1996 KA24E dies intermitantally

[1988SupraDreams]

I have a 1996 Nissan 2WD 5spd KA24E pickup that is displaying a very strange symptom.

The truck will start and run fine most of the time, but every once and a while the engine will start to lobe, sputter, and die. It will do it in hot weather, cold weather, with a cold engine, or with a hot engine. Temperature doesn't seem to effect it. It will do it almost any time. It seems almost random. Revving the engine will sometimes fix it and other times it wont. Spark makes it all the way to the plugs on all four cylinders.The check engine light is not on and there are no codes stored in the ECU.The truck gets Chevron 87 gas only.

Things I have checked and inspected or replaced recently:Timing set to 10 deg before TDC with the TPS disconnected (As per the specifications under the hood)Inspected Spark plugs they are NGK and are gapped properlyInspected Spark plug wires they are bosch and have hardly any use on themNew thermostat at OEM temp.New coolantInspected Radiator cap no damage to sealing surface, and it relieves at the correct pressureCleaned both the Mass Air Flow sensor and the Intake Air Temperature sensor with CRC MAF cleanerInspected Air Filter, clean enough.New oil and filterCar passed compression test on all four cylinders

The truck is my father's and he says that it's been doing this for about 9 months, and it has me scratching my head. A search did not tell me much, and I was wondering if I could get some ideas as to what could cause this.

I was thinking that the EGR might be a possibility, but wanted some confirmation on this before I went through the trouble. I figure that the cap and rotor would be okay since the car runs perfect otherwise, but will be checking them in the morning anyway (Below freezing here).

My other thought was the altitude. The altitude where the truck has been driven for the last year or so is approx 3,500 feet above sea level. I know there is a high altitude control sensor on most vehicles and would think that this one would be no exception. Is the sensor seperate or a part of the ECU?

Any advice is much appreciated.Also, if more information is needed, do not hesitate to ask.

Thanks in advance,Shawn

[ivans]

Two things to check - first is the EGR passages in the intake manifold. Look for the allen socket head plugs that are in the intake manifold. Remove these and you may find that they are plugged with carbon. you can use a pice of wire or a drill bit to clean them out. When you first remove the plugs you may not be able to see into the intake runner, but there is a small hole there - .200" or so in diameter. It needs to be clean all through the connecting passages for the EGR portion of the intake manifold. Take a close look at the way the manifold is constructed and you should see what I am trying to explain.

Second item would be to replace the MAF. You may have cleaned it, but I have seen these that are bad, but can't be detected visually. You can disconnect it while the problem shows itself - if when disconnected nothing changes then it is likely the MAF. If you can swap it with a known good one that will prove if that is the problem.

I don't think you have an altitude sensor on that vehicle, The ECU and the MAF measure air density and adjust fuel accordingly.

[1988SupraDreams]

Thank you very much for your detailed explainations ivans. I will be taking off the EGR today, and if I can get it to display the symptoms again I will unplug the MAF sensor.

What had led me to believe that it might have a HAC sensor is that 87-88 Toyota Supra Turbos have a MAF an IAT and a HAC sensor (Later moved into the ECU in 89-92 Supras). I realized after reading what you said, that the reason my car has one is because it is turbocharged and the car makes different amounts of boost at different altitudes.