madmaxx42

Hello

My 2000 SS has been running good till recently i got the check engine light and p420 and p430 dtc codes

P420 "Catalyst System Efficiency Below Threshold (Bank 1)" and P430 "Catalyst System Efficiency Below Threshold (Bank 2)"

i just put on brand new magnaflow catalytic converters

4 new o2 sensors

been running good till recently i got the check engine light and p420 and p430 dtc codes showing

it was coming and going

then after i changed oil and i put zmax in the oil and lucas fuel treatment in and then the check engine light came on steady....

im hoping my new cats arent bad already

a few members said it could be a body ground problem?.... which i will check this weekend

any other thoughts would be appreciated

thanks

flame

iTrader: (13)

What are all your mods? Are there any exhaust leaks?

madmaxx42

mostly stock, has a cat back? exhuast....not sure if thats the correct name... was on when i bought it

also, just been noticing my radio led's flicker a little...which would support the body grounds theory as a possible cause that someone else posted

i disconnected battery terminals to look for corrosion, they had none

the body grounds i could see from the top of the engine all looked good ...i will be jacking it up probably this weekend to look for any underneath

do you mean, im guessing exhaust leaks before the catalytic converters

i will check that also this weekend hopefully

thanks

lt1pwr1

iTrader: (1)

Big question, what did you replace the o2's with? Bosch? I hope not. If so, try to take them back and get denso's or AC Delco o2's (although I think the AC Delco's will be Denso now). Regardless, many people including myself have had issues with Bosch o2's.

madmaxx42

i havnt noticed any leaks in the exhaust.... i will have to check closer

i replace the o2's with ac-delco

put a new timing chain in ....had the bat diconnected for a while

after the timing chain, because the batt was disc of course teh light stayed off for 2 days....car ran stronger and smoother.....real nice

and then.... the light cam back on again.....seems to always come back on just after i got on and off the throttle a few times....





the worst is and good news is i know it will run good if i find the problem.... so shouldnt be any internal stuff like a piston or whatever

thanks for the help so far

joecar

Which MagnaFlow cats did you put on, the cheap non-CARB ones, or the expensive CARB ones...?

99T/AMAN

iTrader: (1)

Those codes normally indicate that the cats are bad..

bighaas79

The aftermarket cats themselves can set the codes off. They "clean" the exhaust as the federal guidlines say they shoud but they don't necessarily do it in the same way the stock cats do, which may result in downstream 02 sensor readings that may be out of the parameter the stock ecu is looking for which will set off the codes. I have seen this so many times when customers don't want to spend the money on replacing cats with expensive factory cats, so they try to save a buck putting aftermarkets on, and low and behold the light comes back on. My suggestion to anyone replacing factory cats with anything other than stock is to either have the ecu tuned to eliminate the downstreams or if that is not an option see if they can go in and open up the allowable range for the downstreams so they won't be as sensitive.