93 Nissan Pathfinder running rough

VortecJeep

VortecJeep

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Joined
Aug 24, 2005
Location
Concord, NC
A friend wrecked his truck, and is borrowing a 1993 Pathfinder (auto, I assume a 6 cylinder). It runs like :poop:. I briefly saw it last night. He can push the gas pedal, and little or no change in engine speed. Then if he pushes it several more times, it will start accelerating. He has a new set of OEM plugs, wires, and dist. cap he wants me to help put on tonight. I hope that helps. I didn't look, but asked him later on the phone and he said there is no check engine light on. One other thing, he did say that it had been sitting for several months. Could that be bad gas? When he pushes the pedal, it doesn't sputter, it just doesn't do anything much over idle speed until he keeps pressing the pedal several times. I printed out a list of codes for it so I can check it if it does have a code stored.
 
Could be bad gas, but also could be a bad TPS. Hard to say without codes.
 
Got more info. When he first started driving it last week, it was fine. He has run at least two full tanks of gas, so that rules out bad gas I think. Last night we changed plugs, wires, dist. cap, rotor, and fuel filter. No improvement. In park, when you step on the gas pedal, the engine speed actually drops about 100-150 rpm. To get it to rev up, you have to pump the gas pedal 3 or 4 times. It won't hardly move in drive. I should have taken the TPS off to see if it the part that turns was broken where it attaches to the throttle.

I checked voltage on the battery and I don't think the alternator is putting much out. Only about 12.5 volts with the engine running, it should be 14.5. Could a bad alternator cause the motor to not rev up? Check engine light not on and alternator light not on.
 
Today I blew air thru the gas line back towards the tank in case there was a blockage. No change.

I decided to experiment with the TPS. When I took the TPS off, the motor actually revved up like it is supposed to, but then couldn't idle properly, I assume because without the TPS, it was lost. I also manually moved the position of the TPS and no change was detected. Does that sound like a bad TPS? Also, should that TPS be spring return? If I remember correctly, the TPS on my TJ is.
 
can I rule out the mass air flow sensor?

I pulled the air tube off between the air filter and intake to spray some carb cleaner in it. It wouldn't start. I assume because it didn't detect any air flow across the mass air flow sensor. When I reconnected the air tube, it started. Does that rule out the MAF sensor being the problem?
 
The TPS really just tells the computer where the throttle is at. It uses that, O2 sensor and mass air flow to calculate how much fuel to add. So just messing with the TPS won't change the way it runs. To test the TPS you need a analog voltmeter on ohms and move the TPS and it should change resistance in a steady arc. You might try cleaning the Mass airflow sensor with electrical contact cleaner of mass airflow sensor cleaner.
 
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