Thursday, December 21, 2006

IFR spreadsheet for Logged Fuel Pressure

Here's the new, promised IFR spreadsheet that calculates IFR table accounting for the variable Fuel Pressure.


This is NOT a replacement for the old IFR spreadsheet! This is only for people who set up their Fuel Pressure sender units to log. If you don't have such a setup, continue using the old one.

Remember that this will only work if you log your fuel pressure first against a variety of driving conditions. I'm not going to describe how to log it, as I've already seen it set up as the EGR voltage, or as the separate input (just like a wideband). HPTuners and EFILive setups differ as well, so deal with it appropriately. I don't have resources to describe every possible combination of hardware and software here, and this is a more advanced thing to do anyway, so I'd rather not give people a false sense of assurance.

One important note: remember that most pressures in the GM PCM are absolute. IFR for some strange reason, is based not on MAP just like about anything else, but on Manifold Vacuum. In EFILive this is easy, MANVAC is just another PID to pick. In HPTuners, I haven't seen it yet. I tried to make it with a custom PID of BARO-MAP, and then use it to create a custom histogram of the new MANVAC-like PID against the Fuel Pressure PID. Easier said than done, after many hours and help from people that know HPT in and out, I just gave up. This is what you get for hacking custom PIDs into HPT at the last moment, and not having them as a part of design and infrastructure from the get go.
Anyway... If anyone figures out how to get FP vs MANVAC histogram going in HPT without major hacks, please let me know, right now it's a bloody mess.

Just like I mentioned in the last writeup, FP apparently varies even within the same MAP range, making tuning IFR against the logged Fuel Pressure closer to The Truth(TM) but still not perfect. For now, we're still stuck dealing with the VE table making up for non-MAP related IFR variations.

Next up: transforming VE's using the new IFR without retuning.
Stay tuned,


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