need some help here.

[004x41500]

my moms car hasnt been running right, its got a slight miss, but otherwise runs fine. ive changed the plugs, fuel filter twice, seafoamed it. also when you go to pass someone under hard acceleration, it revs up, and then falls flat on its ass, and misses like hell til you let off the throttle, then back to normal after that. with my new scantool i view the live sensor data, though the software i have limits what i can view, i need to get better software as i cant view the mfg specific PID values. though i was able to view the o2 sensors readout as it was running. and these graphs are what i got, the top is pre cat, the bottom is post cat.

presently i suspect a faulty pre cat o2. her car has a little under 100k miles, only owner. its a pontiac aztec fwd 3.8l v6

what do you guys think?

http://i51.tinypic.com/97slmr.jpg

[SmokedRam]

screw all the graphs and charts...is the precat sensor still stock? If it has 100K miles on it then it is time for a new one.

[004x41500]

i agree, but as tight as we are with money, and the fact that the sensor is like 80 something buck more than likey, its on of those things that id have to have a definitive answer.

oh and there are no dtcs being thrown.

[Onk]

replace the 02 sens....

[004x41500]

hmm. i thinkin i might go with my instincts on this one, i looked at the long term fuel trimm, and its running lean, so im leanin towards a faulty o2.

[SmokedRam]

Running lean huh? Have you checked for a leaking upper intake gasket? Those GM engines are incredibly famous for them....wait, I just caught something....you say it's a 3.8 in an Aztek? I thought they only put the 60 degree 3.4 in those...

[004x41500]

oh haha. youre right, it is a 3.4 im sorry. ive checked the outer edges of the gasket for the signs of it going bad, but it looked perfect. and changin the spark plugs and fuel filter did help for a little while, but now it back to square one.

[SmokedRam]

take come carb cleaner and spray around the end of the intake...if you notice a change in the sound of the engine, then you gotta leak. I say this, cause a leaky intake gasket cause cause the ECM to throw a lean code or make an engine run lean and those 60 degree engines are prone to intake gasket failure.

[004x41500]

thats just it, theres no codes, stored, present, or pending.

[SmokedRam]

thats just it, theres no codes, stored, present, or pending.

the O2 can be on the verge of failure...but in my experience with them failing, they cause the engine to run rich, rather than lean...usually causing carbon to build up on the plugs, then dumping raw fuel into the cat, killing the cat...

What do the engine temps look like when it is running? Is it running usually cool?

ON my S10, the failed O2 never tripped a CEL, but the engine fall flat on it's ass and couldnt get out of it's own way...since it wasn't tripping a CEL I had to chase the problem with a new coil, then a new TPS, then a new CTS, then a new CAT, and finally as a last resort I changed the O2...bam prob fixed...

[004x41500]

it runs about 200*-210* at idle sitting still according to my scan tool, that pretty much sounds like this situation, the new plugs helped for a while, the fuel filter helped for a while, and now its all back to square one

[Stealth Mode]

We have the MODUS scanner up at work, the $10k one. If you wanna' bring it by we can toss it on it. We're in Seffner though...

[004x41500]

ya, ive used that one before, and thats quite a ways im over in sebastian on the east coast, my old hs has one and ima try to get in there to check in out.