hks

My c300 has been misfiring and we changed everything from coil packs. Spark plugs and injectors. A compression check was also done and everything is good. I am about to give up on this because everytime I think the problem is solved it starts again. What else is left to changed? The battery symbol came up but I’m not sure if it’s due to the car being parked but do you think that can cause it? Mechanic was saying maybe the auxiliary battery needs to be changed. Also, someone else was suggesting it could be a bad ecu . Any help please

dagger22

Were there any specific CEL codes shown when the mechanic plugged their scan tool into the obd?

hks

just cylinder one misfire

dagger22

so all coil packs, spark plugs, injectors were replaced with new original parts ya?
What were the individual number readout for each cylinder for the compression test?
Do you get random misfire of cylinder one when driving? or it's constantly misfiring till now?
Have you changed out any other parts, sensors?

battery symbol is likely due to the car being parked for long. you can drive the car around longer and see how it goes first. The aux battery (for us its a capacitor box) can be changed out easily if needed.
Lets see what else we can drill down to before looking towards a bad ecu.

hks

yes all parts changed were new parts. When we hooked up diagnostic cylinder 1 live data was all over the place. Cruising around it won’t throw the check light but once you punch it that’s when it starts to misfire.

stockbmw

Bad fuel? Try diagnosis again next week/month with brand name 93/94, possibly with no ethanol like from shell nitro. If not make sure gas is top tier labeled.

hks

New tank of gas and same stuff

hks

Heres a video of the cylinder operations. Check out cylinder one

churrrbro91

Hey guys I'm new to this forums just need some help.

2013 Mercedes Benz C250 - 55xxx KM clean as a whistle bought it brand new from the dealership

So I had a steering angle sensor changed to a after market one because one of the indictors broke off. Turned the car on every single light came on, drove it for a couple of weeks my car started jerking like it was mis firing . Took my car to a mechanic they replace my sttering angle sensor to a brand new one that cost me $2300 drove my car home and it still started jerking abit turned the motor off now my car dosent start at all it only turns to the reds Lights but not engine. can you guys please help me out .

churrrbro91 is online now Report Post

badaholt

Having the same issue with my 68 plate c300 c205

Elvisfan0108

Welcome to the forum. Please don’t hijack a thread like that. People are trying to help the OP. If you are having a different problem, please create a new thread.

chassis

What is the conclusion from this video?

Measure compression. Consider piston cracking as a potential cause for misfire. Read the posts on piston cracking.

Camaroguy72

what he said. Did you do a leak down test as well?

lululu

A leak down test Needs to be done , a compression test may not pick up a piston starting to crack

CaliBenzDriver

These combined problems are really not easy to fix. All the parts that could be sold were replaced so we know it's something else.... (these parts go bad at some point anyway)

Do you have random cylinder misfire or one single cylinder ??

> Check your fuel trims value for negative values indicative of a lean (marginal lambda upstream sensor)

> Scan the car for list of ALL faults as some faults introduce TIMING LATENCIES > MISFIRE guaranteed!

> Battery low voltage is never a food thing around networked computers. Float your battery and try to keep an eye on alternator voltage. Multiple reasons can drain a perfectly good Benz battery.

> Do a quick "car reboot" to solve many weird computer issues such as discharge and misfires.

Let's *NOT* arbitrarily replace the ECU without any evidence because it controls the engine...

NickGamg

Did you ever figure out the problem?
I have a 2019 c300 same issue cylinder 1 misfire. code p0351.

hks

I ended up doing a rebuild and this was my second one. For some reason the pistons keep cracking around the pin area. I ended up ordering some forged pistons from China and they been holding up.

Cosworth2000

Hello, I was looking at the video and I may know the issue. Firstly, you need to take out the Spark Plugs and check the gaps. Before you do any of this, you need to switch the coil of a working cylinder to the cylinder one. If the issue moves, then it's the coil but if the issue remains, then the coil is not the problem and the problem is the spark plug. So see if it's really the sparkplug and not checking the measurement. You can remove the sparkplug from the working cylinder and check it with the cylinder one for gap and then swap the sparkplug locations. IF compression is okay and all it good, you need to look at the injectors in cylinder one as it maybe stuck open or clogged.