VERY random cold start misfire - Stumped
Thread Starter
Senior Member
Joined: Apr 2013
Posts: 339
Likes: 66
1998 E300TD
VERY random cold start misfire - Stumped
Hi All,
I have a cold start misfire that happens to throw a code, maybe once a month and have been chasing various possibilities.
The codes:
P0300 - Random Misfire Detected (Pending, Current, Permanent)
P0305 - Cylinder 5 Misfire Detected (Pending)
P0306 - Culinder 6 Misfire Detected (Pending)
P0308 - Cylinder 8 Misfire Detected (Pending, Current, Permanent)
P0420 - Catalyst System Efficiency Below Threshold (Bank 1) (Permanent)
P0430 - Catalyst System Efficiency Below Threshold (Bank 2) (Permanent)
(I have American racing LTH, race cats and mid-pipe)
What I have replaced:
PCV (but did install a catch can at the same time)
New spark plugs 1-8
New injectors 1-8
New coil pack #8 & #5 (these are the two that pop up the most)
New upstream o2 sensor on bank 2 (5-8 side)
Switched up where I buy gas
Mods:
ROW boxes and MAF
Green Filters - oiled
It's always tied to that bank, but always only 3 of the cylinders not all 4. Most of the time it's 5,7,&8...sometimes just 5&8, sometimes it's 5,6,8....just weird.
The car only has 29.5k miles and has a great service history, so I do not expect cam plates or lobes (not saying it isn't, just trying to rule out the easy stuff first)
I've sprayed carb cleaner around the intake and idle wasn't affected at all (when it was hot...maybe should when it is cold?)
Got any other thoughts?
if it matters this is for a 2011 e63.
As always, appreciate any thoughts.
I have a cold start misfire that happens to throw a code, maybe once a month and have been chasing various possibilities.
The codes:
P0300 - Random Misfire Detected (Pending, Current, Permanent)
P0305 - Cylinder 5 Misfire Detected (Pending)
P0306 - Culinder 6 Misfire Detected (Pending)
P0308 - Cylinder 8 Misfire Detected (Pending, Current, Permanent)
P0420 - Catalyst System Efficiency Below Threshold (Bank 1) (Permanent)
P0430 - Catalyst System Efficiency Below Threshold (Bank 2) (Permanent)
(I have American racing LTH, race cats and mid-pipe)
What I have replaced:
PCV (but did install a catch can at the same time)
New spark plugs 1-8
New injectors 1-8
New coil pack #8 & #5 (these are the two that pop up the most)
New upstream o2 sensor on bank 2 (5-8 side)
Switched up where I buy gas
Mods:
ROW boxes and MAF
Green Filters - oiled
It's always tied to that bank, but always only 3 of the cylinders not all 4. Most of the time it's 5,7,&8...sometimes just 5&8, sometimes it's 5,6,8....just weird.
The car only has 29.5k miles and has a great service history, so I do not expect cam plates or lobes (not saying it isn't, just trying to rule out the easy stuff first)
I've sprayed carb cleaner around the intake and idle wasn't affected at all (when it was hot...maybe should when it is cold?)
Got any other thoughts?
if it matters this is for a 2011 e63.
As always, appreciate any thoughts.
Super Member
Joined: Mar 2019
Posts: 522
Likes: 129
From: Bondi Beach , Australia
2013 W204 C63 AMG P31 Estate wagon
Mine did the exact same thing tonight. when I started it up with lots of oil smoke.
I did a diagnostic with my Carly and showed similar malfunctions as op above.
I let the car run like this during the checking then turned it off and back on after clearing codes.
Now runs smooth as.
I'm wondering if it was oil in the intake that contaminated the O2 sensors as I had moved my car 3 times around our driveway during the day.
I have had the oil smoke happen before after short engine running like moving car out of garage and back in after a few minute.
But it never ran rough like it did tonight.
I did a diagnostic with my Carly and showed similar malfunctions as op above.
I let the car run like this during the checking then turned it off and back on after clearing codes.
Now runs smooth as.
I'm wondering if it was oil in the intake that contaminated the O2 sensors as I had moved my car 3 times around our driveway during the day.
I have had the oil smoke happen before after short engine running like moving car out of garage and back in after a few minute.
But it never ran rough like it did tonight.
Senior Member
Joined: Jun 2020
Posts: 433
Likes: 583
From: Texas
3.0L Whipple E63 AMG
Mine used to get cold start misfires every once in awhile. I would have to turn off the car and restart it to make it go away. After replacing both upstream O2 sensors it hasn't done it ever since.
Thread Starter
Senior Member
Joined: Apr 2013
Posts: 339
Likes: 66
1998 E300TD
Hi all,
Still dealing with this issue, and today i got a real noticeable misfire…enough for a flashing check engine light. Shut down the engine and restarted and it was fine. Codes were for misfire in #5 & 8 again.
In addition to the work in Post #1, i replaced the o2 sensor on bank 1, just in case…but clearly that didn’t help.
