1986 Nissan Pickup:
Engine Cuts Out around 45 mph

Question:

I have a 1986 V-6 Nissan Truck with 190,000 miles. I notice that at speeds around 45mph in 4th or 5th gear it is running fine. Then it cuts out for one or two seconds and then runs fine again. I'm burning 87 octane fuel and the oil and filter have been changed between 3,000 & 4,000 miles ever since I bought the truck new. What could my problem be?

Answer:

There are a bunch of possible causes to the condition you've described. Unfortunately, changing the oil regularly and the octane rating of the fuel you're using has no effect on any of them. The 190,000 miles is another story.

What did you mean by "cuts out"? Did it feel like the engine completely shut down, as if you actually turned the ignition off and then on again a few seconds later? That's the true definition of cuts out. Mechanics can be led in the wrong direction by the improper wording of a drivability symptom. This can cost you time and money. Not that you did, but using cuts out when describing a partial loss of power or a misfire can hamper diagnosis.

The engine is losing fuel and/or spark. Spark loss may be related to a bad distributor cap, rotor or pick up coil, ignition module, ignition switch and any related wiring, connections, grounds, relays etc. Fuel delivery problems include fuel injectors, the computer that controls the injectors, fuel pump, fuel regulator, and, of course, any wiring, fuses, relays, grounds etc.

When looking at a miss or a partial loss of power, a lot of the above may still apply, but we can eliminate a couple of possibilities like the distributor pick up coil and the ignition module. We can also add items like spark plugs, plug wires and several sensors that affect the computer's control of the fuel injectors.

Often an experienced technician can diagnose a problem like this just by feeling the condition during a road test, followed up by a quick inspection of the suspect component. Other times there can be significant labor hours involved trying to figure a problem out.

The point I'm trying to make is that it may be worth the price of a good technician on this one. And communication is really important in getting a car repaired efficiently.

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