todd

[Tyler Townsley]

Originally Posted by tpepmeie

Tyler,
just my $0.02.

Todd

In my book your $0.02 is worth at least $1.00.

You are of course correct. When Jim Smith was trying to tune Ron Ks motor several years ago the car had a lean at this transission and he had the VE tables up to 100 and the car was still lean in transition. We took this to .56 or .57 and solved the problem and were able to back the VE table down some.

The above only applies if you are using secondary throttle plates.

Todd what did you with this when you change the calibration to have both injectors on all the time.

Tyler

[tpepmeie]

Originally Posted by Tyler Townsley

Todd what did you with this when you change the calibration to have both injectors on all the time.
Tyler

I left it alone. So basically had half pulsewidth provided by each injector all the time.

The base fuel calculation has no idea there are two injectors. In fact, the base calculation only knows the constant for 1 injector (.35 sec/gram). The pulsewidth is calculated using this. So, therefore, when you bring the second injectors online with the same calculated base pulsewidth, the scaler has to be used so that you don't deliver twice the required fuel.

Now, about that delay factor....who wants to discuss what effect that has?

Todd

[XfireZ51]

Todd,

Why don't we discuss Proportional Gain?

[bradslt5]

wow todd really know his stuff. this is a good read . when i got a prom from mark haibeck he says he takes some of that out to give a better responce . is that what you mean. i just want to learn all i can . what are your thoughts on tunning is one takes the secondary throttle blades out . do they then run all the time ?

[tpepmeie]

Originally Posted by XfireZ51

Todd,

Why don't we discuss Proportional Gain?

OK. What do you want to know about it? It is pretty simple, and the first of three potential PID parameters to control pulsewidth based on feedback from the O2 sensor. There are primarily two tables at work...one is the base response to O2 error vs. airflow. There is a smaller proportional step at zero airflow (idle).

These steps are then multiplied by a factor, depending on how large the O2 error is. The bigger the error, the larger the multiplier. You end up with an adjustment "count" to modify the base pulsewidth. If the error is positive, fuel is removed and vice versa.

Todd

[XfireZ51]

Originally Posted by tpepmeie

OK. What do you want to know about it? It is pretty simple, and the first of three potential PID parameters to control pulsewidth based on feedback from the O2 sensor. There are primarily two tables at work...one is the base response to O2 error vs. airflow. There is a smaller proportional step at zero airflow (idle).

Isn't there a constant that defines the max airflow to be considered as IDLE? The 7747 code used a separate Prop Gain Bias constant for idle and the 2D table was pretty coarse.
EBL has 2 constants for Prop Gain at idle based on offset and duration and 4 tables.
So 1 Prop Gain table defining a gain based on Gms/sec which then gets further modified by a second table with factors based on O2 Error, right?
Which one do you usually modify and why?
If I change the gain up or down, what would I feel in the way the motor runs?
Why wouldn't I want to be able to modify this in the bin?

Thanks for this. Any more on the disassembly lesson?
Dominic

[tpepmeie]

Originally Posted by XfireZ51

Isn't there a constant that defines the max airflow to be considered as IDLE?

No. Idle fueling is determined by TPS < 2% and vehicle speed <= 0. That combination sets the airflow term to zero.

There is a scaler term available to modify the Prop Steps, but it is not used (ie, = 1.00)

Todd

[XfireZ51]

Originally Posted by tpepmeie

No. Idle fueling is determined by TPS < 2% and vehicle speed <= 0. That combination sets the airflow term to zero.

There is a scaler term available to modify the Prop Steps, but it is not used (ie, = 1.00)

Todd

Thanks Todd. Think I understand what's going on here now.

[Tyler Townsley]

Originally Posted by tpepmeie

Now, about that delay factor....who wants to discuss what effect that has?

Todd

The delay factor is there to let the air velocity catch up to the needed fuel. When you go from 1 to 2 runners in a cyl the increased airflow and pressure change has to be factored into the fueling equation and that is what the factor does.

I hadn't thought about that one in a while. On a removed secondary situation would you lower the delay or remove it alltogeather?

Tyler