HIS4

Well, the story is I replaced my spark plugs with new Bosch Platins (I was already running the same plugs for 40k prior to this). After I replaced the plugs I noticed that I wasn't getting full boost. My car usually peaks at about 17-18 psi and holds it there. Now I'm getting about 13 psi upon going WOT and then it slowly builds to 15 psi.

To me it seems like a simple boost leak somewhere but I did some logging to see if it could be anything else. First I checked for misfires to see if maybe one of the plugs were bad. No misfires at all. So then I logged Boost, timing, MAF, and O2 voltage (I've been getting intermittent CELs with "warm up catalyst" code).

Here are the charts:

<img src="http://home.hawaii.rr.com/his4/Boost_log_073107.jpg">

<img src="http://home.hawaii.rr.com/his4/Timing_log_073107.jpg">

<img src="http://home.hawaii.rr.com/his4/MAF_log_073107.jpg">

<img src="http://home.hawaii.rr.com/his4/O2_log_073107.jpg">

For the O2 logs I wasn't sure which sensor was which since they are not labeled in the log file but that's the order which they were arranged in the .csv file.

I haven't done a pressure test yet but that was my next step. Does anyone see anything other than a simple boost leak somewhere? BTW, these are all third gear runs.

berTTos@pjK04

Did you disconnect your battery while replacing plugs? Maybe your ECU lost learned values?

HIS4

I discovered that my TBB was torn so I replaced that. Before replacing the TBB I wasn't getting more than 12 psi so it has gotten better but not to where it was before. This is why I suspect it's just another boost leak somewhere.

If it was because of the battery, I would think the car should have recovered by now. I also changed the battery last week but shouldn't play a part in this either.

berTTos@pjK04

gotta be a boost leak

Audeye A6

agreed, there are two sets of pipes right where you did the plugs that may now have a loose clamp.

P. Bauer

those aren't under boost though...

808Guy

Kidding. Did you try clearing codes or maybe pulling the ECU. Worth a shot.

HIS4

Not right away but it comes back after a few weeks. I don't believe the CEL and the low boost issue are related. I think replacing the secondary O2 sensors will probably solve the CEL problem. I just have to get under the car and see how easy it is to get to them to see if I can actually do it myself.

In all honesty, if it does come to the point of blown turbos, I'll probably be looking at another car. Maybe a new S4 or a BMW 535i.