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Injector trim related to throttle position

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AEM Infinity ECU, Big Block Chevy, single plane manifold, 4 barrel throttle body.

So with the intake runner lengths different due to the locations of the intake ports relative to the throttle body we have adjusted the gross fuel via trim table with RPM and load as our axises. In this case the it does not take in account for throttle position.

We would like to refine this further because the way the butterflies plates are configured and staged. The two front are gang together and as you increase throttle (>~50%) the rears come into play. This complicates the runner length further as the throttle body's orifices are "changing" the amount of airflow and/or distance it is traveling.

Is there a strategy to create a trim table per injector, that incorporates throttle position, with load and RPM?

Attached Files

Perhaps you could use EGTs to trim each injector ? Is this a possibility for you ?

Thank you Ken for the reply. What I failed to mention is that we do have wideband sensors and EGT's at each primary. With this data we can adjust the gross trim for each injector for steady-state tuning and wide-open throttle.

What we are trying to account for is the varying airflow and volume going to each runner at varying throttle positions. For example, we could have the engine at 3500 RPM and 50kPa, but with different road conditions the throttle could have all 4 barrels at wot, or just the front 2 1/4 cracked open.

As you've seen, using a carburetor-style intake manifold tends to result in different amounts of air being supplied to each cylinder depending on both RPM and throttle angle. If there were a carburetor mixing fuel with the incoming air, the airflow would still be uneven but each cylinder would get a relatively proportional amount of fuel and run reasonably well. With the ECU assuming all 8 cylinders are receiving an equal amount of air, those 8 wideband sensors are probably indicating some pretty significant variances between cylinders.

If you're able to switch to an EFI-style manifold with better runner lengths, that should help with airflow distribution which should help power. If you need to keep the carburetor-style intake manifold due to class rules or some other reason, fuel trims per cylinder can help. The Infinity ECU has 8 tables, named 'Inj1Trim', 'Inj2Trim', Inj3Trim', etc... each table uses RPM as the default x-axis and MAP as the default y-axis. You can change those tables to use Throttle as the y-axis by going to Wizards >> Setup Wizard, open the 'Advanced Trims' page... the option you're looking for is at the very bottom of that page, named 'Inj1Trim-Inj8Trim y-axis'.

Hope that helps,


Attached Files

Thanks SB,

There doesn't appear to be such an option (Advanced Trim) in my "Wizard>>Setup Wizard".

Is there some setting I need to make in order to have this option available to me?

Here are the options available to me now:

Attached Files

It looks like you have the latest version of interface software installed on your laptop but an older version of firmware/strategy inside the ECU itself. You need to get the latest file for the ECU, do that by logging into aeminfinity.com, look for the file named 'v96.2 Inf-710 Universal'.

On second glance, the file you have opened in the software appears to be so old that the software should have forced you to upgrade it already. Are you sure that is the file that is currently in the ECU? It might be quicker to talk this through with one of our tech support staff via the phone, they are available between 8am- 5pm Pacific Time, 800-423-0046. I don't answer those phones but any of the guys should be able to help you check which version is currently in the ECU, get upgraded to the latest version, and configure the y-axis for the InjXTrim tables.

Hope that helps,

Scott B

Thanks Scott. The option for advanced trims became available once we communicate with the ECU. We were surprised that this was the case and thought this should be available when not communicating with the ECU. As we tailored the trim tables we became aware that the are only 9 rows available making 0-100% throttle position not a proper 10% per row.

In any event we were able to do some full ramp runs and pull our lambda readings within reasonable values across all the runners using the trim tables with the throttle position.

I'm glad to hear it worked out, thanks for posting your results. My best guess is you had a very old file opened when you took that screenshot, not a file that was recently saved from the ECU.

It's tricky to decide how many cells each table should have, there's a balancing act of trying to make sure each table has enough cells to be useful without letting it occupy so much memory that it prevents from building other useful tables or strategies in the future. On most EFI setups with a properly sized throttle, there is often little or no difference in airflow from 80-90-100% throttle opening, but I can see how this would get tricky with a multi-blade setup like you described.

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