4 replies to this topic

[kevindh]

Hello,

I am looking for suggestions.

1995 Contour 2.0L Zetec ATX

The car drives and runs well. Starts instantly and idles nice. Good power under load.

EEC-IV codes in continuous memory, 172, 225. All other tests pass.

There do not appear to be any vacuum leaks, or air leaks into the intake.
The EGR valve is working and the passages are clear.
There is a small hesitation when the gas pedal is pressed from idle at stopped, but no hesitation when driving.

The car has twice the allowable limit of NOX emissions, but passes HC and CO.

Any suggestions as to what the problem may be will be greatly appreciated.

I am very mechanically inclined and have most tools, so complicated repair/ testing procedures are OK.

Thanks, Kevin

[kevindh]

Sorry, those codes are for the KOER test not from continuous memory.

[oljeeptk]

Egr valves and later VCT systems introduce exhaust gas into the combustion chamber effectively lowering the combustion below the temp that NOx can form. High NOx is caused by combustion temps over a certain threshold. This can be caused by lean running condition (from a vacuum leak, low fuel pressure, or a shifted O2 sensor), timing too far advanced (incorrect ignition or cam timing can do it.), egr not flowing correctly, carbon buildup in the cylinders or just plain a defective NOx bed in the cat.

[BuckeyeSVT]

Code 172 is Lean Bank 1 and 225 is Knock Not sensed during dynamic test.

From your nOX readings you are definately running lean. I would check the fuel system first, vacuum leaks will set a lean code and throw your emissions out the window. If you have a proper scan tool, check your LTFT and STFT... Check the PCV valve for leaks stemming from sucked in vacuum fittings and rotted rubber lines.

I would start there first, most problems are found there.

-Dom

[kevindh]

Problem solved.

The MAF was reporting less airflow into the engine than was actually occuring, causing the PCU to put less fuel into the cylinders than needed.

Replacing MAF corrected all the fuel trims.