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Discussion Starter · #1 ·
I have a 1985 Nissan 4x4 that loses all power "sometimes" and just barely idles on the side of the road. If I shut the vehicle off for a short period of time I can start it up and drive away. sometimes it runs fine for the rest of the day and sometimes it won't go another mile without breaking down. This problem has been ongoing for several years. Recently I came to the conclusion that my truck appears to run bad on cold damp days. After doing some research I came to the conclusion that I have a carburetor icing problem. I have looked through a nissan repair manual and I am unable to determine how to troubleshoot this problem.

How many ohms should an ohm meter read when the mixture heater is checked? What controls the mixture heater? Is it always on?

I would appreciate some advice!


 

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I may be wrong here but it sounds to me Like you have Dirt in your fuel system
At tleast that's the problem I had but was a little more dramatic then what your talking about so heres a few suggestions you can try first
Replace the fuel filter cheap and easy to replace
then take the frount plate off the carb and carefully slide the float out with out loseing the needle valve pay attention to how the float and the needle fit together then clean out the Carb s fuel bowl real good or if you can use compressed air and blow it out that will save you from takeing the Float out just make shure you keep a finger on the pin the float is mounted on then put everything back together
turn the ignition on and off bout 4 or 5 times to make shure the carb is filled back up
check for leaks (shouldn't be any but check anyhow)
then drive it and see if it helps
as far as the heater under the carb it really doesn't do a whole lot if any good or harm but I believe it is on constantly when the ignition is on all it is is a ceramic grid that heat's up and supposed to help atomize the fuel better but in accuality the cooler the air fuel mixture is the better the vehical will run and save you gas milage in my opinion (when you heat up gas it evaporates)

Nissan_King_84

1984 Nissan King Cab 4x4
http://www.geocities.com/nowheres/Paul_s_720_Page.html
 
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Discussion Starter · #3 ·
At first I thought it was a fuel problem also. Over the last few years I have replaced the filter and the fuel pump, I ran a new fuel and a new vent line, I ran a new hot wire to my fuel pump and I also ran a dedicated ground line. I have repalced the carb and dropped the fuel tank and inspected the tank for dirt to no avail.

I only use my truck for off-roading, hunting and fishing and the truck will run great all summer long but once it gets cold and its snowing, raining or high humidity my truck starts running bad again.

One time when I was disabled on the side of the road I sprayed gumout carb cleaner into the carb and the truck instantly started running better. I believe the gumout melted the ice that was forming under the carb. Several more times after that when I was diabled I used the gumout and my problem went away almost instantly.

I looked back through all the posts to this site and found a similar problem

Subject Re: Problems with my '84
Posted by Bernie (journeyman)
Posted on 4/20/00 06:20 AM
This is a long shot but does it only happen when its damp out and the temp is in the 40s or lower? If so it could be carburetor icing. This happened to me a few years ago. The symptoms I had was that it would run fine for the first few miles, but then it would start losing power. It would get so bad that I could floor the petal and the engine would only go to 3000 RPM in neutral. And like you, if I turned it off for a little while the problem would fix itself. The ice forms on the mixture heating plate and blocks the flow of the air/fuel mixture. Two things to check are your mixture heater and your heat riser system(that tube that runs from the top of the exhaust manifold to the air box) The resistance of the heater should be around 4 or 5 ohms, mine was 40 to 50 when it didn't work. Also, check the big vacuum valve on your air intake that opens the heat riser tube, it might have a hole in it. It these two are good something could still be wrong with them up stream, bad relay or the valve isn't getting any vacuum for example.
Other than that I'd check all the ignition things, plus, wires, cap, rotor, coils. You can check the fuel level in your bowl too. There is a window with a dot on it. The fuel level should be right at the dot. It doesn't sound like this is your problem but it's real easy to check.
Let me know if you have any more questions.

Bernie
'86 720 "The Stain"

I am some what convinced that I have an icing problem. My problem is my ceramic heater ohms out at 200 ohms. I also checked one out at the dealership and it also ohms out at 200 ohms. Is 200 ohms right? If so mine must be good. and what ever is controlling the heater must be bad. I checked the lines going to my heater and there is no voltage going to them.


 
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