MGV101 Posted February 28 Report Share Posted February 28 Had an issue with an EVO8 suddenly running very lean at idle/light loads. The car was tuned around a year ago without any issues. Turned out the issue had to do with the MAP sensor calibration. With the engine stopped, the MAP sensor was reading around 7kpa lower than the BAP sensor. An offset of 7kpa will definitely have a huge effect on fuel calculation on high vacuum and a quick recalibration seem to have fixed the fueling issue. If this was an external sensor, I would most likely be checking for grounding issues or suspect the sensor was replaced by the owner. However, this is happening with the onboard MAP which is literally on the same circuit with the ECU with the same reference ground so there should be no signal/grounding issues. Could this be an indication of the MAP sensor going bad? Is there anyway to read the MAP calibration value in the map so I can make sure the calibration had not been tempered with by the owner causing the issue? Thank you! Quote Link to comment Share on other sites More sharing options...
dx4picco Posted February 28 Report Share Posted February 28 have you checked under the bonnet that no one is sucking on the Map tube? Quote Link to comment Share on other sites More sharing options...
MGV101 Posted February 28 Author Report Share Posted February 28 The vacuum hoses checked out fine and if it was partial blockage or leak I doubt calibrating the sensor again would have fixed the problem. Whoever sucking on the tube must have strong lungs. MAP was at the low 30s on idle (before I recalibrated the sensor) when it should be at around 40kpa. Air density was reading 20% lower than it actually is, so I was getting 20% less fuel. Quote Link to comment Share on other sites More sharing options...
koracing Posted February 28 Report Share Posted February 28 9 hours ago, dx4picco said: have you checked under the bonnet that no one is sucking on the Map tube? Map tube suckers are a nuisance. 7 hours ago, MGV101 said: The vacuum hoses checked out fine and if it was partial blockage or leak I doubt calibrating the sensor again would have fixed the problem. Whoever sucking on the tube must have strong lungs. MAP was at the low 30s on idle (before I recalibrated the sensor) when it should be at around 40kpa. Air density was reading 20% lower than it actually is, so I was getting 20% less fuel. Were you able to successfully recalibrate the map sensor? Usually it has to be within 5kpa of BAP for the map calibration tool to work. Quote Link to comment Share on other sites More sharing options...
MGV101 Posted February 29 Author Report Share Posted February 29 Yes it calibrated just fine. I guess the 5kpa is based on the "default" calibration of the sensor? For example, maybe previouly the sensor was 3kpa above the "default" calibration and now it is 4kpa below allowing a 7kpa swing. But the strange this is, why did it suddenly change? Quote Link to comment Share on other sites More sharing options...
Vaughan Posted February 29 Report Share Posted February 29 There is a chance water has gotten into the sensor and it is going bad. Keep an eye on it for now, you can also measure voltage of the sensor with the hose removed and do some maths (or change it from MAP to a GP Pressure) to see what the value is without the offset. Quote Link to comment Share on other sites More sharing options...
MGV101 Posted February 29 Author Report Share Posted February 29 Thank you. Should I assume the default calibration of the internal 7 bar sensor to be 0 at 0.5v and 7bar at 4.5V without any offsets? Quote Link to comment Share on other sites More sharing options...
Vaughan Posted February 29 Report Share Posted February 29 52kPa at 0.5V and 676kPa at 4.5V Quote Link to comment Share on other sites More sharing options...
koracing Posted February 29 Report Share Posted February 29 2 hours ago, Vaughan said: 52kPa at 0.5V and 676kPa at 3.5V I'm sure you meant for that to read 676kPa at 4.5V, not 3.5V. Quote Link to comment Share on other sites More sharing options...
Vaughan Posted February 29 Report Share Posted February 29 yes, 4.5V will edit that Quote Link to comment Share on other sites More sharing options...
koracing Posted February 29 Report Share Posted February 29 Per manufacturer datasheet: Vout = VS*(0.0012858*P+0.04) ± Error -> Thus (Vout-(VS*.04))/(VS*.0012858)=P. For an output of 0.5v: (0.5v-(5v*.04))/(5v*.0012858) --> (0.5-.2)/(.006429) --> 0.3/.006429=46.7kPa and for 4.5v is (4.3)/.006429=668.8kPa - unless my math is wrong. Is there some additional built in error correction done by Link to get to a nominal value of 52 and 676? Quote Link to comment Share on other sites More sharing options...
Vaughan Posted March 1 Report Share Posted March 1 I am unsure, is just what I read from the code. Quote Link to comment Share on other sites More sharing options...
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