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unfortunately I've been having a problem with misfiring in my 5.5L M273 on cylinder 2 for a few weeks now. The code in the fault memory is P0302. When I look at the misfire count in Xentry, all cylinders besides cylinder 2 have 0 misfires, while cylinder 2 is misfiring strongly. The check engine light comes on and sometimes flashes, after which, as far as I know, the injection of cylinder 2 is switched off so that the catalytic converter is not damaged by the frequent misfires. I notice a rougher running after the engine control light flashes, and I can feel that the second cylinder is not running anymore. When restaring the engine, everything is back to normal, check engine light may turn of or stay on.
These misfires only occur when the engine is warm. If I start the car cold and leave it until it reaches 70 degrees +-, the cylinder does not misfire. The misfiring also only occurs when the car is stationary. When I drive 500 km on the highway, I have no check engine light and the vehicle feels like it has full power. If I stop at traffic lights for 30 seconds after driving even long distances, the check engine light may come on and/or flash, but only sometimes. It also happens that I can drive in the city with lots of traffic lights without an engine control light.
However, if I shift the transmission to N or P at a red light and keep the engine speed at 1000-1500 rpm, the misfiring and the check engine light do not occur either. I have therefore already tried in Xentry to set the engine idle rpm to around 900 rpm (maximum) and to adjust the ignition in the early or late direction (via Xentry), as well as to inject more or less fuel ("rich" or "lean" injection via Xentry), but none of this has helped.
I have already swapped the ignition coil, spark plug, injector and the injector seals. I have also replaced the intake manifold and throttle valve gaskets, and checked the wirings and spark plug connector. Two years ago, the previous owner replaced the intake manifold with a new one from Pierburg. Plastic parts had broken off the old intake manifold and damaged the valves of bank 1, where the affected cylinder 2 is located. In the course of this, the cylinder head of bank 1 was overhauled and the valves replaced. The timing chain was not replaced because the timing was good. After the cylinder head was overhauled, the car ran smoothly until a few weeks ago.
The car has a mileage of approx. 250,000 kilometers.
I suspect an electronic problem, possibly with the ECU, as I've read either on this or another forum that someone has had a similar problem with M273 or M273 engine.
My question is, what is the best way to proceed to find the fault? Does it make sense to have a compression or pressure loss measurement carried out before sending in the ECU for costly repair, or are faults in this area unlikely with my fault pattern?
Cyl 2 spark plug was oily, the seal between the valve cover and the spark plug appears to be leaking a little, but this is unlikely to cause misfiring (even after swapping the spark plug and coil), is it?
I thought I'd post this here on this adjacent topic rather than creating a new thread. I'm putting in new fuel injectors in my M273 using new Standard Motor Products injectors. Of the eight I bought, four are missing the top brass colored port. I've not done this job before, and don't know what to make of it, other than that brass port on the OEM old ones and four of the Standard new ones is probably important. I watched an FCP Euro video carefully, and it appeared their parts on a Mercedes video also did not have the port. Can anyone clarify what it is, and confirm it should be there? The Standard part numbers were all the same and otherwise identical.
those links to the inlet trumpet switching are so well hidden....
check the solenoid valve - left front down by the dip stick tube - you can also get a tube and suck on the three diaphragms in your picture to try and see if anything works
@nath h, what did you do with those injectors - bought normal ones ?
unfortunately I've been having a problem with misfiring in my 5.5L M273 on cylinder 2 for a few weeks now. The code in the fault memory is P0302. When I look at the misfire count in Xentry, all cylinders besides cylinder 2 have 0 misfires, while cylinder 2 is misfiring strongly. The check engine light comes on and sometimes flashes, after which, as far as I know, the injection of cylinder 2 is switched off so that the catalytic converter is not damaged by the frequent misfires. I notice a rougher running after the engine control light flashes, and I can feel that the second cylinder is not running anymore. When restaring the engine, everything is back to normal, check engine light may turn of or stay on.
These misfires only occur when the engine is warm. If I start the car cold and leave it until it reaches 70 degrees +-, the cylinder does not misfire. The misfiring also only occurs when the car is stationary. When I drive 500 km on the highway, I have no check engine light and the vehicle feels like it has full power. If I stop at traffic lights for 30 seconds after driving even long distances, the check engine light may come on and/or flash, but only sometimes. It also happens that I can drive in the city with lots of traffic lights without an engine control light.
