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83' 720. Engine turns over and then immediately dies


E-Rock

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I'm new to working on cars and I'm attempting to tackle this myself since I don't think it's a big problem. I bought the truck 4 months ago. It has a newly rebuilt engine and has nearly 10,000.00 worth of work in the damn thing. The guy who owned it before me was a nut... I haven't had a single issue until yesterday. The bolts that hold on the air filter had come loose so I replaced them. I don't think I did anything to the carb during this process but I'm not sure. I find it unlikely anyway. I also strapped down the battery because it was loose. That's all I did. After doing this the truck would turn over and then immediately die. Perhaps it's a coincidence.

 

As long as I'm giving it gas it will continue to run but will die as soon as I let off. I replaced the fuel filter and disconnected the soft line on the engine side of the fuel pump and it was shooting out fuel. I went ahead and replaced all of the soft lines in the back. I've read a lot of threads about this problem and it seems to be fairly common. All fuses appear to be intact. I can hear the fuel relay click over when I turn the key.

 

I know this topic has been covered a lot, but perhaps someone can help with my specific case...

 

Thanks in advance.

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This is fine where it is. If you want it moved just ask a mod, don't start another post exactly the same.

 

 

Have someone turn the key (don't start it) on off on off, while you listen near the carb. You should hear a click sound coming from it when the key is turned. If not, turn the key to ON and move the round electrical connector at the right rear side of the carb. Move the wires around and see if it clicks when you do this.

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I wiggled all of the wires around with the key turned and didn't hear any clicks. Thank you for the help.

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Yes but did you first....

 

 

Have someone turn the key (don't start it) on off on off, while you listen near the carb. You should hear a click sound coming from it when the key is turned. If not, turn the key to ON and move the round electrical connector at the right rear side of the carb. Move the wires around and see if it clicks when you do this.

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The clicking sound should be the idle cut solenoid turning on with the key. Without it, no fuel can get to the idle circuit and without gas it simply won't idle.

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So NO clicking when the key is turned on off?

 

Replace the second fuse over from the left (closest the door)... it's a 15 amp and never trust them by looking at them. Replace it. This is the fuse that powers the idle cut and when replaced we can assume that we have power to it now.

 

If it still does not click you will need to get a $5 test lamp to check for power right at the solenoid.

 

 

These are invaluable for tracing power or grounds.test_light.jpg

 

The round plug at the back of the carb is...

 

ECCelectrocarbZ24engine.jpg

 

There should be 12 volts on the R (red) wire to the solenoid B (black) should go to ground. On the harness end it's Yellow and Red/Yellow

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I havent had time to get to the store to buy a fuse and test lamp, but I just wanted to make sure I'm looking at the right thing. It's the red wire coming off the back that is connected to the off white/yellowish wire that goes to the carb....correct? It looks to be pretty shredded, as you can see. Also, the throttle valve switch wire (if I'm not mistaken) is clipped...as you can see.

 

-6_zps623b620e.jpg

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Yes it idled because the choke was on.

 

 

That carb has been replaced. The blue wire (under that black cover) goes to the choke. The red wire should go to the idle cut solenoid.If you can't figure it out just join the idle cut to the blue choke wire. This will be on when the motor is running.

 

Friggin previous owners.

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See if there is power to the idle cut solenoid wire (red). It has to have power to it to open the solenoid and let gas into the idle circuit. That's the click sound you should be hearing when you turn the key to on.

 

The reason it idles this morning is because the choke was on. This adds extra gas and engages a fast idle cam to rev the motor up. As soon as the motor warmed up and the choke was off there was no gas to idle on.

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In an EMERGENCY you can unscrew the idle cut solenoid and remove the plunger and screw it back in.  It disables the idle cut so you can drive the truck, but it causes run-on when you stop the engine and worse gas mileage. 

 

I had to do this once because my solenoid ITSELF went bad.  Got me home and to work for a week before the new solenoid arrived.  All good now. 

Do NOT leave it that way.  It's best to fix the problem.  But in a pinch it'll get you by.

 

Measure the voltage at the solenoid first, though.  Also, make sure the GROUND wire is good from the harness plug to the manifold.  (If you have it) 

Mine has this, and a broken wire there will also cause a no idle.

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So I replaced the fuse and tested the wires going to the choke and to the idle cut solenoid. Both seemed to have power. I'm using a commercial electric voltage detector. What shoulfd I do now? Thank you so much for the help.

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It's the HEX shaped thing on the back of the carb that the red wire goes to. Just unscrew it. There is a spring and a pin inside so watch for them to fall out. As suggested, remove them and screw back in. Now the fuel should be able to get down into the idle circuit and it should idle.

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