AEM EMS load reading
02-19-2008, 05:50 PM
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AEM EMS load reading
Hello,
I am having a tuning quirk and would like some assistance. My AEM EMS (according to my logs), is seeing about 2/3 psi less boost than actual value. I just purchased a brand new map sensor from Honda.
According to my log, my car is making 2.6psi of boost at WOT at 6645rpm. According to my Defi boost gauge, I am seeing peek boost of about 5.5 psi at the same rpm at WOT. Before switching to the EMS, I have dyno'd my car and my Defi gauge proved accurate.
Can anyone think of any reason why my MAP sensor might be outputting lower than true boost pressure readings?
Thanks for any direction you guys can point me in!
J
*edit*
Can anyone host a couple screenshots of my logs?
I am having a tuning quirk and would like some assistance. My AEM EMS (according to my logs), is seeing about 2/3 psi less boost than actual value. I just purchased a brand new map sensor from Honda.
According to my log, my car is making 2.6psi of boost at WOT at 6645rpm. According to my Defi boost gauge, I am seeing peek boost of about 5.5 psi at the same rpm at WOT. Before switching to the EMS, I have dyno'd my car and my Defi gauge proved accurate.
Can anyone think of any reason why my MAP sensor might be outputting lower than true boost pressure readings?
Thanks for any direction you guys can point me in!
J
*edit*
Can anyone host a couple screenshots of my logs?
02-19-2008, 06:01 PM
#3
does the boost sensor see positive pressure when the map doesnt?
You might have the voltage of the map sensor setup incorrectly on the ems? is the boost gauge seeing vacuum from the same place the map sensor is?
You might have the voltage of the map sensor setup incorrectly on the ems? is the boost gauge seeing vacuum from the same place the map sensor is?
02-19-2008, 06:52 PM
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Originally Posted by PeanutButter,Feb 19 2008, 09:52 PM
Is the defi mechanical or electric?
02-19-2008, 07:10 PM
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Originally Posted by Soul Coughing,Feb 19 2008, 10:01 PM
does the boost sensor see positive pressure when the map doesnt?
You might have the voltage of the map sensor setup incorrectly on the ems? is the boost gauge seeing vacuum from the same place the map sensor is?
You might have the voltage of the map sensor setup incorrectly on the ems? is the boost gauge seeing vacuum from the same place the map sensor is?
02-19-2008, 09:36 PM
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Originally Posted by NFRTurboTerror,Feb 20 2008, 12:03 AM
I think he was asking if you had the right map sensor selected in the EMS?
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02-20-2008, 05:32 AM
#8
Both of your sensors are close and are likely reading appropriately. I'll try to explain and give some appropriate links.
The issue is that your DEFI boost gauge reads gauge pressure and your AEM reads absolute pressure. Because you're in SLC, the DEFI will always read a few psi higher than the AEM. If you happened to be at sea level on a day with standard atmospheric conditions, the readings would be the similar.
MAP sensor = Manifold Absolute Pressure sensor. MAP sensors have no concept of boost/vacuum, only absolute pressure within their calibrated range. The AEM EMS uses the absolute pressure from the sensor minus a standard atmospheric pressure to create it's idea of vacuum/boost. If you compare 'boost' values from the AEM to any other 'boost' values, they will always be off due to the conversion from absolute to gauge pressure. Any time the local conditions aren't standard, it will guess vacuum/boost wrong. Luckily, necessary fueling is determined by absolute pressure with very little impact from gauge pressure (vacuum/boost). In the EMS, I set things up to display kPa instead of vacuum/boost. kPa is a system of units based around absolute pressure. This skips all of the unit conversion issues.
Further explanation.
Go here
http://www.turblex.com/altitude/index.cfm
Enter 0 ft elevation
Sea Level absolute pressure is 14.7 psia
Enter 4221 ft elevation for SLC
Salt Lake City pressure is 12.58 psia
The difference between the two is 2.12 psia. This is how far your AEM will be off of your mechanical gauge on an average day.
So, when your AEM shows 2.6 psia, your mechanical boost gauge should show around 4.72 psi of boost.
Here's a quick double check. With the motor off and the piping equalized to atmospheric pressure, what MAP value does the AEM show? On the average day in SLC, it should be around 86 kPa or 4.3 in Hg of vacuum. Keep in mind that this value will change on warmer or cooler days or even when storms come through.
