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New Owner of a 720 (with many problems)


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#1 Brandon.fair

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Posted 18 May 2017 - 10:50 AM

hello all,

 

I just purchased a 85 720 an it runs but it was bogging down when I pressed the gas petal down passed the 1/3 point and smelled rich(as hell). So my first thought was that it need the carb tuned up. but today all of a sudden that issue went away and now it doesn't want to idle. It will run if I keep my foot on the throttle. The vacuum lines are completely shot so I'm thinking that might be the culprit. I'm looking for some info on possible other causes to these issues. I was told by the salesman that the truck sat for a very long time. Any info will help. Thanks in advance


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#2 datzenmike

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Posted 18 May 2017 - 11:43 AM

These trucks will smell rich as they warm up because the choke will be on. Once warm, about 10 min take the top off the air filter, the choke plate should be open or vertical.

 

There were two carbs, one with an oxygen sensor. Do you have an O2 sensor in the exhaust manifold?


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#3 Brandon.fair

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Posted 20 May 2017 - 04:03 AM

I think this is an o2 sensor but I have suspicions haha

 

saxmdl.jpg


1985 King Cab

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#4 Charlie69

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Posted 20 May 2017 - 05:55 AM

Welcome!  Please start a build thread so it is easier for us to help you, all these different threads will become buried quickly.  If all your questions are in one thread it is also easier for you to check your build thread in the future to see if this is a reoccurring problem.  Picture of carb please.


Here is my build link:
http://community.rat...s-66-520-build/

 

Here is my 86 720 2WD King Cab Thread

http://community.rat...20-king-cab-dd/

 

Here is my 85 720 2WD King Cab ST Build Thread

http://community.rat...20-king-cab-st/

 

Here is my Photo Bucket Album Link:
http://http://s477.p...arlie69_Datsun/


#5 datzenmike

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Posted 20 May 2017 - 06:07 AM

Yes. This means you have the electronic feedback carb. Check the round electrical connector at back of carb. Are all (6) wires there? Try wiggling them as the often do not make good contact. Turn ignition on off on off without starting. You should hear a soft clicking sound from the idle cut solenoid.


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#6 Brandon.fair

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Posted 20 May 2017 - 06:54 AM

Are you referring to these wires?

 

t80wno.jpg


1985 King Cab

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#7 datzenmike

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Posted 20 May 2017 - 07:59 AM

Yup. Get that sorted out and it may work better.

 

Got a better picture of the carb??


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#8 Brandon.fair

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Posted 20 May 2017 - 09:22 AM

6s50ll.jpg2nty7mu.jpg2ngg847.jpg


1985 King Cab

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#9 Brandon.fair

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Posted 20 May 2017 - 09:25 AM

The connector is shot. most the pins are not sticking out far enough to make a connection with the other half. 

 

What the best way to fix this issue? I was thinking about getting some spade connectors. I don't want to half ass it though


1985 King Cab

"We blow stuff up that blows stuff for a living."


#10 datzenmike

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Posted 20 May 2017 - 09:46 AM

ECCelectrocarbZ24engine.jpg

 

Here's where they go.

 

The Idle cut or anti dieseling solenoid cut fuel to the idle circuit when the key is off. If not working... no idle.

 

Choke heater electrically warms the choke ti turn it off as the engine warms up.

 

Throttle valve switch tells the computer if idling or full throttle to set pre programed air fuel ratios.

 

Air fuel ratio solenoid constantly adjusts the mixture with feedback from the O2 sensor.

 

 

If there is a failure in the system there is a small chance that the air fuel ratio solenoid could set a dangerously lean mixture so there is a built in 'limp home' mode that is extra rich. This would allow no harm to the engine till it is fixed but it runs poorly and gives terrible mileage.


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#11 Brandon.fair

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Posted 20 May 2017 - 10:45 AM

Is there a way to test each component to ensure that it's working properly? 


1985 King Cab

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#12 datzenmike

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Posted 20 May 2017 - 12:24 PM

You can but need a factory service manual (FSM) for your year. You should have one anyway as they pay for themselves almost every time you use it. Try e Bay or Amazon. It describes what is happening and how to check and set adjustments

 

Besides the throttle position and, O2 sensor, other inputs to the computer are the ignition, water temp, vacuum switch, (full throttle heavy load) battery. All these are needed to set the mixture properly.


