what does this mean?

[myold96]

my check engine light came on in a 96 ranger 2.3 the exhaust consists of a catalytic converter and about two or three feet of pipe. the code reader said po420 the only other problem i have is my a/c copressor is siezed not the pully bearings just the compressor,can they be rebuilt or is it safe to buy a junkyard special not knowing what junk went through it

 

[Rangurr]

Is this code new or did you do anything before that seemed to make it come on? (when did you cut the exhaust back?)

You can definitely rebuild it. I would just go ahead and get a JY special out of those two choices but that's just me.

Here's a link to a pretty nice writeup on how to rebuild one (yes, I know it's Nissan but it still has some useful info) http://forums.nicoclub.com/how-to-r...ssor-just-in-time-for-summer-too-t267157.html

 

[Rangurr]

Also, here's info for an FS-6 which may help you a bit as it is more similar to the compressor you would have.

 

[RonD]

The exhaust system on the 4cyl should have two O2 sensors, one near the engine(upstream) and one after the Cat Converter(downstream).
The computer compares the levels of these as a test to see if the Cat converter is working.
P0420 Catalyst System Efficiency Below Threshold (Bank 1)

So it could be the Cat is not working as well as it should or the downstream O2 sensor is not working as it should.

I have never done this test but have read that if engine is warmed up, and you shut it off then disable the spark in one cylinder and restart, yes with a miss, you will cause a rich exhaust which should cause the Cat to heat up red hot....if it is working.

 

[myold96]

i fixed the exhaust by adding the rest of the exhaust,man is it a lot quieter,any way that solved the low efficiency problems something to do with proper backpressure or something by the way my fuel mileage went up also it is amazing when you put things together like the engineers say to they work much better i will get the a/c compressor from the wrecking yard payday and change the reciever/drier and orfice ube and flush the system outalso because who knows what went through the system when the compressor seized.

 

[adsm08]

The best test of a cat's function is to get a scanner with live data capabilities, pull up the signals from the upstream and downstream sensors, and compare them.

The upstream will normally switch between about .2 and .8 volts, and should give a nice smooth sweeping sine wave looking pattern. The downstream should hold steady around .6V with occasional spikes and dips related to sudden throttle events.

If the downstream signal looks like the upstream signal the cats are shot.