Tim
PS: This all links back to AEM's boost compensation. It assumes that when you double absolute pressure, you double the fueling needs to the motor (if all else is constant). Of course, this is where VE comes into play as well. By using boost comp, you essentially turn the base fuel table into a VE table. I also use the base fuel map to tune for different A/F ratios (if the fuel map only tuned for VE and there were no other fuel modifiers, then the a/f ratio would be the same everywhere). The other way to tune for different a/f ratios is the throttle mod (then the base fuel map could potentially really be a VE table), but I found it unsatisfactory. I wanted a/f ratio to be determined by load and other factors, not throttle position. With a responsive turbo, you can get high loads at low throttle position and I didn't want those areas to be artificially leaned out.
The issue is that your DEFI boost gauge reads gauge pressure and your AEM reads absolute pressure. Because you're in SLC, the DEFI will always read a few psi higher than the AEM. If you happened to be at sea level on a day with standard atmospheric conditions, the readings would be the similar.
MAP sensor = Manifold Absolute Pressure sensor. MAP sensors have no concept of boost/vacuum, only absolute pressure within their calibrated range. The AEM EMS uses the absolute pressure from the sensor minus a standard atmospheric pressure to create it's idea of vacuum/boost. If you compare 'boost' values from the AEM to any other 'boost' values, they will always be off due to the conversion from absolute to gauge pressure. Any time the local conditions aren't standard, it will guess vacuum/boost wrong. Luckily, necessary fueling is determined by absolute pressure with very little impact from gauge pressure (vacuum/boost). In the EMS, I set things up to display kPa instead of vacuum/boost. kPa is a system of units based around absolute pressure. This skips all of the unit conversion issues.
Further explanation.
Go here
http://www.turblex.com/altitude/index.cfm
Enter 0 ft elevation
Sea Level absolute pressure is 14.7 psia
Enter 4221 ft elevation for SLC
Salt Lake City pressure is 12.58 psia
The difference between the two is 2.12 psia. This is how far your AEM will be off of your mechanical gauge on an average day.
So, when your AEM shows 2.6 psia, your mechanical boost gauge should show around 4.72 psi of boost.
Here's a quick double check. With the motor off and the piping equalized to atmospheric pressure, what MAP value does the AEM show? On the average day in SLC, it should be around 86 kPa or 4.3 in Hg of vacuum. Keep in mind that this value will change on warmer or cooler days or even when storms come through.
Tim
PS: This all links back to AEM's boost compensation. It assumes that when you double absolute pressure, you double the fueling needs to the motor (if all else is constant). Of course, this is where VE comes into play as well. By using boost comp, you essentially turn the base fuel table into a VE table. I also use the base fuel map to tune for different A/F ratios (if the fuel map only tuned for VE and there were no other fuel modifiers, then the a/f ratio would be the same everywhere). The other way to tune for different a/f ratios is the throttle mod (then the base fuel map could potentially really be a VE table), but I found it unsatisfactory. I wanted a/f ratio to be determined by load and other factors, not throttle position. With a responsive turbo, you can get high loads at low throttle position and I didn't want those areas to be artificially leaned out.
02-20-2008, 07:33 AM
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Originally Posted by timg,Feb 20 2008, 09:32 AM
Both of your sensors are close and are likely reading appropriately. I'll try to explain and give some appropriate links.
The issue is that your DEFI boost gauge reads gauge pressure and your AEM reads absolute pressure. Because you're in SLC, the DEFI will always read a few psi higher than the AEM. If you happened to be at sea level on a day with standard atmospheric conditions, the readings would be the similar.
MAP sensor = Manifold Absolute Pressure sensor. MAP sensors have no concept of boost/vacuum, only absolute pressure within their calibrated range. The AEM EMS uses the absolute pressure from the sensor minus a standard atmospheric pressure to create it's idea of vacuum/boost. If you compare 'boost' values from the AEM to any other 'boost' values, they will always be off due to the conversion from absolute to gauge pressure. Any time the local conditions aren't standard, it will guess vacuum/boost wrong. Luckily, necessary fueling is determined by absolute pressure with very little impact from gauge pressure (vacuum/boost). In the EMS, I set things up to display kPa instead of vacuum/boost. kPa is a system of units based around absolute pressure. This skips all of the unit conversion issues.
Further explanation.
