Injector Parameter Tuning Question

Decipha's custom GUFX strategy covers all 89-93 foxbody ecu's including the 88 mass-air california ecus.
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Joined: 2021 Nov 28, 15:12
Location: Lincoln, RI
Vehicle Information: 1989 F-250 5.8L w/ S5-42 Trans, 4x4 Drivetrain
A9L converted, SEFI, 2 HEGOs, 3" exhaust w/ shorty headers, 24lb/hr Accel Injectors, BBK 76mm MAF

Injector Parameter Tuning Question

Unread post by ThatGuy »

I've been working to improve the fuel modeling in my tune, and I've been making use of the various history tables to do so (thanks to decipha for making them available), but having issues. I've mostly been using the N_IMAF_IEGOs (Fuel Error 1+2 Filtered, but I have no wideband so this is just based on KAM/LAMBSE) history table, and noticed that my fuel error across any IMAF ad count is very inconstant as RPMs change. Generally, at low RPM/higher ad counts fuel error suggests I need to enrich (error greater than 1), and at higher RPM/lower ad counts I need to lean out (error less than 1). My error is fairly large, with fuel errors being +/- 8% across some individual add counts.

The injectors are Accel 24# injectors (rated at 43.5psi). My fuel pressure regulator is a newish replacement, and the rail is the factory fuel rail. Fuel pressure with no vacuum is approximately 39-40psi, the FPR drops it to about 34psi at idle/high vacuum conditions. The MAF is a 76mm BBK "Calibrated 24#". I started my injector slope tweaks from the Accel datasheet values/injector reference, and the MAF transfer comes from the "Calibrated 24#" reference.

To try to fix this error, I have been decreasing my high slope value and increasing my low slope value. After changing these values, then resetting the other SP* values as needed to get the proper scaling, I usually take a 20 minute drive with some highway and backroads to mature the KAMs. However, my two slope values are now over 25% different from each other, and I still have not been able dial out this error across any specific ad count. I've only seen minor change, which makes my think I'm missing something. My goal ultimately is to get each ad count to have a consistent fuel error (within +/- 3%), and then have confidence that I can use that fuel error to dial in my MAF transfers.

I'm wondering if my test procedure is including too many transient conditions, making my numbers confusing, or if maybe my injectors just have terrible flow characteristics. Any thoughts would be appreciated. Thanks!
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Re: Injector Parameter Tuning Question

Unread post by decipha »

high slope and offset are posted all you have to dial in is break point and low slope
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