Need help! Engine Misfire Saga On 99 S500 - Mercedes-Benz Forum
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post #1 of 12 (permalink) Old 04-14-2011, 06:29 PM Thread Starter
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Need help! Engine Misfire Saga On 99 S500

I really could use some help, advice, direction on this. I've been trolling the forums but can't put anything together on this issue.

I have a 1999 S500 with 112,000 miles. A great car!

Last week, a heat exchange hose coupling failed, and it was located near the center of the firewall. I replaced the fitting, the engine never overheated, and that situation is fine. It did get the area near the firewall quite wet, but it looks like mostly plumbing in the area, not mostly electrical.

A day later the Check Engine light comes on and the car is running rough. I guessed at a bad coil due to the water dump. I read the codes and they were:

P0300 Mult. Cyl Misfire
P0308 Cyl 8 Misfire
P1519 Camshaft Timing Solenoid

I figured I'd start with the #8 coil and replaced with a new MB part. It did not change the problem with rough running and the check engine light.

I have noticed the problem is worse once the car reaches operating temperature.

Pulled codes again and got P0300 and P0308 (no P1519).

Cleared codes, drove until Check light came on, read codes again and got the same two again.

Pulled cover, checked coil connection, and eyeballed any other connections in the engine compartment for anything obvious.

I am at a loss - any suggestions on the next step?
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post #2 of 12 (permalink) Old 04-14-2011, 06:42 PM
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Just my 2 cents ,if i understand the problem right then this is where i would look 1st .
Maybe the 2 sparkplugs near the firewall on each side got some water down the base , the water would just sit down there if it hasn't dry'd up ,who knows what damage it did to the plugs themself's ,it may be a good idee to check or even replace the plugs .
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post #3 of 12 (permalink) Old 04-14-2011, 06:55 PM Thread Starter
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Thanks!

That helps! I never thought it might be a fouled/bad plug - but a great place to look. I'll pull the number 8 and replace. (The plugs are fairly new - less than a 5,000 miles on them so I think I will be ok on pulling just the one). Thanks again!
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post #4 of 12 (permalink) Old 04-14-2011, 06:56 PM
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I would bet that the live datastream reading's on the o2 sensor's are way out of whack. If you can do datastream, try watching the voltage on the o2 sensor. Starting out the fuel mixture will be a little rich. As it reaches operating temp the switch time should be within a half second or so. The voltage should be between .200v to .900v and switch from high to low and back every few seconds. The multiable misfire lead's me to believe that you are having a back pressure problem.

The only thing I can suggest if you can not do a datastream is to pull the plugs on the same side of the #8 cyl, see if they look differant on the electrode's from those on the opposing side. If one side plug set looks black and the other side does not you may need to look into it further.
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post #5 of 12 (permalink) Old 04-14-2011, 09:53 PM
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Originally Posted by S500Joe View Post
That helps! I never thought it might be a fouled/bad plug - but a great place to look. I'll pull the number 8 and replace. (The plugs are fairly new - less than a 5,000 miles on them so I think I will be ok on pulling just the one). Thanks again!
replace the spark plugs (ALL). Use the OEM plugs ONLY (Non-Resistor, Copper Core)

Oh MAN!!!
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post #6 of 12 (permalink) Old 04-14-2011, 11:59 PM
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Originally Posted by S500Joe View Post
That helps! I never thought it might be a fouled/bad plug - but a great place to look. I'll pull the number 8 and replace. (The plugs are fairly new - less than a 5,000 miles on them so I think I will be ok on pulling just the one). Thanks again!
About a year ago or so doing my routine maintenance on the car , it didnt need anything as she drove flawless without any problems , however i changed ALL the sparkplugs etc ... and the Day after the engine didnt sound to good ,sort of misfiring on 1 cylinder ,i check't the plugleads etc... maybe one wasn't push'd in properly , still misfiring so i rang the mechanic if it could be a faulty sparkplug and he said that he would'nt rule it out (there is more to this but not important), anyway ,i board another set of NGK Sparkplugs ,changed them and all was good ,no more misfiring . Conclusion : Sometimes the new sparkplugs can be faulty ,1 is inaf to cause the misfiring .
(Next car i buy will be a V12 and rebadge it V8 ,so i have 4 spare cylinders & plugs ,looks like 8 aren't inaf ,LoL.) .
Ciao
BTW: i know i could have just unplugged 1 plug by 1 to see and find the faulty plug ,well last time i did that (different Car ,Alfa Romeo) i got electric shocked so never again will i do THAT ,i prefer to waiste 50 bucks & do the job again.

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post #7 of 12 (permalink) Old 04-15-2011, 12:24 AM
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Originally Posted by S500Joe View Post
I am at a loss - any suggestions on the next step?
If you hear that your car is misfiring, I would make sure that you actually
did replace number 8, and not the other side.

These engines with coil-on-plug, are easier to fault find, since you are not
dealing with high tension on top of the coil.

Remove the air filter, and the cover. Then remove the low tension connector to each coil
in turn. Even more degraded running, its not that cylinder. No change, you
have found the candidate.

When you have found the cylinder, do a test where you swap the coil to
another location, but keep the plug. If the fault moves with the coil, well, its
the coil. If it stays, it should be the plug. Also do consider the high tension lead
between the coil and plug, in the same way.

I still think that you have water down one of the plug holes. Either blow it
off by air, or warm the engine up, without the cover on, to let it evaporate.

I've had both. Misfire after a to heavy engine wash, and a faulty coil.

br,
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W123 230E 1984
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post #8 of 12 (permalink) Old 04-15-2011, 12:29 AM
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i used the copper core plugs and they are not that good. mine i had two bad coils so i ended up replacing all so i dont go through repairs later also i had the expensive bosch plugs ($10 each and dealer said use oem only and to tell you guys the truth the expensive ones were better then oems)

i am running oems right now and they cause a misfire in the mornings but once warmed they are perfect. but the expensive ones were great in general.
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post #9 of 12 (permalink) Old 04-17-2011, 09:50 PM Thread Starter
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Solved!

Thanks to everyone for their input. Finally warmed up enough here in Minneapolis to get under the hood again. I pulled the coil, and sure enough, the area around the spark plug was damp/wet. Dried it out and no more misfire! To make things even nicer - the Check Engine light went out by itself on the test drive! I feel a bit sheepish for not checking this automatically - but the assistance all of you gave me helped me avoid an expensive visit to the dealership! THANKS!!!!!
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post #10 of 12 (permalink) Old 06-10-2019, 10:35 PM
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1999 S 500 Misfire front Driver side cat turns red after 10 Min

Unfortunately, I do not know how to find my forum or my replies unless someone send me a personal message on my [email protected] or is in my private messages. OK all plugs, wires,injectors, boots,MAS Sensor have been changed in the 199 S 500 with only 112,000.00 miles car parked from last 10 years driven once a month for may be ten miles. Even pulled out ECU and had it reviewed and cleaned as one mechanic said neither its burn nor any smell or broken points. Its been almost 6 moths from one mechanic to another and no one can figure out except only P308, ASR and ABS Light. # 8 suppose to have the pressure(now I forget names of things so use what I can). Mechanic said had opened the [email protected] Sensor and looked at CAT and it is fine. Also CAT does not make a different noise then rest when hit with hammer. I don't want to give up. In addition to prayers anyone interested in the Prize or gift, please let me know. Fuel filter and pump seems to be working fine.

Thanks
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