[updated:LAST EDITED ON 31-Oct-02 AT 07:40 PM (EST)]Hello,
I hope someone out there can help me. My 92 explorer failed nj emissions for hc & co. My trouble code identified the oxygen sensor to be the problem. I changed the sensor , reset the computer & still have the same problem. You can smell the emissions and my idle is not steady it goes from 500 rpm to 1000 rpm back to 500 to 1000 and so on and so on. Can anyone give me a suggestion? This is driving me crazy.
Thanks

 

The emissions and idle problem may be unrelated. I would check the fuel pressure. If it's too high, then the engine will run rich. Also, cleaning the MAF is worthwhile. It's easy and cheap to do so there's no excuse for not doing it. Dirty MAF is a common problem.

The idle problem could be a dirty IAC valve. They can get sticky, causing the fluctuating idle you describe. Many times these can be cleaned up and replacement isn't necessary.

Besides the HC and CO, do you have the O2 numbers?

 

There is more to PCM tests than just dumping the codes and replacing parts. You should run both the KOEO (key on engine off) self test and the engine running test. Your vehicle is EECIV and these tests have been fairly standard fare since 83 model year, with some minor variations for different sensors used.
KOEO will identify any sensors which fail out of range checks in a non running (but warmed up) vehicle. Engine running tests will put the engine thru a full range of dynamic tests and is more valuable in determining a marginal sensor or control solenoid.
Both tests are relatively easy to do and require only a modest amount of equipment to perform (Analog voltmeter). If you do not have one, go down and spend 15-20 for a good manual for your vehicle and run the tests as it describes them. This should help you pinpoint any sensors that need replacing.

Of course, if you have been runing the vehicle for a long time with problems, you may have damaged your catalytic converter to where it is no longer effective and will have to be replaced. Most muffler shops should be able to replace it with an aftermarket that will pass emissions tests for $100-$150 each.
As the other poster stated, the erratic idle is probably related to a sticking IAC solenoid. Get your car running fairly well again , run it for 30-50 miles to allow the cat to heat up enough to burn any fouling out then try the emissions test again. If it fails, get the cat replaced.
Dialtone

 

Change the fuel pressure regulator. Some of these wear faster than others and can cause some strange problems. Pull the fuse to the fuel pump and measure the current. Should be around 5A. If it drops below 4A, you have a problem in the fuel system. This is helpful if you don't have a pressure gaufe setup.

 

Also, on the 92 4.0 enginges there are 2 oxygen sensors. One is on the left exhaust manifold and the other is in the dual converter Y-pipe.

Mike

 

No, there is only one oxygen sensor on the 1992 4.0 Litre v6 and it is at the crossover in the exhaust Y pipe, just before the cats.

 

After replacing my o2 sensor, plugs, wires, air filter, and adding fuel injector cleaner to my vehicle. I saw your suggestion to change my fuel pressure regulator, Which I did. I paid $63.36 for it at advance auto parts. The difference is unbelievable. It idles alot smoother, uses less gas, and my emissions reading went from HC 474ppm co 2.72 ppm to HC 42 ppm co .10 ppm. Thank you for your advice, It saved me alot of money and headaches. Also, Thanks to all who contributed your suggestions. It is much appreciated.