Erratic idle 1980 2f (1 Viewer)

[Oregon LC]

After sitting in a garage since 2001, I finally got it running...well sort of.

This rig was improperly parked by the PO and when I got it it needed the typical replacement of rusted out/rotted parts. Here is what I have done: new fuel tank, sending unit, rebuilt fuel pickup tube, new soft fuel lines, hard fuel lines have been cleaned/flushed out, carb fully rebuilt by @65swb45, all new vacuum tubing properly hooked up (I think?) And finally new battery.

The strange thing is that it starts right up and idles great, but it dies after a minute or two. Then when I got to restart it won't run unless I have my foot into it, It dies as soon as I take my foot off the pedal. Smells like it's running rich too.

If I go to restart the next day it idles perfectly and then will die after running for a short time and then goes back to running rough for the rest of that evening.

The charcoal canister is a bit of a concern for me as there is a good amount of vacuum when I open the gas cap. Since I noticed that problem I have just been leaving the gas cap open until I have time to rebuild it.

Has anyone experienced the same issues I'm having? This truck is 100% stock, all Federal emissions are intact as far as I can tell.

 

[JohnnyC]

Check for vac leaks?... but... have a hunch it may be the intake manifold cracked just under the carb ... take a flashlight and look down the carb

 

[Oregon LC]

Check for vac leaks?... but... have a hunch it may be the intake manifold cracked just under the carb ... take a flashlight and look down the carb

I failed to mention that I fully refurbd exhaust and intake manifolds with all new gaskets and a block off plate between intake and exhaust. The original intake manifold had at some point been cracked but properly repaired.

 

[samatulich]

Get a vacuum gauge.

 

[ToyotaMatt]

Get a vacuum gauge.

 

[ToyotaMatt]

I failed to mention that I fully refurbd exhaust and intake manifolds with all new gaskets and a block off plate between intake and exhaust. The original intake manifold had at some point been cracked but properly repaired.

I noticed in photo # 1 your Fuel Cut Off Solenoid is all

Taped Together ? it appears to have maybe wiggled loose from

vibration Possibly , You Need this Part working for sure .....

in addition to Re-securing and or replacing the Broken Connector

Housings , Verify through a simple bench test outlined in your 2F

Engine FSM that this Mission Critical Part is in good working order

and meets spec's .....

 

[Oregon LC]

I noticed in photo # 1 your Furl Cut Off solenoid is all

Taped Together ? irt appears to have maybe wiggles loose from vibration

You Need this Part working for sure .....


View attachment 2143250View attachment 2143251View attachment 2143252View attachment 2143253

The housing is cracked, I could not locate a replacement at the time. Are you selling them?

 

[ToyotaMatt]

The housing is cracked, I could not locate a replacement at the time. Are you selling them?

PM sent...

 

[cbmontgo]

Some other odd things you might want to check, as I’ve been a similar spot before.

EGR. Verify it is working properly and not stuck open.
Emissions computer. Unplug it and see if anything changes to rule it out.
Fuel cutoff solenoid. As mentioned above.
Fuel filter. Make sure it’s clean.

Definitely start with a vacuum gauge.

 

[Oregon LC]

Make good progress tonight.

Finally got the engine to idle. I ended up wiring the fuel cutoff solenoid directly to the battery. Engine runs very smooth and there is plenty of vacuum at idle (see pic).

Now the issue becomes why is there no power to the fuel cutoff solenoid from the factory wiring harness?

I'm guessing the emission control module behind the clutch pedal is the culprit? I didn't have time tonight to pull it out and inspected, but I think that's the next logical step.

Also regarding the emissions control module, when unplugged the engine runs the same but is a little bit quieter from the engine bay area. With the module plugged in it sounds like there is a slight sound of fan hitting radiator. This is not the case, but that is how I would best describe the sound. The sound dissipates for the most part when under acceleration, but returns again at idle. I'm assuming it has to do with the factory emissions controls. When the emissions control module is plugged in I hear the sound and when unplugged the sound is completely gone.

Anyone have an idea as to what the sound could be?

 

[1911]

Finally got the engine to idle. I ended up wiring the fuel cutoff solenoid directly to the battery. Engine runs very smooth and there is plenty of vacuum at idle (see pic).

Now the issue becomes why is there no power to the fuel cutoff solenoid from the factory wiring harness?

I'm guessing the emission control module behind the clutch pedal is the culprit?

Yes, a very common culprit for fuel cut solenoid non-function. The emission control "computer" circuit board connections were cold soldered at the factory, and these tend to crack over time making an intermittent (or permanent) open circuit. It's usually the soldering close to the wiring harness connector for the computer. Some folks have reported success by heating the old solder with a soldering iron and re-flowing it. The easiest way to "fix" it is just to ground the wire that comes from the the FCS to the computer, because that is what the computer does with its circuit wizardry. Then, the fuel cut solenoid will always be open (never "cut"), but in my experience there is no downside to this.

Also regarding the emissions control module, when unplugged the engine runs the same but is a little bit quieter from the engine bay area. With the module plugged in it sounds like there is a slight sound of fan hitting radiator. This is not the case, but that is how I would best describe the sound. The sound dissipates for the most part when under acceleration, but returns again at idle. I'm assuming it has to do with the factory emissions controls. When the emissions control module is plugged in I hear the sound and when unplugged the sound is completely gone.

Anyone have an idea as to what the sound could be?

The computer also has control of the EGR and air injection systems for the smog equipment, so likely one of those, but I don't know.

 

[cbmontgo]

I’ve never totally understood the emissions control module internals, but you can usually find them reasonably priced on the used market if you want to swap it out.

Also, make sure that your engine fuse is good. The fuel cutoff solenoid runs off of that circuit.

 

[Oregon LC]

Yes, a very common culprit for fuel cut solenoid non-function. The emission control "computer" circuit board connections were cold soldered at the factory, and these tend to crack over time making an intermittent (or permanent) open circuit. It's usually the soldering close to the wiring harness connector for the computer. Some folks have reported success by heating the old solder with a soldering iron and re-flowing it.

Very simple fix tonight, everything seems to be functioning great now.

I pulled out the emissions control circuit board and reflowed the factory soldering behind the wiring harness connector. Put it all back together and voila.

Thanks for the help @1911