Zetec P0420 - Experienced Users Needed

Contour Enthusiasts Group Archives

I've been popping P0420 codes recently, and also experiencing a few stalls (no code). I've done a lot of searching and believe that my cat is not likely the problem.

Reference this thread.

Per TSB. Some causes of P0420

�?�??�?· Malfunctioning ECT/CHT
�?�??�?· High fuel pressure
�?�??�?· Damaged exhaust manifold
�?�??�?· Cylinder misfiring
�?�??�?· HO2S wiring concerns (shorted or chafed, bent pins, etc.)
�?�??�?· Damaged exhaust system pipe
�?�??�?· Damaged muffler/tailpipe assembly
�?�??�?· Retarded spark timing

Damaged Catalytic Converter:
�?�??�?· Use of leaded fuel
�?�??�?· Oil contamination/consumption
�?�??�?· Silicone contamination (sealants/cleaners)

I'm determining a game plan and want some grey-hairs to advise. I think I'll first run down the list above, specifically focusing on the checking for high FP & bad ECT.

If these check out ok, I plan on cleaning the IAC, as it's been 4 yrs and ~63K since it's been installed as new.

If I get this far without finding it, then things get fuzzy as to what to check next. Any suggestions from here (or my plan in general)?

PS. My plugs/wires a 6 months old, and I'm not experiencing any misfires, so I suspect my ignition & coil are ok.

Originally posted by fdunford:
...I've done a lot of searching and believe that my cat is not likely the problem...

Actually, it most likely is the problem.

Check with your dealer to see if a reflash is available for your specifc model.

Steve

AFAIK, the PCM reflashing for P0420 is not available for 1996. You are looking at new precat or mileliminators (with gutting of the precat; I think MI does not have smog emissions testing).

Originally posted by projectSHO89:

Originally posted by fdunford:
...I've done a lot of searching and believe that my cat is not likely the problem...

Actually, it most likely is the problem.

Check with your dealer to see if a reflash is available for your specifc model.

Steve

that and the pcm reflash is for the duratec only I believe

at 181k if the O2 sensors haven't been changed maybe try that first but most likely the cat is cooked

Originally posted by Tony2005:
the PCM reflashing for P0420 is not available for 1996.

This would support what I found (or didn't find) via search.

Originally posted by Tony2005:

You are looking at new precat or mileliminators (with gutting of the precat

If it weren't for the stalls I started getting, I'd tend to be in agreement with you. I'm not convinced that a bad precat would cause stalls?

Originally posted by BrApple:

at 181k if the O2 sensors haven't been changed maybe try that first

They were changed about a year and a half ago. I think I read in a search thread that the O2 tests were done before the cat eff test. If true, I suspect the sensors are ok.

Originally posted by fdunford:

If it weren't for the stalls I started getting, I'd tend to be in agreement with you. I'm not convinced that a bad precat would cause stalls?

you do not have a precat on a zetec, they are only on the duratec. the cat is bolted right to the exhaust manifold

if you have no codes for the O2 sensors and the only code is for the cat then it is most likely the cat.

at least on the duratec the cat monitor sensor should read about .7 volts at idle, if you graph the O2 sensor with the cat monitor over top the cat monitor should follow behind the O2 sensor when driving, if it doesn't that means there is an issue with the cat. IIRC the closer to 1 volt you are the richer the system and I believe the closer to .1 volts you are is lean, but it might be just the opposite.

Originally posted by BrApple:
... the closer to 1 volt you are the richer the system and I believe the closer to .1 volts you are is lean, ...

You are correct.

Originally posted by BrApple:

if you have no codes for the O2 sensors and the only code is for the cat then it is most likely the cat.

I'm not challanging you, but am simply asking your opinion as to the stalls I started getting about the same time. Do you think a low cat eff would cause them?

Originally posted by BrApple:
if you graph the O2 sensor with the cat monitor over top the cat monitor should follow behind the O2 sensor when driving, if it doesn't that means there is an issue with the cat.

They show the graph in the TSB Figure 5 & 6. Looks hard to graph w/o the correct tools.

if the cat has become plugged up then it could cause stalling

either way the pcm is telling you that there is something wrong with the cat so I really don't think that it would be much else

Originally posted by BrApple:
if the cat has become plugged up then it could cause stalling

I've seen plugged cats and they get cherry red and the vehicle will hardly idle, let alone run.

I'll see what I find and post the results (this may take a while

)

I'll keep checking back for more replys...

FP is fine, but, I the exhaust pressure seems really low (which supports a partially clogged cat).

I can place my hand over the exhaust and keep it covered, while it's idling. That seems like a strong indicator to a cat starting to plug. Agreed?

Zetec test for blocked (plugged) exhaust.

A good cheap way to test for a blocked exhaust is to remove the upper O2 sensor, and see if the performance improves. Battery needs to be disconnected before uninstalling and installing O2 sensor. Good luck.

Sounds good, but I'm not experiencing any performance problems to speak of (other than a few stalls, spread out over ~500 miles).

I used an NGS+ tester to pull ECT today at lunch. I also ran KOEO and KOER with no codes.

It's 52 degrees out, and after 15 minutes ECT got to 171 degrees. Seems like it should have reached the thermostat rating (180 or 192 degrees).

ECT looks suspicious to me and would like opinions. I wonder if the t-stat is not closing all the way?

If I disconnect the upper o2 sensor and it runs better, is it the precat or the o2 sensor?

Originally posted by Contour_dave:
If I disconnect the upper o2 sensor and it runs better, is it the precat or the o2 sensor?

I've been told Zetecs do not have precats. So it is the main (and only) catalytic converter which is plugged.