Electric Choke Kills Spark

[carrera205]

Just finished building a 5.7 vortec. I hooked the red power wire to the switched power on the coil and then grounded the black wire to a grounded bolt. When the engine wouldn’t fire I started checking things out and figured out it wasn’t getting spark until I unplugged the ground wire from the electric choke then it would fire right up. Once I had it running I tried to plug the ground back in to test and sure enough it kills the engine.

Whats happening here?

 

[Grub54891]

Where did the wire that was there before go to? I don't have the specifics right in front of me but it's in the harness and switched on with the ignition key. Not directly to the coil.

 

[Scott Danforth]

Just finished building a 5.7 vortec. I hooked the red power wire to the switched power on the coil and then grounded the black wire to a grounded bolt. When the engine wouldn’t fire I started checking things out and figured out it wasn’t getting spark until I unplugged the ground wire from the electric choke then it would fire right up. Once I had it running I tried to plug the ground back in to test and sure enough it kills the engine.

Whats happening here?

you killed the spark. the ignition is what pulses the ground - it does not go to the ground directly. stop with the ground wire to the - coil terminal.

 

[carrera205]

So this wiring harness I don't believe has a specific wire for the electric choke since it was setup with the older heat expanding choke with a quadrajet initially. This is a totally new engine i've dropped in. I had the positive wire from the choke running to the coil and the ground running to just a grounded bolt. Guessing i need to find a new place to capture switched power.

 

[achris]

Where did the harness come from (engine serial number would be best here)?

Choke and ignition are completely separate. The only way for the choke to kill spark is if the choke is shorted and is dropping the voltage down far enough for the ignition module to drop out. Measure volts at the coil+ with and without the choke connected.

Chris.........

 

[carrera205]

Sorry not in a spot to get the serial but it was from a 89-90 5.7 alpha one mercruiser. I spent almost 30 minutes today with a voltmeter looking for an alternate location for a switched power source and found one at the gas tank switch but it only has switched power when the selector is on my port tank so for now I’ll just have to make sure if I’m cold starting I switch to the port tank to give the electric choke some juice. It’s not perfect but since I’m headed out to the lake for a week I needed a “fix” for now. Ultimately I think I’ll run a relay and new circuit for switched power items.

 

[wellcraft-classic210]

Sounds like you may have a short circuit in your wire to the electric choke or in the electric choke itself. Can yo tell us the ohms reading from your red wire ( disconnected from the coil ect ) to GND. I dont know the exact ohms value for your setup but it should be over 4 ohms.

Have you had any blown fuses ? It could also be a corroded or weak wiring connection to your coil and the choke aggravates the problem.

You can also check for a solid 12 volt supply voltage with and without the choke connected to the + side of the coil. If its dropping off that's a sign of a weak connection.



Hope this helps.

 

[Grub54891]

If you temporarily run it to the fuel sender, when you turn off the fuel switch for that tank after warmup the choke will cool off and close again. Then you will be running rich.