MongoosC5

ok, I had my car dynoed (dynojet, pretty day) a while back and instead of 444 RWHP I got 395 RWHP and a goofy looking a/f curve I was getting about 13 at idle, then it would go over 15 untill it got close to 3000rpm, then it would go to about 11 and stay there. I sent the computer back to MTI to have them check things over and they said everything was just fine. Most everyone I ask says that its the O2 sensors (the front only, rear O2's have been deleted). So anyway, not seeing any harm in doing so, I replaced the O2 sensors and have pulled fuses 16 & 23, doing an overnight relearn.

So...was I correct in placing the front O2's and doing a relearn or does my problem lie deeper? I havent been getting any codes at all. Its been this way for a while but just now was getting to where it would "miss" at low rpm's.

Would goofed up O2's cause me to lose 50 RWHP?? and if not, what? Help!

Also could someone describe to me what a "good" O2 sensor should look like? Mine have a white powdery look, as do the spark plugs on the passenger side (didnt check the driver's side plugs, probably should).

I was told by someone at an autoparts store that O2 sensors can get "lazy" or give false readings without throwing a code.

ANY help or info would be greatly appreciated!

Mongoos

ZO6Les

The A/F at idle and partial throttle is, I believe, factory set at 14.7 and doesn't change with tuning.

Under WOT most tuners will run a little leaner up to 4K, then a bit more fuel (richer) 4K to redline, but this varies among tuners, timing and mods so there is no one answer.

"Most" tuners run 12.8 A/F, +/- .4 or so, so your 11.0 is a little rich IMHO and that will cost you a few HP on the top end but nowhere near the drop you are seeing - for that answer you need to look elsewhere. Also that A/F is pretty close to the stock settings so that is why you won't get a code.

As far as the 02's go I suspect you wasted your money, unless you have been running leaded gas the sensors should be good for at least 50K miles, and a data log is the best way to see how they are performing.

I always prefer custom tuning on the dyno with LS1Edit or equiv.,by an experienced tuner, vs "mail order" tuning for exactly what you are going through.

Les

Gonzo

Can't comment on the o2 issues, but I'll throw in a couple things I leanrened when I had a similar situation.

The car is set to run rich to begin with.

You want to lean it out some but not to much for fear of detonation

Your mods affect the tune. i.e. my intake vs another

Most important thing I learned is:

Where do they put the A/F ratio sensor????????When they Dyno.

Truthfully it should be put into the system before the cats, because they are there to burn gases and can affect an accurate reading.

Mine ran fine on the first dyno where it was dyno tunned, then I went to a dynoday, and everyone was shocked by my A/F ratio.

Bottom line at the dynoday the A/F sensor was a tailpipe sniffer that did not fit exactly into the exhuast, so we set it up on a jack stand and put it in as well as we could. the reading was way off.

I called my to dynotuner to ask whats up, he told me he puts a Bunghole?? into the headers before the cats with a screw in plug. when he dyno tunes he removes the plug and gets his A/F ratio just as it comes out of the engine. Further he said a sniffer is not as accurate and putting it on a jack stand was silly.

He redyno'd mine, and explained it all to me. Cars runs great thats all I know for sure

MongoosC5

no extra holes in the headers, so Im thinking MTI uses a sniffer which is what they dyno here used.

one of the things that prompted me to get it dynoed was a while back I noticed it had a strong gas smell that it didnt have before. also, when I would drive it hard for a moment then slow to a stop, it would idle at around 2000 for a few seconds before returning to normal.

when I talked to the guy at MTI (Jason, I think) he said they use LS1Edit and program to stay at 13 a/f from idle to redline and that there should be no change at all. and when I faxed him a graph of the a/f he said it looked exactly like it did when the car was bone stock, thats when I sent them the computer and they said everything was fine with it.

could the readings from one dyno jet be 50 rwhp off from another? and if not, where did my power go? I can even feel that its lost some power. before I had to short shift 1st because when it would go over 4000 rpm the back end would just skate around. now it holds rock solid all the way up.
i know i know, not the best judge of power there is..but still...

thanks for the replies!

Cobra4B

Check all your intake connections, they can come loose over time w/ lots of WOT (torquing the motor), but that'll cause idle problems and surging... what I'm saying is check all the simple things first. I do know that white powdery spark plugs are a sign of being dangeriously lean. Good luck and keep us updated.

Gonzo

Yes dyno'd differ, Mine was about 25 rhp less on the second dyno. ?????

3XBlack6spd

shouldn't be a 50 RWHP difference...thats an awful lot. There may be some more conditions that could have affected your numbers.....Was it much hotter outside...or more humid..that could have a considerable affect...was your car in the right gear (4th)? and as to your A/F concern...you don't really want to be more than 12....that's a pretty good rule of thumb. Now if I could just get mine down from 13.4!! I'd be ok. Good Luck.