catylitic converters

[derrick79]

this question is actually for my 97 sierra. its got a 5.7 vortec in it and i was wondering if i can cut the cats out without setting off any engine codes. i live in northern canada so they are not sticky about having cats on a vehicle.

thanks

[1981 ss chevy]

i always take cats off my vehicles the first day i have them i have done this to a 93 sierra but  your 97 has more computer systems, just see if there is a censor plugged into the cat anywhere is not i think your good to go.

[Irish_Alley]

If u have a o2 sensor on or after the cat then no but they do make a dummy sensor that will make the ecm think all is good

[VileZambonie]

Yeah you can get an O2 sensor simulator for after the catalytic converter. There are several different types.

[Irish_Alley]

thats the word i was looking for thanks vile

[treestandjunkie]

I had mine cut off of my 98 z 71 and it dont run as good as it did before. And it dont get as good of gas mileage for some reason. I could not find any o2 sensor simulators. I was told that jegs had them but when I called they said they dont make them anymore. So I dont know where you can get them?

[liftedchevys87]

Would the truck running crappier be because the o2 sensors effect the ECM's output for fuel mixture, etc?

[Captkaos]

Most vehichles (like the 98) have primary and secondary 02.  The ECM will throw codes if either of them are missing, and it can cause it to get worse than optimum mileage.  We typically turn the rear o2's off on some cars/trucks on the ECM.

[VileZambonie]

Pre cat O2 sensors and A/F (Lambda/Wide band) sensors are for calibrating injector pulse width. Post cat O2 sensors are only for catalyst efficiency monitoring and have no effect on driveability and fuel economy. They're essentially there for making sure the catalytic converters are functioning properly.

[SUX2BU99]

A trick I used to see was zip-tieing the downstream 02 sensor to the frame, essentially making it see no emissions at all. For those that did it (Dodge Dakotas) didn't seem to have problems with it. Would it make the ECM think that the downstream 02 sensor was seeing 'perfect' conditions?

[VileZambonie]

Sux, I don't see how that would work considering it would be missing a viable ground through the sensor body and most importantly the air outside contains approx 21% oxygen! That sure would indicate the cat isn't oxidizing! Anyway here's an example of a cat efficiency monitor


This diagnostic test monitors catalytic converter efficiency, the ability of the catalytic converter to perform its function in reducing exhaust emissions of hydrocarbons, carbon monoxide, and oxides of nitrogen. This test is only run once per ignition cycle and only after the catalytic converter has warmed up to operating temperature. Catalytic converter efficiency is calculated using data collected from the pre and post-converter oxygen sensors during steady state driving conditions. In general, the pre-converter oxygen sensor signal should fluctuate like those of the front and rear oxygen sensor. The post-converter oxygen sensor signal should fluctuate less than the pre-converter sensor. The catalytic converter efficiency test is performed in two stages. The first stage calculates post-converter oxygen sensor deviation, difference from the average value, compares these deviations to the maximum allowable deviation, based on air flow, and records a failure if those deviations are excessive. The second stage is only run if the first stage fails or DTC P0420 is currently set. The second stage averages the difference between the deviations calculated in the first stage and the maximum allowable deviations. If the second stage average is too high, DTC P0420 will set.

CONDITIONS FOR SETTING THE DTC

Test Conditions



DTC's P0101, P0102, P0103, P0117, P0118, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0139, P0140, P0141, P0143, P0144, P0146, P0147, P0151, P0152, P0153, P0154, P0155, P0171, P0172, P0174, P0175, P0300, P0441, P0502, P1133, P1134, P1139, P1140, P1153, P1154 or P1441 not set.
DTC P0420 test has not run this ignition cycle.
Catalytic converter at operating temperature.
ECT 75°C (167°F) or greater.
IAT is -28°C (-18°F) or greater.
Air flow between 15 and 35 grams per second.
Average MAP signal less than 59.3 kPa.
Difference between current MAP signal and average MAP signal less than 8 kPa.
Vehicle speed between 20 and 75 MPH.
Throttle position greater than 2.2 degrees.
Engine speed 3000 RPM or less.
Closed loop fuel control enabled.
Front and rear oxygen sensors ready.
Commanded air/fuel ratio 14.7 to 1.
Short term fuel trim not limited.
Failure Conditions



Stage 1 average difference between actual oxygen sensor deviation and maximum allowable deviation greater than 93 millivolts.
Stage 2 average of the average differences calculated in stage 1 is greater than 9 millivolts.
ACTION TAKEN WHEN THE DTC SETS



The PCM will illuminate the Malfunction Indicator Lamp (MIL) when the diagnostic runs and tails.
The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC



The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.
PCM battery voltage is interrupted.
Using a Scan tool.
DIAGNOSTIC AIDS

Fuel with a high sulfur content can cause a marginal converter to look bad. Check fuel quality.

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.



Checking for conditions that can cause the catalytic converter efficiency to appear low. Inspect and repair problems, if any, before proceeding.

[SUX2BU99]

Beats me Vile why it worked but it seemed to. There might have been implications that weren't so easy to detect though like performance or fuel mileage affected that people didn't notice or report initially.

[autorepr]

Howdy

  What are you planning to use the truck for? I would seriously just leave it on if it's not clogged. It's free flowing enough that your probly not going to gain anything from removing it and as a plus the exhaust fumes won't smell as bad? What muffler and pipes do you have on it? They're probly the most restrictive part of the exhaust system.

[derrick79]

well i had a 98 z71 single cab short box with the exact same engine and mods and i bought it with the cats already so i dont know how he did it. but anyway i ran true dual no cats with flowmaster super 44s with 3 inch tips and it sounded absoutely awesome. so i would be running something like that on this 97.