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Discussion Starter · #1 ·
Hello.

On the '12-'14 limited has anyone watched there catalyst temperature while driving? Mine peaked at 1,623 degrees while oh a long hill going 75mph on the highway. Is this too hot? It came right back down and usually settle some where around 12-1300 degrees, maybe a little less if it's town driving. Just wondering if that's a sign of impending trouble and one of those bottles of snake oil (cataclean) could help before it's too late? I have been having trouble with high long term fuel trim numbers bank 1 +17 and bank 2 + 19/20 and everything in between. My scan tool doesn't tell me if the A/F ratio is in stoich 14.7:1 it just says 100:1. But I think I heard that's another way of saying 14.7:1. So the cat shouldn't be getting any raw fuel causing the temperatures to be so high right?

My other question is about 02 sensors. If I understand correctly the upstream sensors should be constantly switching, while the downstream (behind the cats) should be stable? And if they are switching a lot this can mean a problem with the cats? So my question is, when the cats are changing temperature (rpm increase, speed increase/decrease ect) wouldnt the downstream 02 sensors mv be switching too? My theory is because the exhaust going into the cats is changing from one amount to another amount, so the cats are going to change the amount of oxygen they put out in proportion to what they took in, and the 02 sensors would reflect this. If the input to the cats were steady then the output would be and the 02 sensors would remain at one fixed number. (Assuming your cats were good). So going down the road (someone else driving me watching the scanner) and seeing the downstream 02 sensors switching semi often (not near as often as the upstream) would not be a fair test, as the rpm, speed, engine load and other factors are effecting what's being fed into the cat? I hope this makes sense. Thanks guys!
 

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I know that I was recording my cat temperatures for a while - let me dig through my logs to see if I can find one that has the cat temps. But off-hand your temps sound normal to me. In fact, let me check the tune to see what it considers "normal" (one it gets to a tune-set value, the car will richen the fuel mixture to help cool off the cats) - it's called "COT" (Cat Over Temp)...

Anyway, here are the values I see in my stock tune for COT:

Low: 1,661
High: 1,697
Extreme: 1,742

The are also parameters (Min/Max Enrichment) that determine how much fuel to add to the fuel mixture to help cool the cats (based on the low/high/extreeme cutoffs). Stock tune has min set to 1.03 ad max set to 1.30 (1.03 adds 3% fuel and 1.30 adds 30%).

So based on those values, you're fine. If I remember correctly, I'd only go into COT mode after heavy-throttle situations, like really hammering the car on the highway. Then COT mode will kick in for a bit until the cats get below the "low" temp).

Hope that helps!




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@kb3gup - for as much as you are getting into this stuff, you really should download the HPTuner "demo" software (it's the same software that you use if you buy the HPTuner hardware and is fully functional - but obviously, you can't actually write tunes without the HPTuner hardware).

This way, you could look at the stock Impala tune to see stuff like this - it really is interesting stuff! Plus, I could also send you some of my logs to see how certain sensors "trend", etc...

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Discussion Starter · #4 ·
@kb3gup - for as much as you are getting into this stuff, you really should download the HPTuner "demo" software (it's the same software that you use if you buy the HPTuner hardware and is fully functional - but obviously, you can't actually write tunes without the HPTuner hardware).

This way, you could look at the stock Impala tune to see stuff like this - it really is interesting stuff! Plus, I could also send you some of my logs to see how certain sensors "trend", etc...

Sent from my HP SlateBook 10 x2 PC using Tapatalk[/QUOTE

Once again you're a life savor. I really appreciate the leg work on that! I finally said the heck with it and was in the process of ordering the HP tuner. But my better half told me to bookmark the page and wait and see what santa brings me :D. It will be nice one way or another to have a decent scanner to see what's going on. I'd love to get a varas (may not be spelling that right) with the scope and test leads, but new those things go for $10,000! But that's snap-on for ya. I'll post back on the other post (assuming I can get past the malware) after the smoke test tomorrow. Thanks again!!
 

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@kb3gup - An interesting article from this months RockAuto newsletter - it describes how the Evap system works and it mentions that a malfunctioning evap system may cause a vacuum leak and/or fuel trim issues. I know that you replace one of the evap components, but who knows, it might be worth trying to replace the other one as well (the canister in the back by the fuel fill neck) - especially since the EVAP stuff is known to fail relatively early on these cars...

Anything, I just thought that it was a good article... Here is a copy-and-paste of the article:

An Earful of EVAP

My oldest daughter starts drivers education classes next month. She has already done a few dozen laps around the high school parking lot with me nervously twitching in the passenger seat. She also now pumps the gas. I give her tips while she pushes the correct octane button, inserts the nozzle and squeezes the pump handle. I always finish up with a reminder to tighten down the fuel tank cap. That tip has generated the most questions. As with many other questions from a teenager, the answers are not always as obvious as they first appear to be.

Will a warning light on the dash light up immediately if the gas cap is loose? No, the "Check Engine" light or its equivalent may not come on until many miles and days have passed. Why is that?

The fuel tank cap is part of the Evaporative Emission System (EVAP). EVAP prevents gasoline vapors from escaping from the fuel tank. Onboard Diagnostics (OBD II) monitors the air/fuel ratio, ignition and some other systems continuously, but EVAP is one of the systems that is typically only tested once per trip.

