Fuel Cut Off Help w/ pictures

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Saw your PM --

Vac leaks? Vac hoses correctly routed. Any borken cracked hoses? Big hose to brake booster?

Check the A/C idle up (disconnect the vac. hose and block it and see what happens.... In my above pic, it's the hose to the diaphram just under the green connector).

Do a search for this issue, there's gotta be other suggestions out there...
 
To revive a long dead thread...let me just say that thanks to this post I finally tracked down the stumble/flat spot/crappy performance I've been chasing and tinkering with for months.

When I did my de-smog I apparently misidentified the fuel decel vacuum switch on the drivers' fender well and removed it completely, not knowing what it was. I had the hose coming from the decel port on the carb going to the spaghetti manifold but simply capped the other end thinking as long as it wasn't creating a vacuum leak it should probably be fine.

Come to find out the computer was activating the fuel cutoff solenoid the whole time I was driving around. It's amazing how crappy this thing can run when the fuel gets pinched at 1800 rpm. Couldn't figure out why it was so lean....go figure.

Many, many, many thanks -I've lost so much hair over this and had at one time or another questioned every component on my truck to the point that I was going nuts.

$1.97 for a pack of ring connectors and about 3 mins in the Home Depot parking lot...I've literally found a new truck. It runs like it's new.

Big take away #1) If you don't know what it is or what it does - don't mess with it.
#2) The answer to most issues is somewhere on this forum. Took me months of reading other people's symptoms and troubleshooting to find it, but it was here.

Loving life right now.
 
Jesper said:
To revive a long dead thread...let me just say that thanks to this post I finally tracked down the stumble/flat spot/crappy performance I've been chasing and tinkering with for months.

When I did my de-smog I apparently misidentified the fuel decel vacuum switch on the drivers' fender well and removed it completely, not knowing what it was. I had the hose coming from the decel port on the carb going to the spaghetti manifold but simply capped the other end thinking as long as it wasn't creating a vacuum leak it should probably be fine.

Come to find out the computer was activating the fuel cutoff solenoid the whole time I was driving around. It's amazing how crappy this thing can run when the fuel gets pinched at 1800 rpm. Couldn't figure out why it was so lean....go figure.

Many, many, many thanks -I've lost so much hair over this and had at one time or another questioned every component on my truck to the point that I was going nuts.

$1.97 for a pack of ring connectors and about 3 mins in the Home Depot parking lot...I've literally found a new truck. It runs like it's new.

Big take away #1) If you don't know what it is or what it does - don't mess with it.
#2) The answer to most issues is somewhere on this forum. Took me months of reading other people's symptoms and troubleshooting to find it, but it was here.

Loving life right now.
Click to expand...


Jey Jesper - thanks for the follow up. What exactly did you do to fix it? Tahnks!
 
@Comet, fuel decel info and why you don't want to ditch it. Feel free to tell me to screw if I'm way off base.
 
@NeverGiveUpYota you rock! I just installed the fuel cutoff directly to the fuel filter vacuum. Is that right?
 
Huh? Fuel decel? God sorry mines all apart; cyclinder head is at a machine shop. @CaptClose or @mwebfj60 can verify that one.
 
I am going through this now. I am running a Trollhole carb. Do I still try the greenwire mod?
 
My limited understanding is if you hear the click of the solenoid, you don't need to ground the white/black stripe wire. The green wire gets hooked up to the carb plug. I believe, if I have read correctly, the green wire mod only eliminates the electronics from the equation. Trollhole carb is the same as what I ordered from city racer and I only plugged in the green wire.
 
Comet said:
My limited understanding is if you hear the click of the solenoid, you don't need to ground the white/black stripe wire. The green wire gets hooked up to the carb plug. I believe, if I have read correctly, the green wire mod only eliminates the electronics from the equation. Trollhole carb is the same as what I ordered from city racer and I only plugged in the green wire.
Click to expand...
Solenoid can still be faulty even w/ an audible click. At minimum have you pulled it off the carb and check the tiny little o-ring (in the pix below where my thumb is pointing is where it would be)... ? You can find a replacement at an Ace. They have a great assortment. Mine when looked w/ a magnifying glass was dry rotted. You'll need a 12mm (if memory serves right) wrench and you'll need to remove the bolt that pivots the ACC to be able to remove the solenoid from the carb.

image.webp
 
Comet said:
@NeverGiveUpYota you rock! I just installed the fuel cutoff directly to the fuel filter vacuum. Is that right?
Click to expand...

