Talon Werner

Recently decided to clean my valves and fuel injectors because I was experiencing a misfire on cold starts. Got everything cleaned up and thought I did a pretty good job, (used a zip-tie brush, some dental picks, and finished with walnut shells from a media blaster) but when I put everything back together and tried starting her up the misfire was way worse. It almost sounds like the timing is off it's so bad. I can't think of what could cause the problem though, everything is back together exactly how it was, all electrical connections are made and all mechanical parts are back in place. I replaced the O-rings and spacers on the injectors but kept the old gaskets on the intake and throttle as they had recently been replaced when the water pump was replaced about 5,000 miles ago. Any ideas?

habbyguy

Did you replace the plugs after the cleaning? I'm thinking that one or more of the plugs might have been fouled by some of the debris you liberated during the cleaning process.

Talon Werner

Haven't tried it yet, I'll give that a go after work today

Talon Werner

So I pulled the plugs to check them out, the one in cylinder two looked a little worse for wear and the coil pack was in much worse condition than the other 3. I also ran a compression test and cylinder 2 was at 120 while the others were at 180. I remembered while doing this that there was a screw on the manifold that looked like it had been mounted in helicoil and I think that it had stripped or pulled out because I couldn't get the screw to tighten at all. I forgot about this after taking a break and finished the job, but is it possible for that loose screw to be allowing that much of a vacuum leak through the gasket?

habbyguy

I'd definitely replace that plug - and probably get a replacement coil while I was at it / in the area. FWIW, I'm a big fan of using OEM used coils, since they will normally outlast the rest of the vehicle, and you know it's going to work right.

Low compression isn't a good thing. I'm thinking that it could possibly have something to do with that cylinder not firing, which might cause the unburnt gas to wash the lube off the cylinder.

I doubt that any loose screws would affect compression (don't think Audi designed any screws that enter the combustion chamber). Could potentially cause a vacuum leak - I'd suggest slathering it in blue (semi-permanent) Locktite and re-installing it, just to be safe.