Strange emissions problem 1990 240sx

[rhb00904410]

I live in California, and my car failed emissions as a gross polluter. The mechanics had it for about two weeks trying to find the problem. They replaced the distributor, plugs, air filter which helped, but would not fix the problem.

After running numerous tests, the best they could do was determine a strange side-effect with the EGR valve. They had never seen anything like this before. With everything hooked up as normal, the car fails on the HC, CO, but passes on the NO.

If they disconnect the EGR hose and plug it, the car passes on the HC and CO, but fails the NO.

The mechanic says that a properly working EGR is supposed to lower the HC and CO. They believe the EGR is working, as it is lowering the NO when connected.

Make: 1990 240 SX SEMiles: 191,000

Two years ago I had to put a new radiator and thermostat to pass emissions. (They said the car was not running hot enough). Other recent work includes repacing some broken manifold studs.

Any ideas on how to fix the emissions problem? What can I tell a mechanic to get this fixed?

[NISTECH]

do a leak down check on your fuel system see if an injector is leaking. The EGR has minimal effect on hc and co its primary function is to control NOx emissions. Have him do a test on your O2 sensor as well as moniter it and see what the condition is, rich or lean if it is registering lean something is wtrong with the O2 since your failure indicates this car is running rich. It may likely be the MAF sensor has a poor ground have him check that first as it is very common on the early 240, after he checks the MAF have him check your coolant temp sensor.

If you can post your exact readings. Obviously your car was run on a dyno since the test is measuring NOx.