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Discussion Starter #1
has anyone here dealt with head gasket problems on an m112 v6? my 99 e320 has had a random misfire/rough idle since a couple days after i got it, and I'm starting to believe the head gasket may possibly be failing.

the car has an occasional rough idle/misfire that comes upon startup and goes away after you recycle power. it throws a p0305 code and feels like cylinder 5 doesn't start up with the rest of the cylinders. when it's doing this, itll misfire as long as the car is on, no matter how long its left on. as soon as you turn it off and back on, it runs smooth. I've replaced the plugs and swapped coils/wires from 4 and 5. I've also swapped in another injector and still no solution.

the car can sit for hours and not overheat, and theres no signs of coolant mixture. I've noticed the temp gauge does fluctuate between 80 and 95 degrees but never actually reaches 100, and cools back to 80 once its moving. I was told this was normal?? I also revved the engine and theres no bubbles, but does put out a white mist when it's cold out... I'm out of ideas and at my wits end with this car and ready to pull my hair out lol
 

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1998 E320 base sedan @ 160kmiles
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Have you done the compression test on cylinder 5 ?

Crankshaft position sensor related issues (missing a pulse or two) can cause a misfire issue. This is difficult to diagnose without proper tools.

Possibly, it is an intermittent wiring issue (from the ECU to cylinder 5 ignition coil), or an ECU issue.

Also obtain the freeze frame data from the scanner and post here. When the fault code appears, check the fuel level in the tank. In some cases, fuel levels less than 1/4 tank can cause misfire(s) due to fuel starvation.
 

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Discussion Starter #3
Have you done the compression test on cylinder 5 ?

Crankshaft position sensor related issues (missing a pulse or two) can cause a misfire issue. This is difficult to diagnose without proper tools.

Possibly, it is an intermittent wiring issue (from the ECU to cylinder 5 ignition coil), or an ECU issue.

Also obtain the freeze frame data from the scanner and post here. When the fault code appears, check the fuel level in the tank. In some cases, fuel levels less than 1/4 tank can cause misfire(s) due to fuel starvation.
I haven't done the compression test yet, I was actually on the way to a radiator shop to see if they could examine the coolant. I'll try to do a compression test though. I've never used a compression gauge to be honest.
 

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Green '02 E320 Wagon
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Oh no, not you too! I've got the same symptoms - temp between 80-95, misfire when driving which will stop if I turn off/on the car, rough idle, swapped coils, checked plugs.

How about we both get new crankshaft position sensors. I replaced mine in 2013 at 100k mi because the car wouldn't start when it was warm, only when cold. Maybe it's time to replace it again at 150k mi after six years.

I have the Snap-on EEPV600 compression test kit. It was very easy to use on my Volvo V70 whose plug shafts open straight up. I haven't tried it on the E320 both because the plugs are hard to access and because of the dire warnings in the compression test DIY by G-AMG.

I'm going to ask in the DIY thread about a simpler way to do this test, hoping the experts will weigh in. I'm going to not ask compression related questions in my misfire thread, but keep them here instead.
 

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Discussion Starter #5
Oh no, not you too! I've got the same symptoms - temp between 80-95, misfire when driving which will stop if I turn off/on the car, rough idle, swapped coils, checked plugs.

How about we both get new crankshaft position sensors. I replaced mine in 2013 at 100k mi because the car wouldn't start when it was warm, only when cold. Maybe it's time to replace it again at 150k mi after six years.

I have the Snap-on EEPV600 compression test kit. It was very easy to use on my Volvo V70 whose plug shafts open straight up. I haven't tried it on the E320 both because the plugs are hard to access and because of the dire warnings in the compression test DIY by G-AMG.

I'm going to ask in the DIY thread about a simpler way to do this test, hoping the experts will weigh in. I'm going to not ask compression related questions in my misfire thread, but keep them here instead.
I'm at a radiator shop right now and it's a confirmed head gasket.
 

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1998 E320 base sedan @ 160kmiles
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6,015 Posts
Oh no, not you too! I've got the same symptoms - temp between 80-95, misfire when driving which will stop if I turn off/on the car, rough idle, swapped coils, checked plugs.

