Still getting a P0303 code after plugs and wires
Thread Starter
Junior Member
Joined: Aug 2018
Posts: 15
Likes: 0
s500
Still getting a P0303 code after plugs and wires
I don't drive my s500 very hard but I put my foot into it the other day and the check engine light came on. It was running really rough with the light on. My code reader gave me a P0303 code. Misfire in cylinder 3. I cleared the code and ordered new plugs and wires. (Bosch OEM). I drove it for a few weeks while the parts came in. It ran great once I cleared the code and the light never came back on.
I had a local shop change the plugs and wires and replace my valve cover gaskets while they were in there. The next day, I decided to test it. I floored it and it took off like a rocket but the light came on again. Same code. New coil packs are about $50 each. I know the easy answer is to just order all new packs but I had some questions first.
Do I have to order all 8 new or can I just order a new one for cylinder 3?
I got one from the junkyard to test it first. The car ran exactly the same but when I floored it, the light came on again.
So I know my only problem is cylinder 3. Could it also be the injector? Should I just order 1 new pack and test it first before I order all 8? What else could it be?
Thanks for the input.
I had a local shop change the plugs and wires and replace my valve cover gaskets while they were in there. The next day, I decided to test it. I floored it and it took off like a rocket but the light came on again. Same code. New coil packs are about $50 each. I know the easy answer is to just order all new packs but I had some questions first.
Do I have to order all 8 new or can I just order a new one for cylinder 3?
I got one from the junkyard to test it first. The car ran exactly the same but when I floored it, the light came on again.
So I know my only problem is cylinder 3. Could it also be the injector? Should I just order 1 new pack and test it first before I order all 8? What else could it be?
Thanks for the input.
MBWorld Fanatic!
Joined: Jan 2008
Posts: 6,150
Likes: 533
Mercedes
I don't drive my s500 very hard but I put my foot into it the other day and the check engine light came on. It was running really rough with the light on. My code reader gave me a P0303 code. Misfire in cylinder 3. I cleared the code and ordered new plugs and wires. (Bosch OEM). I drove it for a few weeks while the parts came in. It ran great once I cleared the code and the light never came back on.
I had a local shop change the plugs and wires and replace my valve cover gaskets while they were in there. The next day, I decided to test it. I floored it and it took off like a rocket but the light came on again. Same code. New coil packs are about $50 each. I know the easy answer is to just order all new packs but I had some questions first.
Do I have to order all 8 new or can I just order a new one for cylinder 3?
I got one from the junkyard to test it first. The car ran exactly the same but when I floored it, the light came on again.
So I know my only problem is cylinder 3. Could it also be the injector? Should I just order 1 new pack and test it first before I order all 8? What else could it be?
Thanks for the input.
I had a local shop change the plugs and wires and replace my valve cover gaskets while they were in there. The next day, I decided to test it. I floored it and it took off like a rocket but the light came on again. Same code. New coil packs are about $50 each. I know the easy answer is to just order all new packs but I had some questions first.
Do I have to order all 8 new or can I just order a new one for cylinder 3?
I got one from the junkyard to test it first. The car ran exactly the same but when I floored it, the light came on again.
So I know my only problem is cylinder 3. Could it also be the injector? Should I just order 1 new pack and test it first before I order all 8? What else could it be?
Thanks for the input.
Thread Starter
Junior Member
Joined: Aug 2018
Posts: 15
Likes: 0
s500
Thank you.
Replacing an injector doesn't look too difficult. I'll replace all the lower o'rings since the rail has to come off to get to injector.
I am not getting a P0203 code. I think that would be the injector but something is going on when I floor it.
Replacing an injector doesn't look too difficult. I'll replace all the lower o'rings since the rail has to come off to get to injector.
I am not getting a P0203 code. I think that would be the injector but something is going on when I floor it.
Thread Starter
Junior Member
Joined: Aug 2018
Posts: 15
Likes: 0
s500
I ordered a new coil. I haven't had a light come back on but I think it could idle smoother. I tested it twice by flooring it. Both times, the check engine light came on. P0303 each time, no other codes.
I was going to order an injector also but I can't find the O'ring part number. I think I have to take the rail off and all the injectors out on that side. What are the chances of me being able to use the existing o'rings?
Does anyone have a part number?
Thank you
I was going to order an injector also but I can't find the O'ring part number. I think I have to take the rail off and all the injectors out on that side. What are the chances of me being able to use the existing o'rings?
Does anyone have a part number?
Thank you
Senior Member
Joined: Jun 2013
Posts: 262
Likes: 34
From: Houston, TX
'05 S430, '05 S600
99% sure your problem is with the injector. Save some money first and switch out the coil with another one to see if the problem moves with the coil pack. My guess is that it won't matter what you do with the coils, the problem won't go away. I think it is on the fuel side. Good luck!
