Cylinder 3 misfire

[Kimbo641]

I have a Mercedes cla180, 1.6 petrol 2013. Im having bad problems with a cylinder 3 misfire which keeps popping up on OBD. I’ve just today had the catalytic converter fully checked for any problems. I’ve had new spark plugs put in. I’ve had a new coil pack put in. The problem is still really bad. It’s misfiring a lot and very rough when idle and at rpm under 3000. I’m also getting a strong petrol smell which I’m assuming is running too rich hence the exhaust smelling rich on fuel. I’m being told to take it to Mercedes specialist and get it checked by them as can be something in the engine and to get a compression test done etc. I’m also being told to go to an electrician and get it checked out by them.
any advice on what I should actually do and anyone who’s had similar problem? Really need to get this sorted out

 

[Oleks1992]

I have a Mercedes cla180, 1.6 petrol 2013. Im having bad problems with a cylinder 3 misfire which keeps popping up on OBD. I’ve just today had the catalytic converter fully checked for any problems. I’ve had new spark plugs put in. I’ve had a new coil pack put in. The problem is still really bad. It’s misfiring a lot and very rough when idle and at rpm under 3000. I’m also getting a strong petrol smell which I’m assuming is running too rich hence the exhaust smelling rich on fuel. I’m being told to take it to Mercedes specialist and get it checked by them as can be something in the engine and to get a compression test done etc. I’m also being told to go to an electrician and get it checked out by them.
any advice on what I should actually do and anyone who’s had similar problem? Really need to get this sorted out

Any other fault codes? Also worth checking timing and compression of the engine as these are prone to timing chain and sprockets wear

 

[Kimbo641]

Any other fault codes? Also worth checking timing and compression of the engine as these are prone to timing chain and sprockets wear

No it just keeps coming up as cylinder 3 misfire

 

[Bellow]

If it was mine... I'd swap injector #3 with any of the others and see if the misfire shifts to the cylinder now with #3 injector. If not, compression test.

 

[Kimbo641]

If it was mine... I'd swap injector #3 with any of the others and see if the misfire shifts to the cylinder now with #3 injector. If not, compression test.

Thanks for that, I’ll try getting a compression test done now, is there any other way to check the injector rather than swapping them over?

I called my local Mercedes specialist and he was quite rude after I told him I’ve replaced the coil pack and spark plugs he told me to just “change or rebuild the engine” which I know is going to be very costly and maybe not worth it at all. I’m really attached to this car and just want to see it sorted

 

[Bellow]

Thanks for that, I’ll try getting a compression test done now, is there any other way to check the injector rather than swapping them over?

Not really - and I'm only suggesting that to rule out (or confirm) a leaking injector. You could go straight to compression testing and if nothing found there, revisit injectors. The sequence of events doesn't much matter.

 

[Kimbo641]

Not really - and I'm only suggesting that to rule out (or confirm) a leaking injector. You could go straight to compression testing and if nothing found there, revisit injectors. The sequence of events doesn't much matter.

With it being new years etc most garages are telling me I have to wait till next week just for compression test. The misfire is quite bad and rough at low rpm. Is it dangerous for me to drive at all or can I still use the car for shot distance journey (<5 miles)

 

[Bellow]

With it being new years etc most garages are telling me I have to wait till next week just for compression test. The misfire is quite bad and rough at low rpm. Is it dangerous for me to drive at all or can I still use the car for shot distance journey (<5 miles)

I can't answer that.
If it is leaking exhaust valve(s) on cyl #3 probably won't do too much damage (unless a valve drops - catastrophe!) but will be pushing unburned fuel towards the cat. As will a leaking injector (which will also wash oil off the bore and fuel into the oil). Unburned fuel does the cat no favours. Your call, but if you have access to another car - take it.

 

[Petrol Pete]

Take the plug out of number 3 and any other cyl and see if there is a visible difference in colour or if plug 3 is wet . If yes then swap injector 3 with any other and repeat.

If one injector is sticking/over fuelling the best case scenario is an oil washed bore leading to engine wear . the next worse is unburnt fuel destroying the cat , the very worst is the injector jams open and hydraulic lock occurs in cyl 3 destroying the engine. Possibly sending your car to the scrapyard.

Your call.

 

[Kimbo641]

Take the plug out of number 3 and any other cyl and see if there is a visible difference in colour or if plug 3 is wet . If yes then swap injector 3 with any other and repeat.

If one injector is sticking/over fuelling the best case scenario is an oil washed bore leading to engine wear . the next worse is unburnt fuel destroying the cat , the very worst is the injector jams open and hydraulic lock occurs in cyl 3 destroying the engine. Possibly sending your car to the scrapyard.

Your call.

So what would you suggest I do? Also, note I had a minor oil leak which is still not repaired as the mechanic “couldn’t” find the leak

 

[zipdip]

Well a compression test is a must,is it dangerous to run well no but unburnt fiel straight down the exhaust is not going to do the car any good,

 

[Petrol Pete]

So what would you suggest I do? Also, note I had a minor oil leak which is still not repaired as the mechanic “couldn’t” find the leak

? Do what I suggested in post #9 and maybe find a better mechanic.

 

[Kimbo641]

? Do what I suggested in post #9 and maybe find a better mechanic.

Thank you

 

[Bellow]

Take the plug out of number 3 and any other cyl and see if there is a visible difference in colour or if plug 3 is wet . If yes then swap injector 3 with any other and repeat.

Good call re reading the plugs.
Is this a direct injection engine? If so, my earlier comment re swapping injectors is less compelling given the extra difficulty of direct injectors.

If one injector is sticking/over fuelling the best case scenario is an oil washed bore leading to engine wear . the next worse is unburnt fuel destroying the cat ,

All true - but I suspect that the cat may have already suffered...

the very worst is the injector jams open and hydraulic lock occurs in cyl 3 destroying the engine. Possibly sending your car to the scrapyard.

I can't see a scenario where the fuel can be present in sufficient quantity for a hydraulic lock. The engine would have to be stationary (for sufficient cylinder 'fill time' )and then fuel would be denied.
All of the above pertains to injectors. If, it is a burned exhaust valve, I'd fear its further disintegration and catastrophic failure (dropped valve) which absolutely will cause considerable damage.

 

[Bellow]

I can't see a scenario where the fuel can be present in sufficient quantity for a hydraulic lock.

Unless it is a PFI system - with an accumulator...

 

[Bayleaf]

I have a Mercedes cla180, 1.6 petrol 2013. Im having bad problems with a cylinder 3 misfire which keeps popping up on OBD. I’ve just today had the catalytic converter fully checked for any problems. I’ve had new spark plugs put in. I’ve had a new coil pack put in. The problem is still really bad. It’s misfiring a lot and very rough when idle and at rpm under 3000. I’m also getting a strong petrol smell which I’m assuming is running too rich hence the exhaust smelling rich on fuel. I’m being told to take it to Mercedes specialist and get it checked by them as can be something in the engine and to get a compression test done etc. I’m also being told to go to an electrician and get it checked out by them.
any advice on what I should actually do and anyone who’s had similar problem? Really need to get this sorted out

Ok. New plugs /coil pack Does the coil pack come with the plug leads, if so disregard the rest of this post. The strong petrol smell could be due to a plug not firing e.g. bad lead, resulting in a miss fire and unburnt fuel going into the exhaust.
Just a thought.