How about we both get new crankshaft position sensors. I replaced mine in 2013 at 100k mi because the car wouldn't start when it was warm, only when cold. Maybe it's time to replace it again at 150k mi after six years.

I have the Snap-on EEPV600 compression test kit. It was very easy to use on my Volvo V70 whose plug shafts open straight up. I haven't tried it on the E320 both because the plugs are hard to access and because of the dire warnings in the compression test DIY by G-AMG.

I'm going to ask in the DIY thread about a simpler way to do this test, hoping the experts will weigh in. I'm going to not ask compression related questions in my misfire thread, but keep them here instead.
You can remove the starter relay and find out which connectors are the contacts (marked 30 and 87, 30 means always on power, 87 means switched power which the relay does the switching). You can connect your remote starter that applies a short (relay contact closure replacement). The K40's are the same.

You can remove the rear fuse / relay module located fuel pump relay to shut down the fuel. This usually is not required as the fuel injectors will be closed with key out, but you can briefly run the engine to purge the fuel in the rails with the relay out.

The reason why the key turn cranking will not work well is due to tip start limitation of crank time.
 

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1998 E320 base sedan @ 160kmiles
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Common with M104 engines, but rarely with M112. But who knows. And have they actually removed the cylinder 5 plug(s), and looked for coolant on the piston top after pressurizing ? Have they done a smoke test ?
 

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Discussion Starter #11
Common with M104 engines, but rarely with M112. But who knows. And have they actually removed the cylinder 5 plug(s), and looked for coolant on the piston top after pressurizing ? Have they done a smoke test ?
no smoke test or anything like that. just used the pressurizer that they put on the coolant expansion tank
 

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1998 E320 base sedan @ 160kmiles
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Then, I do not believe it is confirmed, but a possibility. You need a good scanner to look at freeze frames, misfire values in all cylinders, fuel trims, etc. Misfire code occurs when a threshold is exceeded. You may have random misfires in other cylinders which can be lower than the threshold which would not generate a code. There are ways that a relative compression test can be done while cranking the engine and looking at the cranking voltage waveform, but this requires special equipment.

Does the CEL flash when it comes up or is it steady ?
 

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Discussion Starter #13
Then, I do not believe it is confirmed, but a possibility. You need a good scanner to look at freeze frames, misfire values in all cylinders, fuel trims, etc. Misfire code occurs when a threshold is exceeded. You may have random misfires in other cylinders which can be lower than the threshold which would not generate a code. There are ways that a relative compression test can be done while cranking the engine and looking at the cranking voltage waveform, but this requires special equipment.

Does the CEL flash when it comes up or is it steady ?
the CEL just illuminates one times and stays for a about a few hours then goes away. then 24 hours later or so, itll start with a shake and the CEL comes back. rinse and repeat.
 

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2002 E55 AMG Sedan
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Regarding the cylinder compression test, you don't need to follow the extensive procedure that G amg did. That's a waste of time. Just do a regular compression test like you would on any car. All you need is about 5 or 6 turns of the starter. Just hold the key on start and then turn it back to position 1 or position 0 after the required time. There's no reason to over think this.
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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What kind of testing did they do? The little testing by the expansion tank where they confirm the presence of exhaust gas? Did they use something like this?

2613311
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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So what color did the fluid turn?
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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Not enough evidence to do a headgasket. I have that same setup, and the fluid turns yellow when in presence of exhaust gas. From blue to yellow. Green is a little too low on the scale of calling it a head gasket issue. It's like you coughing up and I say you only have 1 month left to live based on that cough....there's no basis on that.

Get more thorough testing.
 

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Discussion Starter #20
Not enough evidence to do a headgasket. I have that same setup, and the fluid turns yellow when in presence of exhaust gas. From blue to yellow. Green is a little too low on the scale of calling it a head gasket issue. It's like you coughing up and I say you only have 1 month left to live based on that cough....there's no basis on that.

Get more thorough testing.
my car also loses coolant as well, I'm not sure what else would cause this issue aside from a head gasket.. I think at 238k this engine is due for them as well
 
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