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#13 Brandon.fair

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Posted 20 May 2017 - 03:16 PM

Is there any diffrence in the two RY wires? Also what color is L? It lines up with a blue wire with double hash marks.


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#14 Charlie69

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Posted 20 May 2017 - 05:13 PM

L = Blue

B = Black

R = Red

Y = Yellow

G = Green

LG = Lgreen

Br - Brown


Here is my build link:
http://community.rat...s-66-520-build/

 

Here is my 86 720 2WD King Cab Thread

http://community.rat...20-king-cab-dd/

 

Here is my 85 720 2WD King Cab ST Build Thread

http://community.rat...20-king-cab-st/

 

Here is my Photo Bucket Album Link:
http://http://s477.p...arlie69_Datsun/


#15 Brandon.fair

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Posted 20 May 2017 - 05:17 PM

L = Blue

B = Black

R = Red

Y = Yellow

G = Green

LG = Lgreen

Br - Brown

 

Right, but the diagram above shows two red wires with yellow stripes. On the bundle of wire Im dealing with has two red wires with yellow stripes. So I'm confused as to why. And do they do the same thing? Like positive power supply or something?


1985 King Cab

"We blow stuff up that blows stuff for a living."


#16 Charlie69

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Posted 20 May 2017 - 05:18 PM

As far as the connector goes see if you can snag one from another truck in the junk yard.


Here is my build link:
http://community.rat...s-66-520-build/

 

Here is my 86 720 2WD King Cab Thread

http://community.rat...20-king-cab-dd/

 

Here is my 85 720 2WD King Cab ST Build Thread

http://community.rat...20-king-cab-st/

 

Here is my Photo Bucket Album Link:
http://http://s477.p...arlie69_Datsun/


#17 Charlie69

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Posted 20 May 2017 - 05:26 PM

Not sure without looking at the factory service manual. 

 

ECCelectrocarbZ24engine.jpg

 

In the diagram Mike posted one RY (Red Yellow) connects to the Anti Dieseling Solenoid and becomes R (Red).

 

The othe RY (Red Yellow)  connects to the Air-Fuel Ratio Solenoid and becomes W (White).

 

This is real common in wiring harnesses that a wire will be one color on one side of the plug and a different color on the other side of the plug.

 

Here is a link to my Google Drive 1986 720 FSM PDF.  You will have to send me a request to download the file.

 

https://drive.google...k/view?ths=true


Here is my build link:
http://community.rat...s-66-520-build/

 

Here is my 86 720 2WD King Cab Thread

http://community.rat...20-king-cab-dd/

 

Here is my 85 720 2WD King Cab ST Build Thread

http://community.rat...20-king-cab-st/

 

Here is my Photo Bucket Album Link:
http://http://s477.p...arlie69_Datsun/


#18 Brandon.fair

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Posted 20 May 2017 - 06:04 PM

Did you mean to say the first one you mentioned connects to the anti dieseling solenoid? The red wire


1985 King Cab

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#19 datzenmike

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Posted 20 May 2017 - 07:49 PM

The plug is a mirror image. The upper image with L at 6 o'clock connects to L at 12 o'clock below it. The two unused X pins connect to the two X pins in the bottom image.


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#20 Charlie69

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Posted 20 May 2017 - 08:01 PM

Did you mean to say the first one you mentioned connects to the anti dieseling solenoid? The red wire

Yes you ar e correct and I corrected the post.  Thank you.  Without the full wiring diagram it is hard to tell where the 2 RY (Red Yellow) originate.

 

The 1986 FSM in My google is as close as I can come on FSMs in PDF.  I need to get my 1985 720 manual into pdf format.


Here is my build link:
http://community.rat...s-66-520-build/

 

Here is my 86 720 2WD King Cab Thread

http://community.rat...20-king-cab-dd/

 

Here is my 85 720 2WD King Cab ST Build Thread

http://community.rat...20-king-cab-st/

 

Here is my Photo Bucket Album Link:
http://http://s477.p...arlie69_Datsun/