Help needed starting Chevelle

I would unplug the alternator to see what happens. I have seen bad alternators pull the power away from the coil power line if your MSD uses the alternator field wire with a diode for power.

The contact on the starter solenoid that provides the cranking coil power could also just be dirty. That would be the second small wire that hooks beside the wire from the ignition switch at the starter solenoid.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

snipped-for-privacy@comcast.net wrote:

I see two possible issues:

1) your starter, while spinning the engine over well, is drawing too much current causing a voltage drop. This could be due to the starter itself or wussy, too-small cables, or poor (dirty) connections.

2) 4.5V is SO low I have to wonder, is there a ballast resistor or resistance wire to the coil? Try jump-starting or using a booster pack to get it running, then if it will run, while running check the voltage at the coil again. It should be full alternator voltage (13.7-14.5V) If there is no obvious ballast and you have low voltage at the coil, then your car probably had a resistance wire between the ignition switch and the coil, and whoever dropped in the HEI just hooked it up with the old wire. You should run a new wire from the ignition switch to the coil, 14AWG or so.

also what happens if you hotwire it? i.e. just use a test lead to jump straight from the battery to the coil?

good luck

nate

Nate, Thanks for your ideas.

I have big fat welding cables to the starter with shiny clean lugs. I don't think the problem's there.

I put the hei distributor in myself several years ago. I wired it up to the solenoid I pole (it's a 4-pole ford solenoid up on the firewall).

As you suggested, I hot wired the distributor from the hot side of the solenoid and it started right up. Just for grins I put a volt meter on the I pole of the solenoid and it read 0 while the motor was running. So I'm getting 9.6 V at the solenoid with the ignition key in the Start position and 0 V with the key in the Run position. I believe these cars with conventional breaker point ignition used different circuts for starting and running to power the coil. I guess I'll need to trace that entire circuit and look for a short. bob

If this "Ford Solenoid" is the same as the ones that Studebaker used from '56 up (and I believe it is) then there are four terminals on it... battery, starter, the one for the actual start wire from the key switch, and one for the ballast resistor bypass circuit. Basically useless, as it's essentially the same terminal as the starter, just a smaller post for a smaller wire. If you wired the HEI to that and only to that I'm amazed that it ran at all... something must have been backfeeding from somewhere.

That makes sense (see above.) The reason for that was that the older ignitions actually ran on 8-9V (were actually designed for 6V cars) and for quicker starting, when auto electrical systems were switched over to 12V instead of redesigning the coils etc. they just used ballast resistors to drop the voltage to them, and then when starting bypassed the ballasts so that you'd still have full spark when cranking. The bypass goes dead whenever you're not activating the starter.

Sounds to me like there's still a resistance wire from the ignition switch "run" terminal to the coil, and it just got a lot more resistive. That's the first place I'd look...

HTH

nate

Stock, the power to the distributor when the key is in 'run' should have come from the alternator field wire or the smaller steel wire on the alternator. The MSD normally needs a diode at the connection or in the line to it. This 15 cent diode might have popped.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

snipped-for-privacy@comcast.net wrote:

Can someone explain how this works? I thought that the field would have some low voltage on it, depending on current demand from the rest of the electricals (or alternately, a partial ground, likewise, if the alternator is configured differently from the ones I've worked with) in any case, if I'm understanding the OP correctly, I was assuming that he has a HEI distributor made by MSD, not a MSD ignition box (although I may be mistaken) in any case I stand by my statement that for an HEI to work correctly it must be fed a full 12V with the key "on." Now if he has a MSD box he should follow the instructions that came with it but those are available online.

nate

Mike Roma> Stock, the power to the distributor when the key is in 'run' should have

On the older GM Delco alternators like the one used from 1968 to 1988 on the Chevy, the small steel wire to the back is a switched 12 volts that turns on when the key is in 'run'. This is the 'field' wire and is crimped into the wiring harness with the line going off to the coil power. The line to the coil power has a ballast wire on it sometimes.

So basically when the key is in 'start', a line comes from the ignition side of the starter solenoid to the coil/distributor unit, then when the key goes to run, the power comes from this alternator 'field' wire.

Jumping it like you mentioned gives power in run.

On those systems, the first place I look for trouble or an 'open' circuit is the diode they use to stop a ground loopback. (without the diode, the vehicle won't shut off) Second is to check the alternator for an internal short which can suck the field wire to ground so the coil sees 0 volts. That is why I recommended unplugging the alternator to see if it then runs.

The older Jeeps also have this alternator and GM ignition setup.

Mike

N8N wrote:

Ah, I think I understand now, you're talking about an internally regulated alternator like a 10SI, right? makes more sense now.

nate

Mike Roma> On the older GM Delco alternators like the one used from 1968 to 1988 on

Yes. The wire is probably better called a trigger wire, but it turns the alternator on when it sees 10-12 volts. Those alternators can be used as a 1 wire, once the rpm are up apparently they will 'self excite', but the extra switched wire just makes sure...

When the ballast wire is used from this 'trigger' wire to the coil and it fails, you get the OP's exact symptoms. With the swapped in MSD HEI unit, they usually use a solid wire and a diode as far as I have seen. That is how Jeeps handle it for sure and my old Chevy pickup was the same.

Actually even if the OP wired it strange to some other switched source instead of the original coil's power line, he still should be checking that wire and it's connections.

Mike

N8N wrote:

Thanks for the explanation... I'm actually paying attention to this discussion for purely selfish reasons as I have a one-wire 10SI in my '55, and would like to "convert" it to 3-wire if I ever have to replace it... however the Stude gets its coil power straight off the ignition switch so I don't have to worry about this particular issue (and I have rewired all that stuff anyway as I'm using a MoPar "orange box" - at least for now, I may get a MSD or other box if it goes Tango Uniform)

nate

Mike Roma> Yes. The wire is probably better called a trigger wire, but it turns

You could splice into the coil power for a trigger like they did OEM on Chevies and Jeeps. I guess it is just an easy place to take switched power.

Mike

N8N wrote:

That's one method of alternator regulation. In the other method, full battery voltage is applied to one field terminal, and the regulator varies the effective resistance between the other field terminal and ground. High effective resistance -> low field current, low charge rate. Low effective resistance -> high field current, high charge rate.

right, I got it now. I was envisioning an externally regulated alternator, where the "field" terminal would be between the field coil and whatever was doing the switching. However, it's clear that in this instance the "field" terminal is actually outside of the whole field coil/regulator/ground system and therefore it does have a full 12V. Actually you could have said "just like a VW alternator" and it would have made sense :) except on a VW it goes ignition terminal -> idiot light -> alternator. And the wire is blue. And if you don't hook it up, your alternator won't charge, but the idiot light won't come on. Um, or so I've heard :)

nate