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Re: 94 Nissan Truck KA25E engine
You most likely need to replace said Mass Air Flow Sensor (MAFS). If you disconnect this sensor, the ECM uses other sensor data to "calculate" fuel delivery. Problem is, this method is not good for real time- meaning that when you hit the gas pedal, the ECM has to calculate the fuel needed and the engine doesn't rev up right, causing more of a driveability issue.
I've replaced quite a few of these sensors. Be sure to buy a new Nissan air filter when you buy the new MAFS. Even if you do the work, Nissan will want to see that should you have a parts warranty (12 months/ 12,000 miles) claim. No air filter replacement (with a Nissan part) = no warranty coverage.
This is not the most accurate test to use to check the operation of a MAFS, but it usually gives you an idea if you're in the right area- idle smooths when disconnected usually means you are in the right area.
Hope this is helpful!!
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Check the intake elbow to be absolutely certain it doesn't have a rip or tear in it (them) where it connects to the throttle body, and on Mass Airflow Sensor. There can be no leaks there. Get a spray can of Mass Airflow Sensor cleaner and clean the MAF. Remove and inspect the ribbed elbow, checking for holes worn in it that could leak air. If the amount of air entering the throttle body differs from what is sensed by the MAF sensor, the mixture will be wrong and make the engine run poorly. If there is a leak before the MAF sensor it doesn't affect the running of the engine. If you haven't run Fuel Injection cleaner in the gas, try STP Super Concentrate (2 small bottles or one large). Also check vacuum lines are not cracked (if so replace them). Throttle body must have a good seal to the intake manifold.
If your service engine soon light is on, go to autozone and have the code pulled up. Sounds like you are in limp mode (safe mode). I suspect it is your mass airflow sensor. Its easy to replace but expensive. I recommend getting one from a junk yard and installing it yourself. if you dont have any mechanical experience dont worry. As soon as you see one it will be obvious you dont need experience. It is in the middle of the big tube that connects your air filter to the throttle body. All you need is a screw driver and disconnect one electrical connector. Again, not worth buying new...they cost over $350 new but only $60 at junk yard.
If you want a quicker way to check, dissconnect the big tube from the intake manifold, in essance letting air run directly to the throttle body without going thru the air filter or mass airflow sensor. If the car runs fine with it dissconnected, its the mass airflow sensor. Buy some mass airflow sensor cleaner at an auto store (its specifically made and named mass airflow sensor cleaner). Try to clean it first...Dont touch anything inside with your finger tho.
Sorry if Im sounding like a school teacher but Im not sure of your mechanical knowledge or ability.
If not none of this works , you will have to pull up the code.
Engine will die when you plug it in while running, Plug it back on, start engine, if it runs the same when you unplug it while the engine is running, bad sensor, replace, if engine wants to die when you unplug it, sensor is good, hope this was very helpful.
FROM WHAT I FOUND OUT ON MY SAME TRK ONLY 94' IS THE DIAPHRAM ON THE FUEL PRESSURE REGUALTOR IS SLUGGISH OR BLOWN. DISCONNECTING THE VACCUM LINE AND PLUGGING THE MANIFORD PORT HAS HELPED UNTIL I AM ABLE TO AFFORD THE REGULATOR. TO HELP CLEAN THE OXY SENSOR, SPEED UP THE IDLE AND DISSCONNECT THE BRAKE BOOSTER VACCUM LINE AT THE ENGINE. THE FRESH AIR WILL SOMEWHAT HELP CLEAN THE SENSOR IF IT IS ABLE TO BE HELPED. I AM TOLD THAT THE OXY SENSOR ON THESE MODELS IS CRIDICAL. JACK
I would have the charging system checked for over-voltage and AC ripple. There maybe a hidden wire harness problem if the charging system is okay. Wiggle test the wire harness while the engine is running to help locate the problem area. That is way to many parts replaced.