Engine miss firing
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Junior Member
Joined: May 2011
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97 S420
Engine miss firing
My 97 S420 with 119 engine and 131K miles has me puzzled with a rough engine. I do not have a scanner, and the closest dealer is about 100 miles away. My engine light is on, and when it gets real rough it starts to flash for a short while. When I go to accelerate or go up a slight grade it gets worse. When sitting at a stop light with it in drive and foot on the gas it will get rough after about 30 seconds.
I pulled and replaced all the plugs and noted that non of them stood out as being darker or lighter than the rest. They did have a yellowish look that reminded me of something like possible light sulfer on the insulater. Not the light brown that I was expecting.
Would a MAF sensor cause symptoms like this? My first thought was a plug or coil, but with the plugs being even in looks I am wondering mixture control. Am I all wet?
I pulled and replaced all the plugs and noted that non of them stood out as being darker or lighter than the rest. They did have a yellowish look that reminded me of something like possible light sulfer on the insulater. Not the light brown that I was expecting.
Would a MAF sensor cause symptoms like this? My first thought was a plug or coil, but with the plugs being even in looks I am wondering mixture control. Am I all wet?
Super Member
Joined: Aug 2005
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From: Covington, WA
'96 SL600, '05 S55 AMG, '06 C230
Based on the symptoms, it could be any number of issues. Cleaning the MAF is fairly quick and easy, though I do not think it's that simple. But the problem could be fuel filter, weak fuel pump, a leaky valve in the fuel delivery system, etc. The spark plug color suggests a lean mixture or possibly contaminated fuel but then it could also be caused by the engine computer over-compensating for a different problem. IMHO. Not a lot to go on.
Cheers,
Jeff
Cheers,
Jeff
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1991 300SE
Since it is a 1997, it is equipped with the OBDII diagnostic plug under the drivers side dash. I would consider going to your local autozone or comparable parts store, they should be able to read the codes for free. Have them print them out then do a search for those codes. That would give you somewhere to start without having to take it all the way to the dealership.
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From: Louisiana
03 E500 and Corvette
Since it is a 1997, it is equipped with the OBDII diagnostic plug under the drivers side dash. I would consider going to your local autozone or comparable parts store, they should be able to read the codes for free. Have them print them out then do a search for those codes. That would give you somewhere to start without having to take it all the way to the dealership.
Read the codes publish and you will get more help. You can even buy a OBDII reader reasonable. If you live 100 miles away consider mail order one and use it. One use will save the cost of the reader.The day mine arrived my diesel truck would not start. So I tried out my new reader. It told me the problem and a $4.00 part fixed it. Otherwise a $200 tow to dealer and $200 diagnostic, then parts/labor would would have been way more. I paid about $130 for my reader already paid off 3 times over.
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97 S420
OK, thanks guys. You have given me alot to consider. I will try Auto Zone for the codes since I drive by there all the time. And yes, I think the system is fighting the mixture control based on how it feels. Could the O2 sensor also be a factor? I have heard that they should be replaced every 100K miles, and I am at 131K. I don't know if it has been done or not, I bought it at 126K. That was just a random thought I had the other day. i am still planning on getting the codes. Thanks for your input.
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97 S420
OK, a little follow up. I took it to my local mechanic that had a reader for my car and it came up with a miss-fire on #5,#6, #7, as well as O2 sensor on that bank and a Code for the catalatic as well. My mechanic, swapped coils from left to right and the codes stayed the same except #7 moved to #8 and did not follow the coils. Plugs all looked ok too.
He came up with an idea that my catalatic might be plugged on that side causing excessive back pressure and messing with the mixture on these cylinders and O2 sensor on this bank.
Also note that the exhaust has always had a rich smell to me since I bought it about 4k miles ago.
Any thoughts?
He came up with an idea that my catalatic might be plugged on that side causing excessive back pressure and messing with the mixture on these cylinders and O2 sensor on this bank.
Also note that the exhaust has always had a rich smell to me since I bought it about 4k miles ago.
Any thoughts?
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From: Harbor City, CA
Mercedes-Benz, Porsche, BMW, MINI and more!
Answer
OK, a little follow up. I took it to my local mechanic that had a reader for my car and it came up with a miss-fire on #5,#6, #7, as well as O2 sensor on that bank and a Code for the catalatic as well. My mechanic, swapped coils from left to right and the codes stayed the same except #7 moved to #8 and did not follow the coils. Plugs all looked ok too.
He came up with an idea that my catalytic might be plugged on that side causing excessive back pressure and messing with the mixture on these cylinders and O2 sensor on this bank.
Also note that the exhaust has always had a rich smell to me since I bought it about 4k miles ago.
Any thoughts?
He came up with an idea that my catalytic might be plugged on that side causing excessive back pressure and messing with the mixture on these cylinders and O2 sensor on this bank.
Also note that the exhaust has always had a rich smell to me since I bought it about 4k miles ago.
Any thoughts?
roy@peachparts.com
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Thread Starter
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97 S420
That is a classic fault code combination you get when the Mass Airflow Sensor fails.
roy@peachparts.com
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roy@peachparts.com
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From: Harbor City, CA
Mercedes-Benz, Porsche, BMW, MINI and more!
Hmm
OK, I was thinking that may possible, but would it only be coding on one side? Since last posting, I took car into muffler shop to have the Catalytic converters checked, and they bore scoped them and found them coming apart. So now I am saving some dough to get them changed out. crossing fingers on outcome.
I did say classic, the random misfire on a single bank is a common symptom.
I hope you are lucky.
FYI:
A cheap scan tool.
http://www.google.com/products/catal...d=0CJ0BEPMCMAc
roy@peachparts.com
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97 S420
OK, got the Cats changed and she is running great now with NO check engine lights. I think the cats were damaged by the bad coils that the car had when I bought it. By the time I changed them, the damage had been started and it just got worse and worse with time. The cats were causing mixture to be off, and that caused more damage to the cat..... Now I am driving happy !
