cherbert

I don't have a Bentley and I'd like to check my injector on time to try and troubleshoot my <a href="https://forums.audiworld.com/a8/msgs/104905.phtml">misfire/rough running problem.</a> What measuring blocks do I need to watch for that?

Rocky-in-Connecticut

measuring block 32 for fuel trim.

field 1 is idle. Field 2 is part throttle. If any field is more than 10% it is out of spec. Idle out of spec look for vacuum line leaks esp at combi valve and fuel pressure regulator. Breather lines can also split open. Field 2 out of spec would probably be a MAF.

cherbert

<img src="http://myweb.cableone.net/jerk/a8/measblocks2.jpg">

MP4.2+6.0

I'm new to your posts, but looking them over and all the things it looks like you tried, I would be:

o replacing MAF. It's $135ish for the refurbished one at ecstuning. It's a new sensor, just re using the air tube. These are a trouble spot on Audi's, and if you are up at over 100K miles I would replace. It was a service action on A6 4.2's, which confirmed to me they weren't so hot, and Audi made the running change to Hitachi from Bosch later on. My first one crapped out at 40K miles.

o replacing all the vacuum line. It's not clear if you have, but for $15 and half an hour it's done once and for all. Some places are obvious, but when I finally pulled all of it on my 2000 4.2, I found entire sections that had pretty much rotted away and the braiding was about all the structural support that was left. Shouldn't cause a miss, but will cause some engine roughness.

If you had the later A8 with the $28 coil packs, I would probably just change them all at some point given how deep into this you already sound to be, but I guess you have the older $60 variety where that is a really big investment. Still, consider buying one as a tester for a known good one. At $28, I just bought one as a spare part on a 2000 4.2. I lost two early on, but haven't lost any since. Looking at the ecs site, I notice on A8's they sell the connectors for the coil packs too. I haven't seen that before, but I'm wondering if that's a clue the older ones have connector issues. More generally, I would definitely go over all underhood ignition and fuel related connectors, checking each one for general integrity, and physical damage, etc, and unplug and replug it carefully to break up any light corrosion--everything, including O2, positioning and oil and water sensors, all the ingition connector points, the big ECU connector at the control box, etc. Finally I suppose consider outlier things like a bad knock sensor or crankshaft position sensor (if these cars have that; I'm not sure) that could be throwing your whole engine into a timing tizzy.