Go here
http://www.turblex.com/altitude/index.cfm
Enter 0 ft elevation
Sea Level absolute pressure is 14.7 psia
Enter 4221 ft elevation for SLC
Salt Lake City pressure is 12.58 psia
The difference between the two is 2.12 psia. This is how far your AEM will be off of your mechanical gauge on an average day.
So, when your AEM shows 2.6 psia, your mechanical boost gauge should show around 4.72 psi of boost.
Here's a quick double check. With the motor off and the piping equalized to atmospheric pressure, what MAP value does the AEM show? On the average day in SLC, it should be around 86 kPa or 4.3 in Hg of vacuum. Keep in mind that this value will change on warmer or cooler days or even when storms come through.
Tim
PS: This all links back to AEM's boost compensation. It assumes that when you double absolute pressure, you double the fueling needs to the motor (if all else is constant). Of course, this is where VE comes into play as well. By using boost comp, you essentially turn the base fuel table into a VE table. I also use the base fuel map to tune for different A/F ratios (if the fuel map only tuned for VE and there were no other fuel modifiers, then the a/f ratio would be the same everywhere). The other way to tune for different a/f ratios is the throttle mod (then the base fuel map could potentially really be a VE table), but I found it unsatisfactory. I wanted a/f ratio to be determined by load and other factors, not throttle position. With a responsive turbo, you can get high loads at low throttle position and I didn't want those areas to be artificially leaned out.
The issue is that your DEFI boost gauge reads gauge pressure and your AEM reads absolute pressure. Because you're in SLC, the DEFI will always read a few psi higher than the AEM. If you happened to be at sea level on a day with standard atmospheric conditions, the readings would be the similar.
MAP sensor = Manifold Absolute Pressure sensor. MAP sensors have no concept of boost/vacuum, only absolute pressure within their calibrated range. The AEM EMS uses the absolute pressure from the sensor minus a standard atmospheric pressure to create it's idea of vacuum/boost. If you compare 'boost' values from the AEM to any other 'boost' values, they will always be off due to the conversion from absolute to gauge pressure. Any time the local conditions aren't standard, it will guess vacuum/boost wrong. Luckily, necessary fueling is determined by absolute pressure with very little impact from gauge pressure (vacuum/boost). In the EMS, I set things up to display kPa instead of vacuum/boost. kPa is a system of units based around absolute pressure. This skips all of the unit conversion issues.
Further explanation.
Go here
http://www.turblex.com/altitude/index.cfm
Enter 0 ft elevation
Sea Level absolute pressure is 14.7 psia
Enter 4221 ft elevation for SLC
Salt Lake City pressure is 12.58 psia
The difference between the two is 2.12 psia. This is how far your AEM will be off of your mechanical gauge on an average day.
So, when your AEM shows 2.6 psia, your mechanical boost gauge should show around 4.72 psi of boost.
Here's a quick double check. With the motor off and the piping equalized to atmospheric pressure, what MAP value does the AEM show? On the average day in SLC, it should be around 86 kPa or 4.3 in Hg of vacuum. Keep in mind that this value will change on warmer or cooler days or even when storms come through.
Tim
PS: This all links back to AEM's boost compensation. It assumes that when you double absolute pressure, you double the fueling needs to the motor (if all else is constant). Of course, this is where VE comes into play as well. By using boost comp, you essentially turn the base fuel table into a VE table. I also use the base fuel map to tune for different A/F ratios (if the fuel map only tuned for VE and there were no other fuel modifiers, then the a/f ratio would be the same everywhere). The other way to tune for different a/f ratios is the throttle mod (then the base fuel map could potentially really be a VE table), but I found it unsatisfactory. I wanted a/f ratio to be determined by load and other factors, not throttle position. With a responsive turbo, you can get high loads at low throttle position and I didn't want those areas to be artificially leaned out.
Thank you so much for taking the time to properly explain this to me. I am at about 5000ft ASL, which would explain the difference of about 2.5 psi. NOW I understand and I'm not quite as concerned.
Along the same lines, I was reading an article about effective compression ratio and calculated that, at 5000 ft ASL, my a car with a motor of 11:1 static compression ratio has an altitude adjusted compression ratio of precisely 10:1. Running 10psi of boost, the effective compression ratio is 17.48:1 vs. 18/48:1...This helps explain why those EVO guys can run huge boost all day long at Miller Motorsports Park and not have the issues that the same EVO guys back east had...it also explains why my CRV feels like a complete turd.
Thanks again, Tim!