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TP(Main) Fine-Tuning for 0.1% throttle


krohelm
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When I touch the accelerator pedal gently, e.g., to take off very slowly in a parking lot, my TP(Main) stays at 0 while my mixture goes catastrophically lean and my engine dies.

4age 20v engine, alpha-n, I've run the throttle adjustment routine cold and warm multiple times, it's always exactly the same.  The dead zone at TP=0 is much too large for my throttle bodies.  Can I fine-tune the throttle adjustment wizard's output?  Is there something else I should try?

Edited by krohelm
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The ecu is unaware of the slight pressure on the pedal, it should not help to use accel enrichment.  :-(  I had it on before actually but it didn't help.

Can you physicaly adjust your tps so that its ALMOST at 0.1 when at rest?

I'm a little reluctant to do this.  I'm glad it occurred to you too; I tested my tps connection and it is varying resistance with the lightest of pressure, just as designed.  If I can't get the software to understand it correctly I'll do it though!

Is there any way to adjust the deadzone?  If it's saved in the pclr, which bytes hold the 0% value?  I can hex edit it if I can only find it... 

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Dont think there is a way in pclink to do that and cant help you into the deeper parts of it.

However if you CAN adjust the tps a little that would be the easiest thing by far. There is no problems assosiated to it.

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Did some digging.  Looks like there's an unexpected electrical shift when the engine is running.  I'm not sure why or how, but the ground or 5v reference shifts and effectively sets the throttle position arbitrarily lower after it's started.

I worked around this by manually pulling the throttle to -0.8 to -1.0%% before clicking "OK" on the throttle calibration wizard for "release throttle."  My throttle rests around 0.8 - 1% until I start the engine, at which point it droops over a few seconds to 0%.  It's almost right, and the dead zone, while still noticeably problematic, does not result in an easily killed engine.

Fueling seems to be based on the actual fuel axis tenths-of-percents fuel, while the AN voltages have higher precision.  Fueling should interpolate via the higher precision data source; 0 to 0.1% is a large step in my alpha-n, as is 0.3 and 0.7.  But with no interpolation below 0.1% precision, it's pretty difficult to perfectly smoothly transition onto throttle at idle.

Edited by krohelm
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Fueling seems to be based on the actual fuel axis tenths-of-percents fuel, while the AN voltages have higher precision.  Fueling should interpolate via the higher precision data source; 0 to 0.1% is a large step in my alpha-n, as is 0.3 and 0.7.  But with no interpolation below 0.1% precision, it's pretty difficult to perfectly smoothly transition onto throttle at idle.

The ADC's on the G4+ analog inputs have 10bit resolution.  This gives you about 1023 "steps" from zero to full scale.  0-100% in 0.1% increments is also about 1000 steps, so you are getting the full precision that the hardware is capable of.  One thing that you need to check is the voltage range of your TP sensor.  If for instance it is only giving you a 2.5V change from closed to WOT then you are only going to be using half of the available ADC resolution.

1/1000 of throttle position should be more than enough to get an Alpha-N tune running perfectly fine.  

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The ADC's on the G4+ analog inputs have 10bit resolution.  This gives you about 1023 "steps" from zero to full scale.  0-100% in 0.1% increments is also about 1000 steps, so you are getting the full precision that the hardware is capable of.  One thing that you need to check is the voltage range of your TP sensor.  If for instance it is only giving you a 2.5V change from closed to WOT then you are only going to be using half of the available ADC resolution.

1/1000 of throttle position should be more than enough to get an Alpha-N tune running perfectly fine.  

Just closing the loop on this - yes this is mostly problem-between-keyboard-and-chair.

The first problem here was a lack of a real "load" input into the modeled fuel algorithm.  By switching from BAP load source to MAP load source, all of my low throttle problems disappeared.  There was literally no reason not to use MAP for "load" and TPS for VE table and it works like a charm.  By having variable load at idle, small TPS changes that are not measured are basically just small increases in load and result in additional fuel.  It now only takes 1000rpm to do a slow take off, and easily pulls uphill into my driveway with small throttle opening.  Single best drivability fix since the firing order fiasco :rolleyes:

The second problem is that for some reason I cannot explain, my TPS drops after starting the engine.  By setting it to 0.7-0.8% at rest with the engine off, it drops to 0% once started.  It's a workaround but I'd really like to understand this better.  I attached an image, but my log file is over the max attachment size of 5.4mb.

tps droop.PNG

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The second problem is that for some reason I cannot explain, my TPS drops after starting the engine.  By setting it to 0.7-0.8% at rest with the engine off, it drops to 0% once started.  It's a workaround but I'd really like to understand this better.  I attached an image, but my log file is over the max attachment size of 5.4mb.

 

I think maybe sensor ground might have some load going through it.  Do you see a little step in the temp sensors at the same time?

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I think maybe sensor ground might have some load going through it.  Do you see a little step in the temp sensors at the same time?

No, temp sensors read steady throughout starting.  Maybe it's just vacuum slightly turning the throttle plates?  The TPS is very sensitive (needs to be, as 0.1% is significant) and it seems plausible that 50kpa vacuum could turn the blades slightly.

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