audibmw17

Hello,
I have a b7 a4 that is running like its misfiring. I am getting no misfire codes and have replaced the coils and plugs. Its throwing 00768 (rear heater core temp sensor (G154)) and 00771 (Fuel level sensor (G)). I can't imagine heater core and fuel level sensors to cause crazy misfiring and shaking. Any ideas?
thanks!

audibmw17

the engine light is flashing too.

hedman09

Generally when engine light flashes, then Its Misfiring now, If you have access to a scanner that can view misfire monitiors then you see what cylinder(s) are missing. and go from there
i cant see those code causing that problem but you never know

audibmw17

Yeah I'm pretty sure its number 3 but im not getting any misfire codes at all which is odd.

hedman09

i get all types of cars in at work that misfire and don't throw codes. but if you can see the misses count up on the scan tool on which ones. if its a dead misfire meaning it misses all the time and not under certain conditions you can do a power balance test.- while the engine is running you can unplug each coil one at a time and try to notice which cylinders are active. meaning if you unplug the coil and it sarts to run worse then its not that one misfiring, plug that one back in and move to the next coil and repeat. when you unplug one coil and the engine does not change in response to loosing spark via unplugging the coil then you have now isolated the cylinder that is missing. then again it has to be a dead misfire to be able to diagnose this way.
Hope this helps

audibmw17

Thanks for you help and I did do this and thats how I managed to narrow it down to 3. When I put the new plugs and coils in it changed nothing which has me thinking maybe carbon build up or injectors?

hedman09

Got it, i see yeah these engines are know for both, but lots of issues with carbon build up, but most the ones i have seen come in with a miss on cold starts for carbon build up and then goes away after shortly starting and running.
An injector i could see being dead, but either way the intake has to be removed so you might as well do both injector on #3 and decarbonize the vales, i just put together a Harbor freight media blasting set up for around 170 to walnut blast the intake ports. ive manually cleaned them before at work, but at home ive got the walnut blaster now, need to get mine running and I'm going to test it out.

audibmw17

Great ill give it a try, thanks!

audibmw17

So I just ran my generic scanner on it to see if it would be any different. The only code it was throwing was a misfire in 3 code. Very odd that this would pick it up but not my vgate scanner?

hedman09

that's scan tools for you lol, any time a vw or audi comes in i at work use vcds, cuz if i use our snap on verus edge ( our newest scanner) sometimes i get diff codes than vcds will pull. if you are dead sure its only #3 ( try putting #3 plug on #1 and #3 coil on #2 and vise versa) i know you said they are all new but ive had bad coils and plugs out of the box. then i would do a compression check one #3 just to verify good internal engine components, if so prolly an injector issue