EVAP may actually not even be tested once per trip. Most/all OBD II COMPUTERS DO NOT TEST THE EVAP SYSTEM UNLESS THE FUEL TANK IS BETWEEN 1/4 AND 3/4 FULL. The gas cap is loose when the car leaves the gas station, but the Check Engine light may not come on until the driver has burned through a 1/4 tank of gas and probably a significant amount of time. It can be hard tying together a gas station stop last Saturday with an illuminated Check Engine light on Thursday.

Vapor Canister Purge Valve/Solenoid

Even professional mechanics might get led astray if a customer drops off a vehicle with a full or nearly empty fuel tank. With the "wrong" amount of gas in the tank, a failing EVAP part would not trigger an EVAP diagnostic trouble code (DTC), but it might lead to a DTC from another system. A bad Vapor Canister Purge Valve/Solenoid (sends gasoline vapors to the engine) or Vapor Canister Vent Valve/Solenoid (lets fresh air into the EVAP system) could create a vacuum leak or electrical problem that triggers Oxygen Sensor, Fuel Trim or other downstream DTCs. The much more relevant EVAP DTCs would not start showing up unless the fuel tank got between 1/4 and 3/4 full.

Most dads would just tell their daughter to turn the fuel tank cap until it clicks. My teenager got an EVAP earful from me!

Tom Taylor,
RockAuto.com


Sent from my HP SlateBook 10 x2 PC using Tapatalk
 

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Discussion Starter · #6 ·
@kb3gup - An interesting article from this months RockAuto newsletter - it describes how the Evap system works and it mentions that a malfunctioning evap system may cause a vacuum leak and/or fuel trim issues. I know that you replace one of the evap components, but who knows, it might be worth trying to replace the other one as well (the canister in the back by the fuel fill neck) - especially since the EVAP stuff is known to fail relatively early on these cars...

Anything, I just thought that it was a good article... Here is a copy-and-paste of the article:

An Earful of EVAP

My oldest daughter starts drivers education classes next month. She has already done a few dozen laps around the high school parking lot with me nervously twitching in the passenger seat. She also now pumps the gas. I give her tips while she pushes the correct octane button, inserts the nozzle and squeezes the pump handle. I always finish up with a reminder to tighten down the fuel tank cap. That tip has generated the most questions. As with many other questions from a teenager, the answers are not always as obvious as they first appear to be.

Will a warning light on the dash light up immediately if the gas cap is loose? No, the "Check Engine" light or its equivalent may not come on until many miles and days have passed. Why is that?

The fuel tank cap is part of the Evaporative Emission System (EVAP). EVAP prevents gasoline vapors from escaping from the fuel tank. Onboard Diagnostics (OBD II) monitors the air/fuel ratio, ignition and some other systems continuously, but EVAP is one of the systems that is typically only tested once per trip.

EVAP may actually not even be tested once per trip. Most/all OBD II COMPUTERS DO NOT TEST THE EVAP SYSTEM UNLESS THE FUEL TANK IS BETWEEN 1/4 AND 3/4 FULL. The gas cap is loose when the car leaves the gas station, but the Check Engine light may not come on until the driver has burned through a 1/4 tank of gas and probably a significant amount of time. It can be hard tying together a gas station stop last Saturday with an illuminated Check Engine light on Thursday.

Vapor Canister Purge Valve/Solenoid

Even professional mechanics might get led astray if a customer drops off a vehicle with a full or nearly empty fuel tank. With the "wrong" amount of gas in the tank, a failing EVAP part would not trigger an EVAP diagnostic trouble code (DTC), but it might lead to a DTC from another system. A bad Vapor Canister Purge Valve/Solenoid (sends gasoline vapors to the engine) or Vapor Canister Vent Valve/Solenoid (lets fresh air into the EVAP system) could create a vacuum leak or electrical problem that triggers Oxygen Sensor, Fuel Trim or other downstream DTCs. The much more relevant EVAP DTCs would not start showing up unless the fuel tank got between 1/4 and 3/4 full.

Most dads would just tell their daughter to turn the fuel tank cap until it clicks. My teenager got an EVAP earful from me!

Tom Taylor,
RockAuto.com


Sent from my HP SlateBook 10 x2 PC using Tapatalk

Thanks JT!!

That's a really good point! Is it possible for that canister to fail and not have any issues filling the gas tank? I was always under the impression if that canister failed you wouldn't be able to put gas in your car, as the pump would keep shutting off. Can they fail a different way? That would definitely explain a lot because the smoke test today found no leaks. The engine was sealed tight. This might explain why the trim numbers are much better when I take my gas cap off? Also if it failed could both banks be giving different numbers? (Bank 1- 15 bank 2- 19) or would they be equal? I find though as time goes by the difference between bank 1 and 2 is getting smaller and smaller. I know these are a lot of questions, and I will begin looking into answers I was just wondering if you knew a few of the top of your head? Or another member reading this?

Thank you again for thinking of me with the article!
 

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My girlfriend had a cel on in her car when we first got together. someone had told her not to tighten the cap too tight. for the first few fill ups I did on her car back then it would always burp out some gas right after the pump cut off for the first time. turns out she was not told about packing the tank to the brim. She too got an ear full of EVAP lol
 
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