I dynoed my Impala SS for the first time on the bottle. Very disapponited with the results, graph is all over the place and wideband shows it is scary lean. Car pulled great on the dyno, no audible detonation and the FPSS never triggered (set at 35psi). I was hoping for over 500 RWHP.

What I don't understand is the wideband said I am lean and my o2's said I was pig rich.



As you can see the wideband shows that it's scary lean. And where the wideband shows it's lean is where the power is down.

Here are the logs I pulled from my laptop, the O2's show to be pig rich the entire time. I don't know which to believe.




On my NA runs the wideband showed I was lean and my O2's showed I was rich, so the problem didn't just happen while on the bottle. Any thoughts anyone?

I'm afaid to spray anymore until I figure out what's going on.

 

Very odd - it's possible their wideband and dyno isnt calibrated correctly. I imagine if you were really that lean (15.5 at one point ), then you would have had audible signs of detonation - probably some poping a surging to go along with it.

 

I have never seen a graph that bad before in my life.
Something is not right.
You need to tell them to put the 02 sensor in a bung.
What happens is in some high hp cars you get reversion in the exhaust and you get funky a/f readings.

 

My graphs look pretty similar to your and I had the same problem as you do. O2's say pig rich but wideband was 15-1 all the way across the rpm range NA and on the bottle I spiked to 18-1 and then came back down to 13-1...which is still pretty lean for the bottle. I did not hear any detonation but the graphs scared the hell out of me (they were all over the place). Also at idle my A/F ratio was at 18-1...everyone there could not beleive the car actually idled but it idles fine. I am getting an EGT meter and tune by using that and reading the spark plugs. My numbers were 351rwhp NA and 535rwhp on the 150 shot...this was through a th400 5200 stall (on the bottle), 9" with 35 spline axles, and full slicks so the numbers will read low.

Matt

 

Matt your setup must be really close to mine. I make 352 RWHP NA and was shooting for 525 RWHP on the hose. I am also running a TH400 and my converter flashed to 5,100 on the bottle.

My plugs look OK, don't show any sings of detontation. They are a light green/gray color. The car feels really strong on the bottle but the dyno scared me, not sure what to do from here. Please keep me posted on your findings.

Thanks,
Andy

 

Yeah we must have simlar combos..lol..almost exactly the same numbers. On your dyno graph did you try and set the smoothing to 0 instead of 5? When I do this the graph actaully doubles back and crosses over itself. It is almost like the torque converter is so loose that it will catch and release and catch again as the tires grow.

Matt

 

does the impala come true duals or do you have a true dual setup if not they may have put the wideband in the wrong tailpipe.

 

How do you know your FPSS never triggered? Do you know absolutely that both nitrous and fuel solenoids were open through the whole pull? Do you know for sure that your fuel pressure is good, I suppose, is what I'm wondering.

Dave

 

I have true duals with cut outs right on the header collectors. The wideband was up in the cutouts, right at the header collector. Same location as the O2 sensor.

 

I think I would feel it if the N20 shut off. I have a fuel pressure gauge but it's mounted under the hood right before my fuel solenoid. I plan to go back to the dyno and start over with 50HP jets and work my way up. I'm gonna keep a close eye on my FP gauge this time.

Thet run felt smooth and strong, didn't feel like he nitrous ever shut off.

 

I would think so too, but the graph bounces up and down like a yo-yo, and you're saying it was "smooth" - it's hard to know what's going on here. If you're going back, you might also drop in a light across your FPSS so you know if it's cycling, and of course watching your fuel pressure like you say...

I presume you ran the car just on the motor, and that graph looks fine?

Good luck,
Dave

 

Yeah the graph on motor looked normal, car put down what it usually does. The wideband showed lean on the motor runs too, but my O2's showed rich. I'm gonna email my tuner and see what he thinks.

 

I really don't think it is your fpss. I am having the exact same issues as you and I do not run a fpss. I still think the graph fluctuations have to do with the converter and tires. My NA graph was smooth but lean as well. My graphs look very similar to yours. did you ever check the smoothing on the dyno graph to see if the rpm's go up and down? If you set it at 1 you will see what I mean about the rpm's going up and down.

Later
Matt

 

My bet is a bad jet. You might be jetting wrong causing the o2s to read real funky, but i am far from a nitrous expert. Just my first thought.

 

Here is one of my NA runs. Again the dyno shows lean but my O2's were in the 940-980 range the entire pull.



I don't think it's a jetting issue but I'm not ruling anything out at this point.