o2 sensor issue after new engine rebuild

goshko

New Member
Hi guys, to make this short, I have put 2500 kms on my new engine that was rebuilt last winter with all OEM stuff, oem pistons and rings. Ever since the rebuild the car dosnt run right when I have my oxygen sensor plugged in. The first o2 sensor was brand new from nissan and the 2nd one was a used one off a friend of mine. The symptoms are as follows: the car runs very lean and I feel a big lack of power even in boost when the o2 sensor is plugged in (i tried both, one at a time). I have been running the car mostly without and o2 sensor now and this problem is really getting to me ... does anyone know what can be the problem ?

The car is bone stock except for an air filter + hks ssqv blow off valve.
 
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PobodY

Moderators
Staff member
Eh? You're running two lambda sensors; is one a wideband that you're using to read the mixture with, and the other narrow-band for the ECU?

It should be reasonably lean at idle because there's no load, and there's no point in throwing fuel at it to maintain idle.

Have you done a fault code check?
Have you checked the TPS?
Have you checked the MAF?
Do you have any leaks?
What is the timing like?
 

goshko

New Member
No I am not running two oxygen sensors, I just swapped them one at a time to see if their was a difference.

No fault codes
My maf and TPS voltage seem correct according to ecutalk
I am not aware of any leaks, vaccum sits at -10 psi on cold start and settles down to about -16 when engine is warmed up.
The timing is set to 20 degrees on the crank pully.

I am really out of ideas ! :(
 

goshko

New Member
A mech checked out the fuel pressure on idle and it was perfect ... as for the fuel pump voltage no I have not because this walbro was installed 1 year ago and I doubt it would be defective ... can anyone tell me how to measure the voltage to the pump ? Which connector should be measured ?
 
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stumo

Active Member
A mech checked out the fuel pressure on idle and it was perfect ... as for the fuel pump voltage no I have not because this walbro was installed 1 year ago and I doubt it would be defective ... can anyone tell me how to measure the voltage to the pump ? Which connector should be measured ?
never think just cos something is new it's ok......... have a look under the cover inside the car, i think the pump connector only has 2 wires going to it.
 

goshko

New Member
if my fuel pump isnt getting good voltage wouldn't it affect it in wot ? When I full boost it my afr's go down to 11s ... its only on part throttle and cruising :(
 

goshko

New Member
16 16.5 afr on cruise ... I sometimes hit 17 on first gear part throttle and I feel a lot of hesitations when this happens. Could it be that my stock ecu needs a tune even if the rebuild was done with oem stuff all around ?
 

Fast Guy

Moderators
Staff member
Stock ecu shouldn't let it run that lean. I've tried turning my cruise afr down to 15, but the ecu/o2 sensor holds it at 14.7 all the time, if I turn the o2 sensor off in Nistune it actually ran abit richer. They can hit 10s on full throttle on the standard set up.
You could do with something to connect to the ecu so you can check what it's seeing with regards to the o2 sensor.
Could a faulty fpr cause this?
 

goshko

New Member
My ecutalk (consult cable) is not showing me any signs of bad voltage on any sensor ... O2 sensor varies as I press the throttle ... On idle it varies from 0.4 to 0.8 ... My maf,tps sensor are all showing good voltage ... This car is making me nuts man ! My vaccum is showing -15 mmhg when engine is hot ... Shouldn't I be getting a bit more vaccum on idle ? Could this all be caused by a faulty ecu ? I am at the point where ill just buy one off someone just to see if that's the damn problem ...
 

Fast Guy

Moderators
Staff member
Is it a gtir specific sensor? I believe they're different to some other ones. (unless I'm thinking of something else)

Is you guage earthed to the chassis? (Is it flashing on and off or is it just the video)

Are you running the gauge off the standard sensor or a wideband sensor. It won't work properly with the standard sesor and should be treated as useless if it is.
 

goshko

New Member
My o2 sensor is an s13 sensor and they are identical.
My afr sensor is an AEM wideband sensor and it's not flashing on and off ... its the cell phone video.

Also, this is not faulty readings, I feel the car completly bog down when the 2nd --- shows up on the gauge.
 

Fast Guy

Moderators
Staff member
If they were identical, they would have identical part numbers surely?

Gtir is 22690-54C00
s13 is 22690-50F00
 

goshko

New Member
The sensor is identical, it's been proven many times on the canadagtir forums. Also, the s13 has 2 different sensors, a skinny type and a fat type sensor. For it to be compatible, I had to use the skinny type sensor. The only thing that changes is the connector end on it.
 
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gtirx2

Member
I think an air leak in the exhaust before the sensor can sometimes cause iffy readings.
When using my lm2 on my uno with a small leak it sometimes jumps about to silly lean readings,dont think its ever happened on boost though.
 
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