J Rolfe Posted November 7, 2023 Report Share Posted November 7, 2023 Interested to see if anyone else has run into the same issue. I have a external link 3 bar map sensor into a G4X Fury in a R32 Skyline GTST. The sensor will read within ±5kpa of 100kpa when the engine is not running and when warming up will stay within that value. If I go for a drive and get the engine up to operating temperature then turn it off and on again the car will not start and the map sensor will read way out of value, eg 14.3kpa and will slowly go back up to 100kpa. Sensor is mounted next to brake master. Screenshot attached is after a drive Quote Link to comment Share on other sites More sharing options...
J Rolfe Posted November 7, 2023 Author Report Share Posted November 7, 2023 PC Datalog - 2023-11-7 8;16;44 pm.llgx Quote Link to comment Share on other sites More sharing options...
Adamw Posted November 7, 2023 Report Share Posted November 7, 2023 Its working ok in that log, do you have one when it is not working? Is it one of the current MAP sensors as pictured here?: https://dealers.linkecu.com/3-Bar-MAP Quote Link to comment Share on other sites More sharing options...
J Rolfe Posted November 7, 2023 Author Report Share Posted November 7, 2023 Here is a log file of the car faulting. Will try start but wont idle. Yes it is that sensor that I am using PC Datalog - 2023-11-8 7;37;43 am.llgx Quote Link to comment Share on other sites More sharing options...
Vaughan Posted November 7, 2023 Report Share Posted November 7, 2023 If you remove the hose from the sensor while it is showing a super low value after a drive does it immediately go back up to atmospheric? Quote Link to comment Share on other sites More sharing options...
J Rolfe Posted November 7, 2023 Author Report Share Posted November 7, 2023 No, but It looks like it might go back up to 100kpa a little faster. If i blow into the hose while its connected to the sensor it will go up like usual so it is reading. Quote Link to comment Share on other sites More sharing options...
Vaughan Posted November 7, 2023 Report Share Posted November 7, 2023 Sounds like there is a blockage somewhere and if removing the hose from the sensor at the sensor end doesn't fix it but blowing directly into the sensor itself does then it is in the sensor. Quote Link to comment Share on other sites More sharing options...
J Rolfe Posted November 7, 2023 Author Report Share Posted November 7, 2023 The sensor has done about 50km. Do you suggest I order a new one? Before that ill try blowing out the sensor and seeing if there is something in it. Quote Link to comment Share on other sites More sharing options...
Adamw Posted November 7, 2023 Report Share Posted November 7, 2023 Looking at your log, im leaning more towards there being a bad ground connection or similar. You can see in the pic below the MAP voltage and MAP pressure jump up as soon as the battery voltage drops as the starter engages. The engine will barely have started to turn at this point so there should be no manifold pressure change. After that the MAP voltage is mirror image of the battery voltage (ie the MAP voltage drops 0.3V when the batt voltage increases 0.3V). The 5V output shows the MAP sensor should have a constant supply. So, the question is, why does the MAP sensor voltage seem to be affected by battery voltage? My feeling would be a high-resistance ground or similar? I would try shaking/wiggling/tugging/bending the loom while watching the MAP reading on the laptop. Quote Link to comment Share on other sites More sharing options...
J Rolfe Posted November 7, 2023 Author Report Share Posted November 7, 2023 We suspected a grounding issue with it so instead of it grounding from the ecu originally it is now grounded directly to the chassis. Ill move the ground to the engine block to see if that makes a difference and will check the connections are secure in the connector Quote Link to comment Share on other sites More sharing options...
J Rolfe Posted November 7, 2023 Author Report Share Posted November 7, 2023 This is the log file after swapping ground points. From what I can see when the engine is first cranked the MAP voltage doesnt seem to fluctuate as much as the screenshot you sent me. Am i right? PC Datalog - 2023-11-8 12;16;37 pm.llgx Quote Link to comment Share on other sites More sharing options...
Adamw Posted November 7, 2023 Report Share Posted November 7, 2023 Yeah, looks good in that one, no MAP variance from battery voltage now. But, does the MAP still read wrong when hot? Quote Link to comment Share on other sites More sharing options...
J Rolfe Posted November 7, 2023 Author Report Share Posted November 7, 2023 Dont know yet. Ill take the car for a drive when I finish work and see. Quote Link to comment Share on other sites More sharing options...
J Rolfe Posted November 8, 2023 Author Report Share Posted November 8, 2023 Sensor is still reading weird values after driving vehicle. Jiggled around the connectors at the sensor side and the ecu side to no change. Grounded the sensor directly to the battery but did not change anything. Gently blew out the sensor port but also did not change anything as well as looked into the port and didnt see anything. Checked there is 5v at the sensor connecter and there is. No blockage into the intake manifold. Quote Link to comment Share on other sites More sharing options...
Dean Posted November 8, 2023 Report Share Posted November 8, 2023 8 hours ago, J Rolfe said: We suspected a grounding issue with it so instead of it grounding from the ecu originally it is now grounded directly to the chassis. Ill move the ground to the engine block to see if that makes a difference and will check the connections are secure in the connector You should always ground the MAP sensor to the ECU “sensor ground”, right? So the sensor has a stable 0V and 5V reference, directly in the ECU. Quote Link to comment Share on other sites More sharing options...
J Rolfe Posted November 8, 2023 Author Report Share Posted November 8, 2023 The sensor was originally grounded through the ecu sensor ground but for testing purposes it’s now grounded to the chassis/engine Quote Link to comment Share on other sites More sharing options...
koracing Posted November 8, 2023 Report Share Posted November 8, 2023 I would double check all your ecu grounding as if there is a ground offset of some type - you're going to get variations in the sensor readings. Sensor may have good ground, but ecu is seeing it differently. Any main chassis ground should be removed, cleaned (paint or coatings removed at point of contact to chassis and engine). Quote Link to comment Share on other sites More sharing options...
J Rolfe Posted November 11, 2023 Author Report Share Posted November 11, 2023 Thank you to everyone that helped. It ended up being a issue with the sensor. Quote Link to comment Share on other sites More sharing options...
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