Would secondary o2 sensors cause this problem?
Any other sensors to check, because it’s clearly something caused an actual misfire this morning.
Still dealing with this issue, and today i got a real noticeable misfire…enough for a flashing check engine light. Shut down the engine and restarted and it was fine. Codes were for misfire in #5 & 8 again.
In addition to the work in Post #1, i replaced the o2 sensor on bank 1, just in case…but clearly that didn’t help.
Would secondary o2 sensors cause this problem?
Any other sensors to check, because it’s clearly something caused an actual misfire this morning.
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Senior Member
Joined: Jun 2020
Posts: 257
Likes: 105
From: Toronto
2013 C63 P31
Hi All,
I have a cold start misfire that happens to throw a code, maybe once a month and have been chasing various possibilities.
The codes:
P0300 - Random Misfire Detected (Pending, Current, Permanent)
P0305 - Cylinder 5 Misfire Detected (Pending)
P0306 - Culinder 6 Misfire Detected (Pending)
P0308 - Cylinder 8 Misfire Detected (Pending, Current, Permanent)
P0420 - Catalyst System Efficiency Below Threshold (Bank 1) (Permanent)
P0430 - Catalyst System Efficiency Below Threshold (Bank 2) (Permanent)
(I have American racing LTH, race cats and mid-pipe)
What I have replaced:
PCV (but did install a catch can at the same time)
New spark plugs 1-8
New injectors 1-8
New coil pack #8 & #5 (these are the two that pop up the most)
New upstream o2 sensor on bank 2 (5-8 side)
Switched up where I buy gas
Mods:
ROW boxes and MAF
Green Filters - oiled
It's always tied to that bank, but always only 3 of the cylinders not all 4. Most of the time it's 5,7,&8...sometimes just 5&8, sometimes it's 5,6,8....just weird.
The car only has 29.5k miles and has a great service history, so I do not expect cam plates or lobes (not saying it isn't, just trying to rule out the easy stuff first)
I've sprayed carb cleaner around the intake and idle wasn't affected at all (when it was hot...maybe should when it is cold?)
Got any other thoughts?
if it matters this is for a 2011 e63.
As always, appreciate any thoughts.
I have a cold start misfire that happens to throw a code, maybe once a month and have been chasing various possibilities.
The codes:
P0300 - Random Misfire Detected (Pending, Current, Permanent)
P0305 - Cylinder 5 Misfire Detected (Pending)
P0306 - Culinder 6 Misfire Detected (Pending)
P0308 - Cylinder 8 Misfire Detected (Pending, Current, Permanent)
P0420 - Catalyst System Efficiency Below Threshold (Bank 1) (Permanent)
P0430 - Catalyst System Efficiency Below Threshold (Bank 2) (Permanent)
(I have American racing LTH, race cats and mid-pipe)
What I have replaced:
PCV (but did install a catch can at the same time)
New spark plugs 1-8
New injectors 1-8
New coil pack #8 & #5 (these are the two that pop up the most)
New upstream o2 sensor on bank 2 (5-8 side)
Switched up where I buy gas
Mods:
ROW boxes and MAF
Green Filters - oiled
It's always tied to that bank, but always only 3 of the cylinders not all 4. Most of the time it's 5,7,&8...sometimes just 5&8, sometimes it's 5,6,8....just weird.
The car only has 29.5k miles and has a great service history, so I do not expect cam plates or lobes (not saying it isn't, just trying to rule out the easy stuff first)
I've sprayed carb cleaner around the intake and idle wasn't affected at all (when it was hot...maybe should when it is cold?)
Got any other thoughts?
if it matters this is for a 2011 e63.
As always, appreciate any thoughts.
Could be throttle body plate
Can you verify your fuel trims?
Could be air pump issues
Because it clears up it leads me in the direction of cold starts which would be mechanical (liquid in cylinders or fouled plugs) or air pump airflow related
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Thread Starter
Senior Member
Joined: Apr 2013
Posts: 339
Likes: 66
1998 E300TD
Cold start this morning with my HP tuners hooked up. No CEL.
Lambda fuel trim b1 starts at 1.0, drops down to .87 at its lowest and then back to 1.07. B2 seems to match the same.
44 misfires on Cy 8, 10 on #2, 3 on #3&7, 1 on #1
spark efficiency did drop to like 41%, not sure if that is normal.
MAF sensors stay pretty close too
also, no smoke on startup has ever been noticed.
Lambda fuel trim b1 starts at 1.0, drops down to .87 at its lowest and then back to 1.07. B2 seems to match the same.
44 misfires on Cy 8, 10 on #2, 3 on #3&7, 1 on #1
spark efficiency did drop to like 41%, not sure if that is normal.
MAF sensors stay pretty close too
also, no smoke on startup has ever been noticed.
