Newbie
Hey, I am having a problem when I accelerate at high RPMs. Around 4-5,000 RPMs, my CEL blinks for around 5-7 seconds, but usually goes away soon after letting off the gas. However, sometimes it will stay illuminated. The code I get is P0301. I just bought the car last week so I don't know if this was a problem in the past, but the CEL does not come on at an idle or lower RPMs (2-3,000). I am bringing it to the shop to get a new flex pipe put on because it broke where it connects to the outgoing exhaust pipe. I've read that sometimes an exhaust leak can cause misfires, so this will rule that out. I'm also going to switch coil pack #1 with #2,3, or 4 to see if the problem moves with the coil pack to a different cylinder. If the OBDII reader still indicates the misfire is from cylinder #1, what would be the next step for diagnosis?
Super Member
exactly what car do you drive? or are you talking about? we need year and model!
Quote:
I'll bet my left nut it moves with the coil pack. That coil pack is bad. Trust me, I went through a lot of troubleshooting. The coils are 2 phase after 3500 rpm or so. Meaning they won't misfire at idle like other vehicles. Only when under load. Let me know if that fixes it... But I'm 100% sure it will.Originally Posted by Tom Canino
Hey, I am having a problem when I accelerate at high RPMs. Around 4-5,000 RPMs, my CEL blinks for around 5-7 seconds, but usually goes away soon after letting off the gas. However, sometimes it will stay illuminated. The code I get is P0301. I just bought the car last week so I don't know if this was a problem in the past, but the CEL does not come on at an idle or lower RPMs (2-3,000). I am bringing it to the shop to get a new flex pipe put on because it broke where it connects to the outgoing exhaust pipe. I've read that sometimes an exhaust leak can cause misfires, so this will rule that out. I'm also going to switch coil pack #1 with #2,3, or 4 to see if the problem moves with the coil pack to a different cylinder. If the OBDII reader still indicates the misfire is from cylinder #1, what would be the next step for diagnosis?
Super Member
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That is possible, but i would't be so sure. a bunch of issues cause a missfire on high load. Also a blinking CEL? i've never seen that in a merc. something weird is going on and i have a feeling that its not a merc..Originally Posted by Danny06191
I'll bet my left nut it moves with the coil pack. That coil pack is bad. Trust me, I went through a lot of troubleshooting. The coils are 2 phase after 3500 rpm or so. Meaning they won't misfire at idle like other vehicles. Only when under load. Let me know if that fixes it... But I'm 100% sure it will.
MBworld Guru
Blinking MIL is usually a pressure issue in the fuel tank (often due to a loose gas cap).
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The blinking is notifying you that the issue is happening at that very moment, causing direct problems with combustion. (Misfiring is known to blink) Originally Posted by DanielFD
That is possible, but i would't be so sure. a bunch of issues cause a missfire on high load. Also a blinking CEL? i've never seen that in a merc. something weird is going on and i have a feeling that its not a merc..
The fact that his misfire is isolated to one cylinder, means it is most likely nothing more broad, such as fuel related issues.... or else he would be throwing more codes.
Tom Canino - Did you swap the coil pack? I know that is the issue. Positive.
Super Member
Thats weird, I've seen so many MB's misfire but never seen a blinking MIL. well you always learn something new.
Newbie
Always always look at your plugs first if doesn't smooth out in gear under a load while stopped (brake loading). If it smooths out somewhat thats a sticky injector. Use seafoam at half a tank.
If it doesn't smooth out, pull that plug and read it (brown-normal, white-lean, black-gas fouled). Should it be black, then read the coil (wells test sheet). If the coil checks out then read the connection from the harness.
With as many electrical connections under the hood as there are these days, always check the basics first. Then start looking at connections for loose fit or corrosion.
If it doesn't smooth out, pull that plug and read it (brown-normal, white-lean, black-gas fouled). Should it be black, then read the coil (wells test sheet). If the coil checks out then read the connection from the harness.
With as many electrical connections under the hood as there are these days, always check the basics first. Then start looking at connections for loose fit or corrosion.
Newbie
Quote:
The pump was bad. But I still had my misfire codes.
