My 1985 corolla with 4A-c engine, federal emissions, 2 barrel carburetor is running very rich, even at idle. I'm almost certain it's a carburetetor problem, but I'm not positive. Does anyone know at what engine speed the oxygen sensor feedback system (that leans the mixture as needed) starts to work? I'm guessing it doesn't affect the idle and low rpm mixture. I followed the instructions by putting an analog meter on the two terminals for the oxygen sensor (diagnostic socket by winshield wiper motor) I'm getting a stead voltage around 4 volts, but it doesn't seem to vary. I unplugged the sensor and the voltage went away, so I know I'm measuring the right circuit. Is this oxygen sensor bad? If so, do you recommend I replace it with an aftermarket part?
Ladies and gentlemen, thanks in advance for the suggestions!
When you check oxygen sensor voltage, it should be at around 1,500 to 2,000 RPM. At that engine speed, you should get fluctuating voltage. If voltage is steady or non-existent, the O2 sensor is probably bad. I tend to recommend OEM parts because I have not had problems with OEM parts. If you decide to go aftermarket, look for one with the factory connector so you do not have to splice wires.
A bad O2 sensor is not likely to cause an excessively rich condition in a carbureted engine. Check the float in the bowl and follow Ph@Boy's advice.
Toyota manual says the feedback system is active between 1,600 - 4,100 RPM, when the coolant temperature is above 17C / 63F, throttle position switch is on, and the vacuum switch is off (i.e., vacuum is below 3.35" / 85mm). But even if the feedback system doesn't work right it shouldn't cause much trouble because all it does is lean out the mixture slightly at times, not enrichen it the way many feedback systems do.
The factory manual says to hold the engine at 2,500 RPM for 90 seconds, and while maintaining this speed, measure the voltage at the E (brown) and Ox (black-white) terminals of the socket. It should fluctuate between 0 - 7V at least 8 times within 10 seconds.
The feedback system won't work if the throttle position switch never opens and closes. It's supposed to close when the speed in neutral or park reaches 1,800 RPM, and this is adjusted by disconnecting the switch from the computer and measuring the switch's resistance while slowly raising the RPM in neutral or park until there's continuity. The adjustment screw is at the end of the throttle positioner linkage. There are two screws there, and the one farthest from the throttle positioner is the one you want to adjust. The throttle has to be opened only a tiny amount to trigger the switch, and with the throttle closed there should be less than 1/16" clearance between the adjustment and switch.
Is it possible that SeaFoam caused varnish in the fuel tank to dissolve and clog the fuel filter or carb?
The power valve opens an extra metering jet to let in more fuel when when the the gas pedal is floored and the manifold vacuum is low. I don't know if a leaking secondary fuel cut solenoid valve can also cause a rich idle (wouldn't the closed secondary throttle plate prevent much fuel from being sucked into the engine?).
The only brands of carburetor rebuild kits I've used are Tomco and CarQuest/Standard, and some of their parts seemed inferior to the factory ones:
coil springs had far fewer turns.
Tomco's fuel cut solenoid o-rings turned rock hard in a few years, and one broke off and lodged in the brass body of the float valve, which had large slots instead of small holes that would have prevented this.
Standard's accelerator pump shaft rubber bellows became brittle and cracked in about ten months, allowing gas to evaporate out the carb. CarQuest gave me a whole new rebuild kit, and I apply grease to this bellows to prevent rot (can't use silicone spray).
Neither aftermarket float valve had a filter screen to block debris, and this allowed a piece of old fuel hose that had shed off to lodge and hold the valve open.
OTOH the directions and gaskets were fine (actually corrected a mistake in the factory manual, where the two fuel cut solenoids were mixed up), the o-rings for the venturi body didn't deteriorate noticeably, and the auxillary accelerator pump diaphram was as good as the factory original's .
If the heater and choke wires aren't installed exactly as original, including their clip holders and the choke linkage cover, the linkage can bind.
