Nissan Repair: Nissan cefiro E-A31 high fuel consumption, crank angle sensor, nissan cefiro model

Question
Hi Mr.Calvin Iwashita San,

My current vehicle is 1990, NISSAN CEFIRO, model E-A31, RB20E
2.0L(EFI) ECCS engine.

It's speedo meter reading is over 200,000 KM.
EFI fuel pump was just replaced cause of malfunction as well as one
fuel Injector also replaced.
Throttle switch & sensor, MAF sensor, Crank angle sensor and engine
temperature sensor are OK.
But there is no exhaust gas sensor (O2 sensor) and manifold hole for
the sensor is plugged for long time (During first owner period)

Unfortunately fuel consumption is pretty high (23- 28 KM/imp gallon;
City drive and 35-38 KM/ Imp gallon High way drive).

I'm going to install HHO generator cell kit to save the fuel cost.

Question:- How much effect fuel consumption without O2 sensor. Should
I re-install O2 sensor?
Please give me your valuable suggestions for the diagnosis.

Warm regards,
Khin Maung Nyo.

Answer
Aloha Khin -

I am assuming your check engine light is on, then?

My answer is yes, the O2 sensor should be replaced. Is the intent and design of the engine to run properly with it, otherwise the computer cannot monitor the engine properly. The O2 operates with mini volts, constantly sending the computer information on what the exhaust mixture is, adjusting rich and lean all the time. In the long run, yes, fuel consumption could rise if the O2 is left out.

Hope this helps -
aloha
Calvin