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Old 02-22-2011, 08:40:16 PM   #1
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Engine ground

What is the purpose of the engine to firewall ground strap? Everyone I ask has a different reason for its use and noone agrees with what the other one says.
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Old 02-22-2011, 08:45:36 PM   #2
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What answer are you looking for?

The distributor is grounded to engine by a wire, and the engine is grounded to the firewall. Doesn't sound like much but remember there is a paper gasket between the distributor and intake.

That's just one example I can come up with without a lot of thought.

If you don't want to run that particular ground, then don't. And BTW, who are you asking; just asking?
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Old 02-22-2011, 09:00:34 PM   #3
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Helps stop radio interference from the distributor. Some even put a capacitor on the alternator.
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Old 02-22-2011, 09:07:13 PM   #4
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Quote:
Originally Posted by COPO
Helps stop radio interference from the distributor. Some even put a capacitor on the alternator.

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Old 02-22-2011, 09:14:32 PM   #5
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Because the engine is grounded directly to the battery but nothing else is.
The only other connecton between the negative post on the battery is a dinky little fusible link running to the fender.
Disconnect your main ground cable from the engine and that link will cook because it's the only way for every circuit in the car to ground.

The engine needs an electrically connection to the car body for all of the lights, accessories etc. to function.

In a factory car....
The motor mounts are rubber insulated, as is the transmission mount.
The radiator is rubber mounted so the trans cooler lines won't even make a good ground.
The exhaust system is hung by rubber straps and the fuel line has a rubber connection too.

About the only thing left to ground the body to the engine is.... The shifter cable.
People have actually burned up shifter cables because they had no engine ground strap.
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Old 02-22-2011, 09:33:54 PM   #6
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so the ground from the bat to the alternator bracket doesnt sufice?
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Old 02-22-2011, 10:31:17 PM   #7
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Since the engine/transmission is rubber mounted for the most part, the lights and accessories need a path back through the engine, back to the battery. Though you may have a ground on the fender for the front lights etc to function, it's a long way back to the tail lights.
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Old 02-22-2011, 10:32:28 PM   #8
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If in doubt.....use the ground strap and be done with it. Definitely ain't gonna HURT anything.
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Old 02-22-2011, 10:33:27 PM   #9
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the batt ground to the engine the ground will get from the motor to the firewall and frame they will either go through the tranny cable or throttle cable or the wire you install
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Old 02-22-2011, 10:35:52 PM   #10
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Quote:
Originally Posted by 70sbudget
so the ground from the bat to the alternator bracket doesn't suffice?

Not for the circuits grounded through the body.

A bare, braided copper cable bolted to the rear of the passenger head and the firewall works perfectly for this electrical connection and prevents damage to incidental connections like the throttle or shifter cable.
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Old 02-23-2011, 08:34:05 AM   #11
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Quote:
Originally Posted by CorkyE
What answer are you looking for?

The distributor is grounded to engine by a wire, and the engine is grounded to the firewall. Doesn't sound like much but remember there is a paper gasket between the distributor and intake.

That's just one example I can come up with without a lot of thought.

If you don't want to run that particular ground, then don't. And BTW, who are you asking; just asking?
I am just asking becouse I have heard so many different answers. If GM put it there, its there for a reason so I am going to run it.
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Old 02-23-2011, 11:11:53 AM   #12
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I had a 68 Camaro with a 327/350 hp engine in it that would randomly not want to start (it would turn over but not fire). By chance I found that the ground strap from the firewall to the engine (which I vaguely remember being under a valve cover bolt) was loose. By it being loose it would either make ground or not have ground = no spark or spark.

Think of all the mounts that are in the drive line as electrical insulators: rubber motor mounts, rubber transmission mount, rubber spring mounts, rubber hangers on the exhaust. So the engine is "floating" on insulators which then requires a grounding strap to tie the motor to the chassic ground.
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