P1174 Lean Code Disco 2 Upstream O2 +20%

Fanuvkorn

New member
Nov 3, 2019
4
0
Ohio
2004 Discovery 2. Replaced up and down O2s. Replaced MAF with Bosch MAF. Replaced Cat Y pipe. Replaced Throttle Body gasket.

I am getting a P1174 and P1171 after a drive on the highway. I saw that on deceleration my Upstreams Drop to 0v and my short term fuel trim goes to +20%. This only happens on deceleration from high speeds. I have not done a smoke test for vacuum leaks. I suspect that it is upper intake or fuel injector O-ring. Pics of readings below.
 

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JUKE179r

Well-known member
Sep 14, 2016
761
95
Suffolkshire, UK
From the RAVE manual...
P1171 - System too lean (bank 1) / Additive injector adaptive fuelling - lean limit exceeded LH bank
P1174 - System too lean (bank 2) / Additive injector adaptive fuelling - lean limit exceeded RH bank

Brake booster possibly bad and sucking air? I read the brake booster was the cause of both codes on another forum..
aarcaris94;581582 said:
... But I was watching my fuel trim levels while I was driving and every time I braked the Fuel Trim would shoot up really High. So after talking to the shop and having them drive it they were able to pin point it on the booster.
 

Fanuvkorn

New member
Nov 3, 2019
4
0
Ohio
From the RAVE manual...
P1171 - System too lean (bank 1) / Additive injector adaptive fuelling - lean limit exceeded LH bank
P1174 - System too lean (bank 2) / Additive injector adaptive fuelling - lean limit exceeded RH bank

Brake booster possibly bad and sucking air? I read the brake booster was the cause of both codes on another forum..
Brake Booster is good. . . Thanks for the info.
 

GS70350

Member
Jul 21, 2020
9
0
HUNTSVILLE alabama
Defective maf, cheap reman, low fuel pressure, or an air leak between it and throttle will cause this. Injector o ring will affect one cyl, or one bank only not both equally. A o2 sensor or other bank dependent part will not cause equal fuel trim values on the opposing bank and is not the issue. You need to consider leaks that affect the engine as a whole, several vacuum lines enter the plenum before it branches off to individual runners and I’d look upstream from there on toward maf for any leaks, and do a fuel pressure test. Maf sensors seem to be common for me to swap. Best to use a good one, I’ve had bad luck with remand and copies.
 

Fanuvkorn

New member
Nov 3, 2019
4
0
Ohio
Defective maf, cheap reman, low fuel pressure, or an air leak between it and throttle will cause this. Injector o ring will affect one cyl, or one bank only not both equally. A o2 sensor or other bank dependent part will not cause equal fuel trim values on the opposing bank and is not the issue. You need to consider leaks that affect the engine as a whole, several vacuum lines enter the plenum before it branches off to individual runners and I’d look upstream from there on toward maf for any leaks, and do a fuel pressure test. Maf sensors seem to be common for me to swap. Best to use a good one, I’ve had bad luck with remand and copies.
Thanks for the info. I just had the Injectors and plenum gasket replaced yesterday. No codes threw about 4 cycles. The only thing left is a vacuum leak somewhere. Everything else is new. No cheapo stuff.
 

SDDisconDefender

New member
May 28, 2022
2
0
San Diego
All, I know this is old but wanted to go though what I did I had 2 codes p1171 and p1174. I sprayed carb cleaner around and found that something under the upper intake was sucking in air. Here were the fixes.
1) erg to throttle body was cracked and sucking in air.
2) injector seals were dry and leaking
3) replaced intake gasket and throttle body gasket.
Put it back together and then still had p1174.

1)Checked voltage and had 14.3 volts
2) checked exhaust manifold and found a leak at the down pipe
3) changed manifold and down stream gaskets on bank 2

no codes