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Rpm needle shaking only at idle code p0302 cylinder 2 misfire.
Rpm needle shaking only at idle code p0302 cylinder 2 misfire.
Hey guys it’s my first time writing on the forum. A couple of months ago I realized that my rpm was fluctuating up and down and the car seemed to be shaking a bit mostly more when the car was cold, once it warmed up the shaking would diminish. Brought it to the garage and no one could see the problem. Recently a check engine came out p0302 cylinder 2 misfire. The sparks plugs (all of them) and coil have been changed on cylinder 2. I went to Benz and the told me that it was the fuel injector, it was changed and unfortunately the problem persisted. They then could not diagnose the problem. They wanted to open the engine up to “explore” which would have been 3000$ just for labour. So I said yaaa no. The misfire stops after 2000 rpm’s. I’ve recently brought to a euro dealer and they told me I need a new engine, while another mechanic said it’s impossible that you need a new engine since the misfire stops after 2000 rpm’s and there is still compression in cylinder 2. Diagnostic Diagnostic
They performed compression tests in the cylinder which came to 198 psi. (Mercedes) the car is a 2013 c 300 with 86000 km on it. Won’t be spending crazy money to put a new engine inside if it’s something else. Anyone got any ideas? Seems like no garage can solve this problem… so car drives fine on the highway no shaking, only when idling and coming to a stop below 2000rpm does it shake.
Misfire at idle seems to be commonly caused by an incorrect air-fuel mixture. Causes for that besides spark plugs, fuel injector or coils can be sticking valves, weak piston rings, vacuum leak, faulty o2 sensor, bad pcv valve or defective ECU. Some of this would require opening the engine or at least going in with a borescope to diagnose. Since it's isolated to a single cylinder it's most likely an issue with that cylinder. If it's a sensor issue, pcv valve, vacuum leak or ECU issue it would most likely misfire on other cylinders, too.
Last edited by superswiss; 02-12-2024 at 09:17 PM.
These diagnosis are a process of elimination. All this is a bit academic without knowing what codes you have. If you don't have your own scan tool, you should invest in one.
My thoughts are:
Leak down and compression tests indicate your rings and valves are OK in Cylinder 2. Plugs and coils are OK as you've stated.
The misfire test that the scan tools do, don't measure the actual presence of electricity at the spark plug. They measure changes in rpm when each cylinder is meant to spark. So you need to work out if you actually have a spark below 2000 rpm and when cold.
Assumed the injector for Cylinder 2 works and has adequate pressure.
First up, I'd get an old fashioned spark plug tester (they're very cheap from any auto store) and make sure that you actually have a spark in Cyl 2 when cold. Compare to a known good cylinder to see if the rate of fire looks similar.
Check all your ECU connections and all the wiring to make sure everything fits and there's no corrosion.
If you have decent spark, then its a fuel or air issue or something like a crankshaft position sensor. Start with the spark. It might be signalling an electrical/ECU or harness problem. Based on what you've said, I'd say the engine is fine. But get it scanned and come back with the codes.
Last edited by BlackML550; 02-13-2024 at 04:06 AM.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
1st, how many miles on the car and how long have you owned it?
Sounds like all the bases have been covered trying to diagnose the problem without tearing into the engine. Combustion can only occur when there is sufficient compression, fuel, air, and correctly timed spark. Injectors, coils and spark plugs have all been checked, as well as cylinder compression.
And to be clear, the problem occurs whether the engine is cold or at operating temperature?
The misfires (or rough running) occur below 2000 rpm. Does the CEL flash or just comes on steady? Get yourself a proper scan tool, such as a LAUNCH Creader Elite 2.0 BENZ (~$160 USD on Amazon) or even XENTRY, and monitor for misfires using the data stream. You may still have misfires, but can't detect them at the higher RPM. If they are actually occurring, I would check the wiring harness for any damage, such as from rodents--the signal could be shorting out.
A long-shot, but have you tried removing the knock sensor and cleaning the contact surfaces on the block and connector?
