Injector data transfer question Gen 4 to Gen 3 Flex Fuel

[JakeRobb]

Is it always “convert the nominal psi rating to kPa, then take that value and go from there to that+80?

That’s from nominal to +11psi. Why? When does the PCM use such high values? Is that used when referenced against MAP, so that the injector know it’s spraying +58psi into -7psi due to vacuum, and we account for the extra pressure differential when computing how much fuel to deliver?

[blindsquirrel]

80kPa vacuum in the Gen 3 files is the same as a 480kPa Delta in the Gen 4 files, assuming both are non-referenced and 58PSIG in the rail. Mixing PSI (unspecified) and PSIA and PSIG and kPa hurts my head, too. 'Rail pressure' is PSIG, MAP is kPa absolute. 'Delta' is gauge/absolute agnostic, unless you're looking at one of them in A and the other in G. Which we are when trying to describe this using fuel-pressure-gauge-relatable numbers for rail pressure.

Gen 3 0kPa vacuum and Gen 4 400kPa Delta are both 58PSI vs normally-assumed baro.

screenshot.11-08-2023 20.12.01.png

(this same Delta range applies to the big Offset tables, too.)

screenshot.11-08-2023 20.12.31.png

In the Gen 4 files, to use the cells left of 400/408 you'd have to have either: less than 58PSI rail, or; 58PSI rail with more than normal atmosphere in the manifold (boost). For cells to the right of 480, it'd have to be either: more than 58PSI rail, or; 58PSI rail with less than 20kPa MAP (unpossible). But the Gen 3 files can't calculate for anything higher pressure than 0kPa vacuum, or lower pressure than 80kPa vacuum. So the only way anything outside the Gen 4's 400-480 range matters is if the Gen 3 is using some base pressure other than 58PSI.

[blindsquirrel]

(This is just for background info, not strictly needed if the only goal is a late-Gen-4-to-Gen-3 conversion spreadsheet. There aren't any good injectors you'd want to use in a swap from this year range, or, if there are, those same injectors were carried over into the year ranges ('07-'09) where the existing old spreadsheet is able to convert them.)

The Delta tables appeared in 2006 (edit: 2007). Before there were FPCMs and variable fuel pressure used in anything. So, the unhittable areas were just filled in with placeholder numbers:

screenshot.11-08-2023 20.37.37.png

...but in the very first 2006 Gen 4s, they did something altogether different:

brain aspload.png

Negative vacuum!!!!11one

[blindsquirrel]

(note: The screenshots above are for comparing formats/axis labels only, the actual injector data has not been converted between them)

[JakeRobb]

Thanks, that’s helpful!

To be clear, I think that was generally a “yes” to my interpretation: the 80kPa ranges allow the PCM to account for manifold vacuum, knowing that a stronger vacuum is going to mean a larger pressure differential between the rail and the intake port, and therefore more fuel being injected for a given dwell time. (Leaving out the additional complexities of a boosted scenario as they don’t apply to me.)

Agreed on mixing absolute and gauge pressures hurting the brain. I didn’t consider that here, sorry.

[1BadSlug]

Sorry, I never did come back to this after I got it all sorted out and working.
Everything is clear as mud and worked great. Thanks again for the help!

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