One day my 99 C280 was riding fine the next day it has a Check Engine light and running ruff.

Ran a scan and got a P0305 misfire on cylinder 5. I replaced the plugs and it was running great for one day and the check engine poped up again and the same code P0305

I then change the Ignition Coil and nochange, shouldI replace the plugs again? maybe a bad coil will damage the plugs?

Ihave not change the cable yet or could it be the injectors?

Please help me any testing I can try...

 

Hi,

So did the removed plugs look worn? Replaced with OE spec plugs?
Were the plugs an unusual colour etc.

No need to buy new parts.
Simply move parts from lets say Cyl 5 to Cyl 1 (one part at a time) and observe if the misfire stays with the original cylinder or moves.

Any other codes set?

Could be ign (plugs, leads, coil) or fuel (injector, wiring damage) or something more serious like piston / valve damage which can be checked out with a cylinder compression test.

Using any coolant?
Using any oil?

Just a gut feel and since you have already changed the plugs I go for Fuel.
Checked fuel rail pressure?

Could you have contaminated fuel (water) with Cyl 5 being the worst affected due to its position on the fuel rail?

Good kluck.

 

Yes I replace all 12 plugs and the looked fine and 1 coil and rotated the coil from cyl 5 to cyl 1 and the code stayed the same.

Is cylinder 5the last cylinder on the fuel rail? Front right side of engine is that correct?
or is ont left side where the airfilter is located?

 

Did you clear/reset the code and are advising that it came back with the same code despite changing the coil, and lead?
.... or are you saying that the code didn't disappear when you changed the plug / coil?

 

Sorry I was away for the holidays.

Yes I cleared the code and after3-5 min. the code pops up...

It could be a fuel problem because the car runs greatonce you get going over 20 mph.

I added stuff to the fuel to try to clean the fuel system.

Sould I change the fuel filter and have a pro-fuel injection cleaning?

 

Hi,
Since you have changed the plugs and also replaced coil 5 it would appear to be fuel.

You should however swap plug lead 5 with a similar length one from elsewhere. Don';t pull on the leads. This damages them. Use an open ended spanner to gently prize the spark plug connectors off.

Does the same code reappear yet again after clearing.

If so do the same swap out routine (don't waste money on new parts till you are sure what the issue is) but change injector 5 for one of the others.

What you are trying to establish is how to move the problem.

If a swap of components doesn't work then that increases the chances that you have a cylinder problem which requires a compression test or possibly a fuel rail pressure issue but this last one is less likely,.

Fuel filters get changed all the time when they are not at fault.
Since they are relatively cheap and once you have established that you can't move the problem to another cylinder it won't do any harm. The filter includes a pressure relief valve in it which could be the cause of low rail pressure.

Come back once you have exhausted these ideas.

 

having same issue with same cylinder on a 2005 c240,.