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Discussion Starter · #1 ·
So I recently bought this car with 50,000 miles. The check engine light flicked on and has stayed on due to a p0171 lean fuel code. It's got a new fuel filter already installed. With a little time it started misfiring and within 2 days began to run very poorly. (The code was also apparently a backed up code). So I unloaded a can of seafoam into it and still no changes. Checked the pressure on the fuel lines and they are good! Now it's misfiring so I bought new spark plugs to fix that issue, however I highly doubt it will fix the lean code issue. So I'm thinking new fuel injectors? Possibly new maf sensor?

I can't really drive it as it's slow to accelerate due to the fuel issues.
 

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It could be an O2 sensor. Do you have a scan tool to watch the values in real time? FWIW when we first bought the '05 I had a lean code all the time. Nothing fixed it. (Eventually it needed O2 sensors but not at this time) So I finally figured out that some gorilla had removed the air bonnet without loosening the hose clamp that goes around the throttle body. There was a big crack along the bottom leaking air AFTER the MAF sensor. Result: lean mixture and the accompaning code. So consider an upstream vacuum leak.
 

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You say you checked fuel pressure, that's good. Was it checked with a gauge and compared to spec. Just cracking the line and seeing fuel spray out is not a good check, and that is what might be done if a gauge is not available. Checking for air leaks around the manifold, air inlet below the MAF sensor, or vacuum lines is a good place to look. If you have a DVOM you can tap in to the signal wire of sensors and monitor their response. Connect your DVOM and drive the system rich then lean to see it responds. You can fool the ECM by connecting a wire to the signal terminal of the O2 sensor, then hold one end of the wire in on hand while touching the pos. battery terminal with the other hand. Using your body as a resistor, you can fool the ECM into thinking the system has gone rich and you will notice a change in the engine,, smoothing out until it gets too rich then changing back when you remove your hand from the battery. The O2 sensor works by creating a small current, low voltage that ranges between .1 and .9 volts. Signals over .5 volts tells the ECM the system is always rich, below .5 volts is lean, wanting more fuel.
 

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Say Red. What do you mean it
needs a timing job.
Help me out here,. Do you mean cam chain & valve train, or spark plugs and ignition module?

50k miles is not a bunch for these engines yet a 15-18 yr old plastic can cause all sorts of vacuum leaks. Chafed wires to the fuel injectors can open them up and lean misfire will toast a cat in little time.

a reasonable priced code scanner will show If the O2; sensors are operating, now these Cobalts are known for braking the Valve cover vent to the air snorkel/plentum this causes an air leak down stream of the mass air flow sensor. That and a dirty air flow sensor can cause a lean condition.
 

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Discussion Starter · #6 ·
You say you checked fuel pressure, that's good. Was it checked with a gauge and compared to spec. Just cracking the line and seeing fuel spray out is not a good check, and that is what might be done if a gauge is not available. Checking for air leaks around the manifold, air inlet below the MAF sensor, or vacuum lines is a good place to look. If you have a DVOM you can tap in to the signal wire of sensors and monitor their response. Connect your DVOM and drive the system rich then lean to see it responds. You can fool the ECM by connecting a wire to the signal terminal of the O2 sensor, then hold one end of the wire in on hand while touching the pos. battery terminal with the other hand. Using your body as a resistor, you can fool the ECM into thinking the system has gone rich and you will notice a change in the engine,, smoothing out until it gets too rich then changing back when you remove your hand from the battery. The O2 sensor works by creating a small current, low voltage that ranges between .1 and .9 volts. Signals over .5 volts tells the ECM the system is always rich, below .5 volts is lean, wanting more fuel.
Yes it was checked with a gauge. Thanks for you're advise. I'll update when I've figured it out lol, that's the problem with these codes.... it could be any little thing setting it off. The good news is the car was in very clean condition when I bought it. So none of the lines appear to be in bad condition, thus begins the process of elimination.
 

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Discussion Starter · #7 ·
Say Red. What do you mean it

Help me out here,. Do you mean cam chain & valve train, or spark plugs and ignition module?

50k miles is not a bunch for these engines yet a 15-18 yr old plastic can cause all sorts of vacuum leaks. Chafed wires to the fuel injectors can open them up and lean misfire will toast a cat in little time.

a reasonable priced code scanner will show If the O2; sensors are operating, now these Cobalts are known for braking the Valve cover vent to the air snorkel/plentum this causes an air leak down stream of the mass air flow sensor. That and a dirty air flow sensor can cause a lean condition.
Yeah I think my next course of action will be replacing the MAF sensor entirely. It did something weird at first when I unplugged it, it made no difference to how it was running. Then tried to clean it a little and plug it back in and unplugged it again and it finally registered it was missing. So a little weird. I'll keep yall updated.
 

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Discussion Starter · #8 ·
Say Red. What do you mean it

Help me out here,. Do you mean cam chain & valve train, or spark plugs and ignition module?

50k miles is not a bunch for these engines yet a 15-18 yr old plastic can cause all sorts of vacuum leaks. Chafed wires to the fuel injectors can open them up and lean misfire will toast a cat in little time.

a reasonable priced code scanner will show If the O2; sensors are operating, now these Cobalts are known for braking the Valve cover vent to the air snorkel/plentum this causes an air leak down stream of the mass air flow sensor. That and a dirty air flow sensor can cause a lean condition.
I'll have to invest in a scanner probably in order to tell for sure if it's the 02 sensors. What kind do you recommend? I don't believe there's a leak as the car was very clean under the hood and appears well maintained. No signs of rot as of yet however can't be to sure I'd probably have to smoke it out to see but I don't have a smoke machine lol.
 

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I made my own smoke machine like this.
I used an old soldering iron and a small electric air pump.It really did work. I used mineral oil which is more expensive than you think. FWIW I fought with a MAF sensor on a Firebird for months before I broke down and bought a new one. Fixed! EDIT: that HF 5 minute epoxy is some seriously good stuff.
 

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Discussion Starter · #10 ·
I made my own smoke machine like this.
I used an old soldering iron and a small electric air pump.It really did work. I used mineral oil which is more expensive than you think. FWIW I fought with a MAF sensor on a Firebird for months before I broke down and bought a new one. Fixed! EDIT: that HF 5 minute epoxy is some seriously good stuff.
I'm new to owning a car in general lmao, so I'm highly unprepared and learning + gathering my own tools. It's my first car, and I expected some issues to come up now it's just trying to figure my way around them! I think I've learned quite a bit so far and atleast have some direction as to what I'm doing/looking for (thank god for friends lmao). When I have the new MAF installed I'll update from there. It sucks though when I drive it I can get it to accelerate but as soon as u hit the breaks it's back to working it up to that point again, rough idles in park and when breaks are pressed she's running about as effectively as a lawn mower and it makes me saddd. Lol
 

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So I recently bought this car with 50,000 miles. The check engine light flicked on and has stayed on due to a p0171 lean fuel code. It's got a new fuel filter already installed. With a little time it started misfiring and within 2 days began to run very poorly. (The code was also apparently a backed up code). So I unloaded a can of seafoam into it and still no changes. Checked the pressure on the fuel lines and they are good! Now it's misfiring so I bought new spark plugs to fix that issue, however I highly doubt it will fix the lean code issue. So I'm thinking new fuel injectors? Possibly new maf sensor? I can't really drive it as it's slow to accelerate due to the fuel issues.
07 G5 P0171. ran a live data scan. short term furl trim too high 28% at idle. Measured MAF Gm/s around 2.8. Replaced MAF, Gm/s increased to 4 apprpximately. SHRT FT went to 0% perfect.
 
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