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Discussion Starter #1
Ok ever since i put my new motor in i have been running lean according to my air/fuel gauge. Before it used to search when cruising around but now as soon as i turn the car no it pins to a certain spot in the yellow and dosent move no matter if i punch it (it does go down when i let off) or if im just cruising it just stays there and dosent search. Well because of this my CEL is on and it says i am running lean in bank 1(also says my o2 sensor is malfunctioning). Also i am getting horrible gas mileage and puffs of black smoke come out when i shift. I am pretty sure this is because the computer is trying to correct the leaness and i am running rich.

So my theory is that i missed a ground wire somewhere when i put the new motor in because when we did the swap my a/c wouldnt work (compressor would kick on then shut off and light would blink) but as soon as i cut the ground wire and regrounded it i had no problems at all. So do you think my theory is right and i missed a ground. Does anyone know where the ground for this is or perhaps which wire is the ground on the 02 sensor?

any help will be appreciated.

Rick
 

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i think you answered yourself. sounds like an O2 sensor problem.

if you've connected the A/F gauge to sensor1 (or bank1 as bluespacebomber likes to call it), it should "search" while you cruise around.
 

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Discussion Starter #3
ok but does anyone know where the ground wires to the pre-cat 02 are or which wire comming off the 02 itself is the ground. If i can figure out which wire it is i can just cut it under the car and ground it under the car.
 

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the gauge's signal wire (usually purple or green, depending on the gauge) should be connected to the blue wire on the pre-cat o2 sensor harness.

Make sure the gauge's ground wire is connected to a good engine ground (the ground point on the cylinder head is a good spot)

Do not connect the ground to the o2 sensor ground under any condition!
 

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why dont you put it on the dyno or find someone with an 02 sniffer, those guages are horribly innacurate.

thats the only way to tell for sure what your running, black smoke is from runnin to rich, I used to get it all the time with no cat and stock ecu
 

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Well, his gauge helped to diagnose a problem...

Most A/F gauges are for rough, at-a-glance approximation anyway (rich, stoich or lean) If you want an accurate A/F ratio, then you get a wideband gauge like the AEM wideband controller/gauge. those will actually give you an actual A/F ratio in a numeric form.

You can get a rough idea of your A/F ratio from one of the standard gauges, even on the celica. it may not be all that accurate, but it's useful for diagnosis of problems with the fuel system (good for an educated guess). If you are tuning on a dyno, remapping, etc. you definitely want to use a wideband, but the narrow-band gauges have their purpose as well...

Rick, have you double checked the fuel system too? are the injectors clean? adequeate pressure? fuel filter?

Definitely double check the o2 hookup, the sensor may be bad, but if you are running lean from a clogged injector or something, that would throw a CEL as well...

The ground cable could be an issue... Try connecting the gauge ground to the cylinder head, an improperly grounded A/F gauge could definitely be the cause: Without a direct ground to the engine, some of the current from the sensor is bled off to the chassis, causing less current to go to the ecu, as well as picking up interference from other electronics in the car, resulting in a weaker than normal signal from the sensor to the ECU. Hence, it thinks you're running lean, and throws a fit (as well as a CEL).

Remember, the o2 sensors are also grounded to the exhaust fitting, which in turn is grounded to the cylinder head. To keep the signal strong and clean, the circuit must be isolated; it also helps to keep the ground leads as short as possible.
 
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