86F150CA Posted October 21, 2020 Share Posted October 21, 2020 Does anyone know what the resistance should be on a healthy Idle Air Control valve? I am seeing 39.5 ohms. My idle drops and then recovers on a cycle of about 8-10 seconds. Newer IACs seem to expect 7 - 13 ohms. Link to comment Share on other sites More sharing options...
85lebaront2 Posted October 22, 2020 Share Posted October 22, 2020 That is not an idle air control valve, those are found on EFI engines, yours is an idle speed controller and is a small reversible motor with a switch to tell the EEC when the throttle is touching the plunger. The IAC on the EFI engines is a duty cycle solenoid that controls the air flow. What you may need to do is watch the ISC and see it it is moving in and back out, if it is, check the resistance from the tan with red hash to the black with white hash wire with the plunger pushed in (this closes the internal switch). If the plunger is pulling back enough to open the switch then the base idle may be set to high, or the adjustment of the screw that contacts the ISC may be set wrong. If the motor is not moving in and out, then it is not the problem, you have another issue. Link to comment Share on other sites More sharing options...
86F150CA Posted October 22, 2020 Author Share Posted October 22, 2020 That is not an idle air control valve, those are found on EFI engines, yours is an idle speed controller and is a small reversible motor with a switch to tell the EEC when the throttle is touching the plunger. The IAC on the EFI engines is a duty cycle solenoid that controls the air flow. What you may need to do is watch the ISC and see it it is moving in and back out, if it is, check the resistance from the tan with red hash to the black with white hash wire with the plunger pushed in (this closes the internal switch). If the plunger is pulling back enough to open the switch then the base idle may be set to high, or the adjustment of the screw that contacts the ISC may be set wrong. If the motor is not moving in and out, then it is not the problem, you have another issue. Therein lies the rub. My carburetor does have the 4 wire idle speed control motor, a little stepper that has a plunger on the end. It is one of the suspects in my investigation. But it also has what I think is an idle speed control valve that has two wires and presumably reports the air/fuel mixture to the EEC. It is my primary suspect since I can't find any vacuum leaks. The information on the idle speed control motor would be my next question if the IAC (or whatever it really is) isn't the issue so the information is quite useful. Is there a procedure to initialize the idle speed control motor if I wind up replacing it? Or does it self adjust? Link to comment Share on other sites More sharing options...
86 12 Brutus Posted October 22, 2020 Share Posted October 22, 2020 That is not an idle air control valve, those are found on EFI engines, yours is an idle speed controller and is a small reversible motor with a switch to tell the EEC when the throttle is touching the plunger. The IAC on the EFI engines is a duty cycle solenoid that controls the air flow. What you may need to do is watch the ISC and see it it is moving in and back out, if it is, check the resistance from the tan with red hash to the black with white hash wire with the plunger pushed in (this closes the internal switch). If the plunger is pulling back enough to open the switch then the base idle may be set to high, or the adjustment of the screw that contacts the ISC may be set wrong. If the motor is not moving in and out, then it is not the problem, you have another issue. A properly running YFA when starting the truck, the engine will rev up for a few seconds, depending on outside temp. then lower a bit, then lower one more time to idle. check the gasket under the carb and check the bolts. I've had this happen to Brutus, it was a loose carb body. Also a good check is start the truck and disconnect the computer and have the truck run in limp mode. While in limp mode is where you do most of your course adjustments to this carb Link to comment Share on other sites More sharing options...
myrl883 Posted October 22, 2020 Share Posted October 22, 2020 A properly running YFA when starting the truck, the engine will rev up for a few seconds, depending on outside temp. then lower a bit, then lower one more time to idle. check the gasket under the carb and check the bolts. I've had this happen to Brutus, it was a loose carb body. Also a good check is start the truck and disconnect the computer and have the truck run in limp mode. While in limp mode is where you do most of your course adjustments to this carb The two wire solenoid on the side of the carburetor is mixture control. It leans the mixture by applying vacuum to the float bowl to counteract the pull of fuel due to venturi vacuum. Link to comment Share on other sites More sharing options...
1986F150Six Posted October 22, 2020 Share Posted October 22, 2020 The two wire solenoid on the side of the carburetor is mixture control. It leans the mixture by applying vacuum to the float bowl to counteract the pull of fuel due to venturi vacuum. I found this old thread on another forum. Being discussed is the mixture control feature [pintle]. The OP has a 1980 vs. the 1986, but this is because it is a California vehicle. https://www.ford-trucks.com/forums/1299408-carter-yfa-carburetor-puzzle.html Link to comment Share on other sites More sharing options...
85lebaront2 Posted October 22, 2020 Share Posted October 22, 2020 The two wire solenoid on the side of the carburetor is mixture control. It leans the mixture by applying vacuum to the float bowl to counteract the pull of fuel due to venturi vacuum. It is the mixture control, but it doesn't apply vacuum to the float bowl. If you remove it there are 4 separate little chambers in it's top and the bowl cover. It regulates the amount of air bled into the mixture on both the idle and main circuits. The 7200 VV does apply vacuum to the float bowl through a stepper operated pintle valve. Link to comment Share on other sites More sharing options...
86F150CA Posted November 9, 2020 Author Share Posted November 9, 2020 It is the mixture control, but it doesn't apply vacuum to the float bowl. If you remove it there are 4 separate little chambers in it's top and the bowl cover. It regulates the amount of air bled into the mixture on both the idle and main circuits. The 7200 VV does apply vacuum to the float bowl through a stepper operated pintle valve. Update: The truck passed smog with a little carburetor tweak from my mechanic. It eliminated the wide fluctuation of rich/lean which resulted in smooth idle. I want to thank everyone for their suggestions I think I learned a lot. Next project will be finding out why the fuel gage goes from Full to Empty in about 50 miles? And why the temperature gage doesn't register? I have heard there is a voltage regulator in the instrument panel. (I have a after market temperature gage and sensor but it is hard to read). Again, thanks. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 9, 2020 Share Posted November 9, 2020 Update: The truck passed smog with a little carburetor tweak from my mechanic. It eliminated the wide fluctuation of rich/lean which resulted in smooth idle. I want to thank everyone for their suggestions I think I learned a lot. Next project will be finding out why the fuel gage goes from Full to Empty in about 50 miles? And why the temperature gage doesn't register? I have heard there is a voltage regulator in the instrument panel. (I have a after market temperature gage and sensor but it is hard to read). Again, thanks. Congrat's!!!!! Glad it passed. On the fuel gauge, it is probably the sending unit in the tank. They do that. And on the temp gauge, the problem isn't the Instrument Cluster Voltage Regulator since the fuel gauge works and the ICVR powers those two awa the oil pressure gauge. Pull the wire off the temp gauge sender and ground it to the block or some other ground. With the key on the temp gauge should go to full scale in a few seconds. If so the gauge and wiring are good and the sending unit is bad. Link to comment Share on other sites More sharing options...
86 12 Brutus Posted November 10, 2020 Share Posted November 10, 2020 Congrat's!!!!! Glad it passed. On the fuel gauge, it is probably the sending unit in the tank. They do that. And on the temp gauge, the problem isn't the Instrument Cluster Voltage Regulator since the fuel gauge works and the ICVR powers those two awa the oil pressure gauge. Pull the wire off the temp gauge sender and ground it to the block or some other ground. With the key on the temp gauge should go to full scale in a few seconds. If so the gauge and wiring are good and the sending unit is bad. Good deal. Glad you got it running. Those feedback yfa's run very well when tweaked properly. check your bollts and check them often Link to comment Share on other sites More sharing options...
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