Mercedes-Benz Forum banner
1 - 17 of 17 Posts

·
Registered
1999 SL600 | 2001 SL500 (sold)
Joined
·
1,452 Posts
Discussion Starter · #1 ·
2001 SL500 M113

So about 3 weeks ago I had misfires on cylinders 1-4. Replaced all 16 spark plugs with Bosch double platinum plugs. After that didn't work, I took it to a German auto shop and they replaced all 16 wires. For some reason, they used Beru ignition wires instead of OE Bosch. Coils on the misfiring cylinders were replaced with OE Bosch and I had the passenger side upstream O2 sensor replaced with OE Bosch as well, and my CEL disappeared.

3 weeks later the CEL came back and the codes read for misfires on cylinders 2, 3, and 4.

How am I misfiring on 3/4 previously misfiring cylinders after replacing so much crap? Could oil in the spark plug wells be the culprit? I know I need a valve/ breather cover job done but the old spark plugs on the leaking passenger side had very minimal oil on them. One single spark plug had a drop of oil drip to the floor.

Can anybody help? I've spent too much money already, and I'd like to stop.....
 

·
Outstanding Contributor
2005 SL600, 2003 SL55, 1990 300SL
Joined
·
4,579 Posts
Coils on the misfiring cylinders were replaced with OE Bosch...
I wonder if they bothered to scope the ignition circuits and measure the voltages on the secondary windings of the ignition coils.

I would swap the fuel injectors of cylinders 1-4 with 5-8 and see if the misfires move to 5-8 or remain with 1-4.

I don't believe oil in the wells could be an issue.
 

·
Registered
M113 SL500
Joined
·
667 Posts
Can anybody help? I've spent too much money already, and I'd like to stop.....
If you want to stop spending so much money without resolution to your problems, you out to try a more methodological approach to engine problem solving. Also, probably a good idea to find a mechanic who is more adept at problem solving. Any competent mechanic would realize that an entire bank of cylinders misfiring in all likelihood isn't a matter of a spark plug, wire, and/or coilpack going bad on 4 cylinders all at once. Hopefully you're around the mileage it would make sense to replace the plugs and wires as preventative maintenance anyway, and they weren't replaced already.

Are the misfire codes all the codes you got? Nothing else?
 

·
Registered
1999 SL600 | 2001 SL500 (sold)
Joined
·
1,452 Posts
Discussion Starter · #4 ·
If you want to stop spending so much money without resolution to your problems, you out to try a more methodological approach to engine problem solving. Also, probably a good idea to find a mechanic who is more adept at problem solving. Any competent mechanic would realize that an entire bank of cylinders misfiring in all likelihood isn't a matter of a spark plug, wire, and/or coilpack going bad on 4 cylinders all at once. Hopefully you're around the mileage it would make sense to replace the plugs and wires as preventative maintenance anyway, and they weren't replaced already.

Are the misfire codes all the codes you got? Nothing else?
Yep, currently only misfires on 2 3 and 4. Before it was 1 2 3 and 4 plus o2 sensor.

no other codes and bank one primary cat is only two months old. The secondary cats are deleted...
 

·
Registered
1999 SL600 | 2001 SL500 (sold)
Joined
·
1,452 Posts
Discussion Starter · #7 ·
Why was the passenger primary catalytic replaced? Was the reason it went bad figured out and addressed?
It started with the secondary passenger going bad. After deleting the secondaries, annoying cat rattle came back and was determined to be the primary on the same side.

I have no idea why they went...
 

·
Registered
M113 SL500
Joined
·
667 Posts
Ok, well there's plenty of info online as to the possible reasons why cats go bad. Process of elimination at this point, meaning tracking down what is the problem, NOT replacing parts hoping it will fix it. If you don't find the cause, high likelihood you will not only be spending more, but the money you've already spent on a new cat, which I can't imagine was cheap if it was an OE piece, will also go to waste.

Again, think you need to find a better mechanic to help you diagnose problems. What are the odds of both catalytics on the passenger side going bad without a specific cause? Any competent mechanic would have thought of possible reasons why your cats went bad and suggested identifying and addressing these things instead of just replacing the cat and sending you on your way.

Cure the problem, not the symptoms.
 

·
Moderator
1995 Mercedes S420, 1995 SL320, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
Joined
·
2,177 Posts
It's my experience that even many 'good' mechanics are terrible at diagnostics, or just don't want to be bothered with the steps necessary for a proper diagnostic job.

They hear 'misfire' and immediately it's 'coils, spark plugs, wires, done' and then onto the next job. I've experienced this myself even with reputable specialists. Their experience spoils them, and they think their instincts are all they need.

It's important to find a specialist who will actually take the time to diagnose the car properly. I understand that there may be a bit of trial and error involved, but it shouldn't be on your dime.
 

·
Registered
2000 SL500
Joined
·
462 Posts
You (or previous owner) may have had a misfire previously that overheated the catalytic converter. Misfires can dump raw fuel into converter and make them overheat, this is why the check engine light flashes when there's a misfire. Because this problem is affecting the cylinders on only one bank you have to think about what's in common only with the passenger bank cylinders. O2 sensor, catalytic converter, camshaft timing pass side and possibly a shorted fuel injector but I couldn't confirm the fuel injector wiring for this engine. As Bob mention you could swap the 1-4 injectors with 5-8 ones and see if the codes move. A simple vacuum gauge attached to intake manifold can help detect backpressure. late cam timing problems, vacuum leaks and assortment of other problems. You could also check the cam timing by removing the valve cover. Some cars shut off fuel to the cylinders that are misfiring to prevent cat damage but I don't if this the case with your car.

What's the history of the car, mileage, how long have you had it, etc? How did the old plugs look when you replaced them? Do you have a scanner where you can read the O2 sensors and fuel trim values?
 

·
Registered
1989 W124 260E
Joined
·
3,804 Posts
Go out in the dark start the engine up open the hood and lock for blue ot white flashes look all over ht system plug holes hold oil if rocker box gasket is no good i would start there first .
 
1 - 17 of 17 Posts
Top