Fink

OK....

The very first time anything went wrong, the CEL said something about the cat. threshold or something like that was not up to par. So I replaced the rear cat. (I thought it only had one.) The light went off BY ITSELF after a half tank. Came back on about 3-4 days later.

I went back to the dealer, code was the same as before...the service guy, who I trust very much said that it was a bad cat and he pulled back in the shop and low and behold I've got 2 cats.

Order another cat, not knowing it would require a different one than before. Take it to muffler shop, they say can't be done. Thats when this thread started.

So now, I've got the front O2 sensor and rear O2 sensor in the stock locations. I have the front cat. converter removed and replaced with a regular pipe. I've got the new high flow cat in the place of the stock rear one.

Does that make any sense? Maybe I should replace the rear O2 sensor and see what that does for me.

Fink

midiwall

Hmmm, okay, so it sounds like you were looking at one of: (ref: https://www.yotatech.com/~corey/tech/dr_z_obd/dr_z.htm)

• P0420 Catalyst System Efficiency Below Threshold (Bank 1)
• P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)
• P0422 Main Catalyst Efficiency Below Threshold (Bank 1)
• P0423 Heated Catalyst Efficiency Below Threshold (Bank 1)
• P0424 Heated Catalyst Temperature Below Threshold (Bank 1)
  
  
• P0430 Catalyst System Efficiency Below Threshold (Bank 2)
• P0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2)
• P0432 Main Catalyst Efficiency Below Threshold (Bank 2)
• P0433 Heated Catalyst Efficiency Below Threshold (Bank 2)
• P0434 Heated Catalyst Temperature Below Threshold (Bank 2)

(note the "bank 1" versus "bank 2" differences)

From what I understand, on a CA emissions vehicle, each of the P043x codes will come up based on the ECU doing some math against readings from the front O2 sensor and the rear O2 sensor. The rear O2 sensor needs to show cleaner air than the front otherwise it'll throw a code.

I'm not clear on how the ECU computes that the front ("bank 1") cat isn't working right. It would need to compute before/after readings from somewhere... Oh wait, you actually know this answer. You've got a real wideband O2 sensor in there as well don't you? That would let the ECU compute the efficiency of the first cat (the wideband A/FR would have to be before any cat) and that would let it throw the P042x codes.

Ahh... so... there are a couple of new problems now...

a) We need the code to know which cat the ECU thinks is bad...

b) ...but, that's all for naught since you only have one cat now...

c) ...which means that the ECU is surely thinking that the "front" cat is bad, since it's been removed.

so..... (I think) either you need an ECU out of a non-CA 3rd gen (since it won't have the programming to look for two cats; or you need to fake out the front O2 sensor (NOT the A/FR!); or you need to verify that the ECU is complaining about the "front" cat (P042x code) and then... ignore it for the rest of the truck's natural life.

eek.

Maybe I'm wrong... I think I'm hoping that I am.

Fink

Whew...

OK, maybe I should reset my CEL and see what happens after that. Then read the code and go from there? Agreed?

Fink

EDIT: I believe the front sensor is the AF/R

midiwall

It wouldn't hurt... We'd get a clean look at what the ECU is trying to say.


Yeah, I thought about that, and that's the way it is in a single-cat system, but then I'm confused on how the ECU could determine the efficiency of each of two cats. You need a before & after snapshot for each cat to make the call. That tends to say that you'll need 3 sensors.

If the front O2 sensor was there for feeding the ECU A/FR info *and* to determine the efficency of the front cat, then that would mean the sensor would have to come _after_ the cat. And doing that would confuse the reading that the ECU needs to watch for a good A/FR.

Fink

This is all getting WWAAYY too confusing lol

I will get it reset tomorrow and I would expect it to go off again by Thursday. I'll let you know what I find out.

Fink

mt_goat

Here is one more option since I douht you have very strict smog testing in AR: http://www.urdusa.com/product_info.p..._id=1230100014

Fink

Awesome! That looks perfect! I will definitely look into that a bunch more after my CEL goes off again and I figure out what the problem is.

Here is the current situation for those who want to help and keep updated:

Front O2 sensor is in stock location, front cat. has been removed and replaced with pipe. Rear cat. has been replaced with a Car Sound high-flow cat. converter and that O2 sensor is also in stock location. I have no knowledge of how new/old the O2 sensors. The possibility of them being bad is DEFINITELY a reasonable thought.

