Fullpower

2002 Tahoe, 2Bar SD .... IAT moved to TVS1900 intake manifold, ( Post-Cooler ).
Is there any remaining function of MAF ?
Does transmission use MAF data to sense engine load ?
If I remove MAF, will I miss it ?
.

ChopperDoc

You can lose the MAF. Are you doing the tune on it? Failing the MAF will cause max line pressure DTC in your trans. That's pretty much it. Everything else can be tuned with SD, even STFTs. You might miss it when the temperature changes A LOT, which can mess with fueling, or when you go to higher altitudes.

SD if perfectly fine without a MAF. I ditched mine a long time ago.

Fullpower

1-2 shift is pretty 'harsh'... Been that way for years. Corvette servo is only mod on 4L60.
I play around with HPTuners, still have a lot to learn.
temps here are in the 2 to 10 degrees F range this week, no problems, runs smooth, starts and idles nice.
Ran just great through West Texas and Arizona at 98 degrees in early September, and just fine running up 9200 feet elevation to south rim Grand Canyon.... Only real problems noted were poor quality fuel in Canada ( Their 91 octane swill is inferior to the 90 octane Alaskan gasoline, had to pull a few degrees timing for the Canadian sections. )
... So, IF MAF is just taking up space, guess I can use a silicone coupler and hose clamp the intake tube straight to stock airbox?

subeone

iTrader: (5)

if you 2 bar sd your pcm you will not have max line pressure even with the DTC.

ChopperDoc

Sounds like your tune is spot on then. Normally SD on gen III cars doesn't have an altitude correction for VE. Gen IV's do. Check your trans dtcs (under trans diag) and see if the three MAF errors are still enabled. That might cause your harsh shifting. I am assuming you are 100% SD with your OS. I'd verify this by checking to see if your MAF fail is set to 0, and all of your MAF DTC's should be set to MIL on first error. The first three.

If your MAF is indeed disabled, then there is no reason to keep the sensor.

gametech

iTrader: (1)

I'm curious as to what you mean by "altitude correction". Altitude only affects things that are already handled with SD. Pressure and temperature are measured no matter what the altitude.

ChopperDoc

I'm not sure if this is accurate. Are you saying that the pcm will ignore the P0101, 102, and 103 entirely with a 2 bar OS? Last I checked, in order to force the pcm to revert to SD is to fail the MAF. Using this logic, I don't see why it wouldn't be also commanding the max line pressure to the trans. I guess I will go test this out later on my buddies procharged SS. It has me curious now. You might be right, but it's really not hard to just change the codes to disabled.

IF that is not the problem, then you can go to your Trans>Autoshift Properties>Upshift Pressure Modifier and reduce the numbers in small increments until it feels smoother. If this doesn't work, you can adjust your FM current UP a little in the ranges where the shift would occur (towards the left of the table). Force motor current works opposite. The more amps, the less pressure, and vise versa. Do not make huge adjustments here. A few % at a time.

gametech

iTrader: (1)

With the HPT 2barSD OS (and I'm sure EFIlive as well) the OS modification eliminates the max pressure issue with the trans

ChopperDoc

MAP uses differential pressure to calculate VE values under vacuum, and anything under boost. MAP measures the difference in barometric pressure outside the engine and the absolute pressure inside the intake. When the barometric pressure changes, as in no longer the normal 14.7 @ sea level, or 1 bar, (105 kpa), then the calibration needs to be done again for the difference.

So if the MAP thinks baro is 105 (sea level), and ACTUAL baro is 97, then everything will not be correct. This is why gen IV's have high and low altitude VE correction tables. I have never once used one, but they are there if you want to go strict SD on a gen IV. Then they can account for the difference in altitudes and changes in barometric pressure.

