Fj40 carb vacum

[Centermass]

I have a 79 fj40 that starts with the choke out but as soon as the vaccum switches the choke off the engine dies. If I can keep it runing till it get completly warm then it will idle but not as smooth as it should. All vaccum lines look like they are routed correct, new plugs, correct timing, good compresion 125-135 on all cylinders. Any suggestions

 

[PHAEDRUS]

idle circuit ?
Stock carb Emissions stuff in tact??
More info makes it better, First guess is that green wire right in front of the bowl does not have 12 volts going to it.
Dave

 

[Centermass]

It's is stock smog and carb. I used a jumper to make sure that the idle deal made a clicking sound. When the choke is out the engine idles at 1500 rpm the when it gets to the proper temp the thing just dies. I was wondering if one of the vacum line could be hooked up wrong. I have factory smog manuel and I have checked everyline but maybe I missed something

 

[Pin_Head]

Just dies with the choke on and running at 1500 RPM (which is what I think you said)? Or just dies when you push the choke knob in all the way?

Try hot wiring the idle fuel cut off solenoid and see if that helps.

 

[Centermass]

with the choke out correct when the temp sensor that opens the vaccum switch to turn off the choke the engine dies. If I can keep it running till it gets hot then it will run. But a little rough iwill try using a jumper on the fuel cut off thanks

 

[Centermass]

Thank you pin_head. The engine never died. I checked the fsm on how to check the vacuum switch. It appears to be working correctly. D'animal recommended checking the ground from the engine to the body. If you have any suggestions I would appritiate.
Thanks Bill

 

[Pin_Head]

I am a little unclear what is going on. I'm guessing that the truck won't idle w/o the choke on and there is something I am not familiar with that turns the choke off when it warms up. If it won't idle, then either it isn't getting idle fuel or there is a large vacuum leak. Check for leaks first, including the brake booster and if the EGR valve is stuck open. Also try adjusting the idle speed and idle mix screws. If hot wiring the idle solenoid doesn't help, then consider rebuilding the carb.

 

[Centermass]

I will try to explain
If i pull out the choke and start the rig it runs till the choke opener hits 112 degrees. Then the engine dies. I does not run smooth though. At that point it wont run with the choke out or in. When I put the jumper from the battery to the fuel cut solenoid the engine will run with the choke out and even after the choke opener has gotten to 112 degrees. So with the jumper on it will run with the choke out or in and the engine runs smooth. I checked the emission control manual for 79 and it said to check the vacuum switch. According to the diagrahm this controlls the fuel cut off solenoid. I checked to see if had vacuum which it does. Then it shows to check the vacuum switch with the ignition off and on. Off is supposed to have continuity and on is no continuity. I used the multi meter and it is working correctly. I also tested the fuel cut off with the jumper and you can hear it clicking when power is applied to it. When I used the multi meter to check if there is power at the connection between the fuel cut off and the wiring harenees one lead is hot 12volts and the other has no voltage with the ignition on. I should probably take the fuel cut off out and check the o-ring to make sure it is intact. Also with the jumper from the battery to the fuel cut off the engine runs very smooth and as soon as the jumper is diconnected the engine dies that instant. D'animal recommended checking the ground on the engine block to the body. I hope this makes more sense, I have been try to reply with my phone. No high speed internet at home. Thanks Bill

 

[Pin_Head]

Do you have the two wire idle fuel solenoid? (I thought it came in later) If so, then the computer and vacuum switch grounds the green/yellow wire to power the solenoid. It should get power from the engine fuse through the black/yellow wire with the key on. If you have 12V on the black/yellow wire then the engine fuse is good. When you say you are jumping the wire to the battery, I assume you are grounding the green/yellow side, correct? If by grounding this wire the solenoid works, then if the vacuum switch is working, the computer must be bad. Try resoldering all the pins for the connector on the printed circuit board.

 

[Centermass]

Yes, two wires I believe they are black and white wires. I used a jumper to connect one side to the positve side of the battery and the other wire is grounded to the battery with a jumper . I will check the voltage of the black/yellow wire with the key on today when I get home from work. I will also try grounding the wire that goes to the vacuum switch green/yellow. If all these are working correct then I will go to an expection of the computer. I got this rig and started with bad egr cooler, cracked exhaust manifold, missing smog parts, and they bypassed the oil cooler. D'animal helped me get most of that stuff fixed but it it just seems like its one thing after another. Oh well once I get it running, I'll need figure out why the brake light comes on when I step on brake pedal. New mastercylinder blead and adjusted brakes but the light still comes on. I reused the little presure sensors from the old master cylinder so I wonder if they could be all clogged up.Thanks I will update with what I find tonight.

 

[Centermass]

Pin_Head I checked all the voltages on fuel cut off switch and vacuum valve the all test 12 volts. Out of curiosity I used a jumper to ground the white wire comining out of the fuel cut off. The cruiser ran just like if I had used a jumper on both wires. I hope this makes sense??

 

[Pin_Head]

Yes.
The engine computer grounds this wire to turn the solenoid on and provide idle fuel. In combination with the vacuum switch and speed sensor, the computer will turn off the idle fuel when vacuum is high (engine braking) and speed is above 15 MPH to prevent HC emissions and possible detonation of unburned fuel in the exhaust manifold catalyst. If the speed sensor and vacuum switch are OK, then your computer isn't working properly.

 

[Centermass]

so just resolder the connection??

 

[Centermass]

I guess it would be connections on the circuit board??? If it the board is bad can you get a replacement. There is a guy that is great with the x-ray rooms here at the hospital I bet he could trace the problem down if I had to go that far. He knows I am into radio control helis and ia always asking to take a look inside my transmitter. Ive seen him find whats wrong with a large board unsolder the part go to radio shack or a big electronics store and then resolder the new part back on the board and the room is up and running. All the other guys have to find a replacement board and have it shipped in. If you have any suggestion I am all ears. Thanks Bill

 

[Coolerman]

Hmmm not sure I'd want an X-Ray from a machine with Radio Shack parts in it!

Take him the board, he can easily resolder all the components.

 

[1911]

I'm having this same problem, but only intermittently. Fuel Cutoff solenoid is working fine, emissions control box looks to be in great shape (truck only has 54,000 miles on it), I cleaned all connector contacts but problem still comes and goes (no idle witout choke even when hot). I'm thinking about jumping a ground wire straight from the FCS to the ignition switch, bypassing the emissions control box and vacuum switch to see if that does it.

 

[Centermass]

It works took computer out it had several bad solder spots touched them up and it runs great. Thanks guys

 

[Centermass]

Thanks Pin_Head now onto the brakes and rust.

 

[1911]

I'm having this same problem, but only intermittently. Fuel Cutoff solenoid is working fine, emissions control box looks to be in great shape (truck only has 54,000 miles on it), I cleaned all connector contacts but problem still comes and goes (no idle witout choke even when hot). I'm thinking about jumping a ground wire straight from the FCS to the ignition switch, bypassing the emissions control box and vacuum switch to see if that does it.

Figured it out, the vacuum switch for the FCS is bad. Does anyone know if these are still available at a dealer? I guess I'll try on Monday. Meanwhile, it runs fine with the wire unplugged on the switch.