Tach drops signal, fuel gauge pegged full - Team Camaro Tech
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post #1 of 10 (permalink) Old Jul 2nd, 11, 09:52 PM Thread Starter
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Tach drops signal, fuel gauge pegged full

I ran the car up to temp tonight after coming back from the body shop this winter. I have a couple issues that have sprung up that I did not have before it went in.

1. Passenger headlight is running at about half brightness while drivers light is fine.
2. Fuel console gauge is pegged at full when it only has about 1/2 tank.
3. Tach works fine until about 1500 rpm and then it drops off to zero. Let off the gas and it picks back up at around 1500 rpm.

Any ideas from the electrical guru's?

Thanks.

69 SS396 Camaro, 4link, 12bolt posi, Speedtech LCA / UCA's, Hotchkis 2" drop front springs/sway bar, QA'1's, Bilsteins, Wilwood 6 piston front/4 piston rear, Magnaflow stainless exhaust, Lemons Headers, Comp rollers/p-rods/cam, Fikse 18x8.5 and 18x10
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post #2 of 10 (permalink) Old Jul 2nd, 11, 10:02 PM
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Re: Tach drops signal, fuel gauge pegged full

Headlight - maybe ground or bad bulb. Grounds are always an issue with first gens.

Fuel gauge - most likely is the sender ground at the tank strap. Troubleshooter to isolate Gauge, wiring, sender https://www.camaros.net/forums/showpo...91&postcount=2 You can jump the existing tank strap ground to a new clean one with a alligator test lead if it turns out to be that one as a temp fix.

Tach - check the lead on the coil. Maybe loose or bad coil. Factory setup assumed.


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post #3 of 10 (permalink) Old Jul 2nd, 11, 11:04 PM Thread Starter
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Re: Tach drops signal, fuel gauge pegged full

Quote:
Originally Posted by 69-Pace View Post
Headlight - maybe ground or bad bulb. Grounds are always an issue with first gens.

Fuel gauge - most likely is the sender ground at the tank strap. Troubleshooter to isolate Gauge, wiring, sender https://www.camaros.net/forums/showpo...91&postcount=2 You can jump the existing tank strap ground to a new clean one with a alligator test lead if it turns out to be that one as a temp fix.

Tach - check the lead on the coil. Maybe loose or bad coil. Factory setup assumed.
Thanks for the ideas. Headlights are brand new so I will double check the ground. Maybe the body shop didn't tighten the ground on that side properly.
I will check the tank strap ground. Any idea where the factory ground is located?
Coil is a new one. It seemed odd to me that it was fine at lower rpm's and would then quit at that specific rpm.

69 SS396 Camaro, 4link, 12bolt posi, Speedtech LCA / UCA's, Hotchkis 2" drop front springs/sway bar, QA'1's, Bilsteins, Wilwood 6 piston front/4 piston rear, Magnaflow stainless exhaust, Lemons Headers, Comp rollers/p-rods/cam, Fikse 18x8.5 and 18x10
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post #4 of 10 (permalink) Old Jul 2nd, 11, 11:53 PM
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Re: Tach drops signal, fuel gauge pegged full

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Originally Posted by g356gear View Post
Thanks for the ideas. Headlights are brand new so I will double check the ground. Maybe the body shop didn't tighten the ground on that side properly.
I will check the tank strap ground. Any idea where the factory ground is located?
Coil is a new one. It seemed odd to me that it was fine at lower rpm's and would then quit at that specific rpm.
The fuel sender ground is attached to the tank strap at the back of the tank by the muffler housing. The ground gets corroded often when just sitting. If you can crawl under the tank its on the passenger side where the fuel line and return enter the tank.

Hum if the coil is new and the lead is tight could the Tach itself. Factory or aftermarket?


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post #5 of 10 (permalink) Old Jul 3rd, 11, 09:29 AM Thread Starter
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Re: Tach drops signal, fuel gauge pegged full

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Originally Posted by 69-Pace View Post
The fuel sender ground is attached to the tank strap at the back of the tank by the muffler housing. The ground gets corroded often when just sitting. If you can crawl under the tank its on the passenger side where the fuel line and return enter the tank.

Hum if the coil is new and the lead is tight could the Tach itself. Factory or aftermarket?
Tach is an aftermarket repo from eBay.

69 SS396 Camaro, 4link, 12bolt posi, Speedtech LCA / UCA's, Hotchkis 2" drop front springs/sway bar, QA'1's, Bilsteins, Wilwood 6 piston front/4 piston rear, Magnaflow stainless exhaust, Lemons Headers, Comp rollers/p-rods/cam, Fikse 18x8.5 and 18x10
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post #6 of 10 (permalink) Old Jul 3rd, 11, 10:09 AM
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Re: Tach drops signal, fuel gauge pegged full

Steve
I would bench test the tach with a signal tone generator if you have one or access to one and set it to 12 volts DC. Google some how to build one and you can hop over to Radio Shack and cheaply get her done with a 12 volt DC power supply, a few test leads and few different diodes and a switch to test a few "ranges" by switching diodes. Youtube should also have a few ideas. Everett or others here might as well have a way to do it.

