Saturday, I strapped my car down on the dyno and made a few pulls.

The first pull was with a modified MadWolf tune. I added fuel to it to make it safer for my nitrous use.

The car put down decent power (288 HP and 349 TQ). There was some black smoke coming from the tailpipes, and yet the wideband showed that I was lean. AFR: Up to ~18:1

I jumped back to stock PE vs RPM values, and while the AFR came down, so did power and torque. AFR: ~15:1

I added 5 more points (so now I'm at stock PE + 5 points) across the board in the PE vs RPM table, and the AFR dropped by about 1 point, BUT it's STILL lean. And the car lost more power and torque this time as well. AFR: ~14:1

I checked the fuel pressure just a month ago and it was rock solid.

Anyone have any ideas? The dyno operator is going to check the wideband to see if there's anything wrong with it, but I'm looking for other ideas.

Car info:
1996 Formula A4.
3.42 gears
SLP CAI
Hooker LT headers
Mufflex ORY
Magnaflow catback
Comp Cams 1.6 rockers
Crane 10308-1 spring kit
Comp hardened pushrods
GMPP guideplates
LT4 KM
160* thermostat
TB airfoil

 

Black smoke means RICH.
There is no way that you would be at 18 with the tune you have. Not even 15, unless your fuel pump is dying. From what you're describing though, it sounds like the dyno equipment might have been malfunctioning.

 

Ion, thanks for replying.

Last time I checked the fuel pressure was about a month ago (beginning-middle of May) and at WOT, it would go to 42 psi and stay there.

If I were WOT before spraying the nitrous, it would be 42, then start spraying, it would drop to 41 for maybe 1 second and right back up to 42 psi the entire time.

 

sounds like the wideband was far from accurate.

 

was the wideband hanging out of your exhaust tips or was it an O2 wideband?

 

It was clipped inside the tailpipe.

 

I wasn't there when you made your run,(I had just left a little bit before) but if it was showing 18:1 someone clipped the WBo2 too close to the end of the pipe. Mine has shown that before. Also one thing that does make a difference is which pipe they clipped it on, when they did mine, it was showing like 17:1 I was freaking out, I looked and someone had clipped it on the right side tailpipe, mine exits more from the left, so I moved it, and it read the correct a/f. If it was burning black it was RICH, wAAAY RICH

 

I wondered about it.

The wideband even showed 18:1 while cruising up to speed to make the pull. Just sitting there idling it was showing 18:1. It did this both in open loop and closed loop.

The owner is going to check the wideband when he gets home today I think, and we'll see what he says.

 

What about an exhaust leak? Was the WB in the tail pipe?

 

if it was too close to the end outside air may have been hitting it making it seem lean....next time tell them to shove that thing up as far as possible

 

Better yet, pull one of the factory sensors out and screw it in there... no chance of exposure to air.

 

This was the wideband box at the dyno, it had a rubber tube, with a copper sample tube at the end of it that they stuck into the tail pipe.

I saw no screw in sensor.

I do plan to get a wideband unit that will stay in the car. It's just a matter of funds.