| Random Question [message #349581] |
Wed, 23 October 2019 17:33  |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Senior Member |
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Realizing the GMC has a 12v system, what is the actual voltage spread range in terms of voltage and current draw, before failure of the HEI to provide an adequate spark?
Just interested.
Tom
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: Random Question [message #349582 is a reply to message #349581] |
Wed, 23 October 2019 18:07  |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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According to the Motorola data sheet, the chip inside the HEI ignition will function down to 4 volts.
This is with a 300 ohm resistor between the battery and the chip power input.
The battery voltage during cold cranking can drop quite a bit, like maybe as low as 8 volts.
The maximum working voltage is 24 volts. The circuit will shut down if the voltage exceeds 30 volts.
It says in the datasheet:
"At lower Vbatt, the "on" period automatically stretches to accomodate the slower current build-up.
At very low Vbatt and low RPM, a common condition during cold starting, the "on" period is nearly
the full cycle to permit as much coil current as possible."
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
[Updated on: Wed, 23 October 2019 18:08] Report message to a moderator |
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| Re: Random Question [message #349583 is a reply to message #349581] |
Wed, 23 October 2019 18:30 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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The primary side is not the problem. It''s a poor path for spark to ground on the secondary. This causes excessive voltage rise in the coil after the module opens. The voltage rise is also on the coil primary leads (collapsing magnetic field induces voltage in primary and secondary windings).
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Random Question [message #349584 is a reply to message #349581] |
Wed, 23 October 2019 18:40 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Also the "12V system" is better referred to as a 14V system. The battery alone is 12.66V charged at room temp. System voltage is s solid 14.2 after cold start and tapers to mid to high 13s as temps rise to mirror wet cell charge requirements.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Random Question [message #349593 is a reply to message #349581] |
Wed, 23 October 2019 21:19 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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If you suspect a distributor low voltage problem on either the primary or the secondary side of the HEI coil, one of the best things you can to is to add a ground wire from the distributor frame to the engine block. I suggest NOT using a valve cover bolt on the engine. There are two threaded holes on the back of the heads or a manifold bolt could be used.
The distributor is aluminum and it is mounted in a steel hole in the intake manifold. Also I have seen some with a round gasket sometimes installed there. Over time you get dis-similar metal corrosion and a poor connection there that sometimes changes as the engines changes temperature.
On a Dick Paterson rebuilt distributor there is a terminal on the bottom of it specifically for this purpose. On other distributors, a simple small stainless hose clamp could be used.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Random Question [message #349719 is a reply to message #349593] |
Sun, 27 October 2019 17:26 |
Emery Stora
Messages: 959
Registered: January 2011
Karma: 4
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On the inside of the distributor there is a short bolt used to ground the internal wiring harness. You can just replace that bolt with one about 1/2” longer. It will stick out the bottom of the distributor and you cam them put a wire with a a round terminal on the bolt and use a lock washer and nut to secure it. You then run the other end of the wire to a screw or bolt on the aluminum frame of the motorbox.
Easier to do than an clamp and a much better ground
Emery Stora
77 Kingsley
Frederick, CO
> On Oct 23, 2019, at 8:19 PM, Ken Burton via Gmclist wrote:
>
> If you suspect a distributor low voltage problem on either the primary or the secondary side of the HEI coil, one of the best things you can to is to
> add a ground wire from the distributor frame to the engine block. I suggest NOT using a valve cover bolt on the engine. There are two threaded holes
> on the back of the heads or a manifold bolt could be used.
>
> The distributor is aluminum and it is mounted in a steel hole in the intake manifold. Also I have seen some with a round gasket sometimes installed
> there. Over time you get dis-similar metal corrosion and a poor connection there that sometimes changes as the engines changes temperature.
>
> On a Dick Paterson rebuilt distributor there is a terminal on the bottom of it specifically for this purpose. On other distributors, a simple small
> stainless hose clamp could be used.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
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> GMCnet mailing list
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