Ignition troubles...

[Petie724x4]

Has anyone ever had trouble with the keyswitch effecting startups? My 72 with HEI has decided to ramdomly not start, mostly when cold. It will roll and roll and roll, but not "kick". Always has power on both "bat" connection and coil connection at distributor when it is not starting. New cap, rotor, and distributor.
I say keyswitch because when it decides to start eventually, after all the neighbours are watching because I've been rolling over for a while, it seems to be when I let go of the key and it springs back to "run" position. If that makes sense. In the "start" position it seems to roll over all day long, but if I just let go of the key and get lucky, it will kick on the last revolution.
Does this make sense? Anyone with similar troubles? Once warmed up, seems to start a bit more regularly.
Thanx

[Autoblueprint]

Originally Posted by Petie724x4

Always has power on both "bat" connection and coil connection at distributor when it is not starting.

A test light showing power on at the Bat terminal of an HEI does not mean that there is a 12.5 voltage supply...a test light will light when there is voltage present but not tell you what that voltage is.

HEI's require 12.5 volts at the cap Bat connection...so get out your voltmeter and make sure you have 12.5 volts there.

If you find your voltage is lower than 12.5 volts...then you need to find where the voltage is dropping in the wire harness from the Ign switch to the HEI Bat terminal.

If you have 12.5 volts at the HEI Bat terminal...it is possible the the module might be the culprit. Usually the module just goes bad and the vehicle will crank but not fire...but I have seen instances of intermitant "fire" that went away when the module was replaced.

[LockDoc]

Originally Posted by Petie724x4

Always has power on both "bat" connection and coil connection at distributor when it is not starting.
Thanx

I would say it is wired wrong. There is no coil connection with an HEI. (maybe if you have the divorced coil version) There should only be one wire connected to the HEI (12v) unless you have a Tach and it should be connected to "Ign Unfused" connection on the fuse box. If you are using the yellow wire, disconnect it.

LockDoc

[BMERDOC]

I'd have to back Autoblueprint. On an old vehicle test lights have their place but this is a situation where you need to know exact voltage. When did your problem start? Has it always been there? Did you or a PO convert the truck from points (i dont know if this truck had points) to an HEI? IIRC, points had a step down in voltage before the distibutor. You need to know supply voltage before you can continue.

[VetteVet]

What you are describing sounds like a poor connection inside the key switch between the ignition and start terminals when the key is turned to start. The engine will rotate but the ignition source is missing. When it is rolling and you let off the ignition circuit takes over and fires the motor if it is still rolling enough to start. This would only apply if you are using the stock ignition wire for the truck from the key, and not from the ignition unfused terminal on the fuse panel. If you are using the old stock wire you would have to replace the ignition wire on the engine side of the firewall because that was the resistance wire for the stock coil and points which dropped the voltage to them to keep them from burning up. If not then you will get get a voltage drop at the HEI bat terminal and not the required 12 volts just like autoblueprint described.

[BMERDOC]

Ok, now Vettevet has added something. But Vettevet, on this vehicle wouldn't a significant voltage drop indicate a defective ground from engine to Batt ground or across the component? If he has sufficient supply voltage then the switch is good and he should remedy the ground or replace the distributor?

[Petie724x4]

I love this place......
When I say "coil wire" I mean the other connection that plugs into the HEI cap. I always thought 12v power into the "coil" ontop of the cap, then out the other connection to the base of distributor. Anyhow, good point never checked voltage, just test light. BUT, starts awsome after first start up of the day.
When it first started this, I had just put on new cap and rotor. wouldn't run just right and harder to start. Then changed whole distributor (not new, just new to the truck) and ran fine for a day, then back to square one.

[Petie724x4]

Originally Posted by BMERDOC

Ok, now Vettevet has added something. But Vettevet, on this vehicle wouldn't a significant voltage drop indicate a defective ground from engine to Batt ground or across the component? If he has sufficient supply voltage then the switch is good and he should remedy the ground or replace the distributor?

New ground straps/cables? Distributor was replaced, not new, just a parts one I had around, but nonetheless, still have same symptoms.

[VetteVet]

Originally Posted by BMERDOC

Ok, now Vettevet has added something. But Vettevet, on this vehicle wouldn't a significant voltage drop indicate a defective ground from engine to Batt ground or across the component? If he has sufficient supply voltage then the switch is good and he should remedy the ground or replace the distributor?

Yes it would but there would be other problems such as dim headlights or weak horn. My theory about the key switch is wrong because the engine would fail to start at any time not just when it was cold. The ignition wire from the key is still in play if it is being used instead of a separate wire to the BAt terminal on the HEI distributor, like from the ign unfused terminal on the fuse panel. The resistance wire will cause a 2 to 3 volts drop to the HEI. The question remains -what is the key on voltage at the Bat terminal on the HEI? this will answer the question of whether the distributor is wired correctly or not. It would also explain the symptoms of the cold start problems. The voltage drop will not only cause start problems but it would also cause the distributor to misfire and give a weak spark any other time.

From what I have read the problem here is more likely a fuel and carburetor issue. I would investigate a choke or float issue. The next time when it's cold and the engine just rolls then five it a shot of starting fluid and see if it takes off. If it does then the issue is fuel related and not ignition.