code p0171

[edd112]

So following up on my tahoe.
It has an issue only on cold starts, it will idle roughly, and feels like it will turn off. Well, it actually does turn off at times. Did a tune up on it recently and changed fuel filter and had an oil change. After the truck warms up it runs great. Took it to autozone to run some codes and got the p0171 code. It says to replace oxygen sensor(s) and reprogram ECM.
I will attach a picture of the report. Just wondering if anyone has gone through the same thing lately and which 02 sensor should I replace? I've heard it's better to replace both upstream sensors. At 50 bucks a piece, i want to be as sure as possible.

 

[t_ahan]

I would check for intake/air leaks first

 

[lkrasner]

Mine did this with an intake gasket leak. Spray all over seals with carb cleaner, you should get a change in rpm. You can also watch the long term fuel trim on a scanner. It will drop to 0 when you find the leak.

 

[edd112]

Mine did this with an intake gasket leak. Spray all over seals with carb cleaner, you should get a change in rpm. You can also watch the long term fuel trim on a scanner. It will drop to 0 when you find the leak.

No leaks!. Mechanic confirmed it was a bad fuel pump. Will replace it tomorrow. Crossing my fingers!

 

[bottomline2000]

Everything you mentioned leads to intake gasket leak. If it sounds like it's cammed on cold starts and gets better as it warms up its just the material expanding amd sealing the leak it's more than likely the gasket. Don't think the fuel pump would work better as the truck warms up. Also, Bosch O2 sensors are $25 ea on amazon.
Hopefully it's just the pump.

 

[edd112]

Everything you mentioned leads to intake gasket leak. If it sounds like it's cammed on cold starts and gets better as it warms up its just the material expanding amd sealing the leak it's more than likely the gasket. Don't think the fuel pump would work better as the truck warms up. Also, Bosch O2 sensors are $25 ea on amazon.
Hopefully it's just the pump.

Replaced the pump today. Engine still stalling! My mechanic only charged me half price since he didn't like the fact that it still shut down. He said it has to be a leak. Either gaskets or a bad hose. Looks like I gotta take it to the dealer.

 

[bottomline2000]

Like we all said..it's the intake gasket. Rough running is from unmetered air getting into the engine because the weak gasket breaks down. Any mechanic worth half his salt can replace it. There is an upgraded one made out of metal with thicker rubber material that i use.. it's not hard to do. It looks like this...

 

[edd112]

Like we all said..it's the intake gasket. Rough running is from unmetered air getting into the engine because the weak gasket breaks down. Any mechanic worth half his salt can replace it. There is an upgraded one made out of metal with thicker rubber material that i use.. it's not hard to do. It looks like this...

My fuel pump was bad anyways, and looks good man. How much did those run you? And it's possible to do but I don't have the time to do it myself. How much do you think a mechanic would charge to do this job?

 

[lkrasner]

My fuel pump was bad anyways, and looks good man. How much did those run you? And it's possible to do but I don't have the time to do it myself. How much do you think a mechanic would charge to do this job?

I think the new gasket was about $50 at autozone. Much more intimidating job than it actually is difficult. There is a lot to remove, but the whole job only took me maybe 2 hours, and a good 30 minutes of that was just cleaning up the old surface really nice. If you do it yourself, I'd recommend pulling the fuel pump relay then starting the car and letting it burn as much of the fuel as possible. You'll still leak a good amount taking the rails off, but at least the pressure will be gone. That said, shouldn't be more than a couple hours labor for any mechanic. A lot of people would also recommend replacing the knock sensors while everything is already off.

 

[bottomline2000]

My fuel pump was bad anyways, and looks good man. How much did those run you? And it's possible to do but I don't have the time to do it myself. How much do you think a mechanic would charge to do this job?

Thanks man and yeah its good to get the bad pump out the way. If pressure low, yank it! Pretty much everything ikrasner said. It's looks more intimidating than it is. Getting the torque sequence right on the intake the hardest part. I was quoted some ridiculous price at a dealership once and the work was done under warranty.

After pulling the old motor and looking at the gasket they didn't even clean the surface before installing the new one..stuff like that made me start doing my own work and I'm a desk jockey for a living lol..i get dirty for fun.