Comet said:
My limited understanding is if you hear the click of the solenoid, you don't need to ground the white/black stripe wire. The green wire gets hooked up to the carb plug. I believe, if I have read correctly, the green wire mod only eliminates the electronics from the equation. Trollhole carb is the same as what I ordered from city racer and I only plugged in the green wire.
Click to expand...

If you have a one-wire carb (non-stock, non-usa carb), then your decel-fuel-cut system is not going to work, period, as it controlled through negative ground.

decel-fuel-cut-schematic-jpg.201113
 
Good info, not from me! Please disregard my above statements regarding the solenoid and the fuel cut off. Thanks guys and gal for keeping me on the straight and narrow. Carry on.
 
i've been having trouble with idle for a while. at first it was intermittent, and now it's constant. truck has the capability to run great, i am highly confident of that. from my searching, this seems like a typical situation - truck runs fine at speed, but refuses to idle unless the chock is pulled (at least half way in my case) or i put foot on the accelerator.

i checked voltage the connector to the fuel shut off solenoid. +12v. i tried grounding the solenoid, which worked for a few weeks (maybe longer). today, based on this thread, i tried running a wire from the + battery straight to the solenoid while grounding the - solenoid terminal. truck idles fine in this case. i then plugged the stock connector back in and i can hear the solenoid click just like should if it's working, truck won't idle.

so, i connected directly to the battery again, truck idles. grounded the solenoid for a final attempt, it won't idle. i have also checked that the solenoid is getting +12v when connected to the battery, when grounded, and at the stock connector. all are +12v when the key is in the on position. it's also +12v when idling and connected to the battery. because it won't idle any other way, i can't check the voltage at idle when it's grounded or using the stock connector.

what is left to check? old bessie runs great when she is moving. its such a great feeling when she idles, too. alas, she won't. seems the solenoid is good, bypassing the "computer" via direct connect to the battery is good - so i assume the carb is fine, yet grounding the solenoid doesn't give the same result as direct connect to the battery - i expected it should.
 
The fuel cut solenoid gets its signal (power) from the emissions computer. Since you've verified that the FCS works when a separate 12v source is applied to it, the problem must be with the computer.
If I was in your shoes, I'd try to find another used emissions computer and if that wasn't possible I'd completely rewire the FCS with new wires with its power source tapped off the Engine fuse circuit in the cab.
That way it would still work as intended except during deceleration
 
Spike Strip said:
Truck stopped idling even while the ICS white wire was grounded and 12v confirmed ? (and it's a clean good ground?)
Click to expand...
its a good ground, tested with a volt meter at the ground location and where the wire connects.

OSS said:
The fuel cut solenoid gets its signal (power) from the emissions computer. Since you've verified that the FCS works when a separate 12v source is applied to it, the problem must be with the computer.
If I was in your shoes, I'd try to find another used emissions computer and if that wasn't possible I'd completely rewire the FCS with new wires with its power source tapped off the Engine fuse circuit in the cab.
That way it would still work as intended except during deceleration
Click to expand...
i was thinking of running a wire from the fuse box. will give that a try and see how it does. any suggestions on where to find a replacement computer? is it actually a circuit board or just relays?
 
slaterson said:
its a good ground, tested with a volt meter at the ground location and where the wire connects.
Click to expand...

But did ICS work or stop working?

btw, Emissions Computer controls the ICS by switching Ground, not + ... That's why if you ground the white wire it bypasses EC
 
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FJ60 emissions computer is an actual little computer. It has simple logic circuits. Very rudimentary by modern standards.
 
OSS said:
The fuel cut solenoid gets its signal (power) from the emissions computer. Since you've verified that the FCS works when a separate 12v source is applied to it, the problem must be with the computer.
Click to expand...

This is incorrect. The solenoid gets power from the ignition switch through the engine fuse.
But yeah, the computer might not be supplying a reliable ground.
 
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