80L48

Having issues with my Electric Choke and relay. I have a good fuse and good relay. However, when I plug the hot lead onto the carburetor, the choke warning light stays on all the time. My understanding is that it should turn off after the car is running. I have read in other posts that this might relate to an issue with the Alternator Diodes? APpreciate any thoughts on this

MelWff

when the engine is cold is the choke fully closed?
when the engine is fully warmed up is the choke fully open?
the choke coil if it is not burnt out requires a good ground to the carburetor. Have you removed the choke coil, attached the hot wire, grounded the coil assembly and watched the coil move as it heats up?

80L48

Choke seems to work fine but light stays on all the time. it is not burnt out, seems like I have an improper voltage or similar which causes light to stay on

MelWff

I would go back and look at the relay, it's not timing out and turning off the light.
Have you done a voltage check with the engine running, 13+?

80L48

Yes, just over 14 volts as measured at the alternator. Relay has been replaced they both behave the same way. I saw a blog indicating that if there was any AC current coming from the alternator, that this would cause the relay to not open the circuit. I have tested the alternator and it does seem to be allowing some AC current through, so I am going to take t off an have it further tested/rebuilt. Ever heard of this?

MelWff

The test below is for checking a bad diode which will let AC through
3. Checking for a Bad Diode

Usually, a bad alternator diode will cause your headlights or instrument panel lights to flicker or dim and, sometimes, drain battery power overnight, or in minutes.

* To check for a possible bad alternator diode, switch your voltmeter to a low setting on the AC (alternating current) voltage scale.
* With the engine running, touch the meter probes to the battery terminals.
* Your voltmeter should read 0 AC volts.

Any amount of AC voltage would indicate a bad diode, so you'll need to replace the alternator.

80L48

Ok, let's reset and cover some history

Bought the car 6 months ago and just getting down the project list to now pursue the electric choke.

Facts I know:

• Original Rochester Quad carb has been replaced by a Edelbrock 1406 with Electric Choke
• My alternator has been tested and confirmed working correctly
• I have replaced the fuse and the choke heater relay
• At the alternator, I get 14 volts when car is running
• Across the electric choke I get about 12 volts (when the car is in the run position, but not actually running), When running the voltage drops to 2-3 volts.....
• The Choke light comes after the vehicle starts and stays on even after the car has come up to normal operating temperature (it never goes out until I turn the car off).
• If I unplug the positive line to the electric choke, the light goes out. (This is how I have left it for the first 6 months)

Questions I now have:

1. Is there something different about the Edelbrock carb such that I cannot use the original wiring? Edelbrock instruction say to wire direct to the Fuse box and use an ign tab that is hot only when key is in run position
2. What is the expected behaviour? When should the light come on and for how long?
3. What should I see and measure as the electric choke warms up?

MelWff

i found this explanation

When the ignition switch is turned on, voltage is supplied through the warning light to the choke heater. Under this condition, the light is illuminated and the high resistance in this bulb provides a very low current flow to the choke heater so the choke spring is not heated if the driver leaves the ignition switch on with a cold engine. With the ignition switch on, current also flows from the ignition switch through the relay winding and the alternator field to ground. This current flow keeps the relay contacts open.
Once the engine starts, the alternator supplies approximately 14 V to the entire electrical system. Under this condition, 14 V is supplied to both ends of the relay winding, and the current flow through the winding is stopped. Since this relay is normally closed, the contacts move to the closed position and supply full voltage to the choke heater to open the choke. When the choke relay contacts are closed, equal voltage is supplied to both sides of the choke warning light, and this light remains off. If a defect occurs in the system, such as a defective relay, current flows through the warning light and the choke heater to ground. This light is illuminated to inform the driver that a defect is present in the choke heater circuit.

I also found references to the alternator causing the issue

https://www.corvetteforum.com/forums...ht-1981-a.html

80L48

Yes, Thanks, that is my understanding as well.

In my case, if I just turn the key to run (without starting) the Choke light comes on for a second and then goes out (I would expect it to stay on) then If I start the car the light comes on and stays on. Not sure what to diagnose next.... I have 12volts at choke when in run position, but car is off, and then it drops to 2-3 volts when I start the car cold. I am tempted to run a choke wire direct to Ign tab in fuse box, just to confirm voltage and that choke works (heats up).

MelWff

Your voltage readings are the exact opposite of the explanation I provided. The explanation states when in the run position, engine off, the current flows through the bulb circuit providing high resistance and low voltage at the choke. It also states once the car is started you should get full voltage. It sounds like a bad relay or the relay is not correctly wired.

80L48

Good Catch, yes, something odd is happening, I am going to speak to an electrician and see how to test the leads to the relay and ensure the wiring is correct. Wire colors appear to match the wiring diagram I have.
Thanks for all the replies!

80L48

Well after going back and confirming it wasn't the Alternator, the Fuse, the Wiring, or the Carb itself, I went back to the relay that I had just replaced. I checked all the voltage traveling to the 3 connections and confirmed it was reaching the relay as it should. So then I focused again on the relay and started to reconfirm the replacement part was correct. After researching GM Part numbers and the various manufacturer equivalents over the past 36 years, I found the original part number and the current Advance Auto Number (CarQuest). Lo and behold the one they gave me originally was incorrect! physically fit, looked the same on the outside but wrong part!

Here is the table I found for equivalent part numbers:

Thanks for the replies!