Hey guys thx for the responses, so thanks to you guys I spoke to the garage that was telling me the engine needed to be replaced (all your answer and suggestions made me sound like I knew what I was talking about) haha. So maybe he thought ok this guy might know some car stuff so we can’t fool him. What he told me now is that they verified all the ecu connections and harness and everything is communicating properly. They will now check the cylinder for carbon inside. I will update you guys on the results! I’m hoping this will fix the problem.. the car is a 2013 c300 with only 87000 km on it so it would be a shame that I would have to scrap it.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Carbon inside the cylinder? Or on the intake valves? I'm thinking it might be time to find a new shop. It would really help if we knew where you are. I'm guessing Canada.
Carbon can build up on the intake valves of direct injection engines if you are using improper motor oil, changing oil at long intervals (e.g., 10k miles), or do a lot of stop-and-go driving. Rings can also develop carbon deposits, but he's not going to be able to "see" that without taking the engine apart. He may scope the cylinder and look for scoring, but a good compression test should make all of that moot.
I would ask him to explain how is going to check any of this and see if your BS meter registers anything.
I would not scrap the car if it is otherwise in good condition.
I know there are about 1000 posts, so you don't need to take the next week reading them all, but basically our cars use a 2-stage oil pump that operates at either 2 bar or 4 bar, depending on engine speed. 3500 rpm is the change-over point. However, there are quite a few of us that have disconnected the solenoid that restricts the oil pressure to 2 bar below 3500 rpm. Disconnected, the engine gets much better lubrication throughout the rpm range, especially on startup. The purpose of the 2-stage pump is primarily, if not only, to save a minuscule amount of fuel to keep environmentalists happy, which is also a moot point since they are now shoving EVs down our throats.
There is a connector to the solenoid at the engine block right next to the crank pulley on the right or passenger side of the engine. I've easily reached the connector on both my cars by removing the air intake hose and reaching down from the top. There are pictures in the thread.
Just to clarify I live in Quebec Canada where we get both ends of the spectrum in weather from -40 to +40. As well I do a lot of city driving as you can see a 2013 with only 87000 km
on it. I change the oil when the indicator tells me to, so pretty much I’m running on the same oil all year cause I’m not doing 10 000 km. Only the service b I believe (or A) is due that’s when the oil is changed. The garage advised me that they will remove the intake manifold and spray walnut shells in the head valve and ports. Hopefully that that might solve the problem and remove the carbon buildup (if there is any). The problem gradually got worse, it was not all of a sudden a couple of mi the back during the summer there was a hint of vibration and from there it got worse until the engine came on. The car does a lot of idling unfortunately in winter (I know it’s not ideal) just sucks getting into a cold car lol.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
OK, get a price for the walnut shell cleaning. I've never had it done, but I am pretty sure it's not cheap. I would want them to show me how bad the carbon build up is before agreeing to that procedure. It's more like sand blasting the top of the intake valves with crushed walnut medium. When done, they have to ensure everything is vacuumed out, etc. Go watch some YouTube videos on walnut blasting.
Secondly, stop relying on the notification to tell you when to change oil. Use a good quality synthetic oil that meets MB Specification 229.5 and change it every 5000 miles or 6 months (or more often if you wish). The type of driving you do makes you susceptible to carbon build up.
@JettaRed instinct is correct. All of a sudden we've gone from needing a replacement engine to a carbon clean. I'd be taking it for a 2nd opinion from people who aren't going to try and gouge you, like your current shop is trying to do. For the record, they simply didnt have enough reason to suggest a new engine was required. I'd be running for the hills from whoever you went to.
You're now armed with information and knowledge. Use it to your advantage and find someone who knows what they're doing.
Last edited by BlackML550; 02-14-2024 at 04:31 PM.
The m276 engine really doesn’t have carbon problems. Im just about to tap 100k on my C300. I had 2 Audi’s one time I was fixing with very similar issue, 1 cylinder misfiring at idle but gone while driving. Both were fixed by replacing the hpfp some how. I’d have them smoke the intake system, you could also have an intake plenum gasket bad on cylinder 2 runner, I’ve seen that as well. This symptom is also similar to one where there is an intake leak.
