Ls1 P0131 code
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Teching In
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Ls1 P0131 code 
Looking for some input, I recently started having a problem with my O2s reading excessively low on both banks, but only throwing the code for bank 1. It may just be coincidence, but it started right after replacing the alternator, old one was only putting 11.9 volts and throwing code, new one puts out 14.8 at first start then pulls back to about 13.2 if I remember correctly.
Anyway, the short term fuel trims are way out of whack at 50% it is not running lean, in fact it is running really rich.
What could be causing this? The driver side 02 sensor is new, but still reading the same as the old one. I dont think it is a vacuum leak as the map sensor readings are the same as when it was running good. Looking for suggestions as this has got me stumped.
Last edited by Matt Mohatt; Jul 12, 2024 at 08:59 AM.
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Joined: Jul 2022
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From: Alaska
Sounds like an Exhaust leak ...
Have any Broken exhaust manifold bolts ?
Once you get your spark plugs that oilly, you'll have rampant misfire, dumping raw fuel into exhaust will fool O2 sensor into false readings, and cause PCM to dump MORE fuel.
TR6 plugs are a step COLDER than stock. How much manifold pressure are you running ?
.
I'd start with FRESH spark plugs, correct heat range and replace exhaust manifold gaskets, extract and replace any broken bolts.
Have any Broken exhaust manifold bolts ?
Once you get your spark plugs that oilly, you'll have rampant misfire, dumping raw fuel into exhaust will fool O2 sensor into false readings, and cause PCM to dump MORE fuel.
TR6 plugs are a step COLDER than stock. How much manifold pressure are you running ?
.
I'd start with FRESH spark plugs, correct heat range and replace exhaust manifold gaskets, extract and replace any broken bolts.
Thread Starter
Teching In
Joined: Dec 2018
Posts: 20
Likes: 0
Sounds like an Exhaust leak ...
Have any Broken exhaust manifold bolts ?
Once you get your spark plugs that oilly, you'll have rampant misfire, dumping raw fuel into exhaust will fool O2 sensor into false readings, and cause PCM to dump MORE fuel.
TR6 plugs are a step COLDER than stock. How much manifold pressure are you running ?
.
I'd start with FRESH spark plugs, correct heat range and replace exhaust manifold gaskets, extract and replace any broken bolts.
Have any Broken exhaust manifold bolts ?
Once you get your spark plugs that oilly, you'll have rampant misfire, dumping raw fuel into exhaust will fool O2 sensor into false readings, and cause PCM to dump MORE fuel.
TR6 plugs are a step COLDER than stock. How much manifold pressure are you running ?
.
I'd start with FRESH spark plugs, correct heat range and replace exhaust manifold gaskets, extract and replace any broken bolts.
Look to what can be affected by changing the alternator. You had to disconnect and reconnect wires, and now you are running at a higher system voltage. This leaves the possibility of a ground wire not being put back right, which could affect everything. You could also have tuned around low fuel pressure from the low voltage, or bad injector data on the voltage vs offset table. Without knowing more specifics on your fuel system and what tuning has been done for this build it is all guesswork. And there is absolutely nothing wrong with using a 6 heat range spark plug in this build.
Thread Starter
Teching In
Joined: Dec 2018
Posts: 20
Likes: 0
Look to what can be affected by changing the alternator. You had to disconnect and reconnect wires, and now you are running at a higher system voltage. This leaves the possibility of a ground wire not being put back right, which could affect everything. You could also have tuned around low fuel pressure from the low voltage, or bad injector data on the voltage vs offset table. Without knowing more specifics on your fuel system and what tuning has been done for this build it is all guesswork. And there is absolutely nothing wrong with using a 6 heat range spark plug in this build.
Even before this new problem, I am surprised it ran at all on that hack job of a MAF only tune. Unfortunately, that is what that "tuner" is well known for. As for the current problem, if you can't find any wires partly disconnected, or bad grounds somewhere, you will have to go back to basics and check everything. Starting with a large cam and a terrible tune is not going to make it easy. Maybe something will be noticeable when you get a log file to upload.
