Repairing LT1 Z28 catalytic converters
09-27-2013, 08:39 PM
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Repairing LT1 Z28 catalytic converters Hey guys I'm new to this whole forum thing and I just had a quick question and I don't know if I posted this is the right place or not. But I went to a muffler shop and got my exhaust diagnosed from a engine code and they said it was both catalytic converters and they needed to be replaced. They are charging me $887 at one shop and $857 at another. And my problem is that my car was apparently bought in California and it has to have smog legal catalytic converters put on it which costs a lot. And he said the car would still have a trouble code if I got anything other then te expensive 50 state legal cat. Is this true? And if so can you erase the California emissions off the ecu? (I'm sorry if that's a dumb question). And is there any good High flow 50 state legal cats? One of the muffler shop guys said magnaflow is a horrible cat to get for a z28 which is strange and he wants to get me a DEC cat that's around $300-400. Any help would be great! O and I live in oregon if that helps. And the car is a 1996 z28
Last edited by Z28LikeABoss; 09-27-2013 at 08:51 PM.
09-27-2013, 10:19 PM
#2
Welcome!
Before you spend a boatload of money on replacing your cats, try to clean them first.
Do a search on "Seafoam" and you'll get enough information to get started.
Good luck!
Before you spend a boatload of money on replacing your cats, try to clean them first.
Do a search on "Seafoam" and you'll get enough information to get started.
Good luck!
09-28-2013, 12:17 AM
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Alright sweet I should have thought about trying that! How do you go about seafoaming the cats or to where it gets to that direction?
09-28-2013, 06:49 PM
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The trouble code is p0430. I thought it would be unusual for both to go out at the same time as well. I will try to find a y pipe I found a x pipe on summit for $135 I hope that'll be good enough. Thank you all for your answers!
09-28-2013, 07:52 PM
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Code p0430 and the one muffler shop won't even put them on even if I buy the 50 state legal ones he just said no I can't do that and walked away which is fishy to me
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09-28-2013, 09:11 PM
#8
That being said...
- It might not be a cat problem. This code is thrown by the second post-cat O2 sensor. It is possible that your sensor could be bad and incorrectly reporting a problem. http://www.obd-codes.com/p0430 Before you sink $$$ in to a new CAT, you should confirm the function of the O2 sensor by having someone look at its waveform on a special scanner OR switch the left and right sides. (If your P0430 turns to a P0420 when you switch the post-cat sensors, then you know its the sensor and not the cat.) If you do this - very important - be sure to use anti-seize compound on the O2 threads each time you switch them. Otherwise the threads can weld themselves to your exhaust pipe.
- It could be a bad cat. The ceramic substrate that holds the platinum is fragile and hitting road debris, etc. can break it. When that happens, gasses don't flow through it efficiently and the performance of the CAT and your car will diminish.
Its illegal to circumvent pollution controls, so no reputable shop will replace your CAT with a part that isn't spec'd for your car. You might see what the cost of the part is from a parts store. With the credit on the core, it may be worth your while to buy the correct part yourself and pay a buddy to install it with a nice case of beer, etc.
Hopefully, its just an O2 sensor.
10-01-2013, 10:19 AM
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If its the cats, I've heard of people running a spacer which makes the o2 not go in all the way so it reads a lower pollution number and the code goes away.
10-01-2013, 11:12 AM
#10
That being said...
- It might not be a cat problem. This code is thrown by the second post-cat O2 sensor. It is possible that your sensor could be bad and incorrectly reporting a problem. http://www.obd-codes.com/p0430 Before you sink $$$ in to a new CAT, you should confirm the function of the O2 sensor by having someone look at its waveform on a special scanner OR switch the left and right sides. (If your P0430 turns to a P0420 when you switch the post-cat sensors, then you know its the sensor and not the cat.)
Hopefully, its just an O2 sensor.
- It might not be a cat problem. This code is thrown by the second post-cat O2 sensor. It is possible that your sensor could be bad and incorrectly reporting a problem. http://www.obd-codes.com/p0430 Before you sink $$$ in to a new CAT, you should confirm the function of the O2 sensor by having someone look at its waveform on a special scanner OR switch the left and right sides. (If your P0430 turns to a P0420 when you switch the post-cat sensors, then you know its the sensor and not the cat.)
Hopefully, its just an O2 sensor.