However, if I shift the transmission to N or P at a red light and keep the engine speed at 1000-1500 rpm, the misfiring and the check engine light do not occur either. I have therefore already tried in Xentry to set the engine idle rpm to around 900 rpm (maximum) and to adjust the ignition in the early or late direction (via Xentry), as well as to inject more or less fuel ("rich" or "lean" injection via Xentry), but none of this has helped.
I have already swapped the ignition coil, spark plug, injector and the injector seals. I have also replaced the intake manifold and throttle valve gaskets, and checked the wirings and spark plug connector. Two years ago, the previous owner replaced the intake manifold with a new one from Pierburg. Plastic parts had broken off the old intake manifold and damaged the valves of bank 1, where the affected cylinder 2 is located. In the course of this, the cylinder head of bank 1 was overhauled and the valves replaced. The timing chain was not replaced because the timing was good. After the cylinder head was overhauled, the car ran smoothly until a few weeks ago.
The car has a mileage of approx. 250,000 kilometers.
I suspect an electronic problem, possibly with the ECU, as I've read either on this or another forum that someone has had a similar problem with M273 or M273 engine.
My question is, what is the best way to proceed to find the fault? Does it make sense to have a compression or pressure loss measurement carried out before sending in the ECU for costly repair, or are faults in this area unlikely with my fault pattern?
Many thanks for any help and answers!
Did you ever figure this out? I've been having same issue for months now. #6 cyl for me. Same thing though. I replaced coil, plug, injector. Even a new batter since the old one was a little low on voltage. Sometimes the car goes a month and around 700 miles without any misfiring. The out of the blue it will be back to misfiring. It's getting worse though. Hot weather is here and yes getting bad.
Check the intake flaps. Maybe a piece of plastic broke off near cyl 6. Boroscope it thoroughly. Also look inside the cylinder.
Check compression on #6 and at least 1 other cyl.
Did you ever figure this out? I've been having same issue for months now. #6 cyl for me. Same thing though. I replaced coil, plug, injector. Even a new batter since the old one was a little low on voltage. Sometimes the car goes a month and around 700 miles without any misfiring. The out of the blue it will be back to misfiring. It's getting worse though. Hot weather is here and yes getting bad.
I've got one of these launch creader orange non-directional scanners which has saved me a lot of money the last couple years. I don't know how to access fuel pressure or anything like that but it will shows #6 misfiring while idling. Once I get above 20 it's usually goes away. In fact some times I just have to turn the car off and back on a couple times and the problem goes away. For instance last week it had been driving fine for a couple weeks and 300 miles. I went to the gas station and filled it up and immediately upon starting it was misfiring. It smoothed itself out after a couple of blocks. But not that the weather here has been in the high 80s low 90s seems to not be going away at all the last couple days. It's been doing this for a year and it's just so random I'm guessing there a bad wire or something. I always do my own repairs other than rebuilding things like engines, transmissions, differentials. Like I said I replaced the coil, plug and injector. Also out a fresh battery in because the old one was 5 years old and showing 11.9 volts when the car is not running. I was about to replace the alternator and see if that could be a problem not giving enough juice but idont want to throw parts at it anymore. I've got it scheduled for a private shop I've used before this Monday. I'll be sure to post what they find. There isn't any loss of power when it's not misfiring. Car drive more like a sports/muscle car than a luxury car. Oil is fine. Coolant is fine. No over heating. I never checked compression because it will go for weeks running fine and powerful. Only code i get are p0300 "random multiple misfire" and p0306 "#6 cyl misfire".
Like I said I'll be sure to post what the private euro shop says. I hate having to take it to a shop. Last time I took it for the air suspension not raising or lowering they said it was a bad air pump release valve. They quoted $1100 to replace. I bought a pump myself and replaced it along with the valve part with all the lines. Anyhow that was t the problem. Glad I did it myself and replaced it in about 20 minutes for about $200 in parts. Problem is there a broken wire somewhere connecting to the air pump. I use my scanner about once every 2 weeks to engage the pump and top off the air in the shocks and rais them. Luckily they don't have any leaks and only drop a couple millimeters every 2 weeks.
Like I said I'll make sure to post what the shop finds.
I hate when I read threads and people just disappear without stating if the found a fix or not.
