[Oaktown 986]

Originally Posted by ARModen

I believe people are directing you to the intake/maf based on the O2 sensor errors. These are more likely caused by the misfires. Gas that's not completely burnt in the cylinders when they misfire ends up partially burning in the exhaust manifold. This gives the O2 errors and can lead to cat failure.

I think the misfires can either be caused by incorrect timing, or an electrical/computer issue. If it was a timing chain issue, you'd probably just have errors on one bank. If it was an IMS failure (both chains) you'd hear your valves high fiving your pistons. So probably electrical/computer related. Of course that's 90% of the car!

For fuel, I'd check and make sure you have pressure at the test connection when the car is cranking. A pressure tester at autozone is only about $20. It connects to a test connection on the passenger side fuel rail. You can position it so it's visible from the drivers seat while you're cranking the car over. You can rent a set of "noid lights" for free ($20 deposit again autozone) and check the fuel injectors at the same time in almost the same location.

Electrical problems usually have lots of symptoms in cars that are so dependent on electronics. Have you had issues with any of the following not working: alarm, remote, windows, top, radio, lights? Dirty battery terminals or a failing ignition switch can cause your problem, but usually come with a dozen other issues.

Computer issues can be checked with a durametrics or shop tester. If you're able to read codes with a regular OBD2 scanner then the DME is probably working. It may still be the cause of the problem if it's getting bad inputs. A bad MAF should cause it to run like crap, but shouldn't throw off the timing because it affects fuel/air ratio not timing. Failed cam/crank sensors are more likely to cause misfires because they are timing inputs.

Your input is quite useful and well thought out, and highly appreciated. I've been using a standard OBDII sensor, and my O2 codes have been active for a couple months (I don't drive it all that much, figured I could let it slide until winter). WIth that in mind, I will also get the pressure tester and start there; these $20 testing solutions are great to isolate this, and the tools will be forever saved for use with future vehicles (my audi is a troublemaker even though it's only 3 years old).

All the electronics on the car have been in perfect working order; however the battery did recently die after I was gone in South America for 3 weeks. Perhaps something is bad in the charging system?

Jon