Fuel cut solenoid not closing when it needs to (1 Viewer)

[MGTS]

I recently noticed that the "engine braking" was not as effective at it used to be. With the engine running, I checked the vacuum switch by manually pulling vacuum on it. When enough vacuum is applied, the computer should see the change and tell the solenoid to turn off. Nothing. Engine still purring away. I've checked continuity on the vacuum switch, it's working fine. When I unplug the solenoid from the harness, the engine dies immediately, so that's working fine. I've checked the wires that go from the vacuum switch and the solenoid to the computer. All have continuity and do not accidentally to frame. I've run wires to bypass the harness (connecting directly to the computer/ground). Nothing. I bypassed the computer by connecting the solenoid ground to the vacuum switch. THAT worked, but it was cutting out at idle, so I can only assume that the computer figures out when to cut the solenoid based on other factors.
Perhaps this is something related to the speed sensor or RPM? I got a used computer from Curiser Corps, but no difference.
I have not changed anything recently. I keep up on maintenance and everything is pretty shipshape. 300k miles. CA all its life, no rust.

 

[ToyotaMatt]

I recently noticed that the "engine braking" was not as effective at it used to be. With the engine running, I checked the vacuum switch by manually pulling vacuum on it. When enough vacuum is applied, the computer should see the change and tell the solenoid to turn off. Nothing. Engine still purring away. I've checked continuity on the vacuum switch, it's working fine. When I unplug the solenoid from the harness, the engine dies immediately, so that's working fine. I've checked the wires that go from the vacuum switch and the solenoid to the computer. All have continuity and do not accidentally to frame. I've run wires to bypass the harness (connecting directly to the computer/ground). Nothing. I bypassed the computer by connecting the solenoid ground to the vacuum switch. THAT worked, but it was cutting out at idle, so I can only assume that the computer figures out when to cut the solenoid based on other factors.
Perhaps this is something related to the speed sensor or RPM? I got a used computer from Curiser Corps, but no difference.
I have not changed anything recently. I keep up on maintenance and everything is pretty shipshape. 300k miles. CA all its life, no rust.

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[OSS]

there's no guarantee that the replacement used computer works properly either.

The computer will use RPM input and vacuum input (from the vacuum switch) to turn the fuel cut solenoid on & off.
If you've verified without a doubt (using the emissions manual recommendations) that the vacuum switch works as it should, then there's two more suspects left- the rpm input into the computer and your used replacement computer.
If both of those worked properly and the vacuum switch works, the FCS will open & close during deceleration.

 

[Spike Strip]

At speed (above 1800 RPM), when you take your foot off the skinny pedal, manifold vac momentarily shoots up closing the Vac switch (allowing ground) and this causes the Emissions Computer to CUT ground to the ICS, closing it, momentarily, to reduce that rush of fuel from the high vacuum.

It's most likely your Emissions Computer, although there is a very crude VSS (vehicle speed sensor) in the Speedometer that sends info to the Emissions box.

Almost every Emissions Box I've come across is faulty. I doubt the used one you rec'd was tested - It wouldn't be worth their time to do so, properly. I've got about 10 on the shelf that I would gladly send out for repair, if I could find an old skool electronics shop to fix them. They're a very simple thing for someone who what they're doing.

There are a few threads on people 'reflowing' the solder points where the 10-pin connector attaches to the PCB and that seems to work. I've never tried.

If you do decide to have your Emissions computer repaired and find a shop, let us know.

Otherwise, ground the white wire from the ICS to the carb body and that removes the Decel circuit from the loop.

 

[Gretsch]

There are a few threads on people 'reflowing' the solder points where the 10-pin connector attaches to the PCB and that seems to work. I've never tried.

I have actually done this with success on mine. But I could visibly see breaks in the solder joints. Can see the post here if interested. I had intermittent idle issues. Grounded mine to the carb for awhile as @Spike Strip mentions but then wanted it working right so tried the solder re-flow. Worked for me.

I do wish there was a known electronics shop that would repair these properly however. Not sure how many folks would get them repaired but I for one would be interested.

 

[MGTS]

I tested the contacts on the board and they are all good. I'm going to test the speed sensor like Spike said

 

[Spike Strip]

It could be a component on the board rather than a solder connection. I had one that would intermittently go out and it was temperature related.

Easy to check the Speed Sensor though with a multimeter per the FSM directions.

 

[fjc-man]

You didn’t say what year your 60 is but I think the early ones might have been wired like my 5/79 Fj40. With the speed signal to the emissions Ecu coming from the ignition coil. If yours comes from the speedometer and is inoperative maybe this would be a fairly easy work around. To fix your speed signal problem that is....

 

[MGTS]

Speed sensor works fine and the wires going from the cluster to the ecu are fine

 

[Spike Strip]

Well, if the Decel isn't working, it's either switch, wiring or Computer, if ICS and other components are known good.

Like I said, I had one truck where the ICS would intermittently not function. Computer seemed ok, as far as the solder points for the connector went, but I finally swapped it out for the last NOS one in the universe and problem went away.

You could just ground the white wire out of the ICS and never think about it again, or spend $$ to send the Box to A1 Cardone... Last I checked they would 'rebuild' it, but it was expensive.

Did you reflow the solder points or just check for continuity? Could be temp sensitive.

 

[MGTS]

Well, if the Decel isn't working, it's either switch, wiring or Computer, if ICS and other components are known good.

Like I said, I had one truck where the ICS would intermittently not function. Computer seemed ok, as far as the solder points for the connector went, but I finally swapped it out for the last NOS one in the universe and problem went away.

You could just ground the white wire out of the ICS and never think about it again, or spend $$ to send the Box to A1 Cardone... Last I checked they would 'rebuild' it, but it was expensive.

Did you reflow the solder points or just check for continuity? Could be temp sensitive.

Checked solder points. All good. ICS turns off and on with ignition, it just doesn't do it on decel and at the correct rpm. Runs fine otherwise. I think I'm just going to leave it

 

[Spike Strip]

 

[Spike Strip]

Another thread reminded me the Vacuum Switch is grounded through its body to the fender ... Make sure those connections are clean/good.