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stumped on stalling out problem....


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Hey All,

 

I come to the forum with my stalling 84 2wd 720. I stalled out on me last week, I let it sit for 20 mins and got it home (50 miles) with no issues. this happened again a few days ago and after letting it sit a while got it home and started trouble shooting.

 

It was due for an oil change so I did it, checked the fluids, got new distributor cap, Wires, plugs, and cleaned the distributor rotor. 

 

Once it got back up to normal running temp it stalled again....I had a lot more trouble getting it started, so I had it towed home.

 

It's getting fuel, the pump, filter and relay are quite new and appear to be functioning perfectly well.

 

I had an odd hunch that the ignition coil was going, so I changed it; still has same problem.

 

It  runs fine when cool and when it gets to normal running temp it just gets weak and pumping the gas does nothing until it eventually stalls. The first thing I do is jump out and see if the electric fuel pump is on which it is.

 

Oh and the alternator, and battery test fine.

 

I think it is a spark related but I'm not sure. Does anyone know if these are signs of needing a new distributor??? Anyone have any experiences with a distributor only failing once it has heated  up???

 

 

 

Thanks,

 Dave stuck on my bike in Portland (which isn't that bad)

 

PS, My dad insists that it's vapor lock, but I drove the truck all summer last year with no issues...

 

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You need fuel and spark to run an engine. Find which is missing and fix it rather than guessing and buying parts. There is no substitute for deduction. Well unless you count lucky guess as a tool.

 

The coil... first there are two coils so replacing one is less than a 50% chance of a 5% chance that it's even a coil OR you have the right one in the first place. The only way to know that the coil isn't working is to test it and see if there is spark or not. Take the lead off the distributor cap and place an old spark plug in the end. Lay it on a grounded surface and have someone crank the engine over while you watch. There is spark or there is no spark. Now try the second coil lead. Spark means the coil is good. No spark means that something is wrong but not necessarily the coil(s). Some coils can quit when they heat up but the chance of both coils at the same time is vanishingly small.

 

I'm going to assume that the ignition isn't the problem.

 

 

Fuel...

 

While the engine is warming up the choke is on. Cold engines need a richer mixture to run efficiently as the engine warmth isn't enough to fully vaporize the fuel droplets. This rich condition can easily mask a hidden lean condition when the engine is normally warm. When the choke is shut off the lean condition asserts it's self, and the engine begins to act up.

 

If it lacks power when driving the lean condition is likely a blocked primary jet lessening the fuel delivered to mix with the air. Usually removing the jet and cleaning it and the fuel bowl of sediment fixes the problem.

 

If the problem is it not idling properly then this is in the idle circuit. The idle circuit has it's own separate fuel supply. Two things.

 

1/ The idle cut solenoid isn't turning on and opening, allowing fuel flow into the idle circuit. Turn ignition on / off /on / off, and listen for the click sound near the rear of the carb. Clicking presumably means the idle cut is working. 

 

2/ blockage in the idle circuit stopping fuel from getting through to the idle circuit. Your '84 likely has no provision for adjusting the idle mixture and it is set at the factory and sealed so owners can't tamper with it. In the picture below is a Z24 carb with the sealing plug removed. Just drill a small hole in the aluminum plug and drive a suitable size wood screw and twist it out. Now the idle adjustment screw inside is available. Remove it but count the turns so you can put it back at the proper setting. Remove also, the electric idle cut solenoid, but have a care as there is a spring and plintle inside that can fall out and get lost..... a passage connects them. Using a can of carb cleaner with a straw, direct the spray into both openings to dislodge any dirt. Replace everything. You can leave the old plug covering off if you want. 

 

carbidlemixscrewZ24Large.jpg

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Hey,

 

Great advice. The plug for the idle mixture screw had already been removed. I took out the screw and spring and sprayed cleaner in as you said, replaced the removed screw and went to the cab to start it up to burn off the cleaner as the back of the can said to do, when I turned the key there was fuel in the carb, I could see it in the little glass window, I ran the engine for about 25 seconds when it stalled; this confused me because it hadn't been stalling out this quickly! After I let the Fuel pump on Accessory in the cab for a minute I checked the carb window and there was no fuel in there!!!  Now I think the whole problem may be due to a sticking float. You were certainly right, its a fuel issue and not a spark issue, Thank you! 

 

I'm off to work until Friday when I get back to the truck. I'll clean the jets like you recommended as well as check to see if the idle solenoid is functioning correctly(i need a 2nd set of hands or ears to check that) but I think all signs point to a sticking float. Is the replacement of the float reasonable to do while the carburetor is still on the engine, or should I plan to remove it?? 

 

Thanks for your help. I'll get back to the thread hopefully with a running truck

 

Dave

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There is a relay for the fuel pump. I believe there is a timer involved also. Turn key on and timer comes on and runs the pump (10-30 seconds??don't know how long for sure) If you do not start the timer times out and pump shuts off. If you engage the starter the relay comes on during cranking and when the key is released the timer begins again. If the engine starts, alternator charging and oil pressure light off will keep the relay on continuously. If the engine stalls the timer starts then shuts off the pump. If oil pressure is lost the timer begins and then shuts the pump off. This is a safety device... in the event of an accident the engine stalls or oil pressure lost the pump does not keep pumping fuel, reducing the risk of a fire.

 

http://dlarson.hubpages.com/hub/The-Datsun-and-Nissan-Pickup-Fuel-Pump-Relay-What-the-Haynes-Automotive-Repair-Manual-Wont-Tell-You

 

 

To keep the pump running the relay needs a good charging alternator and oil pressure (red oil light on dash out)

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