ChopperDoc

Good to know. Learn something new everyday. I just disable them anyway, that and my 1870 and trans overtemp. It takes so little time to do it I never once thought to research that. Plus most of the cars I tune are N/A, but all the principles are the same. Lately though I have tuned a few boosted cars, including my friends procharged SS.

gametech

iTrader: (1)

You have a complete misunderstanding of a MAP sensor. It measures ABSOLUTE pressure, with no regard to anything else. The MAP sensor gives absolutely zero ***** what any other pressure is. This is quite unlike an analog vacuum or boost gauge, which would measure the difference in pressures.

ChopperDoc

No, in order to even measure VACUUM, as in at idle, or decel, you need a reference. That reference is already programmed into the MAP, as in key off you should see it jump to 105, or around there. When you are sitting at idle, a stock cam will idle around 40-50 kpa, so what that means is 105-50= 55kpa of vacuum. When you put a bigger, less efficient cam in there, it can idle all the way up at 70kpa. That is only 35kpa of vacuum. It works the opposite of a pressure sensor, because the reference is barometric pressure.

subeone

iTrader: (5)

I've tuned more than 700 vehicles, I am sure of what I am saying. You won't have line pressures with any upgradeable OS.

gametech

iTrader: (1)

Absolute sensors measure based on 0. You do not reference anything else. That is what I meant by my previous post. Your basic understanding is wrong.

ChopperDoc

No, it references barometric pressure. When you go WOT, the pressure will build until it equalizes with outside pressure (up to 105 kpa). Unless you have boost, that's where the story ends. When you close the throttle, pressure will drop very quickly and pull a massive amount of vacuum (low MAP numbers 15 kpa min), which simply means the outside pressure is much higher than the inside pressure. That's how an engine works, by creating low pressure in the intake which will pull in air from outside. The MAP measures the difference. On gen III cars there is no sensor cal for baro. On gen IV's, there is.

Here is an article that explains it better than I do:

http://www.aa1car.com/library/map_sensors.htm

ChopperDoc

I don't doubt you there. I was unaware of that. No worries.

ChopperDoc

You are partly right though. Above 1 bar/14.7/29.92/105 kpa (all of those are references for MSL < "Mean Sea Level") then yes the map just reads what it reads. It always just reads what it reads, really (so you're right about that, I never disputed that), but the initial reference is the BARO. Anything above this (numbers above) is impossible for an N/A car. Going above baro brings in the need for a 2 bar or higher MAP sensor. That would be why it's called boost. You are then forcing in more air than what would be normally present in the atmosphere. And if you don't think altitude has an effect on all this, then I don't know what to tell you.

I've been flying on and fixing multimillion dollar helicopters for over half my life. I know a few things about physics. I have been building cars for even longer, 20+ years now, and tuning them for a good while too. I still learn things everyday. But on this subject, talking about pressure, altitude, and what that means for a SD tune, it's simple physics, which is my realm.

Technically vacuum is not actually a term in physics. It's just a difference in pressures. That's all it is. So if a MAP has to measure "vacuum", then what is that number different from? Zero? Then please enlighten me as to what zero is? Absolute zero? I wasn't aware that MAP measured in Kelvin.

gametech

iTrader: (1)

You have a great understanding of physics, but not so much how the MAP sensor works. Yes, I mean it is referenced to zero pressure when manufactured. If it indeed referenced baro, it would be damn near useless for any car that ever changed climate or altitude. If you take a MAP based gauge and a analog vac/boost gauge up to altitude in a forced induction situation, the analog gauge may show significant boost while the MAP based gauge hasn't even registered sea level yet.

ChopperDoc

Scan with the key on and you'll see what the reference is. Mine always says "102" kpa, key on engine off. Most will say something around there, supposed to be 105, but nothings perfect.

joecar

Absolute pressure has no reference.

Gauge pressure is defined as being referenced to 1 standard atmosphere.

For example, when you measure rail pressure, the gauge shows 400 kPa (58 psi), this is 400 kPa gauge pressure or 500 kPa absolute pressure (...so an injector's pressure difference would be absolute rail pressure minus MAP).

And engine vacuum is referenced to the prevailing barometric pressure, this is what a vacuum gauge shows.