2018 GLS550 - M278 Very Weird Misfire Issue, Help Needed!
#51
MBWorld Fanatic!
#52
MBWorld Fanatic!
About 5 years ago we had a brand new vehicle. Within about 500 miles it started throwing a misfire code for one of the cylinders. The dealer tried a compression test, new coil, plug, injector, etc, all to no avail. Finally they put a new cylinder had on it and it's been fine ever since.
Did your mechanic scope any of the other cylinders to see if they looked the same?
Did your mechanic scope any of the other cylinders to see if they looked the same?
Last edited by John CC; 02-27-2023 at 04:45 PM.
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chassis (02-27-2023)
#53
Junior Member
Thread Starter
As said he took the car to his own shop and worked on it for approx 2 weeks then came back to me saying "cylinder 8 has bad cylinder walls, no scoring yet but Silitec layer almost gone this is why I see shiny cylinder walls, so replace the engine or sell it as is".
#54
Junior Member
Thread Starter
About 5 years ago we had a brand new vehicle. Within about 500 miles it started throwing a misfire code for one of the cylinders. The dealer tried a compression test, new coil, plug, injector, etc, all to no avail. Finally they put a new cylinder had on it and it's been fine ever since.
Did your mechanic scope any of the other cylinders to see if they looked the same?
Did your mechanic scope any of the other cylinders to see if they looked the same?
#55
Dear Forum Members,
I used to read MB World forums for years but this is the first time that I feel hopeless and need help...
I have a 2018 GLS550 and around 20k miles, a very weird misfiring problem started. This is what happens:
- Sometimes (30-40% of cold starts), engine starts with immediate misfiring at cyl 8 after cranking, check engine light blinks and stays on, turning off/on does not help, after driving for 2-3 mins and engine gets a bit warm then I turn off/on the engine, everything turns back to normal, car runs perfectly smooth with all cylinders on, no performance issues. Even sometimes, check engine light goes off too!
- The main problem is the misfiring when driving. A very hard shaking starts if I drive at high gears (6-7-8-9) with high load (more than 50% of throttle) and engine rpm between 1,800-2,200 rpm. Under these conditions, an immediate shaking starts (not everytime but 60-70% occurrence), check engine light starts blinking and stays on, engine control unit shuts off the misfiring cylinder and everything comes back to perfectly normal if I turn the key off/on and restart the engine. When I check the fault codes, I see 100% cylinder 8 misfire and 75-80% of the times cyl 7 and 6, and very rarely cyl 1 and 4.
To overcome this very annoying problem, I tried these:
- All spark plugs have been replaced, ignition coils replaced, nothing changed.
- All injectors sent to Bosch center, cleaned and tested, reinstalled, nothing changed. If I change the position of the injectors and recode them for new locations, still the same old cylinders misfire. Nothing moves with injectors.
- I opened up the engine wiring harness top section, checked and rewired all injector/ignition coil wires, common +12V and ground points. Nothing changed.
- Cold compression test done. All cylinders are around 215-220psi and above, very very good. No problems seen.
- All 8 cylinder tops and combustion chamber checked with flex camera, cyl 8 has more carbon deposits on the piston than the remaining 7 but nothing seems severe. I removed the complete intake manifold, cyl 8 intake port seem more CLEANER than the other 7 but all of them shows heavy carbon deposit, more or less. SO I decided to clean the intake ports and valves. With brake cleaner and thinner, I removed all carbon deposits from the ports and valve bodies. Problem is still there.
- I replaced all 4 knock sensors, nothing changed. If I drive the car with knock sensors unplugged, the problem is 90% goes away but performance goes significantly low, naturally.
- I test drove the car with Xentry connected, low/high fuel pressures, intake and boost pressures, engine temp, 4 camshaft angles etc all values are in the range. When I increase the load and start the shake/misfire, I see cyl 8 and cyl 7 misfire counters goes up like crazy and eventually engine computer shuts off cyl 8 and sometimes 7 too.
- Finally I tried STP intake valve cleaner fluid to clean the possible remaining carbon deposits (an experienced MB mechanic told me M278 engines are very sensitive to intake valve carbon deposit), no help.
I have ZERO performance issues, car literally flies if you push hard on high rpm's, no smoke, no hesitation. Throttle response is very very good. If you go over 2,200 rpm and floor it, car is like a rocket.
Under this circumstance, I think the engine is good mechanically. I am considering to change the engine wiring harness thinking about my past experience on my ex Ferrari 599GTB, showing 'transmission failure - hydraulic pump pressure low" error and putting car to neutral which makes car non-driveable for 5-10 mins and comes back to normal until next occurrence in maybe 1-2 months. I saw many similar 'mystic' problems caused by wiring harnesses.
Last note: I drove a 2013 GL550 some years ago, that one was showing similar cold start misfire thing but I discovered a service bulletin about it, reprogrammed the engine computer and problem solved forever. This time, there is no such solution
Any other experiences/comments on this mystery?