I went to the dealership today and had my CEL reset. Next step is to post on here again to tell you guys what code it throws next.

I want to thank you all very much for your help, especially 'midiwall', thank you very much you have been a great help! I appreciate it!

Thanks again guys!

Fink

EDIT: I gotta be honest, this thing is MUCH stronger now! I guess with that first cat. removed it flows a whole lot better, I can easily tell the difference in power! Another note for those of you who may have to do this or are just wondering, the sound of the exhuast has a MUCH louder rumble to it. So overall, except for the CEL going off again (maybe it won't, but I think it will) that is the only down side to this forced modification. I will be interested to see how my mileage does after this. I think my fuel gauge is screwed up, this morning I turned the car on and it said I had a quarter tank, turned it back on after my afternoon class and it was almost empty! So I will have to troubleshoot that problem before I can get an accurate mileage number.

midiwall

Nah, do it the easy way...

The next time you pump gas into it, let the pump stop when the handle valve triggers (the "click"), i.e., don't top off. Reset the trip odometer, then drive for a while. 100 miles, 150, 200... whatever.

Pump gas again, and stop pumping when it clicks. Get a receipt, climb back into the truck and write down the mileage from the trip odometer on to the receipt. DON'T FORGET TO RESET THE TRIP ODOMETER AGAIN!

When you get home, find a calculator and divide the mileage by the quantity of gas you put in (it's on the receipt, and accurate to 3 decimal places). The result is your economy in miles per gallon. For example: Trip odometer said 183 miles; you pumped 11.896 gallons, so 183/11.896 works out to 15.38 mpg.

MUCH more accurate than your fuel gauge.




And, you're very welcome! the O2 faker is cool. But, if you throw a code again, please post it back here and see if we can figure out what's going on before we start faking out O2 sensors.

Fink

I always calculate my mileage and put it into Excel...but the mileage isn't the problem. The actual gauge fluctuates up and down randomly.

Right now it said I've gotten 118 miles on a quarter tank of gas...I WISH!!

I will post on here if it throws a code again so we can figure it out. Thanks!

Fink

midiwall

Ahh, okay... I though you were talking about "waiting until it hit the 3/4 mark, figure that's 12 gallons and calling it good". Other folks have done that...


Carry on then!

cootees

Did the shop move your 02 sensors at all? The reason I ask is that when the exhaust fumes travel throughout the pipe the exhaust is actually swirling around the wall of the pipe. The 02 sensor placement is critical. You have up to 1/8 of an inch of play to move the 02 sensor otherwise the exhaust will miss the sensor and this could be the reason it is throwing a code.

midiwall

(welcome to the forum!)


Ummm, ahhh... ummm...

An 1/8 of an inch? Do you have a document source to support that?

While there is science to a good exhaust system, there's no way that the tolerances of O2 sensor location are anywhere near that tight.


There's quite a bit of pressure in an exhaust system. That pressure comes from a lot of gas volume in a confined space. There's PLENTY of gas in the pipe to feed an O2 sensor, even at idle.

My front sensor has been moved 3 times in the last 3 years. It's nowhere near the "stock" location. Since "stock", I've added headers, spent some time with 3" piping, then 2.5", then a complete re-work from the end of the headers on back, through the cat and on to the tail.

Each time the front (and rear for that matter) sensor has moved. I've never thrown a code as a result of any of the work.

cootees

I can retrieve documentation. I am am exhaust supplier for many muffler shops. When I was speaking with my Magnaflow Rep. that is what he stated to me and I am pretty sure the guys at magnaflow/carsound know what they are talking about. Let me find some information and I will post it up.

midiwall

That'd be great. 'cause if the rep is right, then there are a LOT of people out here throwing codes and having lousy engine performance. ..which I don't think is the case.

fwiw, I can't find anything dictating such a critical location of the sensor. Even the highly-technical articles I'm reading don't mention it...

Here's a higher level FAQ from Bosch:
http://www.boschusa.com/AutoParts/FAQs/OxygenSensors/

Here're a couple of geekier papers from independents:
http://www.asashop.org/autoinc/dec2002/mech.cfm
http://home.flash.net/~lorint/lorin/fuel/lambda.htm

I have more technical references, but they're outside this scope.


