94_z28_ss

I have a 1994 z28 LT1, 6 speed maunal, runs great will not pass smog (2nd time). The smog tech said to check o2 sensors & egr valve.

The car throws the following codes:

1. #11 Malfunction Indicator Lamp Circuit Problem.
2. #84 Output Driver Module (OMD) fault. Skip Shift Circuit.

*Cold*
CODES PRESENT YES

A.I.R. PUMP OFF
AC CLUTCH OFF
AC EVAP (o F) 72
AC PRESS (PSI) 7.05-8.88
AC PRESS (V) 0.24-0.25
AC REQUEST OFF
BARO ("HG) 30.30
BATTERY (V) 11.9
LT FUEL TR CL 0
LT FUEL TRM L 128
LT FUEL TRM R 128
EVAP DUTY (%) 0
COOLANT (oF) 75
EGR DUTY (%) 0
EGR VLVPOS 0
ENGINE RPM 50
KS COUNTER 0
FC1 RELAY OFF
FC2 RELAY OFF
IAC POSITION 117
IDLE REQ RPM 3188
INJ L PW (mV) 0
INJ R PW (mV) 0
KNOCK RET (o) 0
LOOP STATUS OPEN
MAF (gr/S) 0
MAP ("HG) 30.19
MAP (V) 4.88
IAT (oF) 75
O2S LEFT (mV) 4
O2S RIGHT (mV) 102
RUN TIME 00:00
SKIPSHFT ENA NO
SPARK ADV 0
THROTTLE (%) 0
TPS SENSOR (V) 0.71
VEH SPEED (MPH) 0


SMOG TEST REPORT:

AT 15 MPH
RPM 1267, CO2 14.2, O2% 0.6, HC 9, CO 0.01, NOX 1079 [FAIL]

AT 25 MPH
RPM 2013, CO2 14.2, O2% 0.5, HC 11, CO 0.01, NOX 657 [PASS]

ANY SUGGESTIONS WOULD BE GREATLY APPRECIATED!! THANKS!!

Injuneer

Those codes aren't going to affect performance/emissions. DTC 11 indicates the SES bulb is burned out or the wire is disconnected. DTC 84 indicates someone unplugged the "skip shift" solenoid on the tranny to eliminate the annoying skip shift feature.

A single frame of scan data isn't going to tell you much. And you have to have the engine running. Your engine wasnt even running (MAF = 0 gps, run time = 0sec, MAP = ~BAR = 30+"Hg, pulse widths = 0), not warmed up (coolant temp = 75*F, PCM in open loop). About the only thing you can determine from that data is that the MAP sensor is working and the TPS closed throttle voltage is OK (0.71V).

You posted the HC, CO and NOx readings, and indicate you failed at 15 MPH. What are the pass/fail thresholds for each of those? I'm going to guess it was the NOx that was too high. Was the engine running hot? Is the EGR system operating?

94_z28_ss

Fred,

At 15 MPH [FAIL]
HC Max=58, AVE=24, MEAS=9
CO Max=0.34, AVE=0.03, MEAS=0.01
NOX Max=586, AVE=342, MEAS=1079

At 25 MPH [PASS]
HC Max=34, AVE=15, MEAS=11
CO Max=0.32, AVE=0.03, MEAS=0.01
NOX Max=706, AVE=320, MEAS=657

The engine was not running hot and I'm not sure about the EGR system. I put a vacuum pump on the EGR valve and it has a slight leak.

Thanks for you help!!

Injuneer

You have several possibilities:

-EGR system not working. The purpose of the EGR is to reduce NOx

-running on the lean side. That would lower HC and CO, but increase NOx

-engine running very hot - lowers HC and CO, increases NOx (You've ruled this out, assuming your dash gauge is accurate)

If you pulled a vacuum on the EGR valve and it leaked, the valve is not going to work correctly.