Well, shoot, i was wrong then.The emission computer will allow the FCS to close under conditions of hi rpm and hi manifold vacuum, like you suddenly let off the gas. It will open back up when the rpm comes down or you open the throttle to lower vacuum. Per the manual, this system cuts off part of the fuel in the slow circuit of the carburetor to prevent overheating and afterburning in the exhaust system. This is called the deceleration fuel cut system, first seen in the 1979 manual. I know earlier trucks had basically a hard wired solenoid on the carb that was not controlled by the emission computer. I'm not a carb expert so I couldn't say what the purpose of that was.
I had posted earlier about our idle issues, which now appear to be solved. The original FCS would click, but we replaced it anyway. The replacement would also click, but we still had idle issues. This included when the FCS was powered directly from the battery. We replaced with another FCS from a reputable supplier, problem is gone!Quickly did some tests with digi multi meter:
1) Checked ground/contact with main wiring harness on the chassis side (the green plug/harness that plugs into FCS itself from main): Good
2) Checked switched power on the main wiring harness: 11.5v (did not start car)
3) Checked ground/contact on carb with general point on chassis bolt: Good
4) Checked ground/contact on shorter wire (green plug) on FCS to carb: good
5) With FCS disconnected from main harness, hard wired FCS directly to battery - nice loud click
6) Plugged back together (cleaned with contact solvent) and Switched 12v to listen to FCS - and having trouble hearing it as I have some kind of emission/other relay clicking (its normal), so need to get the wife to get my ear away from the relay that is also switching on. CONFIRMED: strong click with key turn.
7) Checked 15A fuse for Engine - metered fine with contact, but does have original Toyota fuse here ( I was wrong in my post above as it being aftermarket). I do not think this is the issue.
Open to other suggestions.
See page #1 - filter was replaced with OEM. Tank was not flushed or inspected.Late to the party gents. @Last Flight Out do you know the condition of your fuel tank and fuel filter? Sure sounds like you might have some crap that has made its way in the idle circuit in the carb. You can try removing the idle adjustment screw on the base of the carb and blasting it with carb cleaner to try to unseat the blockage. Then reseat to the same depth and see if you can start it.
I run a generic clear filter from NAPA on mine so that I can see what the condition of the filter is at all times.
I’ll reflow 13 when I have the box out again . It’s super easy to work on these archaic computers….just fussy to figure out why.
Testing FCS function of 81+ emissions computer.
Yes this is what I have been doing. All viewed and inspected under loop. Again, I can spot cold solder joints easily enough.When I found the cold solder joints it took the use of an eye loop magnifier to clearly identify three cold joints (connector).
Each solder joint should have a nice visible flow at the base of the board and around the conductor. Any small cracks must be mitigated by reflowing. Like I mentioned previously, this solved my random stalling issues for good.
X2 … I’m about ten years after I rebuilt my first Aisin and converted my rig back to stock and I’ve had no issues. That said and it’s about time for another rebuild.The carbs are just fine...once tuned and or cleaned/ rebuilt they prove long maintenance free service lives.
Whether it’s carb or EFI, I’d pull my tank and make sure it’s clean and rust / debris free. I was thinking your issue could be an obstruction in the idle circuit, without eliminating the source you may have future issues. Best of luckThat’s what I am stating to consider now…