Chevy & GMC Vans

This is insanity. Replaced my mass air flow sensor, my ignition coil and fuel pump, all pretty recently. Now on the way to an appointment today the Astro threw a code--check engine light came on. When i pulled into the parking lot of where i was going, i killed the motor and pulled the code. P0420, catalyst efficiency low. Correct me if i'm wrong, but this is a catalytic converter code, right?

Those who have followed my posts already know the the shifting out of second gear problem i'm having. I tend to believe that if i replace the catalytic converter, I'll still have a bad tranny (also referencing horrible noise at higher speed with foot on or mostly off gas). WTF?! Were the vans built after y2K programmed to self destruct after 100,000 miles?!

So, enough venting. I have the title. I'm going to address this. Van has 124,000 miles on it. Fuel pump, ignition coil, plugs and wires are new. What do I do first? Or this pretty much a sure sign of a dying cat covert--ie: do I just order a cat converter from Rock Auto first and do that?

I would clear it first and then see if it comes back to begin with. Do you have smog testing in your part of town?

No emissions testing in my county, fortunately. So, I cleared the codes when I was out today. One was pending, one was already posted--hence the engine light. Then I drove 30 miles home. No more codes over that distance.

Anyway, before I cleared it, I got the freeze frame data. Here it is, if it means anything to anyone:

throttle position: 0.0%
engine RPM: 589
load value: 2.7%
air flow rate: 4.63 gr/sec
map sensorL: 37 kpa
coolant temp: 201 F
short term fuel trim2: 0.7%
long term fuel trim2: 3.9%
short term fuel trim3: 95.3%
long term fuel trim3: -99.3
short term fuel trim4: 65.6
long term fuel trim4: -66.3
vehicle speed: 0 mph
fuel system1: open
fuel system2: open

A code P0420 by itself will be a bad cat convertor. Period.

I am not aware of your tranny problems but, if your cat convertor is restricted it can cause shifting problems because it will affect the intake pressure readings that the computer uses to make decisions about when to shift. Also, could your noise be a loose cat convertor honeycomb?

I just looked on Rock Auto. They have one from Eastern Catalytic Converters (part 50294) for about $300. Will this job require any welding? How difficult is it to do?

I had a shop just cut out the old one and weld in the new one I bought on e-bay. No need to buy a complete "Y" pipe assembly. I used something like this.

v8famvan wrote:
I am not aware of your tranny problems but, if your cat convertor is restricted it can cause shifting problems because it will affect the intake pressure readings that the computer uses to make decisions about when to shift. Also, could your noise be a loose cat convertor honeycomb?

Is this really true? My van doesn't seem to shift fast enough, really gets hung up from a stop light. I had the tranny rebuilt as it had 180k on it, but the problem is the same. No solenoids were replaced with the rebuild if that might effect shifts.

I have a p420 code and have been trying to determine a sensor or cat replacement.