Limits of stock MAF MAP Sensors

C

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cmitchell17
Sep 8, 2008
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I am trying to get my 500rw tune smokeless and Im using the maf limiting tables but there isnt enough resolution once my tune gets to the higher mm3 cells on the pulsewith table.

Ive tried commanding more boost but I never see any higher than about 30.2 actual boost on my logs. Is this the limit of reading? Is there any way you can scale the sensor to make it read higher? I don't have a mech boost gauge so I don't know what I am actually getting, but I would like to try to see if adding a couple psi would put me into the 2.4g/cyl cells of my maf limiting table giving me full fueling when ever I go above about 3000rpm.
 
Dozerboy

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Thats the limit of the sensor I don't think there is anything you can do about it. You really need to get some gauges before you over speed that turbo like several other have done.
 
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cmitchell17
Sep 8, 2008
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So I guess if I commanded more than 30, which looks like its the highest efi live is reporting it, then would the ecm keep trying to increase boost and never reach it untill it hits the max vane tables?
 
C

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cmitchell17
Sep 8, 2008
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The GM.BOOST_DMA is not a supported parameter. Is there something I have to log with it? Im logging baro also.

Im pretty sure I am maxing out the maf sensor, becuase it will stop at like 66lbs/min. But what is wierd is that I am using finger's eq pid (thanks) and it still seems like it is working even when I reach 66lbs/min+. I don't know how it would be working unless its using speed density to calculate airflow and even then my boost is maxing out at around 30psi?


I guess you just can't have drivability and no smoke on 500rw+ tunes. When you have pulsewidths that are forced to go almost straight up it makes tuning everything almost impossible.
 
othrgrl

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You can make over 500hp on a stock turbo while being almost completely smokeless at WOT. The tune can be very drivable but pretty much no matter what if you stomp it at low RPM/low boost it will smoke until the RPM and boost come up. Rolling into the throttle you can drive it with very, very little smoke.

Putting the MAF sensor in a bigger pipe allows it to read more Lbs/minute at a given voltage, but the MAF Flow Rate table (B0201) maxes out at 66.14 LBs/minute so all you end up doing is flat-lining at 66 at about 4.2 volts, rather than being at 63 at 5 volts. From the factory the LLY's MAF sensor and table are close to matched as far as maxing out at the same time. Move the sensor and you are still limited by the table to 66.

My MAP sensor used to max out at 43.6 PSI absolute/28.8 PSI boost; when I built the motor I cleaned the MAP sensor up (EGR and PCV soot) and now it is reading up to 52.8 PSI absolute/38.3PSI of boost. You are correct that if you command over what the sensor will read the ECM will close the turbo up to max vane "looking for" more boost.
 
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cmitchell17
Sep 8, 2008
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I have my Maf tables to where my truck has very little smoke before the turbo is spooled. There is just a slight haze, but once it gets to the top airflows on the maf limiting table I am forced to allow full fueling or else I might not get it. There is just not enough resolution at the top of the table.
It will be in the 2.4g/cly cell then once rpms get above 3000 at wot the grams per cly will drop back in the 2.2 range. So my tune is basically smokeless untill it hits the higher airflow cells in the maf limiting table. Then it smokes.

With the map sensor maxxed out I don't know my boost but with 3100us at 160mpa with a EQ of 1.05-1.10 is what I get at WOT and it climbs with rpms as airflow drops.

I don't know if my maf limiting is hurting spoolup but It takes about 4 seconds to get to 30lbs. I need to test it without any maf limiting.
 
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cmitchell17
Sep 8, 2008
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I wonder if it is wasting fuel by having the fueling stay the same when airflow drops and rpms increase. For gas I think you want it just rich enough to make sure all the avalible air has fuel to burn with. The reason why it is sometimes overly rich on a gasser is to control egts, but I guess thats the opposite for a diesel.
 
Fingers

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[email protected] said:
The GM.BOOST_DMA is not a supported parameter. Is there something I have to log with it? Im logging baro also.

Im pretty sure I am maxing out the maf sensor, becuase it will stop at like 66lbs/min. But what is wierd is that I am using finger's eq pid (thanks) and it still seems like it is working even when I reach 66lbs/min+. I don't know how it would be working unless its using speed density to calculate airflow and even then my boost is maxing out at around 30psi?


I guess you just can't have drivability and no smoke on 500rw+ tunes. When you have pulsewidths that are forced to go almost straight up it makes tuning everything almost impossible.
Click to expand...

My PIDs are not correct once the MAF sensor maxes out. I still need to finish the speed density part. Maybe this week.

If you switch the MAF to a larger tube, you can get more range, but as mentioned, you tables don't go higher anyway. Instead, you just tune around the MAF readings knowing they are actually some multiple of the reading.

The other part of this is at higher revs and fueling, your boost performance is fairly consistent.
 
C

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cmitchell17
Sep 8, 2008
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Ok thanks for the help, your pid makes tuning out the smoke really easy. I would have never been able to do it without knowing the eq. It is also really accurate.
 
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Power and economy are not equal. Also, if you have anything other than the LLY with stock injectors, the factor used in the PID will not be accurate.
 
Fingers

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Yes, but I don't know what the factor would be for those engines. Even for the LLY, I adjusted it manually so when the ratio read "1" there was just a hint of smoke out of the pipe.

And it does not use mm3 from the tables to calc fuel usage since we all dink with that. It uses total pulse duration(s) and pressure to calculate fuel injected.

Remember folks, this is just a tool to help keep you honest when making fueling adjustments. It has it's flaws but is far better than seat of the pants guesses.
 
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