Update - The mechanic just called to ask what kind of gas I use...I said, "Costco". He said, "Do me a favor come and pick up the car. Drive all the fuel out of it and fill it up with Chevron Supreme". He said, in 80% of the cases the misfire will go away. If it comes back after a full tank of Chevron bring the car back to him. Not sure what to think. He's the owner/operator
and 30+ years working on Mercedes. Thoughts?

 

I don’t know why it’d make a difference. Costco gas is tier 1 fuel grade. But who knows.. if that’s it it’s surprising to me so please keep us updated.

 

Earlier I noticed you said the spark plugs and injectors are covered in carbon.. You could be leaking oil through the spark plug tubes and into the cylinder. How did the spark plugs look when you pulled them out? They would have oil on the threads. Could be a simple valve cover gasket job

 

issanesh98, the cylinder end of the spark plugs and injectors had what looked like black dust (carbon) caked on the tips. I don't recall seeing any oil build up on them but thanks for the suggestion. I haven't drove the car to empty the tank yet but that's my next step. Then refill with Chevron to see what happens.

 

Running thru a tank of fuel seems like a reasonable approach. Sounds like a good mechanic.

The Top Tier is just for the additive package, but other things can happen (i.e. water seeped into storage tank) that could cause fuel to be bad.

I've gotten bad fuel before and it made the vehicle run like crap. I actually drove 120 miles just to burn thru the rest of the tank...

Good luck..

 

Not sure where the OP lives, but here every drop of gasoline comes from one refinery in Corpus Christi. Only difference between brands is the additive stuff they dump in the truck before heading to the stations.

 

Glock, thanks. Yeah, I drove the car 40 miles to run that gas out I still have a little over 1/4 tank to go before I can fill it back up.

Tom, I'm in Northern California. I think you're right...the only difference is the additives to the gas.

Update -
I cleared the code and took it for a drive as mentioned above. The car drove nice and smooth with no check engine light. I parked the car here at home in the driveway. A few hours later went back out to drive it again. This time it idled rough immediately even before I backed out of the driveway. The check engine light came on right away. I drove it around town and pulled the code. This time there were
multiple misfire codes (never happened before).

P0300 (Combustion misfiring has been detected) NEW
P0302 (misfiring cylinder 2) SAME AS BEFORE
P0304 (misfiring cylinder 4) NEW

I've read up a little on P0300 since this a new one. It sounds like it can be a vacuum leak and/or a lean fuel condition. I plan to connect the reader up and try to pull some data and share it. Hoping someone will see the readings and shed some light on the situation. In the meantime, I'll do as the mechanic said and drive the rest of that gas out.

 

Just pulled this data while the car was idling. Please let me know if anyone sees anything abnormal? Thanks again!


Low fuel pressure – 5.06 bar

Rail Pressure (actual value) – 75.16 bar

Rail Pressure (specified value) – 77.10 bar

Y94 (Quantity control valve) – 0.86 A

Voltage of oxygen sensor upstream of catalytic converter – OFF

Voltage of oxygen sensor downstream of TWC[KAT] – 0.42 mV

Heating of oxygen sensor downstream of catalytic converter – OFF

Pressure sensor upstream – 981.41 mbar

B28/7 (Pressure sensor downstream of throttle valve) – 508.86 mbar

B28/15 (Compressor impeller pressure sensor) – 980.58 mbar

Short Term Fuel Trim – Bank 1 0.0%

Long Term Fuel Trim – Bank 1 -4.7%

Intake Manifold Absolute Pressure – 52.0 kPa

Ignition Timing Advance for #1 Cylinder -2.5%

Oxygen Senor Output Voltage (B1-S2) – 0.415V

Short Term Fuel Trim (B1-S2) – 99.2%

Commanded Evaporative Purge – 0.0%

Fuel Level Input – 42.4%

Catalyst Temperature Bank 1, Sensor 1 – 251 degrees C

Catalyst Temperature Bank 1, Sensor 2 – 307 degrees C

Control module voltage – 13.97V

Absolute Load Value – 42.0%

Fuel/Air Commanded Equivalence – 0.997 Ratio

Relative Throttle Position – 3.5%

Short Term Sec. 02 Sensor Fuel Trim B1 – 0.0%

Long Term Sec. 02 Sensor Fuel Trim B1 – 3.1%

 

Do you still have the old spark plugs?

 

No, I threw them away. What were you thinking? A clue? I wish I hung on to them...the mechanic asked me if I still had the old injectors as well. I threw them away along with the plugs.
The car is really running rough now. I don't think I can even drive it enough to run that gas out of the tank. If feels like it wants to die at idle. Sigh.

 

I don't think you literally have to run it out of gas.. If you run it down as far as you can and refill it that should help dilute anything if there is an issue with the fuel.

Maybe add an additive for water in fuel (Heet, Stabil) for good measure.

 

Glock, makes sense. Problem is...it's idling so rough now I don't think it'll make it to the gas station at this point. Not sure what changed? It was running OK at least drivable with that single misfire.

 

I know you changed the coil packs but rough idle could be related to that.

 

Update - The car idled fine today so I drove it to Chevron to fill it up. I still had a 1/4 tank of Costco gas in there so I added 3/4 of Chevron Supreme. I plan to drive it around today to see what happens.

 

keep note if this issue appears then the car is cold or hot as it seems to be a trend to me. Also, Recheck all your connections especially the electrical which is a possible cause.

