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Car has been running great then got a misfire on #4 this morning. I got home and swapped the coil with #3 to see if it's the coil, but still got misfire on #4. Going to check the plug and compression tomorrow when everything is cool, but is there anything else I should look for? Just under 101k miles as of today. Here is a list of maintenance and mods:
When I got the car, replaced camshaft on passenger side, all the cam gear adjusters, timing chain, coolant lines for the turbos, spark plugs, coil wires, and all 4 O2 sensors. Also replaced all brake pads and rotors. Aux battery replaced just before 100k miles and transmission service completed at 100k.
Modifications: Pressertech Stage 2 tune, intake spacers, BMC air filters, exhaust resonators deleted and an X-pipe put in, aluminum intake pipes, and Creative Steel motor mounts to handle the increased power.
As some preventive measures I installed cam sensor harness extenders, and the oil pump solenoid mod.
The rear subframe was replaced under a factory recall and the springs were as well because they rusted out. Also, the coolant inlet pipe in the back of driver side head was replaced with the updated version. New blower motor and resistor for the HVAC.
Car has been running great then got a misfire on #4 this morning. I got home and swapped the coil with #3 to see if it's the coil, but still got misfire on #4. Going to check the plug and compression tomorrow when everything is cool, but is there anything else I should look for? Just under 101k miles as of today. Here is a list of maintenance and mods:
When I got the car, replaced camshaft on passenger side, all the cam gear adjusters, timing chain, coolant lines for the turbos, spark plugs, coil wires, and all 4 O2 sensors. Also replaced all brake pads and rotors. Aux battery replaced just before 100k miles and transmission service completed at 100k.
Modifications: Pressertech Stage 2 tune, intake spacers, BMC air filters, exhaust resonators deleted and an X-pipe put in, aluminum intake pipes, and Creative Steel motor mounts to handle the increased power.
As some preventive measures I installed cam sensor harness extenders, and the oil pump solenoid mod.
The rear subframe was replaced under a factory recall and the springs were as well because they rusted out. Also, the coolant inlet pipe in the back of driver side head was replaced with the updated version. New blower motor and resistor for the HVAC.
You have this well cornered, it should run better.
You said nothing about your 3x fuel pumps... what are your fuel tank & rail pressures and cyl. compressions?
Last edited by CaliBenzDriver; Mar 5, 2026 at 06:27 PM.
Car has been running great then got a misfire on #4 this morning. I got home and swapped the coil with #3 to see if it's the coil, but still got misfire on #4. Going to check the plug and compression tomorrow when everything is cool, but is there anything else I should look for? Just under 101k miles as of today. Here is a list of maintenance and mods:
When I got the car, replaced camshaft on passenger side, all the cam gear adjusters, timing chain, coolant lines for the turbos, spark plugs, coil wires, and all 4 O2 sensors. Also replaced all brake pads and rotors. Aux battery replaced just before 100k miles and transmission service completed at 100k.
Modifications: Pressertech Stage 2 tune, intake spacers, BMC air filters, exhaust resonators deleted and an X-pipe put in, aluminum intake pipes, and Creative Steel motor mounts to handle the increased power.
As some preventive measures I installed cam sensor harness extenders, and the oil pump solenoid mod.
The rear subframe was replaced under a factory recall and the springs were as well because they rusted out. Also, the coolant inlet pipe in the back of driver side head was replaced with the updated version. New blower motor and resistor for the HVAC.
Start by removing your spark plugs on the bank where the misfire is on. Check all three spark plugs and see if any are different than the rest. It will tell you a lot, like if youre running too rich or too lean. It could be a stuck open injector (more than likely) or something else. I had this same problem and it turned out to be a bad injector.
a leak down/compression test will be great as well, but start with checking the plugs.
Going to remove plugs and get compression and fuel pressure today. I don't have a scan tool that reads fuel pressure, so hoping I can get a good read with the old Schrader valve tool.
Going to remove plugs and get compression and fuel pressure today. I don't have a scan tool that reads fuel pressure, so hoping I can get a good read with the old Schrader valve tool.
If you're going to keep this car... handheld scanner will pay for itself. You need to be able know what the ECU is doing.
MB misfires have many sources: lean trims require scanner to read LTFT.
Not swapping good parts blindly saves ressources: time & money.
