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Misfires on all cylinders

Tiny
DIVIDES
  • MEMBER
  • 2008 MERCEDES BENZ CLS63
  • V8
  • 2WD
  • AUTOMATIC
  • 120,000 MILES
This is actually a cl63 but I didn't see an option for it, its an AMG 6.3l. I bought it non runner even though it starts and barely drives. When I scanned it it came with misfires on all cylinders, has oil and coolant, does not overheat if left running, but I can only drive it short distance as in getting in and out of garage and it stalls a lot. Hardly any response to the throttle, if I pump it a bit I can get it to rev. But check engine light is flashing. Where would you start on something like this?
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Monday, June 7th, 2021 AT 4:57 PM

41 Replies

Tiny
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I am leaning towards a clogged up/blocked catalytic, especially if it's an aftermarket. I have not checked whether it is yet. Or maybe a fuel delivery issue or a bad ECU, no way that all 8 misfire even if the motor has a head gasket or is bad.
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Monday, June 7th, 2021 AT 5:50 PM
Tiny
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You are correct. That if all cylinders are missing then it is something that affects all cylinders. This would be air or fuel.

So I would start with checking fuel pressure and make sure it is okay.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

If the fuel pressure is ok then we need to check for exhaust restrictions like you are suspecting. To do this, I would just remove the up stream o2 sensors and see if the throttle responds better. If it does then the converters are backed up.

If it does not then we could still have an issue with the torque converter. Does the engine rev normally in park or neutral? In other words do you only get this misfire or poor throttle response when in gear?

Lastly, do you only have the misfire codes or do you have others?

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Thanks
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Wednesday, June 9th, 2021 AT 11:17 AM
Tiny
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Once I hit the pedal several times I can get it to rev, still misfiring. That is in park as well, so the misfire throttle is in park or in gear.
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Wednesday, June 9th, 2021 AT 11:36 AM
Tiny
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How much fuel pressure should there be when off and when running? Also checked battery and is good and alternator charging.
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Wednesday, June 9th, 2021 AT 11:37 AM
Tiny
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Just to confirm because it is critical, you have the 6.3L? If so, then max PSI is 90 but operating PSI will be lower. However, do you have any codes for fuel pressure too high or low?
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Wednesday, June 9th, 2021 AT 8:01 PM
Tiny
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No codes other than misfires, have not done a thorough scan but I will. Yes the 6.3.
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Wednesday, June 9th, 2021 AT 8:23 PM
Tiny
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I think we have an electrical issue. I changed 4 coils, then cleared it, and started it, still misfiring but gave me a misfire for another cylinder. This car has so much wires/amps in the trunk that was left in it, they only removed the speaker box they had in it, must be expensive stuff. I have never seen anything like this before.
Anyways, there is an additional battery in the trunk with all the amps and wires. Unless I am mistaken this battery has nothing to do with the car itself. So I disconnected the negative battery just in case it has an effect.

Reason I suspect an electrical issue is because the cluster and lights and the whole car just goes off on its own, even before disconnecting the rear battery. While I am scanning it it does that. Once I turn the ignition off and then remove it and reinsert it it comes back to life, and there is flickering a lot.I measured the battery which is not an AGM under the hood and its 12.20. While running around 14. Very strange.I will send you pictures, and videos
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Thursday, June 10th, 2021 AT 11:06 AM
Tiny
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Attached.
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Thursday, June 10th, 2021 AT 11:07 AM
Tiny
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Measured the rear battery and it's 10.95, am trickle charging it. I also realized this is the second battery as well which runs the electronics so it must be connected.
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Thursday, June 10th, 2021 AT 11:48 AM
Tiny
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Just to take a step back. I should have asked for a video before because that is not just a misfire. When you are revving the engine it sounds like it is knocking pretty bad. It could be just dead cylinders but have you checked compression on this engine?

https://www.2carpros.com/articles/how-to-test-engine-compression

Either way, it sounds like this has some serious issues so before we dig further into the other issues, I would suggest confirming the base engine is okay.
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Thursday, June 10th, 2021 AT 7:39 PM
Tiny
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Misfires on these engines always sound like a knock, I have owned several Benz v8s, but once you rev it high enough to be solid there is none of that. But these cars are so sensitive to voltage I know that, also the misfire went away on most except 5 for now, am waiting on the battery to be fully charged before I start it again. No I have not measured the compression yet, I cannot even turn it on without starting it enough to measure a compression cause of the electrical issue.
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Thursday, June 10th, 2021 AT 7:58 PM
Tiny
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A lot of that is also a backfire from cylinders that are not igniting right.
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Thursday, June 10th, 2021 AT 7:59 PM
Tiny
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Where is the fuel pump fuse on this car? I also found while diffing a code p0336 for crank position sensor. Where is it on this engine so I can see if there are any broken wires?
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Friday, June 11th, 2021 AT 8:28 AM
Tiny
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Lights stopped flickering since I charged the rear battery.
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Friday, June 11th, 2021 AT 8:30 AM
Tiny
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Also, after I turn it over and starts for few second I try my best to keep it running but there is barely any throttle response. After it shuts off am hearing a hissing sound from bank 2. Regardless of how good the motor is why would I not get any throttle response.
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Friday, June 11th, 2021 AT 8:36 AM
Tiny
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Also I hear hissing after I turn it off on bank 2.
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Friday, June 11th, 2021 AT 1:31 PM
Tiny
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Let's monitor the cooling system pressure or put 15 PSI to it because that would be the only thing that would pressure bleed noise only after the engine was running. Does it stop or appear to slow down and stop? Does it stop if you turn the ignition on or start the engine again?

https://www.2carpros.com/articles/radiator-pressure-test

As for the throttle input that is most likely due to the ECM shutting it down due to this extremely poor running. Basically it doesn't want you to damage the engine so it shuts that down.
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Friday, June 11th, 2021 AT 2:47 PM
Tiny
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I want to do a compression test on 2 cylinders on bank 2, do you know where the fuel relay is? Or fuse? I will remove two spark plugs and measure both cylinders or 4, I don't need to remove all do i? And dry I guess. Also, keep the gas to the floor when doing that? And what is the range if PSI I should look for?
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Sunday, June 13th, 2021 AT 6:56 PM
Tiny
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Pictures of some of the plugs, and the top of cylinders. Can't find the fuel relay to remove and do a compression test.
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Sunday, June 13th, 2021 AT 8:07 PM
Tiny
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It may just be the flash but some look okay. However, others appear to be very carbon fouled. That means there is too much fuel going through the engine. Either due to misfire or leaking injectors. Based on this we need to check the fuel pressure and see how long it holds after the key is shut off. Basically how long does it take to bleed down.

Also, to do the compression test, you are going to have to use the relay control module in the trunk because you don't have a traditional relay. If you just unplug this module then the pump won't run. Or you can do the clear flood method as you stated where you hold the pedal to the floor and crank the engine but this is best with two people. I attached the process from the manual to do this test.

Plus here is a guide that will help as well:

https://www.2carpros.com/articles/how-to-test-engine-compression
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Monday, June 14th, 2021 AT 6:35 AM

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