[nytrainer]

68 350 (Muncie) with HEI distributor. Engine will turn over and start but as soon as key is released it dies. Not a carb issue. If I keep key in cranking position it will run but haven’t run it long that way because I don’t believe starter motor would disengage. Seems to me maybe key switch (original)? Any ideas appreciated as I don’t necessarily want to change out switch if not needed. I have 12vdc at cap with key in run position. Thanks

[JSPONT]

Bad ignition switch. On the top of the column under the dash would be my guess.

[6869GTO]

Is this a new issue to your car or is the HEI a new change?

[nytrainer]

New issue. Been running the HEI for years although I have original distributor. Out of the blue problem. It first simulated a carb issue where the accelerator pump loses seal and won’t squirt fuel (had that happen on other 68 we have). Looking deeper ruled out carb issue (was a Cliff rebuild a couple years ago) especially after it would run with key held in cranking position.
If I do need switch I suppose I could swap out wafers to use original key but hoping it’s something else I may be overlooking.

[Bill Hanlon]

Run a jumper wire from 12V + battery post to the HEI's power connector and try again. I know you said that "I have 12vdc at cap with key in run position. ", but humor me.

[nytrainer]

Originally Posted by Bill Hanlon

Run a jumper wire from 12V + battery post to the HEI's power connector and try again. I know you said that "I have 12vdc at cap with key in run position. ", but humor me.

This is along the lines of what I was thinking but since I saw 12vdc I was thinking switch BUT I would certainly give that a try. So I pull out connector from cap and replace it with 12vdc source? Will I need similar connector to do so or alligator clip up inside where connector was?
Thanks

[Bill Hanlon]

A blue female crimp-on connector will fit onto the HEI connector. Like this: https://images-na.ssl-images-amazon....QL._SX425_.jpg

[nytrainer]

Thanks Bill, I went outside, made up a jumper wire with connector and she fired right up. Expectedly it didn’t shut off until I removed 12vdc from the jumper wire. So Switch?

[nytrainer]

I should clarify that it didn’t shut off when ignition was turned off (then did when I removed 12vdc to jumper). Also gen light lit after turning ignition off (while engine still running via jumper).

[Bill Hanlon]

Originally Posted by nytrainer

So Switch?

Switch or whatever was done to install the HEI has broken. I'm no expert, but somehow the resistance wire or ballast resistor would have been bypassed when the HEI was originally installed.

I'll bet the 12V you measured on the HEI power connector is a lot less than 12V when plugged in and the engine is trying to run.

[nytrainer]

Thanks Bill and others. I’ll try to find a switch schematic and ring out the switch pins in different key positions before I replace.

[Greg Reid]

You have a 'start' position and a 'run' position on the ignition switch. Both have to have voltage. If 'start' voltage is missing, it'll have 12 volts when you release the ignition key but not when you are holding it in the start position. Sounds like you are missing the 12v supply when holding in 'Start'.

[nytrainer]

Originally Posted by Greg Reid

You have a 'start' position and a 'run' position on the ignition switch. Both have to have voltage. If 'start' voltage is missing, it'll have 12 volts when you release the ignition key but not when you are holding it in the start position. Sounds like you are missing the 12v supply when holding in 'Start'.

Thanks Greg. So these 12vdc sources to the HEI coil come from/through the switch connector? Not sure of next step.

[Greg Reid]

Originally Posted by nytrainer

Thanks Greg. So these 12vdc sources to the HEI coil come from/through the switch connector? Not sure of next step.

Yes. In the original points setup, you had a 12v source routed through the switch to the ignition circuit only in the 'start' position. When you release the key, the 12 volts is routed through the resistor wire to the same point in the ignition circuit. The resistor wire dropped the 12 volts down to 9 or 10 volts or so to prevent arcing/pitting the points contacts.
With HEI, you can bypass the resistor wire and just jumper that 'start' 12 volts to the 'run' contact. HEI can handle the entire 12 volts in 'run'.
As far as I can recall, the wires leave the switch and just pass through the firewall to the coil. Can't recall the colors but if you have the prints, look at the ignition switch circuit. I can't remember for sure but I think they are labelled 'IGN1" and 'IGN2'...somebody correct me if I'm wrong.

[Geoff]

This problem is a great example of why measuring voltage on a HEI without the engine running is unreliable.

OP said he got 12v. Obviously under the load of running, the 12v is missing....

Since the HEI has been working OK for awhile, this problem suggests a loose/poor connection in the wiring or a faulty ign switch.

[Greg Reid]

^^ Ah...I did not notice that he said he had 12v with the key in the run position.
nytrainer, if you have 12v when the ignition is just 'on' or, that is, in the run position AND if you have 12v (or close to it) when the starter is turning, or, that is, in the 'Start' position, your wiring is likely correct.

[nytrainer]

Originally Posted by Greg Reid

^^ Ah...I did not notice that he said he had 12v with the key in the run position.
nytrainer, if you have 12v when the ignition is just 'on' or, that is, in the run position AND if you have 12v (or close to it) when the starter is turning, or, that is, in the 'Start' position, your wiring is likely correct.

Went out to check again (son was working the key last night) and I do indeed have 12vdc with key in the normal position (at the coil wire) when the engine would be running. Couldn’t test it with key in cranking position (by myself) but I believe there has to be voltage there because it will actually start and run with key held in crank position.
So it appears 12vdc is present in both positions but as Geoff alluded to measuring 12vdc at HEI coil without car running is unreliable.
Can someone please post (or explain) the wiring diagram regarding the switch? Since only one wire enters the cap (to the coil) I would guess there’s two 12vdc feeds to this wire at some junction point, one feed (ign 1?) from the key switch supplies the voltage during cranking then drops out when key moves to run position and coil wire is then fed 12vdc by ign 2? Almost seems to me like it’s acting like no/nc fingers on a relay where a finger contact isn’t making and you’re not getting expected voltage through circuit when the relay coil is picked up. Since there is no relay in the starting circuit that I’m aware I can only think it’s a bad switch.
I had the dash bezel out a few years ago to replace gauge lens, etc. PITA. Can the switch be changed with bezel removal?. I haven’t really looked at it to plan the replacement yet as there are 6 cars in the family and those daily drivers always jump the line for my time (maintenance! Etc)
Thanks

[Bill Hanlon]

GM HEI ignitions have the coil built into the cap of the distributor. Is that what you have? Or does this car have a stand-alone coil? Asking because of your statement above " I do indeed have 12vdc with key in the normal position (at the coil wire)".

[nytrainer]

Originally Posted by Bill Hanlon

GM HEI ignitions have the coil built into the cap of the distributor. Is that what you have? Or does this car have a stand-alone coil? Asking because of your statement above " I do indeed have 12vdc with key in the normal position (at the coil wire)".

Yes. I’m referring to the wire that enters the cap and calling that the coil wire. Thanks

[nytrainer]

Got her going again. Traced the wire back towards the bulkhead and found the junction where 2 wires (ign 1 & 2?) joined with the one wire going into the HEI cap. It was a soldered joint that was a bit corroded and one of the wires was no longer attached but making contact intermittently as it was taped (but evidently not able to pass the voltage due to high resistance at the failing connection). Cut back wires to clean copper resoldered and shrink wrapped.
Thanks all for the ideas. Glad I didn’t have to change switch etc..