Thread Starter
Senior Member
Joined: Apr 2013
Posts: 339
Likes: 66
1998 E300TD
Checked the wiring...everything looked good. Checked vacuum and secondary air lines....looks good too. Double checked pcv conncections and all is well there. HP Tuner file is attached if anyone wants to take a look. I'm really at a loss.
Edit: I've noticed the long term trims between banks 1 & 2 are way off. Short term trims are close enough. Bank 1 starts at 8.6% and Bank 2 starts at -1.6%. It jumps up to B1 16.4% and B2 is 2.3%
As always, thanks!
Edit: I've noticed the long term trims between banks 1 & 2 are way off. Short term trims are close enough. Bank 1 starts at 8.6% and Bank 2 starts at -1.6%. It jumps up to B1 16.4% and B2 is 2.3%
As always, thanks!
Last edited by 6_Myles; Aug 13, 2022 at 04:36 PM.
Member
Joined: Oct 2017
Posts: 176
Likes: 11
'10 C63 P30
Not quite the same and may not be your issue, but I had a bout of random rough idling - could restart the car and things would be smooth again until one time I started it and it sounded the the engine was blown - was my camshaft adjuster. Just an idea.
Thread Starter
Senior Member
Joined: Apr 2013
Posts: 339
Likes: 66
1998 E300TD
Hi Barry, I have not. Given the lack of burning oil, coolant, and it running like an absolute animal after 5 seconds of idling….that didn’t even cross my mind.
With the LT fuel trims so imbalanced, I am going to throw some downstream o2’s at it and see what happens then.
If not, looks like I’m pulling a compression test and checking the cam adjusters…in that order.
With the LT fuel trims so imbalanced, I am going to throw some downstream o2’s at it and see what happens then.
If not, looks like I’m pulling a compression test and checking the cam adjusters…in that order.
Thread Starter
Senior Member
Joined: Apr 2013
Posts: 339
Likes: 66
1998 E300TD
Update:
Replaced both downstream o2 sensors last night and had, for the first time ever, 0 misfires on cylinder #8 during startup. Got 1 misfire on #5 and 1 on #1…. But that feels normal.
I’ll give it a couple of weeks and see if this is the new normal or if I end up back where I started.
I sincerely appreciate everyone’s input and help on this one.
Replaced both downstream o2 sensors last night and had, for the first time ever, 0 misfires on cylinder #8 during startup. Got 1 misfire on #5 and 1 on #1…. But that feels normal.
I’ll give it a couple of weeks and see if this is the new normal or if I end up back where I started.
I sincerely appreciate everyone’s input and help on this one.
Thread Starter
Senior Member
Joined: Apr 2013
Posts: 339
Likes: 66
1998 E300TD
Alright, i'm digging into the secondary air injection system and have a couple of questions. I turned the pump on via Xentry this morning and can hear it running, can't say I've ever noticed it before. I do not have any SAIS codes.
1. Should the air pump turn on in a KOEO scenario? I have a really loud exhaust so if it only runs for a few seconds after startup, I likely would not ever be able to have heard it.
2. How loud should it be? During the test it was quite audible from inside the car with the hood closed but the driver door open.
3. Does anyone know how to test the valves in Xentry? I only found the pump test.
As always, thanks for any guidance.
1. Should the air pump turn on in a KOEO scenario? I have a really loud exhaust so if it only runs for a few seconds after startup, I likely would not ever be able to have heard it.
2. How loud should it be? During the test it was quite audible from inside the car with the hood closed but the driver door open.
3. Does anyone know how to test the valves in Xentry? I only found the pump test.
As always, thanks for any guidance.
Thread Starter
Senior Member
Joined: Apr 2013
Posts: 339
Likes: 66
1998 E300TD
After drilling down into it, after replacing some hardware, this seems to be the issue. Best we can determine is that I had a failing o2 sensor or injector while we were doing the initial tuning. So when I updated to the ROW boxes, and updated my o2's...the tune was just throwing too much fuel during start up. Working through the tuning side right now with Barry.
Junior Member
Joined: Apr 2019
Posts: 63
Likes: 9
-
After drilling down into it, after replacing some hardware, this seems to be the issue. Best we can determine is that I had a failing o2 sensor or injector while we were doing the initial tuning. So when I updated to the ROW boxes, and updated my o2's...the tune was just throwing too much fuel during start up. Working through the tuning side right now with Barry.
Thread Starter
Senior Member
Joined: Apr 2013
Posts: 339
Likes: 66
1998 E300TD
I did! But it will be hard to pin down because I decided to pull the intake manifold and sand/paint/reseal/new throttle body plate while it was out....I didn't see any signs of cracks or leaks in my throttle body/intake but decided to do it all 'while it was in there'.
It could have been a combination of a bunch of small leaks that I addressed but I have only received one misfire code on start-up since then....and that was after sitting for a long time in really cold weather.
It could have been a combination of a bunch of small leaks that I addressed but I have only received one misfire code on start-up since then....and that was after sitting for a long time in really cold weather.