="5"%="4"%The REAL FIX was determined later that week.
="6"%COIL PACKS
I really had nothing else it could have been after replacing a lot of **** (that needed to be done anyway).
I pulled all 8 coil packs off and replaced them with 8 new coil packs a friend had laying around.
Upon further inspecting my old ones, I found that 6 of them had cracks in them. Similar to what benzing had said earlier in this thread, the coil packs are 2 phase after 4000RPM. The swapping coil packs with other coil packs method was useless because most of them were cracked. Also, even though it is telling you certain cylinders. I wouldnt trust it entirely. It seems to me that in some cases the ECU will throw random cylinders, and sometimes not correct, or not all effected cylinders.
Anyway... I'll bet my left nut, if you replace all the coil packs, your misfire will go away. If you wanna explain the situation a little bit better, you can email me kreck.daniel@gmail.com
Good luck!
Originally Posted by Danny06191
Yes I did fix my issue. The last update I posted on this thread said that I had replaced the fuel pump and sender and that I would get back to the thread with results. Sorry, I forgot!The pump was bad. But I still had my misfire codes.
="5"%="4"%The REAL FIX was determined later that week.
="6"%COIL PACKS
I really had nothing else it could have been after replacing a lot of **** (that needed to be done anyway).
I pulled all 8 coil packs off and replaced them with 8 new coil packs a friend had laying around.
Upon further inspecting my old ones, I found that 6 of them had cracks in them. Similar to what benzing had said earlier in this thread, the coil packs are 2 phase after 4000RPM. The swapping coil packs with other coil packs method was useless because most of them were cracked. Also, even though it is telling you certain cylinders. I wouldnt trust it entirely. It seems to me that in some cases the ECU will throw random cylinders, and sometimes not correct, or not all effected cylinders.
Anyway... I'll bet my left nut, if you replace all the coil packs, your misfire will go away. If you wanna explain the situation a little bit better, you can email me kreck.daniel@gmail.com
Good luck!
THIS!!!!!!!!!!!
4.5 years later, this should still be the accepted answer!
One mechanic "recommended" changing all 4 spark plugs and all 4 coil packs..$850. I went to another Euro auto shop...changed all 4 spark plugs and the one coil pack that was defective ($354) = problem solved.
Newbie
For any one else googling this problem (and saw this thread) I am in the same boat with my CLK55 - various and random cylinder misfire codes AT HIGH LOAD AND RPM (will not replicate if parked and revving).
It started after my plugs were changed out, I also replaced the crankcase breather hoses (cracked) and also added some fuel system cleaner as well as cleaned the MAF sensor.
It also started as Cyl5 misfire, but I swapped out the coils (not wires) for 5 and 6 - however the issue remained at 5 again. After more tests I was able to get a random misfire code.
What I DID notice that it was becoming harder and harder to replicate the issue after each CEL reset. I would have to apply more throttle and load every time to recreate it.
I am going to run through this tank of gas and report back. I wonder if the fuel system cleaner I put in had something to do with it.
It started after my plugs were changed out, I also replaced the crankcase breather hoses (cracked) and also added some fuel system cleaner as well as cleaned the MAF sensor.
It also started as Cyl5 misfire, but I swapped out the coils (not wires) for 5 and 6 - however the issue remained at 5 again. After more tests I was able to get a random misfire code.
What I DID notice that it was becoming harder and harder to replicate the issue after each CEL reset. I would have to apply more throttle and load every time to recreate it.
I am going to run through this tank of gas and report back. I wonder if the fuel system cleaner I put in had something to do with it.
Newbie
So I replaced the MAF, no change.
I pulled the sparkplugs (bosch) out of the offending cylinders and discovered INSULATOR break down - I can see the electrical path on the outside of the plug where it has burned a hole though the insulatior. WIERD.
Replaced all plugs (NGK now) and it runs like a watch.
I pulled the sparkplugs (bosch) out of the offending cylinders and discovered INSULATOR break down - I can see the electrical path on the outside of the plug where it has burned a hole though the insulatior. WIERD.
Replaced all plugs (NGK now) and it runs like a watch.
