[beheivjer]

i keep getting a catalyst below efficency code on my 97, im thinking i have an exhaust leak can you change the manifold gaskets without pulling them? just trying to figure out which way to go its our only car right now and need it so the wife can go to the rest of her LPN classes.

[Doc8224]

its a 97, if you still have the stock mid pipe your cats may well be going bad. check the tailpipes for a rotten egg smell.

[beheivjer]

nope i have a bbk o/r xpipe it is a leak at the manifold i think.

[Doc8224]

if you never put MIL's on it or had a tune to turn off the rear 02's then thats why it is throwing a code.

[beheivjer]

has mils on it right now, but thats not what im asking, it has an exhaust leak, i am wanting to know if you can unbolt enough to get new gaskets in or do they have to come all the way out. This isnt my first stang by the way its just my first 4v. Just had manifold questions that i need answered

[Doc8224]

no they have to unbolt all the way. Ford replacement gaskets aren't the drop in kind but the ones from the parts store will probably be the drop on kind. I wasn't trying to say you didn't what you are talking about, I was just saying what the catalyst code usualy comes from. You shouldn't be getting that code with MIL's. Just sayin man.

[Mustang RacR94]

the manifold/headers has to come off all the way, but you shouldnt be getting that code either way with the MIL eliminators, ive had 3 different MIL eliminators and all them went bad, all I can say is unplug the battery for 10 minutes and recconect it, if the code comes back up after a little, then the eliminators arent working, a exhaust leak before the front 02 sensor should throw that code anyway I wouldnt think, that usually comes up when the 02 sensor detecs that two much of whatever is going thru the rear one compared to the front. with MIL eliminators if there working you shouldnt be getting that code anyway. I know my prochamber leaks all the time right where it meets up with the drivers side header, so I dont know if you checked it out but I would before you go buy a gasket for the header.

[beheivjer]

Symptoms

You will likely not notice any drivability problems, although there may be symptoms.
Causes

A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings

Possible Solutions

Some suggested steps for troubleshooting a P0420 code include:

* Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
* Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
* Inspect the downstream heated oxygen sensor (HO2), replace if necessary
* Replace the catalytic converter

[beheivjer]

it only happens on one side and if i switch the mils to oppisite sides it doesnt follow them

[superbean]

def exhaust leak. Mine throws the p0430 code (the other side), and it has a slick exhaust leak 'tick'

isn't obd2 awesome and finicy! lol

[beheivjer]

i love the exhaust tick that everyone points out along with my throwout clicking all the flippin time