PO303 Options
Thread Starter
Newbie
Joined: Sep 2008
Posts: 6
Likes: 1
From: MN
'17 GLS 450, former owner '01 ML 430
PO303 Options
Hello - proud owner of 2017 GLS450 - I did, or should say attempted, the 50K spark plug DIY with NGK brand 95875 plugs. Thought I had it all done, buttoned up the car drove it 5 miles at highway speeds - all good - hurray saved myself $600! The next day on the way to church it starts lurching. Got it home hooked up the OBD2 scanner and it pulled a PO303 code - 3rd cylinder misfire. That cylinder - as you face the engine - is on the left farthest away from the grill (Question 1 - please confirm this is in fact the 3rd cylinder?).
I figured I probably mangled the spark plug boot pulling it out, even with a boot puller its an awkward position. So I went online to RockAuto and purchased the boot and coil assembly ($52 - NGK). Got the part today, put it in and took it out for a test drive. Same problem - lurching!
Found on the forum that if its not the OEM coil (the OEM is Delphi A276-906-79-00) that it may not 'integrate well' with the other 5 Delphi coils. So I pulled off the NGK coil and put on the original Delphi coil. So now the only new part is the spark plug boot from NGK. Road test again - same problem - lurching!
So now I'm thinking I will call the MB parts department and order an OEM spark plug (perhaps one of the 6 NGK plugs was bad?) and an OEM spark plug boot. Question 2 - other suggestions or ideas?
Appreciate the help! Was hoping to use this as our Christmas traveling car, but those plans are obviously on hold at the moment!
I figured I probably mangled the spark plug boot pulling it out, even with a boot puller its an awkward position. So I went online to RockAuto and purchased the boot and coil assembly ($52 - NGK). Got the part today, put it in and took it out for a test drive. Same problem - lurching!
Found on the forum that if its not the OEM coil (the OEM is Delphi A276-906-79-00) that it may not 'integrate well' with the other 5 Delphi coils. So I pulled off the NGK coil and put on the original Delphi coil. So now the only new part is the spark plug boot from NGK. Road test again - same problem - lurching!
So now I'm thinking I will call the MB parts department and order an OEM spark plug (perhaps one of the 6 NGK plugs was bad?) and an OEM spark plug boot. Question 2 - other suggestions or ideas?
Appreciate the help! Was hoping to use this as our Christmas traveling car, but those plans are obviously on hold at the moment!
Thread Starter
Newbie
Joined: Sep 2008
Posts: 6
Likes: 1
From: MN
'17 GLS 450, former owner '01 ML 430
Conclusion: piece-by-piece testing has led me to conclude that the replacement plug (NGK) was bad. However, a brief internet search revealed that operator error may have been the root cause - over-torquing. So my recommendation for the reader of this forum is don't trust your feel but use a torque wrench when installing plugs.
