LTFT +25%, STFT+35 and I don't understand why

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04-22-2010
Pekka_Perkeles

LTFT +25%, STFT+35 and I don't understand why

Hi,

I got a "base tune" for a supercharged system from a reputable shop. Since the "base tune" was from -99 Vette and the actual car is -97, I copied what I thought to be relevant parameters (60 lbs injector info, VE, MAF, etc.).

For some strange reason LTFT's are now +25 and STFT's also around +35. I'm pretty sure that the injector info is spot on, as well as (stock) VE-table, since this is otherwise stock engine, apart from obvious Vortech supercharger system.

The fuel pressure is around 58 PSI and since this is -97, there is also regulator input from the intake (on front of the throttle body). I reseted fuel trims, but as soon as engine goes into closed loop, STFT's and LTFT's are quickly raising.

Could this be because of failed O2's? Or intake leak? I cannot believe stock engine would need a huge modification in VE to compensate supercharger in the idle.

Here's tune, scan and config attached:
04-22-2010
69lt1bird

If you have a vacuum referenced fuel pressure regulator I think the IFR table should be flat, not sloped.
04-22-2010
Pekka_Perkeles

Quote:

Originally Posted by 69lt1bird

If you have a vacuum referenced fuel pressure regulator I think the IFR table should be flat, not sloped.

I was thinking the same, so we tried without "stock" boost reference. No difference.

Also, stock -97 Corvette fuel tables are not flat, so I don't know if the regulator is really boost-referenced in stock form, but at least there's some kind of tubing.

Anyway, how about following hint:

- in Table display, MAP value is around 40...45 kPa
- in Gauge display, it is less than 18 kPa
- in Chart display, it is around 15...18 kPa
- in Histogram, it is aroud 15...20 kPa

All this at idle.

Something is strange here. Maybe there's some trick that applies for -97 only? Such as keep used bits 24 or less (which I did).

I first thought that maybe MAP sensor is broken, but then would that explain the difference between Table display and other displays? On the other hand, having artificially low MAP value, I think that could be the source of having LTFT's and STFT's that far off?

Any other suggestions?