Contour Enthusiasts Group Archives Forums General Troubleshooting cel? p0420 catalyst efficiency below threshold......

Interesting. Thanks Jim. I'm just wondering if one of O2 sensors wasn't accurate - not completely bad that it would set an O2 sensor code, but bad in that it was giving inaccurate readings, that the computer would interpret that as a bad cat.

I just see no reason why the rear precat would fail after only 58,00 miles on an engine that runs perfect and doesnt burn any oil. Unless the dealer replaced my previous bad cat with another defective cat? But this ones definitely not plugged up - the defective ones were.

I'm tempted to just buy a new O2 sensor - not that those little buggers are cheap, but cheaper than a new precat.

I read the posts on the P0420 OBDII code but was unable to come to a conclusion. It just so happens I'm getting the same code on a '98 V6 SE and I would like to know what it turned out to be. Can anyone help me?

It turned out that my O2 sensors were OK - I tested them first by swapping locations. So my rear pre-cat is indeed bad. But its not plugged as far as I can tell, as I have full power and the engine runs fine. So it basically isn't operating to the efficiency its supposed to, which I don't care about. Especially after finding out that it costs $300 for a new one for the part alone, and the labor to replace it would be at least that much on top of it. Replacing it myself would be a horrific task since its nearly impossible to get at the exhaust manifold bolts. Also, headers cost $600 just for the parts.

So I decided to solve the check engine light by ordering a pair of MIL eliminators from Dallas Mustang, which will trick the computer into thinking the rear precat is fine, and will turn the CEL off.

I haven't had a chance to install them yet as I just got them, but I will this weekend.

I also experience a P0420 error at approx 75,000 miles on the V6. At first would come on intermittantly (seem to be related to extended low speed driving TRAFFIC). I went ahead and purchased a downstream Oxygen Sensor less than $75us (it's no fun to replace the sensor on the rear bank). Now have over 98k miles with minimal problems.

Problems experienced:
approx. 75k miles
WATER PUMP failure, plastic impellor
ignition wires
approx. 97k miles
third set of platimum(sp) spark plugs ?? includes the original plugs Motorcraft, Bosch, now AutoLite

Last summer I had the same codes appear... catalytic converter inefficiency. It was still under warranty so the dealer replaced both manifolds. The new precats work fine. I just recently had the light come on again and I think it is going to be the same problem. I have to read the codes, but if it is the catalytic converter inefficiency then I may have found a pattern.
When the first codes came on, I had been running Nos for a month or so. I had already removed the Nos from the car and about a month later the light came on. I believe it was because I ran rich quite a few times (hit the nos without turning on the bottle ;0).
This last time I ran a ton of top end engine cleaner through my engine and let is set awhile. I let it clean the pistons and intake, then I went to start the car and it wouldn't start. It cranked like it had no compression. I injected a squirt of oil into each cylinder because I suspected that the cleaner had cleaned all the oil off the cylinder walls while I let it set. The motor did indeed start right away after that, but it puffed a ton of white smoke for about 10 minutes.
A month later the CEL light came on.
It appears that the precat efficiencies can be screwed up quickly by oil or excessively rich mixtures.
Take this story for what its worth.

warmonger

Thanks to all for the replies. $300 for the cat is a little steep and I did look into the MIL eliminators from Dallas Mustang. I also priced the Bosch 02 sensor at Autozone for about the same price as the MIL eliminator ($57). I think I'm going to try the 02 sensor for now, not sure when I'll get to it but I'll relay the results (at least 2 weeks)
This check engine drives me nuts!

Some of us have had 3 or 4 sets of precats/manifolds!The cat has always been a problem from day one,its a LOOOOOOOOOONG story,but take my word for it,they will go again & again etc etc.(PS Ford knew of this problem in 1989!!!!)

It's been a while (2 weeks was an understatement) but upon changing the O2 sensor, (drum roll please), nothing! I just wasted $69. The P0420 problem still exists. I tried the O2 sensor on both sides to make sure I had the right bank but no luck. It's gotta be the pre-cat. Heck, I even changed the Thermostat hoping it was stuck on an open loop with no avail. BTW, I had a heck of a time sealing the thermostat up after changing it, took me about 5 re-installs before I got it right. On another note, someone told me that the catalytic converter is warranted for a total of 100,000 miles by law (for all cars, not just Fords). Anybody know anything about this? The saga continues......

Cats are often covered for 7/70 or 8/80. It can vary from year to year and model to model. There should be a warranty guide with the owners manual (same overall size, but thinner). Look it up for yourself.

The cat monitor is a program that is part of the processor on all OBD II systems (95's with OBD I doesn't have it). It does not run continuously, but only after certain criteria have been met. It may run every few days, or possibly not for several weeks, depending on how and where you drive.

The cat monitor uses oxygen sensors upstream of the cat and downstream of the cat. On our cars, it tests the pre cats (built into the exhaust manifolds) only. The main cat is not tested by the cat monitor. The upstream oxygen sensor is also used to control the fuel mixture when the car is in closed loop.

A properly operating upstream oxygen sensor switches rapidly and constantly between rich and lean once it is up to operating temperature. A lean reading sensor will read 0 to .45 volts, and a rich reading sensor will read .45 to 1.0 volts.

A properly operating downstream oxygen sensor with a functioning cat will switch very slowly, almost not at all. If it switches nearly as rapidly as the upstream sensor, the cat monitor will recognize that the cat is not effecient and will trip the CEL and set a code.

From the information that you gave, I would not be surprised if replacing the rear sensor did not solve your problem, however, I'm not sure that you have propelry tested it yet. You must clear the code and drive the car until the cat monitor runs again to see if it made a difference. If you did not do that, you are still reading the old code stored in memory.

You can also test the system by using a scanner (not just a code reader) and getting real time readings on the oxygen sensors and see what kind of readings you have. It would help to compare the bank one readings to the bank two readings. Remember that what you are looking for a a slow switching downstream sensor. That means that the cat is working properly.

Good luck.

Bronco,

I just had this problem resolved a few months ago. Your precat on the rear exhaust manifold is clogged. I actually had a p0430, which is the FRONT manifold. However, the dealer screwed up and ordered me a rear one. Needless to say, my CEL came on again about 1 week later with the same p0430 code. This time, they got it right. TWO new exhaust manifolds- ZERO $$$ from me!

BTW, they're covered for 8/80,000 mi.

If you're out of warranty, I'd gut 'em and fabricate some MIL eliminators (there's a how-to somewhere here) or, if I was patient and had the cash, I'd just get some MSDS headers (and wait 4 months to get them)- they're WAAAAY cheaper than OEMs!

Sorry so long winded, hope this helps,