 

Update - Checked all the electrical connections they look good. I've been driving the car around with the Chevron tank of gas. The misfire seems to occur more in the morning when I first turn the car on before it's warm. I can drive it on the highway up to 80 mph no problem. Every once in a while at a stop I can feel the misfire. When I showed my neighbor the data above he's convinced it's the upstream O2 sensor since it shows voltage 'OFF'. He said it should have a reading (any reading) for voltage. Who knows. I told him I'm not planning to buy any parts until I go through this gas to see what happens.

Voltage of oxygen sensor upstream of catalytic converter – OFF

Voltage of oxygen sensor downstream of TWC[KAT] – 0.42 mV

 

The first oxygen sensor before the cat is important. The car relies on its information to enrichen or lean the mixture based on how much oxygen is left in the exhaust gases and basically calculates a measured fuel mixture. Your symptoms makes sense because it seems to run differently during different temperatures. Cooler wind is more dense and requires more gas and if the computer can’t accurately determine and adjust the fuel mixture then it just won’t run right

 

issanesh98, thanks. Yeah, I agree.

Update - I drove around this past weekend with the tank of Chevron Supreme. The check engine light came back on...same code. I called the mechanic yesterday to let him know that the light came back on after driving around with Chevron per his recommendation. He asked me to bring it in 'a couple of weeks' because they're swamped. I can't wait that long I'm too impatient. I decided to take it to the dealership to have them at least diagnose the problem. It's only $195.00 for the diagnoses and then it's up to me to decide whether or not they
perform the fix whatever it is...I'll keep everyone posted. I hope it's not $$$$ we'll see. My car is officially 'in the shop'...

 

Update - When I dropped off the car at the dealership I listed everything that I tried to do to resolve the problem. I think that helped keep the costs down. THEY FIXED THE PROBLEM. Total cost $524.88!! Not bad if you ask me...and the technician provided detailed notes to list what he did to fix it. In addition to the other work they did they noticed that I accidentally installed the variable intake actuator incorrectly somehow. sigh. I have drove the car approx. 50 miles so far without any problems. Keep my fingers crossed! Thanks to all who have offered feedback while troubleshooting!

Technician notes:
INCORRECT INSTALLATION OF VARIABLE INTAKE MANIFOLD ACTUATOR. 2.5H SOLD PERFORMED SHORT TEST FOUND CURRENT MISFIRE ON CYLINDER 2 P030200 AND STORED CODES 30300 30400 30000 AND IN EGS EXCESSIVE FRICTION OF LOCK UP CLUTCH. P2783. ROAD TEST VEHICLE LOW ON POWER AND TORQUE CONVERTER IS CONTRIBUTING TO LOW POWER. FAULT COUNTER FOR MISFIRES CLIMBS STEADILY ON CYLINDER 2. INSPECTED CYLINDER BORE WITH BORE SCOPE, OK. INSPECTED INJECTOR FOR POSSIBLE LEAK INTO COMBUSTION CHAMBER, OK. INSPECTED PLUG, OK. PERFORMED XENTRY COMPRESSION TEST, OK. PERFORMED INTAKE LEAK TEST WITH SMOKE MACHINE, NO OLEAKS. RESET ADAPTION, AND PERFORMED TEACH IN OF ENGINE COMPONENTS. THROTTLE LEARNED BUT INTAKE MANIFOLD WOULD NOT AND SET CODES FOR BINDING AND POSITION FAULTS. REMOVED ACTUATOR AND FOUND LINKAGE MOVED ALL THE WAY TO THE LEFT. THIS CAN ONLY OCCUR BY REMOVING AND REINSTALLING ACTUATOR IN WRONG POSITION. CORRECTED INSTALLATION AND TAUGHT IN MANIFOLD ACTUATOR. PERFORMED SW UPDATE OF MESFI AND TRANSMISSION. EGS SOFTWARE IS REMEDY FOR EXCESSIVE FRICTION IN LOCK UP CLUTCH. PERFORMED ROAD TEST TEACH IN FLYWHEEL. ENGINE POWER AND ACCELERATION NOW NORMAL. NO MISFIRES RECORDED IN FAULT COUNTER AFTER REPAIRS.

 

So what was directly causing the misfire, was it the wrongly installed actuator or did that happen after starting to investigate the problem.

 

NZ-Merc, the actuator wasn't the cause of the misfire. That was my handy work when I replaced the fuel injectors I'm sure. That occurred after I saw the misfire code. However, it did contribute to not allowing the engine to 'learn' apparently. When I look at the write up I don't see anything specifically calling out the remedy to the misfire. I'm guessing it's a combination
of all steps below that fixed it.

I think the fix was a combination of things:

1. RESET ADAPTION
2. PERFORMED TEACH IN OF ENGINE COMPONENTS
3. PERFORMED SW UPDATE OF MESFI AND TRANSMISSION
4. GS SOFTWARE IS REMEDY FOR EXCESSIVE FRICTION IN LOCK UP CLUTCH
5. PERFORMED ROAD TEST TEACH IN FLYWHEEL

 

But it must be nice to get it back on the road. Does it seem to run better then before after cleaning the valves? I can’t see there being no difference as they were gunked up.

 

Yeah, I'm interested to hear the answer to this question as well especially after the cleaning and the software updates the car received.

 

Yes! It drives much better...very responsive. The best way to describe it would be to say that I barely press the gas pedal and it goes!
I am the second owner of this car (got it from a dealership 3 years ago). I usually drive in 'S' mode but lately I catch myself cruising
around in 'E'. It's smooth. Funny thing is I'm obsessed with the dam check engine light. I catch myself looking at it all the time...worried
that it'll go back on. So far, so good.

 

ill bet you will get a little better mileage as well, what you describe is 80% likely due to the cleaning. I hope you enjoy your renewed performance 😉!!