Or you can buy a diagnostic tester like this http://www.msdignition.com/product.a...7&terms=tester Plug it in and hook it up

Or sent it off to a rebuild shop for testing.


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post #7 of 10 (permalink) Old Jul 3rd, 11, 10:04 PM Thread Starter
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Re: Tach drops signal, fuel gauge pegged full

So, the passenger ground was not hooked up by the body shop. Problem solved with that issue.

Re-did the coil wiring but the Tach still drops off @ 1500 rpm back to zero and picks up again as the rpm's fall.

Pulled the console gauges and checked the connections there...everything looks good. Checked the rear tank ground and it is still the original connections sealed in undercoating. Wire is perfectly intact.

Wondering if maybe the gauge itself is mechanically bad or physically stuck in the full position. Doesn't move at all when the key is put into the start position.

69 SS396 Camaro, 4link, 12bolt posi, Speedtech LCA / UCA's, Hotchkis 2" drop front springs/sway bar, QA'1's, Bilsteins, Wilwood 6 piston front/4 piston rear, Magnaflow stainless exhaust, Lemons Headers, Comp rollers/p-rods/cam, Fikse 18x8.5 and 18x10
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post #8 of 10 (permalink) Old Jul 3rd, 11, 10:17 PM
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Re: Tach drops signal, fuel gauge pegged full

OK so Headlight issue fixed.
Fuel Gauge -
Follow my troubleshooting test in the trunk, with the wire disconnected from the sender: I think I sent the link to you but in a nut shell...

Unplug the sender lead in the trunk - in a 69 it is the tan/brown single wire connection.
Turn key to on position.
Gauge should read past full.


Now ground the end of the harness leading back to the gauge - NOT THE LOOSE LEAD GOING UNDER THE FLOOR TO THE SENDER.
Turn key to on position.
Gauge should read past empty.


If it does both past full and past empty the gauge is in working condition and harness back to instrument panel is in working order.

If not you can test the ohms being sent to the gauge as described in the troubleshooting guide for the sender test.

TACH issue - I would get a tester or send it to a shop for diagnostics seems like you have done everything you can on it as it is.

Brian


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post #9 of 10 (permalink) Old Jul 3rd, 11, 10:35 PM Thread Starter
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Re: Tach drops signal, fuel gauge pegged full

Quote:
Originally Posted by 69-Pace View Post
OK so Headlight issue fixed.
Fuel Gauge -
Follow my troubleshooting test in the trunk, with the wire disconnected from the sender: I think I sent the link to you but in a nut shell...

Unplug the sender lead in the trunk - in a 69 it is the tan/brown single wire connection.
Turn key to on position.
Gauge should read past full.


Now ground the end of the harness leading back to the gauge - NOT THE LOOSE LEAD GOING UNDER THE FLOOR TO THE SENDER.
Turn key to on position.
Gauge should read past empty.


If it does both past full and past empty the gauge is in working condition and harness back to instrument panel is in working order.

If not you can test the ohms being sent to the gauge as described in the troubleshooting guide for the sender test.

TACH issue - I would get a tester or send it to a shop for diagnostics seems like you have done everything you can on it as it is.

Brian
Thanks Brian,
Do you know where the sender lead is located in the trunk?

Steve C

69 SS396 Camaro, 4link, 12bolt posi, Speedtech LCA / UCA's, Hotchkis 2" drop front springs/sway bar, QA'1's, Bilsteins, Wilwood 6 piston front/4 piston rear, Magnaflow stainless exhaust, Lemons Headers, Comp rollers/p-rods/cam, Fikse 18x8.5 and 18x10
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post #10 of 10 (permalink) Old Jul 3rd, 11, 11:15 PM
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Re: Tach drops signal, fuel gauge pegged full

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Originally Posted by g356gear View Post
Thanks Brian,
Do you know where the sender lead is located in the trunk?

Steve C
Yes right under the trunk latch you will see the connector - Three wires, two bundled and the tan/brown wire is a single connection that then travels through the trunk floor by the fuel filler.

Disconnect it there, and then attach an alligator clip to the harness bundle connection where you disconnected the sender single tan/brown wire and ground it to the trunk latch. This will ground the gauge. This should peg the gauge at past empty. If it does then your gauge and harness are in working order and the sender is at fault.

Even though the ground looks good it may not be, but you can use a multimeter and check the ohms through the sender. Half full tank should be around 45ohms. Use the disconnected end that travels through the trunk to the sender.

Maybe the sender float is stuck, or its bad. Ohms will tell you if it is sending ohms or not.


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