New Owner of a 720 (with many problems)

[Brandon.fair]

hello all,

So I bought a 1985 720 ST King Cab M/T. It has 223k on the milometer (my-lom-e-ter). Now that it's home I've started picking up on all the things I missed at the sales lot. The previous owner(s) did a real bang up job of really F'ing the thing up. So to list a few things that were half-assed are. The headlight switch is not working, so they added a toggle switch to have the head lights turn on and off. Ok no big deal, but instead of mounting the switch some where the just connected 10 feet of wire it the wires on the back of the original switch and just laid the wire across the cab. Next is the truck has about half of the total number of the required amount of bolts and screws to operate. For instance if a part needs 6 screws, it has 3 or less. Everything electronic has been destroyed basically.

 

This will be my build thread and I'll post pictures as I go and I'll update this first post to make it easier for people to find solutions to similar problems they are having 

 

Updated: June 10 2017

Stalling at idle - FIXED - changed fuel filter and clean fuel lines out as well as cleaned carb. I took out anti-diesel solenoid and idle mixture screw and sprayed carb cleaner from the anti-diesel solenoid out the idle mixture screw. It blew some junk out and since then it hasn't stalled.

 

Bogging down passed 3000 RPMs - FIXED - ran some Tech-ron complete fuel system cleaner through and changed fuel filter. Also adjusted float bowl level.

 

Not starting (turn key get one click) - TEMP FIX - have truck in gear and roll forward or backward till driveline "engages" engine.(goal is to rotate the flywheel slightly). I think the starter is binding on the flywheel somehow but I don't know for sure.

 

-Replaced vacuum advance lines

-Painted the window arches

-Changed oil at 224k to Rotella T4 with NAPA Gold filter

[datzenmike]

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?

[Brandon.fair]

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

 

[Charlie69]

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.

[datzenmike]

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.

[Brandon.fair]

Are you referring to these wires?

 

[datzenmike]

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

 

Got a better picture of the carb??

[Brandon.fair]

[Brandon.fair]

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

[datzenmike]

 

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.

[Brandon.fair]

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

[datzenmike]

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.

[Brandon.fair]

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.

[Charlie69]

L = Blue

B = Black

R = Red

Y = Yellow

G = Green

LG = Lgreen

Br - Brown

[Brandon.fair]

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?

[Charlie69]

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

[Charlie69]

Not sure without looking at the factory service manual. 

 

 

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.com/file/d/0B_aTp2Z0MRgBNUt4Wm1pd0NoSlk/view?ths=true

[Brandon.fair]

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

[datzenmike]

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.

[Charlie69]

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.

[Brandon.fair]

My connector is out of order  it appears that someone has pulled out the pins and put them in different places. I went through it and marked it's corresponding pin on the other side but that doesn't line up with the diagram. So I'm concerned that the two RY might be mixed up. As far as I can tell from the diagram. They both are either power supply or ground (back at computer or something) 

[Brandon.fair]

 

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

 

 

Sent, thanks

[Brandon.fair]

So many questions...... is this the auto choke? It has a blue wire solder to it.

 

[datzenmike]

Yes. Blue is the power wire to it. Inside is an electric heater that warms a bi-metallic spring that expands and unwinds, opening the choke. When it cools down the spring contracts and tries to close the choke but the throttle at idle blocks this. When starting an engine cold, step on the gas once and this releases it and it snaps closed.

[Brandon.fair]

Dude your the man! I think I love you haha. Anywayso while working on those 6 wires and the timing advance vacuum lines I noticed I wire that is not connected to anything. It think it's from the alternator

 

 

Also looking at the carb viewing window I saw the fuel level is above the window. I assume it should be at theach dot in the window. How is this remedied?