In-dash boost not matching actual boost
#31
The 997tt will not use the map to calculate load, this is fact. Yes, load is effected by the map sensor but not a true calculation.
Unplug the maf's on a stock turbo 996tt, then unplug the maf on a 997tt with say 3076's. Log actual specified load and corrected specified load and compare vs actual load. It will all make sense...
The ecu isn't trying to guessmimate anything, there are "no maf" airflow tables that run "fake airflow" when maf's fail. We used to set these to "0" so when our customers tried to run mafless on maf based tunes the car would just die.
Im so against the whole mafless idea because frankly there are no real previsions to run speed density in the 997/996 ecu. Just because you can make it work, doesn't mean its the right way to do things.
Unplug the maf's on a stock turbo 996tt, then unplug the maf on a 997tt with say 3076's. Log actual specified load and corrected specified load and compare vs actual load. It will all make sense...
The ecu isn't trying to guessmimate anything, there are "no maf" airflow tables that run "fake airflow" when maf's fail. We used to set these to "0" so when our customers tried to run mafless on maf based tunes the car would just die.
Im so against the whole mafless idea because frankly there are no real previsions to run speed density in the 997/996 ecu. Just because you can make it work, doesn't mean its the right way to do things.
#32
Datalogging anything won't help/prove anything He already know that your dash is reading different the actual boost. Its not a boost leak or bad dv, ect.
My guess, bad map sensor or he car was modified pervious Tom owning.
We saw this problem recently on another car and found this (radio shack special)...
My guess, bad map sensor or he car was modified pervious Tom owning.
We saw this problem recently on another car and found this (radio shack special)...
Then what would be correct to judge it by??..This seems very contradicting over everything you have said in the past about getting real boost from data logging
#33
Fast fwd brought up a good question for me. Difference in gas can cause a .2 bar change in boost? As in if I'm running 91 instead of 93 I can lose that much boost? I figured I would be losing a little power but that's a fair amount.
#34
Lower octane, higher ambient temperatures, higher altitude all will lead to lower power. My max load decreases by about 5% in the middle of the summer when it's hot and humid. Boost goes down as well. OTOH, on cool days in the fall I can reach full target load and the boost is 0.1-0.2 bar higher.
Jon
#35
Hmmm....When I was on a road trip once,,,,I only had a choice of 91 octane as the highest fuel their....My boost did show the same on the dash as with the normal 93 octane but the car lost some pulling power and felt slower to me....
#36
Boost is not a measure of power, although they do go together. As Tony points out above, the map provides a target engine load, and the ecu controls the various inputs (injector time, boost, etc.) are adjusted to reach that load, if it is safely possible to get there. Lambda values, knock sensors, inlet air temps, etc. are all part of the evaluation of engine conditions. Some of the inputs, such as ignition angle and boost level are modified to prevent detonation. You can't provide more air than you can provide fuel for.
Lower octane, higher ambient temperatures, higher altitude all will lead to lower power. My max load decreases by about 5% in the middle of the summer when it's hot and humid. Boost goes down as well. OTOH, on cool days in the fall I can reach full target load and the boost is 0.1-0.2 bar higher.
Jon
Lower octane, higher ambient temperatures, higher altitude all will lead to lower power. My max load decreases by about 5% in the middle of the summer when it's hot and humid. Boost goes down as well. OTOH, on cool days in the fall I can reach full target load and the boost is 0.1-0.2 bar higher.
Jon
#37
To the OP, where is the sensor for the aftermarket boost gauge located relative to the stock sensor location? Pressure loss due to piping and intercoolers may explain the difference in two readings.
#39
Tony, I respectfully disagree. If you datalog a "mafless" tune on a 997tt, the output MAF values show as 0s throughout the RPM range on the Durametric. However, that is not true for LOAD values. They are calculated/appear as "normal". So how do you think these values are calculated when no MAF sensor is present?
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