My car is a Honda (accord) Bullet 1990 model. My car engine got spoilt and when I went to Ladipo market to buy another one, my mechanic suggested that I buy the 1994 engine that it will fit perfectly into it and work better.
On getting back, it was fixed and upon usage, I discovered the engine consumes about 10L/30km which was far far higher than the other engine which consumed 10L/100km. Besides, the idle is not smooth at all. My mechanic has adjusted various controls on the injector part but all to no avail. Sir/ma, I am confused, what do you advise I do? The engine is a 4-plug type and size is 1.6L

A 1990 car you said . Well get that car scanned.it can be scanned via the obd1 port if it hasnt been tampered with

profolusegun014: My car is a Honda (accord) Bullet 1990 model. My car engine got spoilt and when I went to Ladipo market to buy another one, my mechanic suggested that I buy the 1994 engine that it will fit perfectly into it and work better.
On getting back, it was fixed and upon usage, I discovered the engine consumes about 10L/30km which was far far higher than the other engine which consumed 10L/100km. Besides, the idle is not smooth at all. My mechanic has adjusted various controls on the injector part but all to no avail. Sir/ma, I am confused, what do you advise I do? The engine is a 4-plug type and size is 1.6L

Your car is a 1990 so scanning via odb2 is rulled out, your accord engine is a 2.0liter engine.

High fuel consumption more details on your car is it an injection system or carburettor? Aside fitting a different engine what other problems does your car have? Black smoke on tail pipe? Does it stutter or hesitate? Does it idle properly? Please give more information.

The engine uses an Injector. It produces fairly black smoke on tail pipe and does not idle properly. In fact, the idling is not smooth at all.
The only recent thing I did alongside changing the engine is raising the body a bit because the car is too low.

Raising your car is not a very good idea, you might end up damaging cv joints(shafts), and sacrificing vehicle stability. If you want to raise vehicle buy replacement suspension for same brand of car with higher clearance.

Back to your high fuel consumption. Your car has an ecu that regulates fuel injection presently your car is running rich which is leading to poor fuel mileage and possibly in limp mode, my suggestions to your problems are as follows

1. Check for fuel leaks while engine is running

2.Has your return pipe been blocked? If yes remove it. Most mechanics block the return pipe when the fuel pump is failing to increase the pressure getting to the injectors, this form of abuse will cause the injectors to leak or stay on for longer periods.

3. Water Temperature sensors. The ecu receives signals from the water temperature sensor to determine how long the injectors stay on when in operation. A failing or not connected sensor will cause high consumption

4.Oxygen sensor since your car is a 1991 model and oxygen sensors are to be changed every 100k miles ill suggest you just replace. (with a brand new oem one)

5.Faulty or leaking injector. This is a rear occurrence but its possible could be caused by blocking pressure regulation valve or bad ecu(brain box)

6. Retarded timing. Your timing marks might not match up, have them checked.

7. Bad spark plugs

8. Clogged air box (air filter) if your air filter is blocked of the filter head clogged car will consume more petrol

9.Bad wire harness, check your engine wiring to ensure the wires are not ripped and touching each other clean up your wiring if its not in order.

10. After all the aforementioned if car is still consuming petrol you might have a bad ecu/ecm (brain box) best way to eliminate is to find similar vehicle and test to see if you have same problem.

Best of luck.

Sorry I forgot to add MAP , or manifold absolute pressure sensor, on a 1989-96 Honda Accord is located in the engine compartment on the passenger side of the firewall. It is near the top and is easily accessible.

@op, I suggest that you follow all laid out steps by Gazzuz then revert.

If the problem remains you should check if your thermostart is intact, if not replace it asap.

Thanks all. I met a new mechanic and instructed him based on the advice I got here and I am so so happy that it is now consuming even less than it used to. I really appreciate your concern. I am very very very grateful.

Happy to here your car is running fine.

profolusegun014: Thanks all. I met a new mechanic and instructed him based on the advice I got here and I am so so happy that it is now consuming even less than it used to. I really appreciate your concern. I am very very very grateful.

That's nice to hear. So what are you going to do with your former mechanic? Sack him?