SL/R230: Fun with P0303
Thread Starter
Member
Joined: Sep 2013
Posts: 157
Likes: 33
From: Walpole, MA USA
2004 SL500
Fun with P0303
After my son borrowed the SL he returned it and noted a rough idle.
CEL lit. With my reader attached I get a P0303, misfire cylinder 3. Ok, I guess now I play with the engine.
Long story short, hood service position just fits in my garage, spent 30 minutes trying to retrieve a coil pack bolt that I dropped, number 4 CP had a loose wire but no fault, swapped 3 and 4 coil packs. CEL went out. What?
Now I'm just waiting for the CEL to go off again. Strange.
Last edited by sean65; Jun 1, 2019 at 10:34 PM.
Member
Joined: Jun 2019
Posts: 200
Likes: 26
2005 R230 SL-500 / 2017 E300
I would look for a bad connection to the coil, bad plug wire and spark plug next. Have you visually inspected the plug? The cylinder may be starved of fuel caused by a bad injector or other fuel related problem.
Mike.
Mike.
Thread Starter
Member
Joined: Sep 2013
Posts: 157
Likes: 33
From: Walpole, MA USA
2004 SL500
I have not yet removed the plugs (I'll be disappointed if the plugs are gone at 57k miles), but wires and plugs are the next move for sure. I haven't entertained the thought of fuel starvation... that's a good one.
Member
Joined: Jun 2019
Posts: 200
Likes: 26
2005 R230 SL-500 / 2017 E300
You can tell by the color of the plug whether there is no spark or no fuel. If there is no spark the plug will be dark The plug will be very light colored or even white if the fuel mixture is too lean. You can also compare it to a plug from a cylinder that is firing properly.
Mike.
Mike.
Thread Starter
Member
Joined: Sep 2013
Posts: 157
Likes: 33
From: Walpole, MA USA
2004 SL500
I threw a P0303 again this past weekend. This is following full replacement of plugs and wires, as well as previously swapping the coil pack to remove that as a possible culprit. It seems that full throttle tends to throw the #3 cylinder misfire, but no other error.
Next on the hit parade will be the replacement of the fuel injector. I'm not convinced that I'm going to take on that job myself yet, I need to do a little more research on the job.
Next on the hit parade will be the replacement of the fuel injector. I'm not convinced that I'm going to take on that job myself yet, I need to do a little more research on the job.
Member
Joined: Jun 2019
Posts: 200
Likes: 26
2005 R230 SL-500 / 2017 E300
I threw a P0303 again this past weekend. This is following full replacement of plugs and wires, as well as previously swapping the coil pack to remove that as a possible culprit. It seems that full throttle tends to throw the #3 cylinder misfire, but no other error.
Next on the hit parade will be the replacement of the fuel injector. I'm not convinced that I'm going to take on that job myself yet, I need to do a little more research on the job.
Next on the hit parade will be the replacement of the fuel injector. I'm not convinced that I'm going to take on that job myself yet, I need to do a little more research on the job.
P0303 Causes (* = Most Common)
- Faulty or worn spark plugs *
- Faulty spark plug wires or coils *
- Distributor failure *
- Faulty fuel injector *
- Vacuum leak
- Low fuel pressure
- Camshaft sensor defective
- Crankshaft sensor defective
- Engine timing off
- Leaking head gasket
- Low engine compression
- Poor quality fuel
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Senior Member
Joined: Nov 2016
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From: Kirkland, WA
2003 SL500
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Joined: Jan 2015
Posts: 77
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2021 GLE450
Are you using Premium Gas? I had some simulare issues when using regular gas. Once I changed to premium the errors went away. I would also suggest, if you can find Premium without ethanol, it would be better.
Just a thought, Good Luck.
Just a thought, Good Luck.
