Dyno Day - Car Running Lean

[ViPER1313]

Had my car hooked up to a Dynojet today and did 2 back-to-back runs. First run was done in 3rd and the 2nd was done in 4th. Only modification done to the car between the 2 runs was the air intake was popped on the 2nd run. I was very surprised to find out that my car was running very lean at lower RPMs. Other relevant info:

- ~80 degrees outside
-Only modifications to the engine include Summit turbo mufflers and a removed intake silencer.
-New fuel filter and 02 sensors in the past year (02s to fix lean code thrown by computer when I bought the car.)
-No vacuum leaks to my knowledge (although I'm going to poke around a bit.)

Any thoughts as to what might be causing the car to run this lean? I'm open to suggestions.

 

[ViPER1313]

Any ideas at to what would make it run lean at lower RPMs? Only thing I can think of is the fuel pump, although I don't understand why it would start out lean and become richer as the load on the unit increases.

 

[DHMag]

when you replaced the O2s, did you reset the EEC to erase the codes ?

 

[ViPER1313]

when you replaced the O2s, did you reset the EEC to erase the codes ?

Yes, it has been reset many times.

 

[ViPER1313]

Well, I tested the fuel pressure at the rail : 33psi at idle and 39 by about half throttle. I also replaced the MAF with a spare one that I had sitting around (cleaned it with electrical contact cleaner before install.) The car still seems to hesitate at lower RPMS (as seen on the dyno graph.)

This doesnt make sense to me - I figured the car was running pig rich, as it pours out black smoke when you get on the throttle.

Any ideas?? Should I be worried? Cause I'm stumped right now.

 

[Kermit]

That's scary Lean, anyone else dyno that day? Were their A/F results off? How did they do the A/F ratio?

 

[DHMag]

my car has been running lean for several years now with no ill effects. IIRC, it averages about 15:1 A/F.

 

[ViPER1313]

That's scary Lean, anyone else dyno that day? Were their A/F results off? How did they do the A/F ratio?

Many other people dynoed that day, and their A/F ratios were not off. They did the A/F with a tube sucking gasses from the exhaust tips.

I'm going to run the codes tonight and see if there are any IAT codes stored. The mixture got noticeably richer across the board for the second run (the one with the airbox popped so no air was flowing across the IAT.) I'm also going to pull my plugs and see what they look like.

 

[pudge235]

well if they were using a sniffer then the only thing I can think is that there is possibly exhaust leakes somwhere in the front part of the system. The sniffer only can read what passes by it and at higher RPM's the car is pushing more exhaust fumes faster so it can pick up a better reading. Other then that you already replaced the O2's the MAF and reset the computer.

 

[ViPER1313]

Pulled codes today:

KOEO: 219 (Spout Circuit Open Defaulted 10 degrees below dead center), 542 (BS Fuel Pump Code)

KOER: None

Cylinder Balance: 9 (All is Well)

I have pulled the 219 code before, and I can guarantee the SPOUT circuit is not open (look at the dyno graph ) - what would cause the car to throw this code?

Pulled the front plugs today, and they are indeed a bit white. I also looked around for brittle hoses / vacuum leaks and couldn't find anything.