Little Trucks, Big World

When a truck won't start it's usually because it's not getting a spark or it's not getting gas.  I am getting gas as I can see the fume coming out of the carburator's intake when I work the throttle cable.  I thought at first it was getting flooded but now I know it's the coil wire.  The coil wire where it enters the distributor is frozen into the distributor cap.  I actually broke the top of the plastic distrubutor cap trying to pull the wire off the distributor cap.   The parts saleman told me on the phone that the coil may be bad.  He said that the coil may fail when it's hot which sounds a lot like what was going on with my truck. 


I have ordered a new distributor cap and a new coil to replace the one that's bad.  I'll also get a new set of spark plug wires. 


I have the 1986 early model  (manufactured on 8/85 but the sticker said it was an 1986 year model.  It's the 2 wheel drive, NZ24 engine with 4 cylinders and 8 spark plug wires.  It's gas engine and two wheel drive.  I have never replace a coil before so this is new to me.  I can't drive the truck in for repairs as it won't run.  So I'll go pick up the parts tomorrow afternoon and try to put on the new distributor cap.


How do you all mark the spark plug wires so that you can figure out which wire goes to what connection on the distributor cap?  I'll probably just line both the old and the new distributor caps up and then replace one wire at a time so I get them right.  I don't have anything to mark the wires with.  Perhaps they sell some stickers that will affixt to the spark plug wire boots or something at the part store. 



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Most replacement leads/wires are marked...I2...E4....etc.

If not.....pull one at at time and compare length...replace

Thanks.  That's what I ended up doing.  Ijust took the old distributor cap off and removed one wire from it and then put that wire on the new cap.  Worked great. 


I replaced both coils and then replaced the coil wires betten both coils and the distributor cap.  I added too much dieletric grease and the new wires would not stay attached. So I ended up cleaning the plug wire ends with carb cleaner and cotton Q tips and then put them back onto the distributor cap and the coils.  This time they stayed on better.  Still they are not a tight fitting as the original caps were on the original coils.  I also replaced the intake and exhause side spark plugs. Old plugs were full of black suit as I had run some Sea Foam in the gas to clean the inside of the fuel system and carburator.


I noticed that the temperature sensor inside the air cleaner is making a noise.  I may need to replace that.  I checked the air inlet and the vacume motor to see if the butterfly valve was opening and closing to let the hot air exhaust in from the exhaust manifold or clean cool air in from under the hood.  The butter fly metal flap is stiff and hard to move by hand.  Perhaps.  The temperature sensor is helping to contorl the vaccume motor which move the butter fly value in the air intake system. 


I noticed that the air sucking sound going into the carburator is not as loud as it use to be.  The values are noisy and I am have oil leaking out of the valve cover seal near the rear of the engine.  I may need to have the value cover taken off and see if I can clean the old gasket off and have a new gasket installed to stop the oil leak.  I also noticed that the oil pressure is much lower at idle than it is when going down the highway at speed. 

I checked the cylinder compression some years ago and all four cylinders seems ok.  But the engine is noisey so the rings may be worn.   The truck has over 185, 000 miles on it now.  All orginal parts. 


I added some engine retore to the oil a few years back and it got on the spark plugs. It was suppose to fill in micro cracks and scratched on the cylinder walls but all it did was foul the spark plugs. I had it removed and changed the oil and then had to change all the spark plugs as it coated them badly.  I only used that engine restore stuff one time.  Now I just add some heavy duty oil to the engine and put in some valvoline 10W 40 oil with oil changes every 3000 miles. 


Today I found a control unit which is mounted on the driver side firewall and noticed that the wires connected to this thing were a little corroded. These help to control the FDIC thingy. So I cleaned the wire connections with my dremel tool and it's stainless steel wire brush attachment.  I think this has helped.  I also cleaned the connection and the wire connector on the carb for the carb heater. This plastic electrical connector plugs into the two spade wire connectors that come off the passenger side of the carburator. 


Today I drove the truck and got it hot and then stopped the engine and restarted it several times in a row.  So far so good.  But until I can get it to start 100% of the time I won't stop worring about it.  Over the last three weeks or so the truck would only start up when cold and only start up about 50 % of the time when it was hot.


I read that the fuel tank vent lines can get clogged up and cause the engine fuel line to vapor lock.   I used to own a Datson 240Z and it had a fuel vapor lock problem too.   At times in the summer months it would not start. It had to sit for about 15 to 30 minutes before it could be started.  So this may be the same thing occuring in my Nissan 720  1985 truck.


