StoryWorm Posted October 3, 2021 Report Share Posted October 3, 2021 1995 bmw m3. s50b30us. Link g4x. Turbod previously had an RKtunes chip on the OE ecu. just switched over to link. While getting the Ecu set up to drive to a dyno, the ecu stopped communicating with the laptop. I tried manually selecting the port on the laptop. unplugging the ecu and letting it sit for awhile. check the on board computer fueses on the car, both had continuity. finally pulled the ecu out and opened up the cover to see that the led lights on the ecu board were not lighting up. unplugged the ecu to check the main harness for voltage, check pin 54 for 14+ volts from the main relay (ecu power according to the manual) to get 1.4+v. Im thinking it is a power supply issue but i want to make sure im testing it correctly. i test it with the car on. Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted October 3, 2021 Author Report Share Posted October 3, 2021 update. i swapped out the OEM main/ecu relay for another SPDT relay i had laying around. this gave me power to pin 54 with key on. went ahead and plugged the ecu back in. still no communication with the laptop, still no lights on the ecu. however now when i turn the key off and take it out, the cel stays illuminated. this cel goes away when i pull the non oem relay out. it also does not go on when i put the oem relay back in. Tested the ground pins as well (55 and 6). both are not testing for ground, but rather testing the same as the ecu power. so if the non oem relay is in, it tests 12+. if the oem relay is in it test 1.4+ Quote Link to comment Share on other sites More sharing options...
Adamw Posted October 3, 2021 Report Share Posted October 3, 2021 Some of the BMW relays have a non standard pinout so the other one you are trying may not be right. With the OEM relay fitted, and ignition switch on, what is the voltage on pin 27? Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted October 3, 2021 Author Report Share Posted October 3, 2021 the relay i used had the same pins as the bmw one. 30, 85,85, 87,87a all in the same place. pin 27 tested at 12v+ with the harness unplugged from the ecu I also reinstalled my oem ecu +rktunes chip with the oem main relay and the car fired right up and ran as it was suppose to. so im ruling out the supply power as an issue at this point Quote Link to comment Share on other sites More sharing options...
Adamw Posted October 3, 2021 Report Share Posted October 3, 2021 1 hour ago, Adamw said: With the OEM relay fitted, and ignition switch on, what is the voltage on pin 27? With ECU plugged in. Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted October 3, 2021 Author Report Share Posted October 3, 2021 key off: 12.34v+ key on: 10.0v+ Quote Link to comment Share on other sites More sharing options...
Adamw Posted October 3, 2021 Report Share Posted October 3, 2021 Ok, that pin should be near zero volts with Key on - this is the trigger to turn the main relay on. This pin is controlled by the ignition switch pin, can you check you have 12V on pin 56 with ign switch on. Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted October 3, 2021 Author Report Share Posted October 3, 2021 yes i have 12v on pin 56 with ign on Quote Link to comment Share on other sites More sharing options...
Adamw Posted October 3, 2021 Report Share Posted October 3, 2021 Ok, if there is 12V on pin 56, but pin 27 is not at ground then I would be suspicious the mosfet on the bottom board that controls the main relay has failed. These are hugely over-rated so are uncommon to fail on their own without some sort of event such as reverse polarity battery connection but we will need to take a look at the ecu by the sound of it. You will probably find if you ground pin 27 with a little jumper lead or something the ecu will power up. Contact [email protected] to arrange inspection and repair. Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted October 3, 2021 Author Report Share Posted October 3, 2021 will do, thank you for helping diagnose this! Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted October 30, 2021 Author Report Share Posted October 30, 2021 ok so got the linkecu back from service and there is still no connection to the laptop. ive tried 2 different linkecu usb cables. tried manually connecting to the usb ports (all 3 on the laptop) and still nothing. it is showing up in the device manager on port4 with auto search Quote Link to comment Share on other sites More sharing options...
Adamw Posted October 30, 2021 Report Share Posted October 30, 2021 If the blue LED is not on on the ecu then it is not powered up so will never communicate. I saw the service report on that ecu and it said there was no problem with it, it all worked as it was designed when tested here. They did replace the main FET as a precaution just in case. So can you confirm the LED is still no on. Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted October 30, 2021 Author Report Share Posted October 30, 2021 there is no led on with the key turned to the on position. im assuming my laptop can still detect the ecu even though it is not getting power? Quote Link to comment Share on other sites More sharing options...
Adamw Posted October 31, 2021 Report Share Posted October 31, 2021 USB will be detected but you will not get any comms until the ecu is powered up. Can you back probe ecu pin 27 with a paper clip or needle etc and connect it to ground to see if it then powers up. Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted October 31, 2021 Author Report Share Posted October 31, 2021 i get 2 blue LED lights when i ground out pin 27 Quote Link to comment Share on other sites More sharing options...
Adamw Posted October 31, 2021 Report Share Posted October 31, 2021 Ok, so now let try a similar back probe trick, but this time I want you to connect 12V to pin 56. Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted October 31, 2021 Author Report Share Posted October 31, 2021 nothing happened jumping that one to 12v+ Quote Link to comment Share on other sites More sharing options...
Adamw Posted October 31, 2021 Report Share Posted October 31, 2021 Ok, that kind of suggests the main grounds are missing. Its a bit hard to imagine though since there are so many. Can you back probe pin 6 and connect it to ground. See if it powers with that. Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted October 31, 2021 Author Report Share Posted October 31, 2021 probing pin 6 powered it up. 2 blue led lights Quote Link to comment Share on other sites More sharing options...
Adamw Posted October 31, 2021 Report Share Posted October 31, 2021 Ok, that is weird, it seems your ECU is missing its main grounds. Im not familiar with the E36 to know where these wires go, but typically the grounds on BMW's are large brown wires and you will probably find these all crimped together into a single lug on the cylinder head or similar. Pin 6, 55 & 34 should all have direct continuity to ground. If it looks like they are connected to the engine well, then possibly the engine is missing the main ground cable. Quote Link to comment Share on other sites More sharing options...
StoryWorm Posted November 1, 2021 Author Report Share Posted November 1, 2021 i think these main ground cables are known to corrode over time. i will look into this and hopefully return with good news! thank you so much for all the help narrowing this problem down Quote Link to comment Share on other sites More sharing options...
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