Choke Light????

[elwood]

Sometimes when I'm at high speed or accelerating rapidly, the yellow choke light on the speedo comes on. When I slow down it goes off.

What's up with that?

I have an Edelbrock 1406 with electric choke on the truck currently.

[87 STEPPER]

Sound's to me like a wire is lose or grounding out when the eng. torque's check your wire's on the carb choke and id'e look at the engine mount's as well.

[Captkaos]

Ditto to what Bruce said.

[ElGracho]

It's due to low oil pressure.

The choke wire on about 79-86 trucks goes from the fuse panel, through an oil pressure switch directly above the filter, to the choke and then to ground. The light on the dash has 12v on one side and the input to the choke on the other. As long as oil pressure is ok, the light will have 12v on both sides and stay dark. When oil pressure is low, it will be grounded (through the choke coil) on one side and have 12v on the other and light. This is why the choke light comes on whenever the key is on but the engine is off.

[Captkaos]

hmmmm, didn't even think about that scenario. Thanks Joe!

[swervin ervin]

Joe is correct. But on where the switch is located, they were in one of two different places. Mine is in a brass tee up beside the distributor, where the oil pressure sending unit would be.

[elwood]

The choke light doesn't come on when the ignition key is just in the "on" position. The only time it lights, is when I speed up to pass or a big hill, but goes out when I slow down. The oil pressure guage is saying that I have plenty of pressure. Hmmmm.....

[swervin ervin]

Check for a loose wire or connection then.

[gldevall]

I bet that's why my choke light is staying on. When we put the 350 in, the brass tee we put the sending unit back in and a plug in the other side.

[84_chevy]

Can someone clear this up for me I'm a little confused. The sensor beside the distributor controls the Gage in the dash that gives you a general idea of the oil Presure but the sensor down by the oil filter is a low oil Presure switch that would normally light upba oil light on the dash but in our case since there is no oil light idiot light on the dash it lights up the choke light instead. Is this correct?
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[ElGracho]

Basically yes. Here's the wiring diagram. I'm not sure why they did it this way. I don't see how the circuit ever indicates some failure with the choke or even that the choke is doing something good or bad.

[thesickc10]

haha my truck used to do this with my old motor whenever the oil pressure dropped the choke light would come on. Every time i told a friend they all thought ii was nuts. I cant wait to rub this in their faces!!

[84_chevy]

Your right, I don't see how it relates to the choke working or not. It just seems to be an over complicated oil warning light. It sure had me confused.
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[Desert1957]

Its wired that way because they don't want the electric choke coil to get voltage unless the engine is running.

I know it sounds stupid but those GM engineer's think of every weird scenario, Here's one, Someone gets in their truck turns the key to Run position to listen to the radio, after a few minutes , choke coil would heat up and possibly cause a hard start.

Its also a Back up oil pressure warning light, Bulb burns out on the oil light or gauge doesn't work, Choke light comes on with low oil pressure. Might make someone check under the hood.

Desert

[chengny]

The choke is designed to be closed in low ambient, cold start situations.

On these engines, an electric assist choke is incorporated onto the carburetor to aid in reducing the emissions of hydrocarbons and carbon monoxide during starting and warm-up (choke-on) period.

The electric assist choke is designed to give a more rapid choke opening at temperatures of approximately 60-65°F., or greater and a slower choke opening at temperatures of approximately 60-65°F., or below.



The main components of the electric assist choke system, Fig. 39, consist of a thermostatic coil, ceramic resistor, cover, bi-metal snap disc and contact spring. The electric actuated ceramic resistor heats the thermostatic coil, gradually relaxing coil tension and allowing the choke valve to open.
At air temperatures below 50°F., electric current applied to the small section of the ceramic resistor, allows slow opening of the choke valve for good engine warm-up. As the small section of the ceramic resistor continues to heat, a bi-metal disc causes the spring loaded contact to close and apply electric current to the large section of the ceramic resistor which increases the heat flow to the thermostatic coil for more rapid opening of the choke valve.
At air temperatures between 50-70°F., electric current applied to the small section, or both the small and large sections of the ceramic resistor, will produce the amount of heat required to control the choke valve position for good engine operation in these temperature ranges.
At air temperatures above 70°F., electric current applied to the small section of the ceramic resistor and through the spring contact to the large section of the ceramic resistor, provides rapid heating of the thermostatic coil for quicker choke valve opening when leaner air-fuel mixtures are required at warmer temperatures.

The electric current (that the above text refers to) is controlled by the on/off oil pressure switch (as opposed to the variable resistance sender that drives the oil pressure gauge).

The following explains the relationship between oil pressure and choke pull assist:

Many trucks utilize a warning light on the instrument panel in place of the conventional dash indicating gauge to warn the driver when the oil pressure is dangerously low. The warning light is wired in series with the ignition switch and the engine unit--which is an oil pressure switch.
The oil pressure switch contains a diaphragm and a set of contacts. When the ignition switch is turned on, the warning light circuit is energized and the circuit is completed through the closed contacts in the pressure switch. When the engine is started, build-up of oil pressure compresses the diaphragm, opening the contacts, thereby breaking the circuit and putting out the light.

TROUBLESHOOTING
On some models, the oil pressure indicator light also serves as the electric choke defect indicator. If Oil or ENG. indicator light does not light, check to ensure electric choke is not disconnected at carburetor. Also check for defect in electric choke heater, blown gauge fuse or defect in lamp or wiring circuit. If indicator light stays on with engine running possible causes are: oil pressure is low, switch to indicator light wiring has an open circuit, oil pressure switch wire connector has disconnected or on some models, gauge or radio fuse has blown.
The oil pressure warning light should go on when the ignition is turned on. If it does not light, disconnect the wire from the engine unit and ground the wire to the frame or cylinder block. Then if the warning light still does not go on with the ignition switch on, replace the bulb.
If the warning light goes on when the wire is grounded to the frame or cylinder block, the engine unit should be checked for being loose or poorly grounded. If the unit is found to be tight and properly grounded, it should be removed and a new one installed. (The presence of sealing compound on the threads of the engine unit will cause a poor ground.)
If the warning light remains lit when it normally should be out, replace the engine unit before proceeding further to determine the cause for a low pressure indication.
The warning light will sometimes light up or flicker when the engine is idling, even though the oil pressure is adequate. However, the light should go out when the engine speed is increased.


Basically, it is a primitive method of telling the choke that the engine has started - and it's time to start opening. Establishment of oil pressure was a cheap and nearly failsafe input. And it was easy to tap in to.

Remember, this system was implemented in the time between manually operating the choke via cable and before the advent of ECU controlled engines. But, bottom line, it was in response to EPA emissions regulations that were becoming more and more stringent.

[Desert1957]

QUOTE/Basically, it is a primitive method of telling the choke that the engine has started - and it's time to start opening. Establishment of oil pressure was a cheap and nearly failsafe input. And it was easy to tap in to.

Ok, the long version .....LOL

Desert

[84_chevy]

All good info, at least now I can follow the bouncing ball
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