I used to read MB World forums for years but this is the first time that I feel hopeless and need help...
I have a 2018 GLS550 and around 20k miles, a very weird misfiring problem started. This is what happens:
- Sometimes (30-40% of cold starts), engine starts with immediate misfiring at cyl 8 after cranking, check engine light blinks and stays on, turning off/on does not help, after driving for 2-3 mins and engine gets a bit warm then I turn off/on the engine, everything turns back to normal, car runs perfectly smooth with all cylinders on, no performance issues. Even sometimes, check engine light goes off too!
- The main problem is the misfiring when driving. A very hard shaking starts if I drive at high gears (6-7-8-9) with high load (more than 50% of throttle) and engine rpm between 1,800-2,200 rpm. Under these conditions, an immediate shaking starts (not everytime but 60-70% occurrence), check engine light starts blinking and stays on, engine control unit shuts off the misfiring cylinder and everything comes back to perfectly normal if I turn the key off/on and restart the engine. When I check the fault codes, I see 100% cylinder 8 misfire and 75-80% of the times cyl 7 and 6, and very rarely cyl 1 and 4.
To overcome this very annoying problem, I tried these:
- All spark plugs have been replaced, ignition coils replaced, nothing changed.
- All injectors sent to Bosch center, cleaned and tested, reinstalled, nothing changed. If I change the position of the injectors and recode them for new locations, still the same old cylinders misfire. Nothing moves with injectors.
- I opened up the engine wiring harness top section, checked and rewired all injector/ignition coil wires, common +12V and ground points. Nothing changed.
- Cold compression test done. All cylinders are around 215-220psi and above, very very good. No problems seen.
- All 8 cylinder tops and combustion chamber checked with flex camera, cyl 8 has more carbon deposits on the piston than the remaining 7 but nothing seems severe. I removed the complete intake manifold, cyl 8 intake port seem more CLEANER than the other 7 but all of them shows heavy carbon deposit, more or less. SO I decided to clean the intake ports and valves. With brake cleaner and thinner, I removed all carbon deposits from the ports and valve bodies. Problem is still there.
- I replaced all 4 knock sensors, nothing changed. If I drive the car with knock sensors unplugged, the problem is 90% goes away but performance goes significantly low, naturally.
- I test drove the car with Xentry connected, low/high fuel pressures, intake and boost pressures, engine temp, 4 camshaft angles etc all values are in the range. When I increase the load and start the shake/misfire, I see cyl 8 and cyl 7 misfire counters goes up like crazy and eventually engine computer shuts off cyl 8 and sometimes 7 too.
- Finally I tried STP intake valve cleaner fluid to clean the possible remaining carbon deposits (an experienced MB mechanic told me M278 engines are very sensitive to intake valve carbon deposit), no help.
I have ZERO performance issues, car literally flies if you push hard on high rpm's, no smoke, no hesitation. Throttle response is very very good. If you go over 2,200 rpm and floor it, car is like a rocket.
Under this circumstance, I think the engine is good mechanically. I am considering to change the engine wiring harness thinking about my past experience on my ex Ferrari 599GTB, showing 'transmission failure - hydraulic pump pressure low" error and putting car to neutral which makes car non-driveable for 5-10 mins and comes back to normal until next occurrence in maybe 1-2 months. I saw many similar 'mystic' problems caused by wiring harnesses.
Last note: I drove a 2013 GL550 some years ago, that one was showing similar cold start misfire thing but I discovered a service bulletin about it, reprogrammed the engine computer and problem solved forever. This time, there is no such solution
Any other experiences/comments on this mystery?
By any chance do you know which wire supplies 12 volts to the ignition coils?
#56
Junior Member
Thread Starter
There is a thick red and brown cable coming from the engine control unit for all ignition coils common 12V power supply. Trigger signal comes on a separate cable individually for each coil, for sure. Same for the injectors. Why you need to know?
#57
im trying to install a switch/button where it cuts ignition whenever i press the switch/button.
#58
Junior Member
Thread Starter
Ignition coil pack power and ground lines are both fed by engine computer. To have access, it is necessary to open up the engine wiring harness. It is not a big job but a bit messy.
#59
Service Bulliten?
Where did you find the service bulliten below? I have a beautiful low miles ML550. I'm over $5K into repairs for cylinder 5 misfire, and the car is running worse now. I would appreciate any direction you can give.
"Last note: I drove a 2013 GL550 some years ago, that one was showing similar cold start misfire thing but I discovered a service bulletin about it, reprogrammed the engine computer and problem solved forever. This time, there is no such solution "
"Last note: I drove a 2013 GL550 some years ago, that one was showing similar cold start misfire thing but I discovered a service bulletin about it, reprogrammed the engine computer and problem solved forever. This time, there is no such solution "