Ok, go ahead and leave them in there, I make a better living that way. If you want to save moeny in the long run replace them. You cannot clean them reliably on a newer vehicle. The propane torch does not remove all of the old deposits (especially not sulpher based compounds), and the lazy test is not 100% conclusive. I don't know how many people I've dealt with that had a converter fail, and simply replace the converter and then wonder why the new converter burns out. The sensors test good. Once they replace the sensors, the converters stop burning out. The tests for O2 sensors are almost meaningless without a baseline. An inaccuracy in the reading of 1% can result in poor fuel economy, burned out converters, and carbon build up in the engine. O2 sensors are cheap in comparison to fuel or catalytic converters.

In my business, about 90% of all catalytic converter failures are caused by faulty O2 sensors, less than 10% of those are bad enough to trigger a CEL.

You only need to replace the upstream O2 sensors. The downstream sensors are protected from exposure to contamination because they are behind the converters. Worst case scenario if the rear sensors fail is either an O2 code, or a false catalyst code. In either case, you just replace the sensor and clear the codes if it comes to that. Otherwise don't worry about. As mentioned above, the upstream sensors are used for adjusting the fuel trim and to ensure that the oxygen level in the exhaust is always changing. The computer is supposed to cycle between slightly rich and slightly lean.

 

scanner said catalyst system efficincy below threshold bank 2 thanks location still the same

 

thanks- scanner said catalyst system efficiency below threshold bank 2is that still the first one on the passenger side closest to the motor

 

Check HERE and confirm the code number, sounds like it's a P0430.

 

p0430 thats the one is that the 02 sensor thats on the passenger side first one closest to the motor

 

If it's a "catalyst system efficiency" code then it involves the downstream 02 sensor (i.e., the one after the cat converter, furthest away from the motor). Bank 2 is the driver's side. That's why I'm thinking it's probably a PO430.

 

Thank you very much

 

Maybe this will clear it up, picture worth 1000 words

http://autorepair.about.com/library/faqs/bl026h.htm

 

If you have a P0430 code, then replace the upstream and bank #2 downstream sensor. Also look for leaks, as leaks can cause a false P0420/430 code. Catalytic converters do not fail by themselves, they are damaged, most often by too much fuel in the exhaust. This is the kind of problem that replacing the upstream O2 sensors is supposed to prevent. If you were dumping enough fuel to damage the converter, how come the O2 sensors didn't pick up on it? As deposits build up on the sensor element, it will read a higher exhaust O2 level and the computer will compensate by adding more fuel. The sensor may still respond well, but its actual output signal is wrong. The only way you can positively verify an O2 sensor is still good is to compare its signal to that of a known good sensor in the exact same exhaust stream at the exact same time.

BTW Ralph, for you to fix this problem, replace both upstream O2 sensors to restore the vehicle to its original operation, run some product such as seafoam of B12 through the fuel, and reset the codes. If the P0430 code returns, you will need a new catalytic converter. If that is the case, what is the manufacturing date of your vehicle. Ford used different converters before and after 1/30/'98. A lot of companies will probably list that they have converters for both applications, however, the part used for the remainder of the '98 model year was unique to that year, the following model year is different. If they do not list their part as specifically for the second half of the '98 model year, it will not fit (wrong bends and converter and O2 locations are different, will have to be modified)

We carry this part in stock. We actually had it specially made for us because none of the other manufacturers had a listing for it.

 

Bear, my CEL came on for my 99 4.0 OHV and i got codes po171 and po174 i cleaned the maf and iat sensors and the CEL went off but I am still getting terrible gas mileage with no CEL on anymore i was thinking of replacing both upstream O2 sensors and upper and lower intake manifold gaskets. what do you think? truck has 122k

 

Replacing O2 sensors can improve the fuel economy. A leak can rob fuel economy too, but what is the condition of the plugs and wires. I would try them first of all. If it was my vehicle, I would put the O2 sensors on the to do list. One other strong reason for replacing them is that if they are left in there too long, you may not be able to get them back out, at least not easily.

 

I replaced all plugs and wires @ the 100k tune-up. I am going to try the O2 upstream sensors and even though I cannot find a leak around the manifold I figure this is preventive maintenance for a 4.0 OHV