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Old 12-15-2012, 08:37 PM   #1 (permalink)
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load vs absolute load?

i have been trying to find the most MPG friendly way to accelerate and so i have been targeting 80% LOD at 2500rpm. however my LOD easily hits 99% or maximum during acceleration so i have found myself to actually be slowing down. this doesn't seem right, i thought 99% load means i'm going wide open throttle (getting all the torque car can provide at that rpm)? because certainly im not and im only giving about 1/4 throttle?! So someone helped me program absolute load gauge. Now this seems to be more relevant but i have also heard absolute load is not relevant to BSFC? during WOT absolute load maxes out at 95%. it's also usually 10-15% lower than load. it seems though that 75% absolute load actually means 3/4 throttle. so which one should i be monitoring?

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Old 12-15-2012, 09:23 PM   #2 (permalink)
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I haven't even figured out what absolute load even means, but my guess is it is manifold pressure. Absolute load on Torque goes to single digits under engine braking, which is why I say that.

The scenario could be that your electronically controlled throttle is wide open or something like that but the cams are not in "maximum power position". I don't know how cars are actually programmed so I can't be sure but this seems like something that would make sense for the manufacturer to do.
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Old 12-15-2012, 10:08 PM   #3 (permalink)
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hmm thats what i have been thinking. either that or it could be because of torque converter being locked.

after some googling: abs load seems to indicate engine pumping efficiency. so shouldnt this be monitored instead of load for bsfc reasons

Quote:
Ranges from 0 to approximately 0.95 for naturally aspirated engines, 0 – 4 for boosted engines,Linearly correlated with engine indicated and brake torque,Often used to schedule spark and EGR rates,Peak value of LOAD_ABS correlates with volumetric efficiency at WOT.,Indicates the pumping efficiency of the engine for diagnostic purposes.
About PID Calculated Load Value OBD-II Resource
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Old 12-16-2012, 09:39 AM   #4 (permalink)
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When you are at low rpms, throttle position varies load REALLY fast. Your throttle body is sized to flow maximum horsepower, which for you is 170hp. However, you can only achieve 170hp at 6000 rpm. For example, at 2000 rpm maybe you have a max output of 1/3rd that. So, it makes sense that 0-100% throttle at 6000 rpm is going to give you 0-100% load. At 2000 rpm, 0-33% throttle is going to give you 0-100% load.

In reality its even more sensitive because of the mechanics of a butterfly valve. By the time the valve is 50% open its probably flowing 75% of what it can.

Does that make sense?
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Old 12-16-2012, 10:28 PM   #5 (permalink)
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yes i know there is less power down low and so engine loads out easy but still doesnt explain the difference with absolute load and that abs load is more relative to pumping efficiency.
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Old 12-16-2012, 11:07 PM   #6 (permalink)
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do not use absolute load - ever

do not use absolute load
it will always reach 100% even when the system can never reach
100%

use engine load or calculated load
it is a relative calculated value , relative to what the system should be capable of .
a higher value means more power output
a lower value at a constant consistent load would be showing improved FE as compared to the a higher value at the same constant consistent load

it can be used with other PIDs to show improvements or UN improvements
it is (can be) used with fuel trim to determine problems related to flow
like this

here low peak engine load along with very heavy add in real time fuel trim
( short term fuel trim in generic )
at WOT wide open throttle over 4k rpm
shows an UNder reporting MAF sensor , defective new REMAN part

IF fuel trim had been within a few percent of zero
(under the same conditions)
then this would be showing
restriction to flow
clogged cat or restricted air intake

at cruise
lesser load values at the same EXACT conditions shows
improved FE



Last edited by Daox; 12-17-2012 at 09:17 AM..
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