PO420 Code with "Check Engine" light

[John S]

Hello all

New to the forum, hope I can get some help.

My 1996 4.0L Explorer with 136,000 miles on it has had a check engine light coming on occasionally for the last 9 months or so.

I hooked it up to an OBD Reader and got code PO420 Catalyst System Efficiency below Threshold Bank 1.

The light would go away for quite a while. Now the same code is back to stay. My last attempt was to disconnect the battery and although it reset the "check engine" light it came back on after 200 miles or so.

My background is an aircraft mechanic. I drive older vehicles and pride myself in fixing them myself, so I'd really prefer to avoid my local Ford dealer on this one.

I've crawled underneath the Explorer and I see NO exhaust leaks, the senors and catalytic converter physical appearance is good and clean.

So.....where do I go from here.

Thanks,
John

 

[CmdrPopNFresh]

hey john. i tried to send you some info but its too long to pm to you. if want to give me your email in a pm ill email you the ford pin point test for the code you have.....its a fairly short one. only 12 possible steps. and only requires a vacuum gauge and i think a fuel pressure gauge.

usually a code like this is deterioration of the catylic converter.....which is caused by something not working right with the engine (too much fuel or something). just a few thoughts but cracked valve seats, sticking injectors, lack of spark\misfire, fuel pressure could have been a possible cause....


let me know how it goes.

 

[John S]

hey john. i tried to send you some info but its too long to pm to you. if want to give me your email in a pm ill email you the ford pin point test for the code you have.....its a fairly short one. only 12 possible steps. and only requires a vacuum gauge and i think a fuel pressure gauge.

usually a code like this is deterioration of the catylic converter.....which is caused by something not working right with the engine (too much fuel or something). just a few thoughts but cracked valve seats, sticking injectors, lack of spark\misfire, fuel pressure could have been a possible cause....


let me know how it goes.

Hello,
I went to your contact page and it wouldn't let me send an e-mail or PM. I hate posting my e-mail on a forum (because of spammers) but here it is, spelled out vertically

J
J
S
@aol.com

Yup three letters only, just my initials. Sure appreciate the help!!

 

[96eb96]

Hello,
I went to your contact page and it wouldn't let me send an e-mail or PM. I hate posting my e-mail on a forum (because of spammers) but here it is, spelled out vertically

J
J
S
@aol.com

Yup three letters only, just my initials. Sure appreciate the help!!

I PMed you about the PCM flash.

 

[autodrjr]

a 420 code in an explorer is always a cat. the o2 sensors are working because they are detecting it. replace the cat and the code will go away.

 

[96eb96]

a 420 code in an explorer is always a cat. the o2 sensors are working because they are detecting it. replace the cat and the code will go away.

You are mostly correct but in 96 there is a specific issue with an overly sensitive computer. Shame to spend hundreds if you happen to know this.

 

[autodrjr]

my appologies... i was assuming the pcm had the reflash. sorry its still early here lol