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1986 F150 4.9L Feedback carburetor

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86F150CA

1986 F150 4.9L Feedback carburetor

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.

1986 F150; 4.9L; 4 speed Manual;Feedback Carb; California Emissions (EEC-IV/TFI-IV)

85lebaront2

Re: 1986 F150 4.9L Feedback carburetor

Administrator

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.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

86F150CA

Re: 1986 F150 4.9L Feedback carburetor

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?

1986 F150; 4.9L; 4 speed Manual;Feedback Carb; California Emissions (EEC-IV/TFI-IV)

86 1/2 Brutus

Re: 1986 F150 4.9L Feedback carburetor

In reply to this post by 85lebaront2

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

Nick and George
1986 1/2 F150 XLT Lariat 4X2 300 Six - C6 - 3:08 in a 8.8 - Fully Loaded - 8 Foot Box
Owned since new

myrl883

Re: 1986 F150 4.9L Feedback carburetor

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.

Ford Parts Monkey since 1985
1981 F100 Flareside - Black, 302-4V Roller/AOD
1986 F150 Flareside - Medium Fire Red 302/AOD
1989 F150 Standard Cab 4x4 - Dk Shadow Blue 302/AOD
1993 F350 4x4 Crew Cab - 7.3 IDI/ZF-5
I think it's a sickness...

1986F150Six

Re: 1986 F150 4.9L Feedback carburetor

Administrator

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

85lebaront2

Re: 1986 F150 4.9L Feedback carburetor

Administrator

In reply to this post by myrl883

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.

Bill AKA "LOBO" Profile

86F150CA

Re: 1986 F150 4.9L Feedback carburetor

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.

1986 F150; 4.9L; 4 speed Manual;Feedback Carb; California Emissions (EEC-IV/TFI-IV)

Gary Lewis

Re: 1986 F150 4.9L Feedback carburetor

Administrator

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.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

86 1/2 Brutus

Re: 1986 F150 4.9L Feedback carburetor

Good deal. Glad you got it running. Those feedback yfa's run very well when tweaked properly. check your bollts and check them often

Nick and George
1986 1/2 F150 XLT Lariat 4X2 300 Six - C6 - 3:08 in a 8.8 - Fully Loaded - 8 Foot Box
Owned since new

ratdude747

Re: 1986 F150 4.9L Feedback carburetor

In reply to this post by Gary Lewis

Possible thread hijack: I too have had odd sending unit behavior. I replaced mine a year or so ago (the stock one was burned), and the only one that worked at all is a newer "printed" design (not wirewound like the original). It drops to 1/4 a tank pretty quickly, but past there the motion slows (it's consistent and gradual, not dead zones or sudden drops). Almost seems like the sending element (potentiometer) has a logarithmic output (like used for audio volume controls) but the gauge (and stock sending units) are linear. I haven't pulled it out and measured it to confirm this. Just noting that it's quirky and has nearly gotten me killed by my wife a couple times.

---

My idle (similar 300 EEC IV feedback YFA) is around 1600RPM when stone cold at startup (due to the fast idle cam)... when warm (and of the idle cam) it idles around 800RPM or so.

1984 F150: 300 L6, AOD, RWD. EEC IV / TFI, Feedback Carter YFA Carb. Stock everything but radio (for now).

86F150CA

Re: 1986 F150 4.9L Feedback carburetor

In reply to this post by Gary Lewis

Gary,

It took me 6 months to get around to the truck issues, but you were absolutely right on both counts. Temperature sending unit was easy once I knew where to find it. I got help with the fuel sending unit and now it works properly.

Thanks again.

From: "Gary Lewis [via Bullnose Enthusiasts Forum]" <[hidden email]>
Date: Monday, November 9, 2020 at 1:12 PM
To: 86F150CA <[hidden email]>
Subject: Re: 1986 F150 4.9L Feedback carburetor

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.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker in front & 10.25 Spicer/Trutrac in back, & EEC-V MAF/SEFI

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1986 F150; 4.9L; 4 speed Manual;Feedback Carb; California Emissions (EEC-IV/TFI-IV)

Gary Lewis

Re: 1986 F150 4.9L Feedback carburetor

Administrator

Well done! Glad it worked out for you.

Gary, AKA "Gary fellow": Profile