Truck was manufactured on 8/85 according to the stamp on the drivers side door jam.  But the dealers sticker called it an 86 truck.  But the truck has a single row of fuses in the fuse box and according to my Haynes and Chiton manuals the 86 trucks had two rows of fuses and the 85 only have one row of fuses.  Plus this trucks air filter cover looks like the 85 trucks in the service manuals.   This makes it a little more confusing when ordering parts.  I just tell the parts store that it's a late model 85 or an early model 86 and try to match up any new parts with the old parts to make sure that I am getting the right new part.

If your tach needle doesnt jump when you crank the motor your not getting spark

I have an old tack device that I used back in 1970's for working on my old datson 240Z and an old 1972 Datsun 720 truck. 


I also have a timing light that I could hook up to the number one spark plug to check for spark. But the truck runs fine once it's started so if it's a spark problem then it's an intermittant one.  Someone told me that the coils can malfunction more often when they are hot so that's why I replace both the coils in my 1985 truck yesterday. And I installed all new spark plugs too.


Thanks for the help and advice.

OK I checked the tac needle while cranking the engine and it only moves after the truck engine starts. It's not moving at all when the problem occurs and the truck fails to start. 


I think it's the IC module and am trying to figure out a way to get the old IC module off the dissy.  If I can do that job then I can install a new ic module.


One of the guys suggested keeping a spare spark plug with me and testing for a spark when the engine won't start.  I can do that now that I have some extra spark plugs. He also suggested using some canned air and spraying the IC module to cool it off and see if that will make it work for a while.  That's a good idea but I'll have to open up the hook and take the dissy cap off to get to the IC Module.  But I can do that a few times just to test out his theory.  I have a can of air for my computer and other electronics and know how cold it can get when I spray the can upside down.

IF you are looking for great sparkplug wires I custom make them. You wont ever have to buy another set again, I guarantee them to out perform any wire you will buy at any auto parts store and for as long as you own your truck PERIOD! Just see the "FOR SALE" section here and you could also see my pics. Thanx, Ken.

Found the problem. The electrical connections to the FDIC control switch on the firewall passengers side was not making a good contact. After I cleaned these two connectors the truck started fine every time so far.  I tested the choke and found it to be working ok. 


Thanks to all those that replied. 



At the end of the day please dont tell me you bought plug wires without contacting me first?


I already had new spark plug wires put in a couple of years ago. All I had to buy was a new distributor cap and one wire to connect from the cap to the coil. 


The wires on the truck are cable tied together and I didn't really want to have to deal with the spark plug wires unless I absolutely had to.  I'll keep you in mind if I need any wires in the future.  So thanks.

Well the truck is doing it again.  When it gets hot it won't start sometimes.  It's not quite as bad as before but still not 100% there.  I'm wondering if cleaning the wires on the FIDC switch really did anything now.


I did noticed some debri inside the distributor cap in the round rotator thing inside the distributor.  I had replaced the round thing a while back and this week I replaced the Dizzy cap.  Perhaps the old round thing is wearing out or some plastic or metal is chipping off it.  I'll open up the Distrubutor cap when it stops raining and the truck cools off and  clean it out and check it for any wear or damage. 


It will start back up after it sits for about 10 or 15 minutes.  So heat may be the culprit here.


The last few days it rained and was much cooler around here.  Truck started ok during the cool weather period.   Now that it's hot again today the truck sometimes won't restart.  Frustration is high.


I am cleaning and using PB Blaster on the bottom of the fuel pump in an effort to unscrew the bottom of the fuel pump so that I can check the internal fuel fiter inside the fuel pump. Perhaps that's clogged up or something.  I may need to just order a new fuel pump just in case.

Don't fix what isn't broken.


Next time it won't start pull a plug wire off and slip an old plug in it and lay on the valve cover. Crank and look for a spark. If there is spark then it's not electrical.

OK. I'll try that tonight after it gets dark and I can see the spark better.  Good idea. I have a few old spark plugs laying around the garage.


I have been reading these forums trying to see if anyone else had similar problems.  I found that the fuel pump may need to be replaced or the internal fuel pump filter cleaned or replaced.  I have not tested the fuel pump yet. 


Also found that there are some relays that control the flow of fuel.  One of those can go bad.


I also found out that there is a fuel float window that I can look at to see if the gas level is right inside the float chamber.  I need a bright light to be able to see the fuel inside that window.  I'll check that as well.


Does a hot engine need more fuel to start or less fuel?  vs a cold engine. 


I know that a cold engine is choked to make the mixture richer for easier starting as the choke value cuts off the air flow into the carburator throat.






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