Car is 95 hatch running a obd1 p75 on a fully stock b18b1. Tested the car with a P72 ecu as well, still threw the code. Code 3 is the only code present, when you turn the key on there is no CEL once the fuel pump primes then when you start it it idles rough for a few seconds then it jumps up and idles steady around 1200 rpm and the CEL comes on for the MAP.


I tested the voltage between the yel/red wire and body ground, got 5v like normal, tested between the yel/red and grn/wht wires and got 5v like normal, finally tested between the white wire and grn/wht wire (following helms manual instructions) and got 5v as well.


The next step in the tree of troubleshooting would be to test between D17 and D21 and supposed to get 3v, i havent done that yet but if it doesnt have 3v, supposed to replace the MAP, if it does, supposed to replace the ECU. I know the ECU is good since it was used beforehand, plus the p72 ecu tested as well worked fine too. The MAP being used threw no code in my other car the motor came from, we swapped it straight to the EG and now im having this problem with it, so it makes no sense for the map to have somehow went bad in between the swap.


Any other causes for this code to happen if the voltage at all connections all show good and the MAP was good before and both ECU's are known to be in order?


And just to clear it up i know the TPS and MAP arent switched around for someone who may just want to give a quick reply without reading...

 

Are you using the MAP sensor thats on top of the throttle body? I would try swapping it out with another map sensor. Also check for vacuum leaks

 

No vacuum leaks, and I just replaced the entire throttle body with a seperate one I had from another LS with a completely different MAP sensor and its still throwing the code.


So the voltage all reads correct, and i replaced the map sensor, and it still throws the code.


And just for verification after every change ive made i've reset the ecu afterwards before trying again.

 

Fixed. Aparently the yel/red wire at the map (D19 at ecu) had a short or something somewhere in the line, it would give me correct voltage sometimes when i tested it but others not, i repinned that wire and ran a new one and all is good.