Question for c4c5specialst about exhaust system problem

[2000FRC]

I have 2 (header to back flange) exhaust systems. One system I use for the track and the other for street driving. I gutted the small pup cats on one system to increase exhaust flow for track use. After driving for the "pupless" system for a few miles, I got codes P0134, P0140 (relating to insufficient activity in Bank1 sensor1-A and Bank1 sensor 2-B) and codes U1016, U1064, and U1096. Also driving back from the track I noticed my gasoline MPG was extremely low, so It appears that it is running very rich. I have reset the codes, but they come back after a while.

I replaced the "pupless" system with the other completely stock system (has its own oxygen sensors) and the codes DO NOT appear, so the problem is clearly related to the absence of the pup cats on the pipes I use for the track, and possible damage or fouling of the oxygen sensors.

I am puzzled why the sysem with no pup cats (the main cats are still there) is causing these codes and the engine to run extremely rich. The car is certified to California/Northeast emission requirements.

Do you think that I have damaged or fouled the up stream or the down stream oxygen sensors? If so is there any way to clean them so they will function properly again? Is there anyway I can use the "pupless" system on the track and not have this problem reoccur? (for instance using Simulated Oxygen sensors). If not, I'll just go back to the stock system for all my driving requirements.

I thought gutting the pups would be a good way to get a few more ponyies for the track, but this has caused more problems than benefits.

 

[c4c5specialist]

Hi there,
While I cannot really speculate, a few things should be noted.
First, If you drop an o2 sensor, you could damage it.
Second, No, I dont believe that you removing the PUP cats caused the condition, as long as you flushed out the converter material. The material is VERY dangerous, and should be flushed out with water.
As for what happened, something must have happened to those 2 sensors, to cause the codes.
A very simple test, would be to change the sensors when you changed the exhaust, simply to confirm that the sensors are definately bad.
I mean taking the sensors from the exhaust creating the codes, and swap them with another set.
Just remember, when these codes set, the PCM will default, giving you the horrible mileage you have experienced.
The U codes you can disregard, as long as they are H for history, and never a C.
Allthebest, c4c5

 

[2000FRC]

Thanks for your reply. More information about the pupless system follows.

When I gutted the pup cats I put positive air pressure on the tail end of the system which pushed all the dust created out the other end toward the pup cats, so any dust created did not reach the main cats or the oxyen sensors. I also vigerously wire brushed the inside of the pup cats to get out all traces of material. It ws a bright shinney pipe when I finished, but I did not flush with water.

After installing the pupless system, I drove the car for about 500 miles with NO sign of any codes. About 200 miles of this was very hard track driving. Coming home from the track at regular highway speeds and RPMs is when the codes first appeared and the mpg tanked.

My first thought was that I had fouled the O2 sensors downstream of the cats. So, I bought new ones from my friendly Chevrolet Dealer, dropped the pipes and installed them. I did not drop or damage the sensors prior or during the installation. The old O2 sensors looked dark grey and the exhaust pipes downstream of the main cats had a very strange motteled pattern on them which I assumed had been caused from some higher than normal exhaust temperatures. This type of motteled pattern does NOT show up on the stock exhaut system.

Last week I drove the car (with the new O2 sensors in the pupless system) up to Limerock (about 250 mi) drove only 50 miles on the track at very modest speeds (it rained all day), and then coming home, the codes reappeared. I reset them twice and after the second reset, they stayed off and I averaged about 27 mpg coming home.

I later drove the car around home and the codes are back. This is what prompted my original post for help. I did replace the pupless system with the original stock system and everything is fine. No codes.

Can I install O2 sims to eliminate this problem, or can the O2 sensors be cleaned and reinstalled? Or should I just keep using the stock system and forget about using the pupless system?

Thanks again for your help.:cool

 

[c4c5specialist]

Hi there,
It is also possible that the converter in the back is NOT working to its full potential, and the front PUP was making up for it.
I would simply install the other system, and be done with it.
Many people claim gains on the c5 without the pups, although, IMO, not worth the trouble.
I would simply install some FLP headers with high flo cats, before I would mess with the stock system.
Simulators should NEVER be an option, because they only produce problems later on.
Allthebest, c4c5

 

[hawaii-5-lo]

hey c4/c5,could you explain what kind of problems will arise later if using simulators?the reason i ask is,in 6 months i will be getting headers,super high flow cats,x-pipe and stinger cat-back.so the other day i hollowed my cats(99' only 2 cats) i got the two codes for convertor efficiency,0420-0430 if i remember correctly.so i ordered the simulators.although i will only be doing this for 6 months,i will be giving the simulators to a friend who plans on leaving them on his car.maybe i can pass this info to him.i did this for an experament,he plans on hollowing his cats and leaving it like that because we dont have emissions testing in hawaii.i just want to compare the hollow cat system against the new system i talked about above,on the track.thanks,later,Todd.

 

[c4c5specialist]

hey c4/c5,could you explain what kind of problems will arise later if using simulators?the reason i ask is,in 6 months i will be getting headers,super high flow cats,x-pipe and stinger cat-back.so the other day i hollowed my cats(99' only 2 cats) i got the two codes for convertor efficiency,0420-0430 if i remember correctly.so i ordered the simulators.although i will only be doing this for 6 months,i will be giving the simulators to a friend who plans on leaving them on his car.maybe i can pass this info to him.i did this for an experament,he plans on hollowing his cats and leaving it like that because we dont have emissions testing in hawaii.i just want to compare the hollow cat system against the new system i talked about above,on the track.thanks,later,Todd.

HI there,
Well, simulators basically supply a fixed voltage to the PCM. This fools the computer into thinking that the converters are there, when they are NOT.
What alot of people are not being told, is that the rear o2 sensors comprise 25% of the complete air fuel ratio computation. When there is not a correct fuel ratio, fouling of the plugs, carbon buildup, and other problems exist. As the fuel trim tables change, when incorrect with o2 sims, the problems become worse.
People will tell you that you can edit these problems out with an aftermarket programming. You can, but will only create further problems, that are not talked about, or anyone will admit to.
Allthebest, c4c5

 

[hawaii-5-lo]

hello c4/c5 spec,thats interesting,i assumed the o2 sensors would be able to learn or correct,the car has good power now,but it makes sense what your saying,i will defenitly be putting the Random superflow cats on there with my new system,and eliminating the "sims",thanks for your help again,later,Todd

 

[c4c5specialist]

hello c4/c5 spec,thats interesting,i assumed the o2 sensors would be able to learn or correct,the car has good power now,but it makes sense what your saying,i will defenitly be putting the Random superflow cats on there with my new system,and eliminating the "sims",thanks for your help again,later,Todd

Hi there,
The Sims replace the rear o2 sensors, so there is no PCM adaptive learning for a fixed voltage that does not change with oxygen content in the exhaust gas.
This is why the elimination of these is not good for the engine, fuel formulations, and drivability.
Allthebest, c4c5

 

[hawaii-5-lo]

hello again,i pretty much know how the simulators work to fool PCM,the part i was unclear on this,i thought the pre-cat simulator was air/fuel, and the post-cat o2 was to measure the pressure difference in the convertor,for example a clogged cat. i am now very clear on this issue,hopefully everyone else is reading this also,theres alot of cat questions right now,thanks again, are you going to be a C6 specialist also?:cool i would guess yes.later Todd.