i've read all the other threads about this code and what the problems could be. with 117k miles on my '98 explorer, it would seem that a bad cat is probably the issue. next question is what can i expect to pay to get this part installed? autozone has universal fits for 70 bucks. i think the ford replacement part is like 250 bucks or something. why or why not a universal fit? and would you go to the dealer for something like this so they can check the o2 sensors before and after the cat to eliminate them as being the problem? lastly, once your there, would you consider going ahead and replacing the tailpipe and muffler, i.e. everything downstream from the cat on this truck (that i plan to drive for several more years)
thanks

 

Peronally I'd go with the entire shebang...from the engine connection all the way out the tail of the truck. Regarding the universal doohicky...I think one of the concerns would be more restrictive than the stock ford unit. Have you checked your local muffler shop to see what they have. The parts may be about the same with the hangers all correctly placed to suspend it and you'd be able to maintain the proper airflow. I know that Meinike(sp) will sell cash and carry for the parts....next to that, I know that Trak Auto (now Advanced Auto I believe) used to sell the correct cat (had to buy one in a pinch) and it was even a stocked item in one of their low volume stores.

Im sure that Advanced, PepBoys, Autozone, ma-pa's auto parts, as well as NAPA would have a correct unit for the vehicle over a generalized universal kit. Might find the price comparable or lower. Your other choice would be to look at JC Whitney...I've had good luck with other vehicles and exhausts from them and would use them again if the local place was priced higher.

 

This code should not effect drivability or gas mileage. It is a harmless code as long as your cat is not plugged and performance is up to par. I had this code for about two months, then code P0133 would come and go. Shortly thereafter code P0430 showed up as well. Code P0133 was a tip off that the upstream O2 sensor was switching too slow. I think that a sluggish upstream sensor can trigger the P0420 code due to the switching ratio between the upstream and downstream sensors. If you have over 100,000 miles on the original O2 sensors, I would replace the upstream sensors and see if it helps. I keep a code reader in the glove compartment to check for any additional codes from time to time.

I just replaced both upstream sensors on my Mountaineer, however I do not yet know if it will help code P0420 since the vehicle is in storage for the salty winter.

 

fyi, i read somewhere (maybe on this site) that there was a tsb on this issue, and that the first step was to reprogram the pcm, and then only if the code returned, did that indicate a bad cat (or for that matter a bad sensor). yesterday ford dealer told me the same thing, saying that 7/10 were 'fixed' with the reprogrammed pcm. so far so good--but that sure goes into a black hole that i don't understand as far as the new computer programming. at any rate, my cel is gone for now. i'll update the site if that changes. beats a $500 cat replacement.

 

How much did it cost to get the PCM reprogrammed? I suspect they just made the switching ratio between upstream and downstream sensors wider, thus turning off the light. Do you have the 5.0 V8?

 

charged me 142 for the labor. never mind what i think of that. no, i have the 4.0 v6 sohc.
i'm with you, though, reprogramming the computer to basically accept what the old program wouldn't seems like just ignoring some kind of problem, like say, turning the radio up to hear over a noise.
anybody have any other info on this?

 

I suspect Gman's correct on this. As long as emissions were still within parameters, it wouldn't matter. Ford probably set the PCM up originally to recognize inputs from new sensors and a new cat, and didn't consider wear on the system.

 

well, after a couple of months, the same p0420 came back. this time i went to firestone for a full diag on the cats, sensors, everything ($79.99). looks like the sensors are switching slow, and they are saying that cat is bad and the one on the other side is marginal. we're talking some serious coin to replace both cats on this truck. would it make sense to replace the upstream o2 sensors (original equipment) first? or does this diag say I need to replace everything?
you can tell i just don't want to believe what is probably true. the truck is hardly worth much more than what this is gonna cost me to fix it.

 

Q, how did they test the cat .... a true test is temperature, a CAT is a mini afterburner to fire off residual fuel, that being said the downstream side of the cat should be 40+deg C higher than the upstream side, so borrow a laser temp gun, run the engine at 2000+ RPM for 10 min and take temp reading on the pipe 2inches ahead of the cats and 2 inches aft, if you have a differencial of +40 on the aft, the cats are working. note a dirty MAF, poor plugs or intake manifold leak can throw this code as well...

 

Testing O2 sensors on the workbench.

Use a high impedence DC voltmeter as above. Clamp the sensor in
a vice, or use a plier or vice-grip to hold it. Clamp your
negative voltmeter lead to the case, and the positive to the
output wire. Use a propane torch set to high and the inner blue
flame tip to heat the fluted or perforated area of the sensor.
You should see a DC voltage of at least 0.6 within 20 seconds.
If not, most likely cause is open circuit internally or lead
fouling. If OK so far, remove from flame. You should see a
drop to under 0.1 volt within 4 seconds. If not likely silicone
fouled. If still OK, heat for two full minutes and watch for
drops in voltage. Sometimes, the internal connections will open
up under heat. This is the same a loose wire and is a failure.
If the sensor is OK at this point, and will switch from high to
low quickly as you move the flame, the sensor is good. Bear in
mind that good or bad is relative, with port fuel injection
needing faster information than carbureted systems.

ANY O2 sensor that will generate 0.9 volts or more when heated,
show 0.1 volts or less within one second of flame removal, AND
pass the two minute heat test is good regardless of age. When
replacing a sensor, don't miss the opportunity to use the test
above on the replacement. This will calibrate your evaluation
skills and save you money in the future. There is almost always
*no* benefit in replacing an oxygen sensor that will pass the
test in the first line of this paragraph.

 

I had the same issue with my '96.

I went t this site and bought the 02 fooler. Best $10. I spent. It sure beats getting new cat. It is worth a shot.


http://brickauto.com/products.html

 

After taking the Mountaineer out of storage the P0420 and P0430 codes are gone and the MIL is out. Replacing both upstream sensors did the trick, the codes cleared themselves after 6 or so driving cycles. It has been code free for a week now. I hope gas mileage will improve as well.

 

Had the same problems on my 96 4.0. Tried the 02 fooler mine cost 20.00. this worked for awhile. I ended up replacing all my 02 sensors have not had anyproblems since. Mine were very had to remove need a large breaker bar and the a tap to retap the holes befor installing the new ones. (suggest having some one else do it)