I just had a thought. When on the Wide Band on the dyno, a lot of shops use the "up the tailpipe" probe. That seems to be a common practice. HOWEVER, if said car is running a catalytic convertor, that's going to completely throw off the A/F ratio right? That, coupled with the not so hot exhaust gasses, won't give for a very accurate reading, am I right?

 

That's exactly what John Sealock at Woodbridge Dynotech told me last month when I had him dyno tune the Accel DFI setup on my race car. That's why he uses welded in bungs before the cats.

 

Correct on "after the cats"... wont work. The temperature isn't as big an issue with a wide-band sensor, since the meters already incorporate significant circuitry, specific to the actual sensor brand/model, that compensates for operating temperature. But if you "stick it in the tailpipe", and there are cats, you aren't going to get the right results.

I often wonder if that isn't the problem when I see people posting dyno results, and wondering why their car isn't detonating at 15:1 or 17:1.

 

As you suspected and others have confirmed a bung in front of the cats is needed. If the tuning is for WOT only, depending upon the PCM, an existing O2 sensor may be removed and replaced with the wideband. An OBDI 4th gen can be tuned this way for WOT.

Rich Krause

 

This is really making me wonder at this point. If you look at the dyno graph in my sig, the car "leans" out starting at about 4200 RPM, and ended up at about 14.0:1 by 5800 at which point the run was shut down. I'm really starting to wonder how rich/lean the car actually is. The setup it's going through is ASM headers to a Random Tech High Flow Cat and cat back.

The sickening part is that the dyno runs cost me $200 for 3 pulls with wide band. That's just disgusting, especially if I'm not getting an accurate reading.

On the flip side, what if we were to take the cat off, and insert the sensor at the y-pipe collector? Would that give a valid reading?

 

Just remove an exisiting O2 sensor and replace with the wide-band probe. The PCM ignores the O2 sensors at WOT. Or, a bung costs a few dollars and is easily installed. It's a matter of drilling a hole and a quick welding job.

Rich Krause

 

I'm just wondering how pissed I should be at the fact that

A) I'm paying an outrageous price for three pulls with the Wideband on the dyno,

B) that the shop owner won't cut me any kind of break since I'm going to have to dyno the car multiple times to get the best tune,

C) their "wide band" system isn't giving me a true reading, and I'm paying out the *** for nothing at all, or

D) all of the above meaning I'm throwing good 12 bolt money out the door.

a little more than at this point

 

Just to let you know I had mine dynod earlier this year at a shop in Mechanicsville, PA, 3 pulls with wideband O2 for $50, I thought it was a killer deal. I went there on a group dyno day with a bunch of guys from LS1.com, they just had another one two weeks ago. It's probably 2hrs or so from NJ, might be worth the drive for you next time.

www.seymoreperformance.com

 

Thanks for the info. I shot them an email. My girlfriends parents live about 1/2 hour south of Carslile, so Mechanicsburg should be no problem. Thanks!!!!