MAF differences BP Turbo
 

Hey all,

We are in the 11th hour on my BP build. We are tuning via ecutek, and we have hit a bit of a brain twister.

We are seeing vastly different MAF voltage readings between bank 1 and bank 2. During a pull, Bank 1 will go from 2.0V to 4.8V, while bank 2 will read from 2.0V to 4.5V. At any given point in the pull Bank 2 will read between .4 to .7V lower than Bank 1, essentially lagging behind it across the entire pull.

This screams boost leak right, I know. However:

Speed Density is working great. We have the AFR curve spot on throughout the pull. Oddly enough we have a little bit of a difference between the AFR of Bank 1 and Bank 2 right as you step on the throttle. Bank 2 LEANS out a little more than Bank 1 and they come back together at around 3800rpms.

So...... how does this make any sense? We have switched the MAF sensors and confirmed that both sensors read lower in Bank 2, so the sensors are good. If you believe the MAF sensors, then they are telling you there is a boost leak in bank 2 as the voltage is lower.

If you believe speed density, then there is actually MORE air in bank 2 causing it to lean slightly more then Bank 1 as the boost ramps in. As speed density is going to apply the same amount of fuel to both banks, the leaner bank must have more air. We even compensated for this a little bit by adding 2% more fuel to cylinders 2, 4, and 6. Yes, that's right, more fuel to the bank that potentially has a boost leak according to the MAF voltage.:confused::confused::confused::confused:

Mind boggling stuff here. Not really sure what to make of it. We are going to pressure test again to be sure, but speed density is not showing a boost leak, it is actually showing that Bank 2 is capable of pushing more air through it right at spool up. The differences in AFR in the speed density tune is not adding up with the differences in MAF voltage either.

Meaning, with Speed Density, the AFRs are only off slightly 3-5% at most during that spool period. While, with the MAF voltage, a difference between Bank 1 at 4.5V and Bank 2 at 4.0 volts could be 20-30% fuel difference depending on where you are at on the curve.

With Speed Density above 4000rpms full load we get 11.4-11.7 for both banks. Due to the difference in MAF voltage, when we switch to MAF mode, we run lean at the top and have to get off it early since Bank 2 MAF voltage is lagging behind so much it is causing the average afr to climb towards 13 AFR.


At this point no more tuning can be done until we figure this out. Any thoughts are, as always, greatly appreciated.

Thanks

Who is tuning this? You don't have a boost leak, a boost leak would drop pressure, not MAF voltage, which measures flow.


Sounds like you guys are using OEM O2 sensors to measure a/f, which are not accurate in this range.

With ECU TECH, why not use MAP? It is much more reliabe than MAF sensors.

Also, which charge pipes do you have, what boost pressure are you at, and what is your current power output?

PM sent. I would like to thank boosted performance for their dedication to all of their customers and their willingness to assist in this matter.

Thank you, again, for your timely response.

Heh... the assumption is a V motor runs identical on both banks?




....

not identical. but closer than .5v off across the whole pull. maybe this is not an issue from what I am gathering.

I see a pretty big difference between banks, at times, close to a full AFR point. If you're clean and on target with speed density, just use that. It sounds like that's cleaner than most cars out there who are MAF tuned and are running with big differences between banks.

It can be quite a lot. You should look some of the OEM maps for various V motors -- some of them spend a lot of time mapping individual cylinders, not just banks. The difference can be huge.

Add to that a turbo... one bank could be seeing more back pressure sooner than the other, which will impact flow (and yes your MAF will see it).

Thanks all.

Speed Density is coming along fine. We will tune the MAFs up to about 2 volts and switch to Speed Density from there.