You will not find much on dealing with fuel trim. It will tell you what it means and such, but it takes time with it for long periods to learn it.

I have even pefected my methods, and discovered (or invented) whats called proving trim. If the trim shows addl air, I will chock off some air, AND add addl fuel with ether and be sure the trim flips to an opposite (positive or negative) state. This to me proves the state of the trim, long and short term, so I can properly duduct a lean or rich condition.

In other words, too much air is the same as not enough fuel. And this is what I cant explain when it comes to "reading" trim. I can only do it.

Once trim is evaluated, 50-75% of causes can be ruled out.

It is something I can not convey via the web. But I could teach someone who is with myself and the car.

First thing I would do if it were a customer in my shop is my own proper valve adjustment, leakdown, and compression. With no CEL, I'd go right for engine health. These are it.

I'm not sure what you mean about making them "one tighter", but if you are tighter than .008 intake or .010 exhaust you are asking for trouble. Thats how valves burn.

Yes it is only .001, but everything has a limit and you are beyond it. Do it right. No tight VA will hide a problem that a normal VA caused.

 

Another simple and logical explanation is a bad cat converter.

 

Did I mention somewhere that I made them 'one tighter'? If so, mustve been a misunderstanding. I meant that my valves were still in spec, but more towards the loose side, so I tightened them .001 to the tighter side to see if the looser spec valves may have been causing either a noise or other symptom that I was experiencing.

 

Possibility...

I tried to remove the primary o2 sensor for my lunchbreak today but wasnt able to break the seal on the sensor. I unplugged the connector and cranked the car, immediately pulled a CEL, but car seemed to actually be running better even though I didn't get to take it out for a drive. Does the actual sensor need to be pulled to test for a bad cat or will it still be effective if I just unplugged the connector?

If I need to remove the sensor, any ideas on how to break the seal on it? I hooked a 12" crescent to it today and went to beating with a hammer to no avail..

 

Sorry to hijack the thread a little here....

In the Porsche Club of America newsletter in my region (no, I don't own one, but I go to their racing events) there was an article by a mechanic about a Porsche not running well, low on power and fuel economy. It stressed the importance of getting a good history from the owner as they know how their car normally runs. The car had not thrown a CEL.

The mechanic watched the primary O2 sensor on a scope and found it to be "lazy" in it's transitions. He further tested it with snap-throttle and adding ether to confirm it. Sort of like what you stated Billman. He replaced it and it fixed the drivability issue. His position is that the primary O2 sensor can become lazy and and not react quick enough long before it will throw a code. And therefore, he suggests treating it as a maintenance item and replace them every 100,000mi.

Interestingly, in last months issue of Motor Age, and this months issue of Motor magazine are articles on O2 sensors describing the same types of issues. (for those of you who don't know, these mags are industry trade mags that many shops get. They are very, very informative and educational).

So, given that, I just purchased a new primary O2 sensor to replace mine with 160,000 miles.

 

To the OP.....even better than flying Billman to see you, take a road trip to New York, spend a few days there on vacation, and have Billman work on your car!

 

OP, I don't think you can use the primary O2 sensor to tell you anything about the cat. The secondary sensor can tell you things indirectly about the cat, but I don't think that's what Billman was referring to.

I think he meant a "bad" cat can start to clog or break apart inside, therefore increasing back pressure and causing poor drivability. (I don't think it's cause the vibrations you're getting though).

The S has a known issue with cats internals breaking apart. When they do, it'll damage the tip of the secondary O2 sensor. If you pull the secondary sensor and you see the tip dented at all, then the cat is starting to come apart.

To remove a frozen O2 sensor (frozen bolts are common anywhere in the exhaust system), first squirt some WD40 (there is another penetrating oil that mechanic swear by, can't remember the name..Billman chime in), and let soak half hour or so. Use a box end wrench or a six point socket (to get more leverage and avoid stripping), along with a breaker bar or rubber mallet.

When you put it back on, be sure to use a small amount of anti-sieze compound.

 

thanks for the info.

 

Would love to but just don't have the time right now. I'd also hate to get up there and him diagnose a problem that I can't afford. I'd be stuck in NY with a broken car that I'm too broke to fix. lol

 

Thanks for the tips. Someone previously posted in this thread that if I remove the o2 sensor pre cat and go for a test spin, id know if my cat was bad if the car ran fine with the primary o2 sensor unplugged. I tried to do that for lunch today but couldn't get the o2 sensor off so I cranked it with just the connector unplugged and the car seemed to run a little better but threw a CEL immediately. The vibration was absolutely horrid on the way home today, car actually almost stalled a few times. The connector was plugged back in for the drive home by the way.