10-02-2013, 03:32 PM
#13
"An oxygen sensor is not reading (functioning) properly"
If so, what IS the magic sensor on a car that would measure the catalyst efficiency and trigger the system throw the code? The only sensor in the tailpipe after the CAT that I know about is the oxygen sensor. Can you enlighten and amaze us with your knowledge and what would cause this code to be thrown?
10-02-2013, 03:40 PM
#14
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The ONLY way a rear 02 can cause a cat code is if the rear 02 sensor magically starts oscillating as much as the front - thats how the PCM sees a "catalyst failure", it sees the front and rear 02 sensors of one specific bank doing the same thing. Where as normal conditions, after closed loop, the front sensor is going from .1 to .9V continuously and the rear stays on one end of the spectrum (I wanna say low, but I forget the specifics). The 02 sensor is used to diagnose the cat, but if the 02 sensor isnt working, it will throw an 02 sensor code , not a cat code.
I've NEVER seen an oxygen sensor cause a P0420/P0430. Ever. Probably because they can't.
I've NEVER seen an oxygen sensor cause a P0420/P0430. Ever. Probably because they can't.
10-03-2013, 12:24 AM
#15
This is a good article on O2 sensors. It doesn't talk about post-CAT sensors, per se, but it does explain how the sensors get contaminated.
http://www.google.com/url?sa=t&rct=j...,d.eWU&cad=rja
You do bring up a good point in that the wave forms are telling. If one has a good scanner, the waves can be read without the need to switch sensors or change them out on a trial/error basis.
10-03-2013, 09:24 AM
#16
Sensor replacement keeping the DTC from returning usually has other factors involved like replacement of other parts that affect the tune, or simply the resetting of the PCMs KAM (DTC not returning due to detected efficiency varying just above or below threshold). The only time a sensor "fixes" the inefficiency issue is when the PCM is also recalibrated to change the PCM's DTC threshold. BTW - this threshold can be monitored with many PCMs in Mode 6 data. That means I can go into the PCM and read a numeric value for the catalyst efficiency and can determine if it's likely to fail soon, or even if a sensor changes the efficiency readings (which is so unlikely I'll just call it impossible).
The ONLY factor that could trigger a false inefficiency DTC is a leak in the exhaust system between the upstream and downstream sensors.
Food for thought: GM released a customer satisfaction program on our cars for P0420 and P0430 DTCs. Not a single car was fixed with a downstream sensor. ALL had the converter(s) replaced. If the cars could have been fixed with a sensor replacement, don't you think GM would have liked to save several hundred dollars per car by doing so? They didn't even want to change the threshold like many other manufacturers do illegally... cough cough Nissan cough cough.
10-03-2013, 10:22 AM
#17
And my problem is that my car was apparently bought in California and it has to have smog legal catalytic converters put on it which costs a lot.
I would buy some $75 high flow Thunderbolt cats from eBay, have a shop weld them in and get the codes tuned out if they happen to come up.
10-03-2013, 10:00 PM
#18
If you think the OP should go out now and spend the money to replace the CAT, without confirming the outlier causes are an issue, please say so.
Given the OP's sensitivity to cost, I'm suggesting that the O2 sensors should be confirmed as being good before replacing the CAT. If it is the O2 sensor, we'll all be happy and have a
. If it is indeed the CAT, then we'll all be happy as there was no harm done in checking the sensor. (But - there will be no beer because all the money will be spent on the part.)Any one of us would feel like a total terd if we spent $400 for a new cat and found the problem was a $50 sensor. (Particularly when the sensor test in this case is free.)
10-04-2013, 04:08 PM
#19
No, the sensor DOES NOT "report the code". The PCM compares the waveforms of the upstream and downstream sensors. If the calculated efficiency is outside the acceptable range, the PCM triggers the DTC.
Throwing parts at a car is poor practice, yet you're condoning the replacement of a sensor because it's cheap. The diagnosis has already been performed. Certain DTCs require no diagnosis beyond DTC retrieval. Catalyst inefficiency DTCs are among them. I do this for a living. Recommending a sensor replacement for this problem shows as much ignorance on the topic as someone recommending an oil change to cure a bearing knock.
Throwing parts at a car is poor practice, yet you're condoning the replacement of a sensor because it's cheap. The diagnosis has already been performed. Certain DTCs require no diagnosis beyond DTC retrieval. Catalyst inefficiency DTCs are among them. I do this for a living. Recommending a sensor replacement for this problem shows as much ignorance on the topic as someone recommending an oil change to cure a bearing knock.
