Overheat then Misfire
Thread Starter
Super Member
Joined: May 2009
Posts: 673
Likes: 27
From: Frederick
2000 ML320, 2005 E320 CDI
Overheat then Misfire
Was replacing the coolant tank on the 2007 S550 (non turbo) - and forgot to reconnect the coolant lines to the res cap before taking it for a test drive. Car overheated (not to red) and I shut it down. I replaced the thermostat and repiped the lines - filled with coolant.
Brought the engine to temp and got on it testing. Now shows a Cylinder 5 misfire. Swapped the coils - still there. Pulled the plug and it looks horrendous so I swapped with Cylinder 6 and misfire persists - but still shows Cyl 5.
Here are the codes....
Pending:
P0305
P0351
P0355
Again, no smoke - no oil in coolant (res) and no coolant in oil.
What am I missing?
I realize a pressure test is in order to verify a HG problem - but wanted to make sure I wasn't missing something smaller first. I really want to swap the plug and probably will while waiting on responses. The gap was ridiculous.
Brought the engine to temp and got on it testing. Now shows a Cylinder 5 misfire. Swapped the coils - still there. Pulled the plug and it looks horrendous so I swapped with Cylinder 6 and misfire persists - but still shows Cyl 5.
Here are the codes....
Pending:
P0305
P0351
P0355
Again, no smoke - no oil in coolant (res) and no coolant in oil.
What am I missing?
I realize a pressure test is in order to verify a HG problem - but wanted to make sure I wasn't missing something smaller first. I really want to swap the plug and probably will while waiting on responses. The gap was ridiculous.
Thread Starter
Super Member
Joined: May 2009
Posts: 673
Likes: 27
From: Frederick
2000 ML320, 2005 E320 CDI
Very obvious lol. But honestly, with the past month - valid question. I did reset the codes, several times.
Since I posted I changed all 8 plugs with OE NGK 4288 and now the coil pack on Cylinder 1 (the one I moved from #5) is throwing a code. All other codes are clear and didn't come back during a test drive. Looks like I burnt the VERY worn plugs.
I will post back if something else stupid happens.
Since I posted I changed all 8 plugs with OE NGK 4288 and now the coil pack on Cylinder 1 (the one I moved from #5) is throwing a code. All other codes are clear and didn't come back during a test drive. Looks like I burnt the VERY worn plugs.
I will post back if something else stupid happens.
MBWorld Fanatic!
Joined: Dec 2004
Posts: 4,268
Likes: 253
You cooked the coil. Heat plus large plug gap = shorted coil. Overheat a bit more and you will warp the intake manifold... also it is common for more coils to fail depending on the severity of the overheat.
Thread Starter
Super Member
Joined: May 2009
Posts: 673
Likes: 27
From: Frederick
2000 ML320, 2005 E320 CDI
Warp the intake? I read that in another thread but someone mentioned plastic. Mine is Aluminum. I could have misread though.
Honestly, glad it was just a coil and not the head. I will gladly shell out $500 for new coils vs who knows how much for a cylinder head replacement.
Honestly, glad it was just a coil and not the head. I will gladly shell out $500 for new coils vs who knows how much for a cylinder head replacement.
