The boost calculation is more or less straight off the MAP sensor the car has. When idling, this sensor shows vacuum pressure, and on non turbo cars, this should read pretty close to ‘0’ when at full throttle.

On turbocharged cars this will read some larger positive value, but then there is a second problem that not all MAP sensors can measure the full pressure presented at the intake manifold. Some top out at 10psi, others around 18psi

No calibration should be required as this should already be done for you by the ECU, it’s just down to a limitation of the sensor. You may have better luck looking for your manufacturer PID codes to see if they have one specifically for measuring boost using a different sensor and putting that in the custom OBD section in toque (accessed via the settings)

Probably not a question you could answer Ian, but I’ve seen dashhawks and tuning flashers connected through the obd port track boost. I’m curious if they use the same sensors and PIDs?

Cory, on your evo the boost levels seem to match correctly? My only concern is if I’m experiencing boost leak due to it showing lower levels than I’m supposed to be getting.

Sorry, was in Italy for a few weeks and no where near my computer.

Boost is showing correctly for me. If you are wondering about the negative boost showing at idle and cruising, your car wont actually have positive boost until its increasing throttle. Best thing to do is look at dyno charts from the same cars and see how their boost curves look. It obviously wont show the negative boost on their curves, but you can atleast see the normal peak boost and how much it tapers off. Mine for example will reach full boost of about 24psi at 4k RPM and then taper off to about 15/16psi by redline.

Quote from rockaSLC on May 8, 2010, 00:38
Probably not a question you could answer Ian, but I’ve seen dashhawks and tuning flashers connected through the obd port track boost. I’m curious if they use the same sensors and PIDs?

Cory, on your evo the boost levels seem to match correctly? My only concern is if I’m experiencing boost leak due to it showing lower levels than I’m supposed to be getting.

Quote from CoreyZ on May 7, 2010, 18:29
Ian is correct as I had the same worries when I first loaded it up with my evo. The boost gauge is correctly reading my WOT boost and everything in between while also ready the negative number at idle. From what I remember, the engine has a sort of vaccuum naturally which is why the pressure is lower at idle.

Corey, which OBD adapter do you use?

Any problems with the cheap adapter or everything okay?

Hi alhouko!

The boost calculation itself is correct, however there are 2 reasons why it may be giving you a different value than you expect, these are:

a) The vehicle profile information is not entered correctly, or you have the wrong vehicle profile selected. Engine Displacement and VE are important for boost to be calculated correctly on MAF based vehicles. If these aren’t entered correctly, the calculation will be out.

b) For MAP based vehicles, your MAP sensor could be adjusted for atmospheric pressure. In this case, you would need to use the boost adjust field in the profile to compensate for value given by the MAP sensor.

If you have those setup correctly, then you’ll get the right calculation (unless a sensor is faulty, which is unlikely). The type of OBD2 adapter used isn’t relevant to getting this correct or wrong.

Hope this helps!

Ian

Ian I have figured it out. To anyone else looking to calibrate their VE use this site http://www.autoservicetech.com/vecalculator.html

Then all you have to do it log your (RPM, Intake Air Temp, and MAF sensor) plug them into the calculator on this site and you are good to go. It seems pretty close as I am putting out 470hp in my second to top setting on Duramax with EFI Live.

Thanks Ian!

Hi!

Do you have MAP or MAF (or both?)

If you have a MAP sensor and haven’t told the app to ignore it in the OBD2 settings, then the boost reading is basically direct from that sensor to the display with only basic unit conversion done to convert from kPa to psi

If you’re using MAF sensor, then you will need to make sure your engine displacement is correct and also your VE (nearly always 85% for consumer vehicles). It’s also important to make sure ‘Faster Communication’ is enabled in the OBD2 settings (all adapters should be able to function without issue with this setting)

That’s about it – as long as you have the data in the vehicle profile setup correctly, it should read accurate boost. The only thing that can throw it for a MAF based vehicle is a faulty or bad adapter that’s got an error rate above 0 (check in the adapter status screen after being connected for a while for this value)

Hi!

Are you using the latest version from the market? – there was an update to correct under-reading boost some time ago, but you need to have downloaded it for it to take effect.

The reading from the MAP sensor is direct from the ECU (there was nothing about voltages), so if you are at sea level then the reading should be spot on. If you are using MAP and are at an altitude then you may need to use the boost adjust feature to adjust the reading slightly. However, you have mentioned that it is not doing anything when you are using it which likely means your vehicle does not have a MAP sensor (so the app uses MAF instead) You should be able to confirm this in the latest version by looking at the adapter status screen and looking for the MAP sensor if it is present.

The app will ‘Prefer’ a sensor only if it is present, if it is not present then it will default to the next best sensor for an accurate reading.

Make sure you have ‘Faster Communication’ enabled as well – the MAF sensor calculation is a time critical calculation. Other factors that can affect it are bad clone adapters (however you will likely see pausing/hanging dials with this also)

The MAF calculation also relies on correct information being present in the vehicle profile. In particular Engine Displacement and VE (which may range from 75% to 85%) depending on the vehicle.

I have a 2010 evo x, i cant seem to get the boost to read right, can you help?