My lengthy reply is no indication that I know what I'm talking about. ;)
My 85 has two fuel solenoids (which do click when I apply voltage) and my throttle positioner has only 1 vacuum hose and I don't see any throttle switch (where would it be?) The OEM factory manual I bought (on your excellent advice, I do believe) is actually for an 83 (I couldn't find an
85 manual for sale), and there are differences from 83 to 85, but the throttle positioner seems to be the same. There is only one screw that I recall (the car isn't near me now), one vacuum hose and one diaphram that I can see on the throttle positioner. I haven't adjusted that yet, since I want to solve one problem at a time. The Ox sensor testing procedure in the 83 manual is the same that you listed, but it doesn't say anything about a throttle switch. What year is yours and where's this switch?
Also, you talked about the rubber accelerator pump bellow rotting and you said not to use silicone on it. Why not??
The specific carb info you shared is priceless. I'm going to buy a factory needle valve, no matter what, based on your experience. The advice on routing the wires carefully to avoid binding the factory linkages has been duely noted. I'll take some digital pictures before disassemby, noting the routing.
You said, "My legthy reply is no indication that I know what I'm talking about." Well, you've got me fooled. Thanks agin!
Thank you Ray, for responding to my problem with running too rich.
Because I don't understand the circuit, can you post a link where I can learn more what you mean by "closed loop"?
I tested around 2500 RPM on the dash tach and got a steady voltage.
I tend to
What is wrong with splicing Oxygen sensor wires or extending them? I've recently done with crimp butt connectors and about 8" of wire when I replaced an oxygen sensor on a family members fuel injected Chevy (Replaced just as preventative measure, the sensor was only $20)
There is no fuel visible in sight glass when engine is off, and it is in the middle of the sight glass when idling. Do you think there could still be a float problem?
The O2 sensor senses O2 in the exhaust stream, and from the amount of O2 in the exhaust, the electyronic cocntrol unit (ECU) determines whether the car is running rich or lean. The O2 sensor does not provide accurate readings before it is fully warmed up or under wide open throttle (WOT) conditions, so under those conditions, the ECU ignores the signal from the O2 sensor and uses default values to control fuel delivery. This is known as "open loop" mode. The ECU uses the signal from the coolant temperature sender to determine if the engine is warmed up and from a throttle position sensor or WOT switch to determine if the throttle is fully open. If the engine is fully warmed up and the throttle is closed or partially open, the ECU goes into "closed loop" mode and will use the signal from the O2 sensor to control fuel mixture. If the mixture is rich, the ECU will lean the mixture until it is too lean, then enrichen it.
Here is a better explanation:
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There is nothing wrong with splicing O2 sensor wires or extending them if the splice is done properly. The connection is in a pretty harsh environment, subject to exhaust heat and water splashing up from underneath. A crimp connector can allow moisture into the connection and can corrode over time.
The best way to splice an aftermarket o2 sensor is to cut the connector off of the original sensor as close to the sensor as possible, slip some heat shrink tubing onto the wires, then solder the splice, and apply some O2 sensor-friendly RTV caulk over the bare wires. Once the RTV caulk has cured, use the heat shrink tubing to protect the splice. RTV caulk is pretty expensive, and it doesn't keep well so if you add in the price of the caulk, it is often cheaper and easier to buy a sensor with the correct connector.
It has been a very long time since I've looked at the schematics for a carburetor, but I believe that fuel should be visible in the sight glass when the engine is off. If the fuel is draining out, that could be the cause of the rich condition. I do not think the float is causing the fuel to drain out of the bowl.
Mine is a 1986 FWD, and the throttle position switch is located under the fuel bowl window. It's silver cylinder about 15mm diameter and roughly 25mm long with a hard plastic plunger at the rear about 4mm diameter and 8mm long. This plunger should be covered with a rubber bellows to keep out moisture. I've read that some other Toyotas instead use a switch with several contacts, one for each angle of the throttle.
Silicone can turn into silicon dioxide, or glass, inside the engine and seal the oxygen sensor and make it quit working.
Here are some pages from the factory manual for the 1986:
If this is a matter of fuel leaking into the carb, I don't think that the problem is the float valve, provided the fuel level looks about right in the sight glass, because that valve is located high up. I'm not familiar enough with the carb to know where it can leak inside, but have you tried tightening the screws that hold the venturis in the barrel or replacing the o-rings on the fuel cut solenoids?
Actually, do you have a clearer diagram/schematic of just the "rail" and the hoses that runs from one side of the engine to the valve (TVSV) near the thermostat?
The one I have in my manual (and the picture under the hood) don't match the carby/emission set up that is in there.
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