If you're going to keep this car... handheld scanner will pay for itself. You need to be able know what the ECU is doing.
MB misfires have many sources: lean trims require scanner to read LTFT.
Not swapping good parts blindly saves ressources: time & money.
With all due respect I disagree. While I agree with owning a diagnostic tool like an Autel MX808s is something that every DIY guy NEEDS to have for obvious reasons, troubleshooting issues like OP's can be done without an OBD tool for the most part. I diagnosed my misfire issue before i ever bought my Autel. Looked at the spark plugs and noticed one was way more wet than the others. Pointed to a leaking injector right away. Swapped my injectors from Cyl 3 to Cyl 1 and the misfire happened on Cyl 1 instead of 3.
So OP def should look at his spark plugs. He should also buy an Autel or something that can give him fault code readings and live data. But to say not to troubleshoot by swapping parts should be your opinion, and should be a valid TS step.
Last edited by Billyismyname; Mar 6, 2026 at 10:17 PM.
'06 MB S55 AMG; '04 Audi Allroad 4.2; '05 BMW M3 Conv.; '92 MB 500E
Originally Posted by bha280
Going to remove plugs and get compression and fuel pressure today. I don't have a scan tool that reads fuel pressure, so hoping I can get a good read with the old Schrader valve tool.
I don't need a tool just yet. What did the plugs say. If it was a fuel pump I would suspect a whole bank being lean not just one cylinder. I suspect plug, injector (which the plug should tell you) then wiring, in that order. You can always check fuel pressure at the rail if you have that ability.
With all due respect I disagree. While I agree with owning a diagnostic tool like an Autel MX808s is something that every DIY guy NEEDS to have for obvious reasons, troubleshooting issues like OP's can be done without an OBD tool for the most part. I diagnosed my misfire issue before i ever bought my Autel. Looked at the spark plugs and noticed one was way more wet than the others. Pointed to a leaking injector right away. Swapped my injectors from Cyl 3 to Cyl 1 and the misfire happened on Cyl 1 instead of 3.
So OP def should look at his spark plugs. He should also buy an Autel or something that can give him fault code readings and live data. But to say not to troubleshoot by swapping parts should be your opinion, and should be a valid TS step.
Swapping parts is a great step to identify bad components.
I was referring to ppl who replace all their genuine ignition parts blindly with aftermarket to only get no improvement.
OBDII Scanner can save a great deal of time up front.
Last edited by CaliBenzDriver; Mar 6, 2026 at 11:28 PM.
I was able to pull the plugs on that bank to do a comparison, and the one in #4 (where the misfire is) had more soot, the ceramic part (I forget the name) was brown, and the threads looked a little wet.
A compression test showed over 150 in that cylinder, so I don't think that's the issue. I reinstalled all the plugs and coils in reverse order to see if the misfire moved at all, and still got it at #4, so I'm leaning heavily towards bad injector.
Life stuff happened, and I didn't get around to testing the fuel pressure, but I would think the whole bank would have a misfire or there would have been a code if one of the pumps was bad.
When I get the chance, I am going to move the injector to another cylinder and see what happens.
I was able to pull the plugs on that bank to do a comparison, and the one in #4 (where the misfire is) had more soot, the ceramic part (I forget the name) was brown, and the threads looked a little wet.
A compression test showed over 150 in that cylinder, so I don't think that's the issue. I reinstalled all the plugs and coils in reverse order to see if the misfire moved at all, and still got it at #4, so I'm leaning heavily towards bad injector.
Life stuff happened, and I didn't get around to testing the fuel pressure, but I would think the whole bank would have a misfire or there would have been a code if one of the pumps was bad.
When I get the chance, I am going to move the injector to another cylinder and see what happens.
It's more than likely your injector as I've mentioned. Let me know what year and model you have and I might be able to send you a used Bosch injector that fits your car (in working condition - I just replaced my injectors because I like to do preventative maintenance). I have 6 of them so it's no big deal. you can use it to test before spending money and buying a new injector.
