Pathfinder 1988 ran fine but now undriveable

1988 Pathfinder (125,000 miles)- After starting, runs smooth at idle for say a minuite or so. Then when applying throttle revs a little say 2000rpm then cuts out. Also, if I do not apply throttle, after 3 or 4 minuites it starts running rough stumbling and then stalls out. Plugs are very clean. Injectors puff fuel. Crank Angle sensor signal looks good on the oscilloscope. (Also rotating by hand over range of distributor pulses ~5volts and puffs injectors.) The throttle sensor produces a smooth change in resistance from about 2k-8.8kohm. Note: The ECU doesn’t have a rotation mode selector and I haven’t found the way to select the mode and so do not have the trouble code.

What is the likely cause that makes this otherwise good truck undriveable. ie. The most common causes and weaknesses in the Nissan system and suggestions for trouble shooting sequence. Exhaust seems not to be clogged. Fuel completely removed and replace as well as the fuel filter. Fuel pump seems fine ( I pumped the tank empty with it to replace gas incase it was bad.) It is as though there is a fuel:air ratio issue. I unscrewed to see the air flow sensor on the side of throttle body. It looked clean.


Sounds like fuel starvation. Did you do a volume test on the fuel pump??? I suspect the pump isn’t pumping out the way it should.

After the problem developed and before the other tests, I had replaced the fuel filter and used the pump (inition time limited pumping) to pump out the gas tank. It seemed to be pumping quite a strong stream. Do you know what the rate or volume test parameters are? With the air filter off the throttle body, the two injectors make a cloud of fuel when the engine sputters to a stop. It will after starting and running at idle smoothly start sputting and quit without the pressing the accellerator. Could it be a pressure regulator or partially clogged injectors?

Check the fuel pressure. You will need a high-pressure fuel gauge kit that can be tapped into the feed line. It is possible the fuel pump is not pumping up the pressure or the regulator has failed, and letting too much pressure to be released.