2014 Mercedes Benz, gl450 misfire when warmer up
the car coming to the shop with misfire, I swap the coils an replace the spark, plugs and the the engine still misfiring on number 5, check compression and is good, I'm follow and update the software on ecm. and tcm. then replace a injector number 5 and record the quantity digits in the ecm. with no luck, the check engine light flashing and missing very hard after 15-20 min from cold start, and when the engine is an operational temperature if erase the codes the problem come back very fast. if somebody have some information, or idea I'm appreciate, thanks.
If you have a borescope check and see if you've got carbon build up.
Hi Rafael, Sounds like you may need to do an in-cylinder pressure test to determine what is going on. The condition favors a loose valve seat or a sticky valve from what I have seen in many different engines. Have you run a scope test on the #5 coil driver or injector driver to make sure it is not PCM related?
Running compression compared to known good cylinder, very well known for valve issues.
Do a cylinder leak down test…these engines suffer from loose valve guides causing the valve seat to enlarge. You will need to remove the power/drive train assembly to do a head job.
Is that one of the models that requires "indexed" plugs?
By indexed do you mean torqued to the proper torque spec? How else would you index a spark plug? Thanks
Some mercedes models use plug indexing , you must buy the plugs from the dealer and torque to spec. the factory engineered the thread match between the head threads on the head and the threads on the factory plug. in order for reliable ionization and ignition spark to occur the electrode has to be properly positioned in the combustion chamber
Also ,when tuning a race engine , we get an assortment of plugs index them and then figure out the torque that will position the ground electrode as not to interfere with mixture flow, for maximum performance. in the mercedes case they do it to prevent misfiring under load.
Hi Rod, I thought that was racetrack Voo Doo until a top fuel dragster crew chief proved it to me many years ago. The correct placement of the electrode in relation to the incoming air fuel mixture is very critical for efficient combustion. All of that takes place in milliseconds of time repeatedly. These days, people take plugs for granted and figure they will last the life of a vehicle. In…
Really good to know thank you! I am wondering though two other direct injection Motors besides just Mercedes have this recommendation and possible engine damage problems?
I know some BMW engines. Im curious if others do? Would be nice to get a list of all engines that use this.
BMW for sure and several other direct injected engines as well. It's the height/depth of the spark in correlation with injection (burn capability)
I have the same ymm in the shop now with misfire on same cyl #5. I am suspect of valve or seat issues. Will let you know if I find anything.
Do you have a scope? Would really pay off to do some in cylinder pressure tests while running. Preferably with a Pico. Will tell you if a valve is opening too soon/late (valve lash), etc. Also an ignition image might help you here. Keep in mind, besides spark (ignition) there is injection (amount, spray pattern, etc), compression, amount of air, FLOW of air (the way it enters the cylinder)…
thanks for the information you give me guys, I'm be able to solve the problem and it was a valve not sealing good and it was slightly difference in the cylinders compression, 7 cylinders the compression was between 185 psi and 180 psi, and in the number 5 it was 165 psi, thanks for your help, and yes it was an indexed spark plugs.