Like I said I'll make sure to post what the shop finds.
I hate when I read threads and people just disappear without stating if the found a fix or not.
what state are all three suspension level sensors?, the link rods seize up, especially the one hidden rear one above the park brake module
if you swap the coil stick from 6 to one the other side what happens - wire breaks don't magically keep going they usually deteriorate quite fast to 100% failure
worth checking youtube and reminding yourself what cooked engine ECUs do - If I recollect correctly the overheating / ageing makes a capacitor leak and the gunk inside drips through the board and blows up cheap and nasty amplifier chips that bring misfires - toip notch places can replace both bits - but its not cheap Bosch ME9.7
what state are all three suspension level sensors?, the link rods seize up, especially the one hidden rear one above the park brake module
if you swap the coil stick from 6 to one the other side what happens - wire breaks don't magically keep going they usually deteriorate quite fast to 100% failure
worth checking youtube and reminding yourself what cooked engine ECUs do - If I recollect correctly the overheating / ageing makes a capacitor leak and the gunk inside drips through the board and blows up cheap and nasty amplifier chips that bring misfires - toip notch places can replace both bits - but its not cheap Bosch ME9.7
I'll have to check those level sensors after it gets back from the shop assuming they don't say it's going to cost an arm and a leg to fix the misfire. I didn't swap coil packs. I just went and got some from the local junk yard. They had an 07 cls550 in great shape mines a rear impact. So I grabbed two coil packs. Two spark plugs and two fuel injector. All Mercedes Brand. Replaced #6 cyl parts two times each just to make sure one of the parts wasn't bad. And changed each one individual the. Drove for a while. Thought the fuel injector fixed it because it was misfiring before I shut it off and replaced that. Didn't misfire after that for another week and a half. That's what's killing me is the randomness. Car drove fine to the beach and back which was a 400 miles round trip. Then two weeks later I walk out to start it in the morning and it's instantly misfiring. About 10 mins later she's running smooth for the next 3 days. But now it's been 5 days of constant misfire where it's jerking just pulling away from a stop sign.
Common Mercedes ME9.7 Engine Control Unit Failures
The Mercedes ME9.7 ECU is designed to control various aspects of the engine, such as fuel injection, ignition timing, and emissions control. However, when it fails, it can cause a range of problems, including:
Poor engine performance, misfiring even after testing and replacement of ignition and fuel injection components.
I'll have to check those level sensors after it gets back from the shop assuming they don't say it's going to cost an arm and a leg to fix the misfire. I didn't swap coil packs. I just went and got some from the local junk yard. They had an 07 cls550 in great shape mines a rear impact. So I grabbed two coil packs. Two spark plugs and two fuel injector. All Mercedes Brand. Replaced #6 cyl parts two times each just to make sure one of the parts wasn't bad. And changed each one individual the. Drove for a while. Thought the fuel injector fixed it because it was misfiring before I shut it off and replaced that. Didn't misfire after that for another week and a half. That's what's killing me is the randomness. Car drove fine to the beach and back which was a 400 miles round trip. Then two weeks later I walk out to start it in the morning and it's instantly misfiring. About 10 mins later she's running smooth for the next 3 days. But now it's been 5 days of constant misfire where it's jerking just pulling away from a stop sign.
Hopefully the shop won't just guess the problem.
Welp just got it back from the shop they said they couldn't find anything wrong with it. Didn't know why it was misfiring. They said the compression was "a little low" for that cylinder. So for $255.00 I received nothing of any help back. Once I got it home I double checked spark and It has spark. I then took my can of mass are flow sensor cleaner and sprayed a generous amount where the injector sits which is right by the intake manifold gasket. I last did this on a cold day in Jan with brake clean and there wasn't any difference in the misfiring while idling. This time when I did it though I spray a good amount and within 2 seconds the car was about to stall. So that tells my it's either sucking in unmetered air from the intake manifold gasket or hopefully the o ring seal from the injector. Bow my replacement injector is from the junk yard so hopefully the seal is just bad. I have another injector that I'll swap out with either tomorrow or the next couple days. I'll probably put a little sealer around it also just to help that injector seal even if temporarily.
Guess shops now days don't out any extra effort it. I mean if they did a compression test why wouldn't they look for an air leak in the same area? So that was money thrown away.
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M273 Cyl 2 Misfiring
