1JZ Keeps on giving lean code even though its not running lean.

[L0kz]

I recently did a swap on my lex sc300 with a jzz30 1jz
Ever since i have been driving it, the car keeps on giving me a lean a/f mixture code. I hooked up a wideband and noticed it has 15:1 to 17:1 a/f on idle. high 13's:1 on high way cruise 55 mph . 10-11 :1 on WOT

If i am doing fine under load i dont understand why am i getting this code, i cant even clear it off it just comes right back.

Any places i should check that could possibly cause this? Could it be the 02 sensor being lazy as hell?

1JZ
Stock TT
3" downpipe and 3" CAT
Aftermarket Airfilter
New ignition coils
NGK V power plugs gapped to .028
Intank Walbro 255
Stock 370CC Injectors
Dr Tweak harness



Help much appreciated
-L0kz

 

[hvyman]

Could be a bad o2 sensor.

 

[nathaninwa]

As hvyman said, it could be as simple as an oxygen sensor, or even a screwy coolant temp sensor. On the ecu side of things, say your exhaust manifold is cracked leaning out the exhaust so the oxygen sensor is picking that up and adding fuel. Once you have reached the internal trims of added fuel it could pop a to lean code as the ecu is at it limits. Check exhaust connections and cracked manifolds as well.

 

[Radial]

As the stock o2 is a narrow band, it's just active while the engine is in Closed loop (Typical for cruise and idle conditions).
sounds like your wideband shows deviations at one of the Closed Loop areas... idle is supposed to be 14,5-15,0 AFR.

WOT and cruise afr's look ok

I would try to measure the o2 sensor at first.....google testing of narrow band sensors.
It's also possible do disconnect the 02 sensor, and see how it behaves. It should go from lean to quite rich (in the 12 area) for idle.

 

[525gte]

Let idle sound prob like a exhaust leak

 

[L0kz]

I will go ahead and back prob the 02 sensor connector and see the voltage on it. It should be above 0.45Volts on idle from a cold start and go down to 0.45 and bounce back n forth indicating rich lean condition. Honestly car also sounds like it has an exhaust leak on a cold start, how would i check for a cracked manifold? Its not loud as hell while i get on it. Its only on idle where it sounds like it has an exhaust leak.
Coolant temp sensor has been replaced in the past already.
thanks for your inputs everyone.
-L0kz

 

[MadRPM]

For the leak, you should look for black spots or lines. Thats how I found the crack on my wastegate inlet. Also, dumb question: does the line going from intale manifold to map sensor have an inline filter? If it does, a clogged filter might lower voltage readings at idle and cruise, making the car run leaner.

 

[L0kz]

No filter in my vacuum lines going to map sensor. However, I havent done the 12V Modd to the fuel pump which runs fuel pump on 12V all the time. Without the 12V modd the fuel pump has lower voltage on idle and lower rpm range and this is what could be causing it i am not 100% certain . I also found a exhaust leak in my flex pipe in my exhaust using stethoscope. Still have not back probed my 02 sensor because of bad weather and the fact i dont have a garage to do it in comfort. The car is gonna be off to Fusion works this week. Hopefully, by the end of next week when i get the car back i will go get my 3" flexpipe installed on it and then go from there. Will keep you guys updated till i get to the bottom of this.
-L0kz

 

[Radial]

AFR's should not be affected by the reduced fuel pump voltage.

Why:
Fuel pressure should remain constant due to the low fuel demands in Idle, even if the fuel pump voltage is lowered.

The design is quite genius actually.

 

[L0kz]

^^ I actually learned something today. Thankyou for sharing this information, appreciate it.
Although i am not currently tinkering with anything because of the weather and having finals in university. Once its all over, there will be no life because race car!
I always think about all these things before i sleep every night. The fact that 02 sensor is practially under the hood not really somewhere under the car and the leak is after the 02 sensor not before, i get confident that its my 02 sensor. The leak is exactly between 02 sensor and the wideband. But why lean code? No vacuum leak until today i think i generated some vacuum leak somewhere in the system. I feel its in my intercooler pipes somewhere. I'm not worried about it because its going to get FMIC this week:naughty::naughty:, I am currently running soarer side mount intercooler:3d_frown:. Back to the point anyways, shouldnt my wideband be reading lean too all the time? the only thing i convince myself with is that when its under boost pressure everything is getting pushed out so wideband sensor reads whatever it gets because its surely not getting everything because of the leak. Where as in vacuum most of the a/f mixture seeps out of the exhaust leak and wideband barely gets anything to read? Do i make any sense or just sounds like bunch of BS? Please do not be hateful if i am wrong, i would rather be corrected than being called a dumbass lol! I am just trying to go off the basics i know
-L0kz