Just took my JAG for a smog check at at Star Certified Smog Check Station and did not pass. According to ASM Emission Test Results, at 15 MPH under HC (PPM) max is 80 Average 55 Meas 108 failed, but passed at 25 MPH max 45 Average 31 Meas 44. Any suggestions on what could be the problem and possibly what need to be repaired. Thanks

 

Do you have a way to read the LTFT and STFT parameters? You are running a little rich, so either the trims are topped out, or you are misreading the exhaust stream. No exhaust leaks, particularly at the manifold?

 

FLRB46,

Welcome to the Jaguar Forums!

Based on the year and model you stated in the title of your post, I have moved your post from the forum for the X300 to the forum for the XJ40, which is the Jaguar project code for the 1988-1994 XJ6.

As Ross mentioned, it sounds like you have a rich-running condition. Unfortunately, XJ40s are OBDI and standard scanners cannot read the fuel trims.

Off the top of my head, some of the possible causes of rich running are:

1. Clogged air filter.

2. Failing O2 sensor.

3. Failing Coolant Temperature Sensor (CTS) or broken CTS electrical connector or wiring harness: if the CTS fails to inform the Engine Control Module (ECM) that the engine has achieved operating temperature, the ECM may continue to apply cold-start fuel enrichment even once the engine is hot, causing a rich Air-Fuel Ratio (AFR).

4. If the diaphragm in the Fuel Pressure Regulator (FPR) has ruptured, raw unmetered fuel can be inhaled directly into the intake manifold, leading to a rich mixture that the ECM may not be able to correct due to an implausible combination of sensor inputs.

5. Leaking fuel injectors.

6. Failing Intake Air Temperature sensor (IAT or IATS).

Have you checked the Vehicle Condition Monitor (VCM) for any stored fault codes?

Cheers,

Don