W169 A170 misfire.

[Griffs]

Hi can anyone help with some fault codes. My W169 A170 has a misfire. I'm getting fault codes 007A-000, 007c-000 and 0079-000 the computer says that the codes are not recognized in the library, and I haven't been able to find much on the web. The car starts and runs OK for a short while and then starts to misfire on one or other of the cylinders. I have two computers. One is for the MB the other is a generic unit. It just says I have a misfire on one or other of the cylinders. Plugs are good and just changed. I'm waiting on a couple of coil packs and HT leads as it all seems to point toward something electrical. Just wondering if anyone has any other ideas?

 

[Dodipops]

HT leads are fairly common, you can normally look at smooth running counter in the diagnostic data, that would help narrow a cylinder down.

 

[Griffs]

The smooth running counter shows no 3 spark is fairly consistently down compared to the others. 1, 2, and 4 are all at 1.6ish and no 3 is 1.3ish. Hopefully the coils are available tomorrow and I'll give 'em a go.

 

[grober]

Might be worth a visual inspection of the plug/s

IGNITION SYSTEM MERCEDES A-KLASSE [Car] [CHASSIS] (EUROPA)

IGNITION SYSTEM MERCEDES A-KLASSE [Car] [CHASSIS] (EUROPA)

mercedes.7zap.com

 

[tonysmb]

How recently were the plugs changed and did the misfire start at the same time? They're not the easist of plugs to access, so are you happy that the connections of the leads to the plugs is sound.

 

[Griffs]

I've just renewed the plugs as a potential fix for the misfire problem. The old ones looked in great condition though no3 was a little sooty which I take for the missfire problem. It didn't cure the problem, but makes me think coils and / or HT leads might help.

 

[Bellow]

I've just renewed the plugs as a potential fix for the misfire problem. The old ones looked in great condition though no3 was a little sooty which I take for the missfire problem. It didn't cure the problem, but makes me think coils and / or HT leads might help.

HT related mis-fires are more likely to occur under load, If that's when they're happening then you probably have the cure in hand.

 

[Griffs]

New HT leads fitted along with new coil packs. This seems to fixed the problem. and the old girl is running sweet again. As usual it was a long job abs the car is frustratingly fiddley to work on. The old coils were looking quite corroded and there looked like some separation of the insulation due to this. Thanks everyone for your comments.