Hello Group,o

New member here. Audi Quattro A4, misfiring on cyl 4 - code P0304. It did this about 4 months ago and I traced it down to a faulty ignition module, replaced it and all was well.

Yesterday it started again - P0304. Cleared the error and the misfire went away. Took a drive and all was fine until I turned on the A/C and instant misfire and set a code P0304. OK I thought maybe I have a weak coil, so I swapped coil 1 for coil 4. Cleared the code and went for a drive. All was fine, I then turned on the A/C and it misfired again. Set the same P0304 so it does not seem like a coil issue. It seems as though once load is applied, cyl 4 starts to misfire - and only cyl 4.

I'm a bit puzzled? Anyone have any thoughts or advice?

Thank you
Tom

 

change out the spark plugs?

 

Yes, changed out spark plugs, but still the same. If I clear the code it will run fine for a time and then start to misfire again. Sometimes after a few minutes and sometimes after a few days? This is driving me a little crazy. Anyone have any suggestions?

Tom

 

i had issues with missfires too, i changed coils and plugs costs almost 400 bucks... im pretty sure the stupid injectors are bad

 

cyl 4 could have a bad spark plug.

 

A4ROB,

See above. I changed all the plugs when this started happening.

Tom

 

It's very likely an electrical problem, so it's time to get out the multimeter and start digging around. I'd check the coil-pack harness and various grounding points first. The 1.8T coil-pack harnesses are notorious for cracking and causing a variety of electrical issues; obviously, misfires being high on the list.