P0171 and P1170 codes when at low RPMs or idle

[stockysnail]

I'm getting a P0171 and P1170 codes. The short and long term fuel trims seems good above 1500rpm but when it's under that or idling The long term is pretty high and short is a little high as well. When I reset the codes with my scan gauge it comes back on sometime later during a drive or the next time I drive and when at low RPMs or idle. When I decelerate without touching the gas pedal, I see the short term trim at 0, long term somewhere between 32-38, and the AFR at 20.1. Not sure if that's normal, but doubt it.

So far I have:
-Cleaned the MAF
-Replaced the MAF
-Cleaned the intake tube and throttle body.

Things I think it could be based on what I'm reading:
-Failing/dirty injectors
-Exhaust leak I'm not finding
-Front O2 sensor (Part #22641AA640)

Based on what I'm reading it's probably not a vacuum leak based on my info.

Anyone have ideas? See my build thread and the last page of it to see what I've done to it recently, but shouldn't be related as this is a fairly new issue. I've been supercharged for 8 years or so as you'll see in my build.

[Boccaccio]

I had a similiar issue. High LTFT below 1400~1600 and when idling.

Cause was a small exhaust leak in the header - overpipe connection. Remflex gaskets fixed the issue.

Used a shop-vac and soapy water method to pinpoint the leak:

PS. decelerating while not applying throttle/touching the gas pedal will always result in AFR around the 20 mark, perfectly normal.

[stockysnail]

Originally Posted by Boccaccio

I had a similiar issue. High LTFT below 1400~1600 and when idling.

Cause was a small exhaust leak in the header - overpipe connection. Remflex gaskets fixed the issue.

Used a shop-vac and soapy water method to pinpoint the leak:

PS. decelerating while not applying throttle/touching the gas pedal will always result in AFR around the 20 mark, perfectly normal.

Thanks. I'll see if my shopvac can push air instead of suck so I can try this. I assume I'll put tape over the 2nd exhaust hole so it doesn't just push out the other tailpipe.

[Boccaccio]

I used a nitrile glove, taped (painters tape) around the other exhaust tip.

Once you turn on the shop-vac, prepare to laugh :P

[stockysnail]

Looks like I have an exhaust leak with the gasket I put in that was thinner to fix my previous gasket failure in the headers to overpipe, and also a leak in one side of the headers to the engine. Now to find gaskets. I see Grimmspeed has them on Amazon but cost a little more and autozone has some but they don't list the thickness.

[kev0]

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Use this gasket for the header to overpipe. Trust.

[stockysnail]

I got the only gasket I could find at a local store and it's mostly better. As you can see there's still a tiny leak in a couple spots. I didn't try to fix the 2 tiny header leaks yet as that would require more effort to remove the headers which I'm out of effort at the moment. After unplugging the battery and driving around a little, the idle Short Term trims are fluxuating between 0-16 and the long term trim went up to 39 and stayed there after the first couple idles I did. Maybe those tiny leaks still happening are what's still messing it up. I may need to try the previous posters gasket recommendation and order some header gaskets as well to try to get 0 leaks.

[blsfrs]

Somebody please correct me if I am wrong. Small exhaust leaks downstream of the 02 sensors shouldn't cause a problem.

[Boccaccio]

Originally Posted by blsfrs

Somebody please correct me if I am wrong. Small exhaust leaks downstream of the 02 sensors shouldn't cause a problem.

A leak at the overpipe-header will introduce a small bit of oxygen into the system due to exhaust gas reversion and will increase the LTFT values at idle and low throttle input (usually driving in close loop mode - fuel system status - 2).

+1 on using remflex gaskets. Only downside is they are not reusable.

@stockysnail I strongly suggest you fix the leaks before further diagnostics.

[blsfrs]

Originally Posted by Boccaccio

A leak at the overpipe-header will introduce a small bit of oxygen into the system due to exhaust gas reversion and will increase the LTFT values at idle and low RPM-range.

+1 on using remflex gaskets. Only downside is they are not reusable.

@stockysnail I strongly suggest you fix the leaks before further diagnostics.

Are you sure about that? It's a pressurized system. That's why it make bubbles when it leaks. I don't see how any air comes into the system then travels upstream to the 02 sensor especially at higher rpms.

[Boccaccio]

Originally Posted by blsfrs

Are you sure about that? It's a pressurized system. That's why it make bubbles when it leaks. I don't see how any air comes into the system then travels upstream to the 02 sensor especially at higher rpms.

Take a look at this brief but simple explanation (scroll down to the paragraph explaining the basics of gas reversion)

https://nasaspeed.news/tech/engine/t...-of-an-engine/

If there's a leak, it will introduce additional oxygen into the system, and due to reversion, that oxygen will travel all the way to the primary/AFR O2 sensor thus fooling the engine thinking it's running lean.

Had this issue back when I was still NA. A very small leak at the overpipe/header connection (the other connection points, especially the header-engine were sealed/leak-free) produced an LTFT value (at idle and low throttle input) of around 14-16%:

High RPM - Low throttle:

https://datazap.me/u/boccaccio/41020...21&tmax=220.90

IDLE:

https://datazap.me/u/boccaccio/idle-...log=0&data=1-8

Reason was a slighlty warped Overpipe flange (AVO 2.5" ceramic coated overpipe).

Replacing the gasket (used the thick graphite Remplex gasket) solved the issue and brought the LTFT into the +-3% range.

[blsfrs]

Originally Posted by Boccaccio

Take a look at this brief but simple explanation (scroll down to the paragraph explaining the basics of gas reversion)

https://nasaspeed.news/tech/engine/t...-of-an-engine/

If there's a leak, it will introduce additional oxygen into the system, and due to reversion, that oxygen will travel all the way to the primary/AFR 02 sensor thus fooling the engine thinking it's running lean.

Had this issue back when I was still NA. A very small leak at the overpipe/header connection (the other connection points, especially the header-engine were sealed/leak-free) produced an LTFT value (at idle and low throttle input) of around 14-16%:





High RPM - Low throttle:

https://datazap.me/u/boccaccio/41020...21&tmax=220.90

IDLE:

https://datazap.me/u/boccaccio/idle-...log=0&data=1-8

Reason was a slighlty warped Overpipe flange (AVO 2.5" ceramic coated overpipe).

Replacing the gasket (used the thick graphite Remplex gasket) solved the issue and brought the LTFT into the +-3% range.

Thanks for the follow up. The simple complexity of this kind of thing boggles my mind.

[Boccaccio]

No problem

It's usually the "little things" that bite you in the "behind" :P

Hope that stockysnail fixes his problem and that the solution is a simple gasket replacement/rejuvenation.

[blsfrs]

Originally Posted by Boccaccio

No problem

It's usually the "little things" that bite you in the "behind" :P

Hope that stockysnail fixes his problem and that the solution is a simple gasket replacement/rejuvenation.

Yes. I'm finding out that this platform is very sensitive to "little things".