Cpi without fuel it sensor

[StingerKMA]

I heard from multiple members that the Jb4 does not change any parameters using the ethanol readings. So would it be an issue if I install the bms cpi kit without the ethanol sensor since all it does is show you an ethanol reading only? I test my own fuel so I can't justify spending the extra money on a sensor to tell me what I know. Thanks in advance.

 

[Thomby]

It won't change maps (boost), but I was under the impression it used the real-time reading to dial in timing advance. If that's not the case, you're just installing gear for the convenience of seeing it displayed, which doesn't seem worthwhile.

To add to the mystery, at one point I noticed my logs were displaying E85 numbers right around my mix, without a fuel-it kit, and when I asked about it I was told the number is meaningless with no sensor.

But I've also seen older BMS posts saying that in the absence of a fuel-it signal, the JB4 will estimate ethanol content from the O2 sensors (since E85 stoich is about 10:1). And when I looked at my old logs, I saw values of 5, 8, 12 when I was running regular gas ("E10"), and my first tank of "E30" I started seeing logs with 25, 29, 32.

So hopefully one of our gurus can confirm whether the JB4 feeds the ethanol content into its own tuning, and if so whether it'll use estimates from O2 sensors/"fuel wires" as well.

 

[StingerKMA]

Thanks. That is weird I did notice in my logs too that the "e85" and it was not too far off from my mix. I been playing with map 3 4 5. I just did a pull on map 5 (E30) Other than timing adjustments, I have readings of 0.0-0.8 ign and adjustments at full boost which is pretty damn clean. What else am I looking for when log reviewing. What should my trims and FF be? Thank you

 

[Thomby]

What should my trims and FF be? Thank you

There's a whole writeup at JB4tech, but going from memory I believe expected trims are mid-40s around peak torque (2000-4000ish), tapering down to mid/high-20s in the upper revs.

FF is feed forward which I believe determines how aggressively Wastegate Duty Cycle is scaled up and down, so not relevant if you don't have EWGs.

The cylinder-level corrections sound good, but you also want to see absolute timing advance (ign1) building with revs and no sharp drops (except at shifts). This is easier to see on a graph than looking at raw values.

Also good to spot check FP_H (fuel pressure, high), because if you have enough octane at higher maps, another likely limiting factor is outrunning the HPFP's capacity. Values should stay at 10 or above.

And AFR is good to look at -- if you have "fuel wires" (O2 sensor intercepts) the JB4 will lean out your mixture in the upper revs, I think to around 12:1.