Bad mpg==bad o2 sensor?

I've finally got my celiac back on the street after a blown ecu and 10 years.
The car runs fine, the idle is quite stable but i've a little hesitation when accelerating, the rpm drops a bit and the engine quite stalls.
Also the mpg is worst than before something like 20lt/100km !!

I've checked the engine for vacuum leaks, tested for boost leaks, changed the o2 sensor, distributor cap, spark plugs,checked the fuel pressure, i've also cleaned the throttle and adjusted the tps as for bgb.
Nothing!

So i went to the test procedure for the o2 sensor, it could be a bad wiring as i had problems with the distributor's wiring too and had to use an external wire for it.
But the procedure seems really difficult, i've followed it, bridged te2 e1, let it warm up, idling for 3 min, pushed the ac button (with fan speed set to 1) and drove in 5th at 1500 rpm for 2 min... no light come on, so i've disconnected the o2 sensor and tried again, still no light...

I'm running out of idea, how can i check if i'm running in open loop or not? :bangshead: :bangshead: :bangshead:

Exhaust leaks? Sounds like over fueling.

Why exhaust leaks?
Do you mean between manifold and the head before the o2 sensor?
anyway the exhaust is quiet

You can tell if the ECU is running in open or closed loop mode by monitoring the voltage on the O2 input pin to the ECU while cruising (not accelerating/decelerating.) If the voltage is changing between 0V and 1V then it's operating in closed loop mode.

I just replaced the oxygen sensor on my alltrac. I had the check engine light which will come on when the car first starts then eventually went away. Also the car would sometimes start and would have a rough idle and turn off. I also had bad mpg to the point where I would see the gas gauge needle move while I drive. Turned out to be a bad oxygen sensor and bad connection on the sensor it self.

LvX":1hgp94j9 said:

Why exhaust leaks?
Do you mean between manifold and the head before the o2 sensor?
anyway the exhaust is quiet

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Because a pre-O2 leak will make it run rich. Mine had a nasty leak but wasn't noisy. Other options are bad MAF, or a problem with the old start injector circuit.

___Scott___":2eose30e said:

You can tell if the ECU is running in open or closed loop mode by monitoring the voltage on the O2 input pin to the ECU while cruising (not accelerating/decelerating.) If the voltage is changing between 0V and 1V then it's operating in closed loop mode.

Click to expand...

Thanks Scott, i will try

celi703":1g6tglju said:

I just replaced the oxygen sensor on my alltrac. I had the check engine light which will come on when the car first starts then eventually went away. Also the car would sometimes start and would have a rough idle and turn off. I also had bad mpg to the point where I would see the gas gauge needle move while I drive. Turned out to be a bad oxygen sensor and bad connection on the sensor it self.

Click to expand...

same as me, the needle really scares especially in italy where gas is 2$/lt :crazy:

Its seems to be the MAF, i've replaced with a friend's one and now the consumption seems good again, also the car revs better and the turbo seems to respond faster.
thanks underscore for having planted the doubt.
I still have the hesitation to be sorted out, during the weekend i will remove the egr to check if is stuck and will clean the throttle deeply