The m276 engine really doesn’t have carbon problems. Im just about to tap 100k on my C300. I had 2 Audi’s one time I was fixing with very similar issue, 1 cylinder misfiring at idle but gone while driving. Both were fixed by replacing the hpfp some how. I’d have them smoke the intake system, you could also have an intake plenum gasket bad on cylinder 2 runner, I’ve seen that as well. This symptom is also similar to one where there is an intake leak.
High pressure fuel pump. Direct injection uses very high pressures, so the HPFP is what creates this high pressure and if the pump is faulty then the engine is essentially fuel starved. These sit in the engine bay near the injectors. There's also a LPFP (low pressure) in the tank that pumps the fuel forward to the HPFP pumps. There's usually one HPFP per bank if it's a V configuration.
Last edited by superswiss; 02-19-2024 at 09:51 PM.
High pressure fuel pump.
Direct injection uses very high pressures, so the HPFP is what creates this high pressure and if the pump is faulty then the engine is essentially fuel starved.
These sit in the engine bay near the injectors. There's also a LPFP (low pressure) in the tank that pumps the fuel forward to the HPFP pumps.
There's usually one HPFP per bank if it's a V configuration.
Turbo engines feature 2x HPFP with 4x cam lobes
while Non-turbo use 1x HPFP with 3x lobes.
The big deal with HPFP is the actuation valve that controls the 3000.PSI fuel pressure with precise timing in regard to lobes.
So chain tensioners must be working well to keep timings unaffected by Bank1 intake camshaft fwd jerkings.
That is simply acomplished with a combination of good oil pressure, good oil viscosity and good tensioners seal.
When timed properly these engines stop rattling to sound more like diesel when warm.
Last edited by CaliBenzDriver; 02-20-2024 at 08:24 PM.
Hey guys sorry so long for the response, so what the garage tells me is that it’s the piston rings that get stuck. They put a product inside the first time and he says the compression seems to stay (he mentioned that the compression went down and up) as well the rough idle is not as rough anymore. He is now putting the product a second time and he told me that I have to drive the car to make the product more effective. He mentioned that the check engine light might still be on if it still misfires. I’m just wondering can the piston rings cause the car to idle rough but be ok when driving?
They had already cleaned the engine with walnut shells to take out any carbon. They told me that there was not enough to cause any problems. I’m guessing this treatment is not the same? They also told me that to see better results the car has to be drivin.
Walnut shells are used to get the carbon deposits off the back of the intake valves. The piston rings are inside of the combustion chamber. The walnut shells don't reach in there. Sea Foam is a solvent that dissolves the carbon. Can be added to the oil to help dissolve the carbon deposits on the rings from the oil side, but that's really only semi effective. Better to spray it directly into the chamber, then let it soak, crank the engine a few times, get it all out and then start it up.
So after all that’s done, on my end to prevent this from happening again or to better the problem is there any product I can add? If so to where?
Well, you can periodically use sea foam yourself, but that's just addressing the symptoms. The root cause of the deposits in the first place is your worn out engine. Oil is getting past the rings and crusts up on them and/or your combustion is incomplete leaving behind residue that collects on the piston heads and rings. The only real solution to that is an engine rebuild.
Last edited by superswiss; 02-22-2024 at 05:34 PM.
I can’t see how his engine would be worn out, he has like 50k miles according to what he said! That should be just broken in, plus he said they did a compression test, 198psi is pretty darn good. But did they check all the other cylinder compressions??? That’s important and a no brainer imo! I seriously doubt he had any carbon, I took my intake manifold off a few days ago doing the tensioner update and they were clean- I have just under 100k miles. But as mentioned earlier, he should change oil every 5k, or 7500 kilometers. That will help in the long run. I don’t know about this stuck piston thing, how do they know this. As far as carbon on the piston, oil additive won’t get rid of that, they would need to do something like an intake/combustion solution that would come in through a vacuum line. Only way to say for sure if that’s even true is to put a boroscope down the spark plug hole and look. If he doesn’t drive much, varnish can build up on the injector causing spray issues, I’d run some injector cleaner through the system, add it with the gas. VW makes a really good one! There are a few things that would affect the engine. Timing is one, something with the cams or cam phasers could be off, next could be injectors or spark timing/ignition, they check all the plug gaps?? Are the plugs aftermarket?? I’ve seen that. I’d run an engine flush like liqui moly, a friend/customer had issues, the flush had a significant affect/improvement. Intake leak on certain runners can also cause that. I would not condemn his engine. I would also want to know exactly what it is they put in his engine.
