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catalytic converter code, wrong fuel octane?

 
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Impala_03
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PostPosted: Mon Feb 11, 2013 6:07 am    Post subject:  catalytic converter code, wrong fuel octane? Reply with quote

Getting catalytic converter code P0420 is it possible that it's a bad sensor or gas used? after a long trip CEL went away.
2003 impala LS 3.8L this is not have a super charger as much as I wish it had it.


I checked the catalytic converter with a rubber mallet and did not hear anything rattle inside

That long trip I used 91 octane instead of 87 or 89.


I suspect the PCM was tampered with by one of the 5 previous owners. fuel mileage did increase significantly when using 91 octane. +5MPG city and +13MPG freeway

Computer did say 45MPG average, but I think the computer was exaggerating. Rolling Eyes going about 75 mph on I215 (Legal posted limit is 70 or 75 depending on the area)

was getting 34.5 to 35MPG by using pumped in gas X miles traveled. ( 34.5 to 35 is the adjustment for slope at the gas stations.)




87 and 89 Fuel economy has dropped to 17/22MPG and CEL catalytic converter code


NO visible smoke from the tail pipe.

Burning 1 qt per 2k miles. which is in manufacture specification.

Right now I can not afford premium fuel. since it's hitting 4.20+ per gallon.




is there anyway to check if the PCM was tampered with?

I know for sure the BCM was tampered with since I can run QUAD headlights

High beams and low beams at the same time
(DO not ask me how to do it since I do not know)
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Lingenfelter
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PostPosted: Mon Feb 11, 2013 12:48 pm    Post subject:  Re: catalytic converter code, wrong fuel octane? Reply with quote

Was this a one-time set of calculations? Over a longer period, the results will become more accurate.


It is possible to have quad headlights without modifying the BCM - if the switch wears out, all 4 bulbs will remain illuminated all the time. if you can switch yours on and off, maybe some custom work has been done.

I can't see 13mpg being attributed to premium gas alone, unless the PCM was tuned to run 91 and you've been consistently putting in 87 - which will probably ruin your milage, and maybe put you at risk for a lot of predetonation (knock)

In my 2003 LS with NA 3800 engine, I can get 36mpg highway on regular fuel, so your milage numbers on 87/89 fuel are pretty dismal. Admittedly, the 36mpg is a pretty good run for my car.

I'm pretty sure, If you don't want to buy premium and don't care about any potential PCM tuning, you can have the dealer reflash the PCM - this will revert it to factory settings. Let another member here confirm before you do something like that, though.

PS: 87 octane here cost me $4.88 a gallon last time I filled up. Premium is more like $5.22 Shocked

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PostPosted: Mon Feb 11, 2013 2:07 pm    Post subject:   Reply with quote

Changing up your octanes is never going to set a cat code. Not ever.

P0420 is catalyst efficiency low. Suspect catalyst, B1S2 HO2S.

Most likely your cat has been collecting sticky coolant residue inside from your intake leak. This is a long term consequence of LIM failure, along with bearing failure from coolant in oil; oil and coolant that reach the combustion chamber will clog the catalyst.

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Impala_03
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PostPosted: Mon Feb 11, 2013 5:04 pm    Post subject:  Re: catalytic converter code, wrong fuel octane? Reply with quote

Lingenfelter wrote:
Was this a one-time set of calculations? Over a longer period, the results will become more accurate.


It is possible to have quad headlights without modifying the BCM - if the switch wears out, all 4 bulbs will remain illuminated all the time. if you can switch yours on and off, maybe some custom work has been done.

I can't see 13mpg being attributed to premium gas alone, unless the PCM was tuned to run 91 and you've been consistently putting in 87 - which will probably ruin your milage, and maybe put you at risk for a lot of predetonation (knock)

In my 2003 LS with NA 3800 engine, I can get 36mpg highway on regular fuel, so your milage numbers on 87/89 fuel are pretty dismal. Admittedly, the 36mpg is a pretty good run for my car.

I'm pretty sure, If you don't want to buy premium and don't care about any potential PCM tuning, you can have the dealer reflash the PCM - this will revert it to factory settings. Let another member here confirm before you do something like that, though.

PS: 87 octane here cost me $4.88 a gallon last time I filled up. Premium is more like $5.22 Shocked





35 on the way there. South on the I15/I215 light traffic

29 on the way back north on I15/I215 slightly uphill medium/heavy amount of traffic.

I did replace a damaged fuel regulator. only ran it for 10miles to the shop that way.





I notice the engine does in fact run much quieter when running 91 octane.
a few times I thought it had stalled on me , but I checked the rpm to see that it was running. Embarassed




Dan wrote:
Changing up your octanes is never going to set a cat code. Not ever.

P0420 is catalyst efficiency low. Suspect catalyst, B1S2 HO2S.

Most likely your cat has been collecting sticky coolant residue inside from your intake leak. This is a long term consequence of LIM failure, along with bearing failure from coolant in oil; oil and coolant that reach the combustion chamber will clog the catalyst.
Not seeing a loss in coolant.. The only time coolant was lost was due to a broken hose to the reservoir tank. I had to add some after burping the system though. Rolling Eyes
It was set off after I used the arco 87 octane gas



Went away when I used 91 at mobil gas station and was off for the whole trip tell I used 89 octane. that is when the code reappeared


This car has done weird stuff like saying High Beam Out when the tires were low. Rolling Eyes
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PostPosted: Mon Feb 11, 2013 7:10 pm    Post subject:   Reply with quote

Sadly, the BCMs on these cars are mighty fragile. Odd electrical issues are usually a hallmark of a bad BCM and it sounds like you might have one that needs replacing.

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Impala_03
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PostPosted: Thu Mar 07, 2013 2:04 am    Post subject:   Reply with quote

IffyG wrote:
Sadly, the BCMs on these cars are mighty fragile. Odd electrical issues are usually a hallmark of a bad BCM and it sounds like you might have one that needs replacing.


I think there is a major leak in the exhaust system I can feel a lot of warm air moving around under the hood. on the driver side I think the leak is near the back of the engine


I can cover the tail pipe without the engine stalling. my hand does get pushed off after a few seconds though. it is not hot what so ever too. Luke warm at best.

I can also hear a ticking sound as well
I use 91 octane .


sometimes it takes 1 to 1 second & 1/2 to start up
other times when its warmed up it starts instantly.



On a long trip the CEL went off so I assumed it was making a good seal on the exhaust system engine sounded fine as well
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