2007 Mercedes-Benz SL550 Crank but no start
2007 MB SL550 V8. Crank no start. Was intermittent, had to two different local shops and spent over $2k fixing other small things and they say it’s fixed but now most of the time it will not start. I borrowed a pressure tester from O’reily’s and the car started showing 55 lbs of pressure. I did read in a post that the fuel pump should start upon turning the key to the run position but it does not.
If you're tackling this as a DIY project, there are several steps you can take to get closer to diagnosing the problem yourself. Given the intermittent nature of the no-start issue, it's crucial to thoroughly inspect multiple systems.
Drive Authorization:
Scanner Test: You should perform a drive authorization test using a competent scanner. This will help you determine if the key and the car's computer are communicating effectively. Here's a video tutorial that shows you how to do this.
https://www.youtube.com/watch?v=mFEkLEPSaJ4
Fuel System:
Fuel Pressure Gauge: Since you've mentioned fuel pressure, connect a dedicated fuel pressure gauge to the fuel rail and observe the readings while trying to start the car.
Fuel Pump Module: This could be a possible culprit, especially if the pump doesn't prime when you turn the key to the run position.
Diagnostic Scan:
Full System Scan: I'd highly recommend using a comprehensive scanner, like the YOUCANIC UCAN-II, to run a full system diagnostic scan. This could unveil hidden fault codes that are not causing a light to show on the dashboard but may point toward the root cause of your issue.
Given that you've already spent a considerable amount on resolving this, taking a systematic, DIY approach with specialized tools can potentially save you from additional frustration and costs. Good luck with your troubleshooting!
Problem resolved. Did a continuity test on the fuse block were fuel pump relay is (right side vertical slot) to pin #17 on the ECU plug. Continuity was present so issue had to be with the ECU. Replaced ECU and problem gone. I know it’s an expensive part but I would have been thousands ahead had I done this first instead of trying 2 different repair shops that obviously DID NOT know what they were doing. One of the shops was Christian Brothers Automotive. They even have the audacity to charge a much higher diagnostic rate since it is a Euro automobile even though they performed as a parts changer.
Also found that this is not an uncommon issue. There are several terminals that could be re-soldered but I felt replacement was a better solution
Many thanks to YOUCANIC for your assistance
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This is fantastic news! Thank you for keeping us updated. We're thrilled that you were able to resolve the issue on your own. You're doing an amazing job! Keep up the great work!