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Electrical nerds - Failed LH 2.4 ECU diagnosis

holtzboy

holtzboy

Project Procrastinator
Joined
Mar 7, 2004
Location
Cornelius, OR
Would anyone be wanting to dissect my failed #951 N/A LH 2.4 ECU to help me determine what might have caused the no start issue? I looked it over with the naked eye and don't see anything broken, disconnected and/or burnt. I swapped to a replacement ECU and the car seems to idle and drive just fine now.
 
I too have a 951 that is will cause the car to crank but not start. Haven't had time to fiddle with it as I had spares
 
Did you try reflowing all the solder? I bet that it got the same mediocre wave solder treatment as every other piece of Bosch electronics from the time.
 
add a ground wire to the relay to see if you the typical ecu failure

b<iframe width="560" height="315" src="https://www.youtube.com/embed/f2tCRejgFoU" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
 
philski o'flood said:
add a ground wire to the relay to see if you the typical ecu failure

b<iframe width="560" height="315" src="https://www.youtube.com/embed/f2tCRejgFoU" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
Click to expand...

That's a useful demonstration.
If you don't already know . . . The Blue/Green wire he grounded in that video is the control signal wire from the ECU to trigger the fuel pump relay "ON." The ECU does that with a ground signal. The typical failure is the circuit inside the ECU that converts the coil signal into that ground signal. So if this ground trick triggers your relay and thing are better when otherwise it would not trigger the relay, you may have an ECU with that issue.

There are fixes that can be done without having to find a new ECU. I have a page that outlines those options: https://www.240turbo.com/fuelpumprelay.html

Dave B
 
dbarton said:
That's a useful demonstration.
If you don't already know . . . The Blue/Green wire he grounded in that video is the control signal wire from the ECU to trigger the fuel pump relay "ON." The ECU does that with a ground signal. The typical failure is the circuit inside the ECU that converts the coil signal into that ground signal. So if this ground trick triggers your relay and thing are better when otherwise it would not trigger the relay, you may have an ECU with that issue.

There are fixes that can be done without having to find a new ECU. I have a page that outlines those options: https://www.240turbo.com/fuelpumprelay.html

Dave B
Click to expand...

Thank you for the explanation ! Running through no start issues so soaking in all the info !
 
dbarton said:
That's a useful demonstration.
If you don't already know . . . The Blue/Green wire he grounded in that video is the control signal wire from the ECU to trigger the fuel pump relay "ON." The ECU does that with a ground signal. The typical failure is the circuit inside the ECU that converts the coil signal into that ground signal. So if this ground trick triggers your relay and thing are better when otherwise it would not trigger the relay, you may have an ECU with that issue.

There are fixes that can be done without having to find a new ECU. I have a page that outlines those options: https://www.240turbo.com/fuelpumprelay.html

Dave B
Click to expand...

Very nicely documented page! Thank you for providing those resources.

I would use the VW relay to switch (30/87) the system relay 86/2 ground leg, then the existing circuit is unaltered beyond that insertion. Great find!
 
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