Do your self a favor and buy an Autel 808S (you do not need anything fancier, and I'd steer away from those Mercedes specific diags as they're a waste of money. These Autels work for every vehicle and they do the same exact thing the MB specific 3rd party diags do) You can buy the Autel that I have for $380 off of ebay directly from Autel https://tinyurl.com/AutelEbay or buy it off of amazon for $100 more than eBay. This diag is amazing. I actually use it for everything (including doing a valve flush transmission service on my W213 that not a lot of scan tools can do). I've also programmed my Bosch injectors with this Autel.
You just need to take a picture of the serial number on the injector and put in the new number in the autel tool to let the ECU know which injector is in which cylinder so you don't have any issues with spray patterns and such.
not sure what year and model your e class is, but i assume it's either an E500 or E550 since you said it's an M278 engine? If so, don't buy a Mercedes OEM injector. buy a bosch one instead. You'll save $300-$500 per injector. I replaced all of my injector with Bosch OE units and they've been working like a charm ever since. Bosch is who makes the injectors anyways for MB so there is no difference in quality other than the price.
Last edited by Billyismyname; Mar 7, 2026 at 11:26 PM.
It's more than likely your injector as I've mentioned. Let me know what year and model you have and I might be able to send you a used Bosch injector that fits your car (in working condition - I just replaced my injectors because I like to do preventative maintenance). I have 6 of them so it's no big deal. you can use it to test before spending money and buying a new injector.
Do your self a favor and buy an Autel 808S (you do not need anything fancier, and I'd steer away from those Mercedes specific diags as they're a waste of money. These Autels work for every vehicle and they do the same exact thing the MB specific 3rd party diags do) You can buy the Autel that I have for $380 off of ebay directly from Autel https://tinyurl.com/AutelEbay or buy it off of amazon for $100 more than eBay. This diag is amazing. I actually use it for everything (including doing a valve flush transmission service on my W213 that not a lot of scan tools can do). I've also programmed my Bosch injectors with this Autel.
You just need to take a picture of the serial number on the injector and put in the new number in the autel tool to let the ECU know which injector is in which cylinder so you don't have any issues with spray patterns and such.
not sure what year and model your e class is, but i assume it's either an E500 or E550 since you said it's an M278 engine? If so, don't buy a Mercedes OEM injector. buy a bosch one instead. You'll save $300-$500 per injector. I replaced all of my injector with Bosch OE units and they've been working like a charm ever since. Bosch is who makes the injectors anyways for MB so there is no difference in quality other than the price.
I am definitely in the market for a better scanner, but currently have a Carly.
Car is a 2012 E550 4-matic, and if you have the right injector, I'll take it for testing. I did find some Bosch injectors on ebay for $80, so i may just go ahead and get it and send it back if its not the issue.
I am definitely in the market for a better scanner, but currently have a Carly.
Car is a 2012 E550 4-matic, and if you have the right injector, I'll take it for testing. I did find some Bosch injectors on ebay for $80, so i may just go ahead and get it and send it back if its not the issue.
So these are the injectors needed for your Benz.
They are the exact same ones I have in my Mercedes:
I have these four that are in the picture (the OEM ones that came in my E Class). I am really not sure which one of them is faulty. But I can send two to you just in case you do end up installing the one that is leaking if you want to test. They're not hard to replace, but you WILL need to code them in. So I'd suggest buying that Autel. If it ends up fixing your issue, you can keep the injectors I send you. It'll atleast cover half of the cost of the Autel diag tool to save you some money.
Let me know if you want me to send you them.
**Edit - I actually do know which one is faulty. It's the Cyl #4 injector, you can see in the picture it's a lot more corroded than the rest). I just found it and tossed it in the trash so I can send you just the one injector to test**
Last edited by Billyismyname; Mar 8, 2026 at 11:47 PM.
So these are the injectors needed for your Benz.
They are the exact same ones I have in my Mercedes:
I have these four that are in the picture (the OEM ones that came in my E Class). I am really not sure which one of them is faulty. But I can send two to you just in case you do end up installing the one that is leaking if you want to test. They're not hard to replace, but you WILL need to code them in. So I'd suggest buying that Autel. If it ends up fixing your issue, you can keep the injectors I send you. It'll atleast cover half of the cost of the Autel diag tool to save you some money.
Let me know if you want me to send you them.
**Edit - I actually do know which one is faulty. It's the Cyl #4 injector, you can see in the picture it's a lot more corroded than the rest). I just found it and tossed it in the trash so I can send you just the one injector to test**
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