Distributor Ignition wire question

[simplysigns]

I just got my big block in my 78 Blazer and I have a problem.

1. Hooked up all distributor, ignition and starter wires where they go.
2. Engine cranks over but no start.
3. Found the problem. The small wire to the distributor only has 4 volts to it.
4. So just to make sure. I unhooked the small wire and hooked up a jumper wire to the battery. So I get a full 12 volts. Big block starts and run great.
5. Question.... Why do I only have 4 volts? And does the distributor need a full 12 volts?
All wires seem to be fine and some are new.

 

[bradshawtech]

Just guessing here but on your 78' you probably added an HEI distributor when you put in the big block. Using the existing wire from the starter you have a "resistor" wire that reduces the voltage to the old "external coil" ignition system. Change out the wire from the starter to the HEI and you should have the problem solved. For a quick check make sure that you have a full 12 volts there. You probably do or you would have noticed the starter turning slow.

 

[dremu]

'78 should have had HEI from new, regardless of motor. '74 was the last year for points in trucks, i.e. 75 was the first year for HEI.

The old trucks do have a ballast resistor inline with the wire to the points, but yours shouldn't, unless the wiring harness has been fiddled with -- in which case all bets are off.

Anyway, HEI is easy to wire up. Run a nice fat wire, like say a #12, from the dizzy to the fusebox, to a position that's on in crank and run but off, of course, with the key off. You don't want the dizzy powered all the time or your battery'll go.

And yeah, it wants 12V. Less than that and Bad Ignition Things will happen. Ask me how I know =))

Strictly speaking it might do you well to drive a relay from the fusebox and use that #12 (or maybe even #10) from an inline fuse at the battery to the relay to the dizzy, so that you've got a nice fat wire all the way from battery to HEI.

I've been meaning to do this to my sixpack, see if does anything. My truck, being a '74, was a points truck but some PO put an HEI dizzy on it. I didn't think to check it when I got it, but they had used the points wire to feed it and so the dizzy was only getting maybe 6V. Running a new fat wire from the fusebox made a world of difference, but after doing the fat-wire-plus-relay thing for the headlights, it occurs to me that it might make a difference in the ignition as well. (As long as the fusebox voltage never drops below the relay's cutout voltage ... ah well, easy enough to test... hey, another project! Just what I need =))

-- A

 

[bradshawtech]

I figured that it should of had an HEI already but thought I would make some guesses as to what was happening with the wiring.