I can’t see how his engine would be worn out, he has like 50k miles according to what he said! That should be just broken in, plus he said they did a compression test, 198psi is pretty darn good. But did they check all the other cylinder compressions??? That’s important and a no brainer imo! I seriously doubt he had any carbon, I took my intake manifold off a few days ago doing the tensioner update and they were clean- I have just under 100k miles. But as mentioned earlier, he should change oil every 5k, or 7500 kilometers. That will help in the long run. I don’t know about this stuck piston thing, how do they know this. As far as carbon on the piston, oil additive won’t get rid of that, they would need to do something like an intake/combustion solution that would come in through a vacuum line. Only way to say for sure if that’s even true is to put a boroscope down the spark plug hole and look. If he doesn’t drive much, varnish can build up on the injector causing spray issues, I’d run some injector cleaner through the system, add it with the gas. VW makes a really good one! There are a few things that would affect the engine. Timing is one, something with the cams or cam phasers could be off, next could be injectors or spark timing/ignition, they check all the plug gaps?? Are the plugs aftermarket?? I’ve seen that. I’d run an engine flush like liqui moly, a friend/customer had issues, the flush had a significant affect/improvement. Intake leak on certain runners can also cause that. I would not condemn his engine. I would also want to know exactly what it is they put in his engine.
Agreed in principal. My point was more along the lines that simply adding a product isn't gonna be the solution. Carbon buildup in the combustion chamber, all assuming that that's actually what's happening, is a sign of bigger issues. Stuck piston rings is definitely a thing, but yes good question as to how they determined that. I would assume they've gone in with a borescope (I'm assuming that's what you meant, because I don't know what a boroscope is) and saw the carbon deposits. Probably worth asking for pictures to verify yourself.
Last edited by superswiss; 02-22-2024 at 07:07 PM.
Agreed in principal. My point was more along the lines that simply adding a product isn't gonna be the solution. Carbon buildup in the combustion chamber, all assuming that that's actually what's happening, is a sign of bigger issues. Stuck piston rings is definitely a thing, but yes good question as to how they determined that. I would assume they've gone in with a borescope (I'm assuming that's what you meant, because I don't know what a boroscope is) and saw the carbon deposits. Probably worth asking for pictures to verify yourself.
I agree with you on how adding something isn’t the fix. You are correct, I meant borescope. Just out of curiosity tho, I hope he’s putting in good gas and it’s at least 92. I know stuck piston rings and carbon on the pistons happen, but I’ve never seen it personally. I don’t think it’s something that happens often. I’m hesitant to believe it unless the shop provides a solid reason as to how they decided this. I’m more likely to believe it’s something else but that’s just me. Our cars are pretty solid, and MB has kept the M176 engine to the current generations (tho now turbo’d). If that was something that happens I’m sure it would get around. Though if op didn’t take proper preventive care I guess it could happen but still.. it’s almost impossible to diag a car over the internet, especially if it’s not obvious. All we can do is speculate, or argue lol.
I agree with you on how adding something isn’t the fix. You are correct, I meant borescope. Just out of curiosity tho, I hope he’s putting in good gas and it’s at least 92. I know stuck piston rings and carbon on the pistons happen, but I’ve never seen it personally. I don’t think it’s something that happens often. I’m hesitant to believe it unless the shop provides a solid reason as to how they decided this. I’m more likely to believe it’s something else but that’s just me. Our cars are pretty solid, and MB has kept the M176 engine to the current generations (tho now turbo’d). If that was something that happens I’m sure it would get around. Though if op didn’t take proper preventive care I guess it could happen but still.. it’s almost impossible to diag a car over the internet, especially if it’s not obvious. All we can do is speculate, or argue lol.
M176? That's a V8 (sorry mixed it up with the M177 and M178 at first). OP has a C300. Not even in the same game.
Last edited by superswiss; 02-22-2024 at 10:48 PM.
02-12-2024, 08:47 PM