The only thing I can think of is with a non-heated sensor. By nature, they're more sensitive to getting a good sniff, but that's not what we're talking about here. And even so, non-heated sensor placement is more about getting it _vertically_ into the exhaust stream, not horizontally along the pipe.

Maybe that's what the rep meant? He's talking the depth into the pipe and you're thinking placement front-to-back along the pipe?

cootees

I guess it could be.. i'm heading back to work now so I will shoot him an e-mail and ask him about it.

Fink

, you guys are way outta my league!

No code yet, only put about 1/8 of a tank through it so it will take a little while yet I would guess. If it doesn't throw a code that'd be SWEET!! But if you think about it, itd be VERY odd if it didnt, I mean hello?! I just removed an entire cat!!!

Anyway, I will post up when the code is thrown.

By all means though, carry on your conversation, this has become quite a thread of info...a very good addition to YT!

Fink

Fink

CEL WENT OFF!!

Ugh, I thought I was out of the woods...

P0420 - Cat. in bank 1 not performing right (lamens terms)

OK...so, lets review:

Rig came with 2 cats because it was a Calif. emissions vehicle. CEL went off a long time ago, bad cat, I thought there was only one, ordered a Car Sound, had it replaced went on my way. CEL shut off for about a week; came back on, pulled code, same one as the initial time, bad cat., dealer looked at it, said there were two cats b/c of Calif. emissions. So, I ordered another Car Sound cat., same one as before, take it to the muffler shop, they raise it up come back to me and say its the wrong kind of cat.

From the factory the forwardmost cat. has a bend in the front side of it going up to the engine bay where the front O2/AFM sensor is. I figured since I don't live in Calif. I would just cut off the front cat. So I did, CEL stayed off for a long time. Came back on about 2-3 days ago, got code pulled today, P0420, same as before, bad cat. in bank 1 (the one I removed).

So now I have a dilemma, my mileage has decreased SEVERELY I am now only getting about 15-16mpg...I was getting about 19-20.

Somewhere in this thread there was a widget called an 02 sensor simulator or something like that, but I don't think that would work because the 02 sensor is working fine.

What do I do from here???? I asked the muffler shop a long time ago about moving the 02 sensor and they said they wouldn't recommend it because of messing up the ECU. So...do I need to get an ECU from a wrecked 3rd gen non-Calif. emissions and see if that does it? I talked to my guy at the dealer today and he said that doing that my cause other things to cause a CEL going off. Right now I could care less about the light, I just want my mileage and performance to go back to normal. Maybe I should just put another Car Sound cat in a few inches down from where the stock front cat was, obviously not in the same exact position and see if that helps. If not, go from there and maybe try and move the 02/AFM sensor accordingly...I'm really up for anything!

HELP!!!!

AAANNNYYYY ideas are MORE than welcome!

Fink

cootees

I don't know much about the California cars but this makes sense to me so maybe it will to others too. Or maybe we can get more insight about this:

We all know about the strict emissions in Calif. but it seems to me that the ecu would differ slightly from the other 49 states ecu because of the Calif. emissions. You think about it... the ecu was programmed to function with the CARB legal OBDII 02 sensors and cats. The vehicle has since been taken out of California and you wish to retrofit it with a 49 state legal cat. It seems to me that it would be natural for the ecu to throw a code when it is fitted with a less effecient cat. Which would leave 2 options... put carb legal cats on the vehicle or switch the ecu. Or it may be able to be reprogrammed to swich it off of Ca. emissions.

Someone who is more familiar with the Calif. vehicles may be able to tell you if what I think has any truth behind it or not. Hopefully some guys will help throw out some answers to help you get your problem fixed.

Fink

I asked my guy at the dealer about possibly being able to reprogram the ECU out of Calif. emissions he said he had no idea how to do that. Replacing the ECU seems like a pretty sensible thing to do. I wonder how much one of those would run at a salvage yard.

More ideas guys, is this ECU thing a good idea, can the ECU be reprogrammed...yada yada.

Thanks for the quick reply cootees!!

Fink

mt_goat

Why don't you call Gadget about this? http://www.urdusa.com/product_info.p...s_id=120000008
It looks like the cheapest & best solution to this problem. It conditions the signal from the rear O2 sensor and keeps that signal in the proper range the ECU is expecting to see from a properly functioning and healthy catalytic converter.