Misfire - Under hard acceleration

[cl55 amg]

Can anybody help, I have had a misfire issue for a while now. There is no problem when i drive normally, but if i put my foot down to acceleration quickly I get a misfire. If I pull over and restart the car the problem goes away, I have had the plugs changed and also the fuel line drained in case of any water.

What next?

Regards Danny

 

[AndyPCD]

does it misfire every time you accelerate hard if so it would be an idea to test it with a star plugged into it to check the actual values of the engine to see what is going on with it

 

[cl55 amg]

does it misfire every time you accelerate hard if so it would be an idea to test it with a star plugged into it to check the actual values of the engine to see what is going on with it

Yes virtually every time, I did have it on a star last month and they said it had (in the history log) misfired on cylinder 2 and 6. That's why they drained the fuel line as they suspected the water was moving around the line?

 

[startech]

i reckon that you have a fault with the air mass sensor i have seen this several times on the V engines but it definatley worth getting it on a star.

 

[cl55 amg]

i reckon that you have a fault with the air mass sensor i have seen this several times on the V engines but it definatley worth getting it on a star.

I am not very good with cars, would the MAF sensor only cause a misfire under hard acceleration and not normal driving?

 

[startech]

for sure. i did an ML320 today with the same fault as you are describing (misfire under hard accleration then when turned off and started misfire has gone) and it had stored faults with misfire on several cylinders.

 

[cl55 amg]

for sure. i did an ML320 today with the same fault as you are describing (misfire under hard accleration then when turned off and started misfire has gone) and it had stored faults with misfire on several cylinders.

Can these can be cleaned? is it worth trying that or should I replace. Also do you know where they are on the cl55 is it under the plastic cover?

Regards Danny

 

[AndyPCD]

Yes a MAF could cause this as under normal driving the flow of air through it is ok but when you give it a boot full the air flow increases dramatically and then goes out of spec as it is faulty causing the air fuel ratio to be incorrect and cause a misfire.

Because i bet if it went back on the star it will probably has misfire faults with different cylinders

 

[startech]

i dont think you will be able to clean it as i think it is an electrical fault with it. Yes they are under the plastic engine cover at the back

 

[tromppost]

It may be a faulty jet!! I had the same fault on my S320, Mercedes could not trace the cylinder on the star because it always showed more than one. But after lots of juggling around it turn out to be one of the jets.

 

[alexander patie]

i suggest ignition leads, quite common. as has been said the maf sensor is a possibility and will show in the self adaptation values, or with p017* codes. if the only codes were the p030* codes i would go with the leads.

 

[cl55 amg]

OK guys, are the MAF easy to change? and is there anything else I would need to replace at the same time?

Thanks Danny

 

[cl55 amg]

i suggest ignition leads, quite common. as has been said the maf sensor is a possibility and will show in the self adaptation values, or with p017* codes. if the only codes were the p030* codes i would go with the leads.

i can't remember the codes..as this would narrow it down?

 

[startech]

when you change the air mass it is worth getting the adaption data reset as this will make a huge difference to the car. But it will need to go on a star (or good equivelant) to do this

 

[cl55 amg]

when you change the air mass it is worth getting the adaption data reset as this will make a huge difference to the car. But it will need to go on a star (or good equivelant) to do this

sorry for sounding daft, but whats the adaption data? is this what makes the engine light come on?

 

[startech]

i will try and explain it. the engine constantly monitors and measures lots of data from various sensor on the engine the control module then interprets the data and adapts the fueling of the engine as necessary. so if you have a poor air mass the engine control module will adapt to run poorly. Hence resetting the adaption data when you replace the air mass. hope this explains

 

[cl55 amg]

i will try and explain it. the engine constantly monitors and measures lots of data from various sensor on the engine the control module then interprets the data and adapts the fueling of the engine as necessary. so if you have a poor air mass the engine control module will adapt to run poorly. Hence resetting the adaption data when you replace the air mass. hope this explains

Yes it does, thank you can you also explain how to remove the engine cover to get to the MAF sensor?

Regards

 

[stevesey]

Question:

Does the misfire occur at full load e.g full throttle at 2500rpm, or at high revs, but low load e.g 5000rpm at part throttle.

Typically a fault from a weak spark, or plug gaps too wide, will show at full load as there is far more mixture in the cylinders and it's more difficult for the spark to make it's way across the gap. At higher RPM coil/lead faults are more likely to show as the chance of the insulation breakdown and arcing increases if the sparks are more frequent.

Of course trying to test full throttle at 2500rpm )without the revs climbling rapidly to 5000rpm) in a cl55 automatic is interesting . Use the tiptronic to lock it into 5th and find a steep/fast hill perhaps.

 

[Sp!ke]

Me being somewhat old school, I immediately think plug leads when I experience this sort of problem under load.

 

[grober]

My money is on the HT side of things also. You will hardly notice a slight misfire on a big V8 until you put the foot down. A quick test for the Maff is to disconnect it altogether-the ECU will default to backup settings but should still drive reasonably well.