Can a bad tach make an engine run poorly??? - Team Camaro Tech
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Old Apr 29th, 11, 11:28 AM Thread Starter
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DeAngelo
 
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Question Can a bad tach make an engine run poorly???

I have a 67 with a tachometer. It is an aftermarket OEM type tach. It has run perfectly for 5 years. The engine seems to have electrical issues and the tach jumps around a lot and coincides with the engine running poorly. Is it possible thatthe tach is the culprit???
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Old Apr 29th, 11, 11:49 AM
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Don
 
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Re: Can a bad tach make an engine run poorly???

Quote:
Originally Posted by Deangelo66 View Post
I have a 67 with a tachometer. It is an aftermarket OEM type tach. It has run perfectly for 5 years. The engine seems to have electrical issues and the tach jumps around a lot and coincides with the engine running poorly. Is it possible thatthe tach is the culprit???
Can you disconnect it ?

Don
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Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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Old Apr 29th, 11, 01:11 PM
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Russ
 
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Re: Can a bad tach make an engine run poorly???

HEI distributor by any chance ? Seen this a few times mainly with off road trucks where the tach wire and the 12v lead to the HEI are loose. The tach jumps and the 12v is also loosing contact at same time. Things like this can drive you bonkers.

If not HEI, I'd suspect a negative ground problem.

Russ (RJ)
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Old Apr 29th, 11, 02:35 PM Thread Starter
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Re: Can a bad tach make an engine run poorly???

Yes, it is an HEI. And I plan to try to disconnect it but don't know which of the wires to remove. I will play with it. If it doesn't start, then I know I have done something wrong. Will this issue cause my engine to run poorly, sputtering and cutting off?
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Old Apr 29th, 11, 03:01 PM
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Re: Can a bad tach make an engine run poorly???

If it's a GM HEI there are two wires that clip into connectors on the dist cap, labeled TACH and BATT. Disconnect the TACH.


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Old Apr 29th, 11, 04:33 PM
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Re: Can a bad tach make an engine run poorly???

Use an inspection mirror or your wife/girlfriends compact to look at where the wires connect. As Al said the male spades sticking down from the distributor will be marked. Mark each wire and then pull off just the TACH wire. My suspicion is that this will not change your erratic running. I think you may need to pull the BATT wire, carefully crimp the female connector a bit tighter, and then re-install. My thought is you don't have a good connection and this will cause what seems like a misfire when contact is momentarily lost.

Russ (RJ)
The Garlic Capital, Gilroy,CA

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Old Apr 29th, 11, 08:49 PM
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Hector
 
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Re: Can a bad tach make an engine run poorly???

Could be a bad ignition module..

68 Camaro Coup, BBC ,2457 headers, th400 , ford 9", Hotchkiss connectors,
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Old Apr 29th, 11, 10:15 PM
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Re: Can a bad tach make an engine run poorly???

Quote:
Is it possible thatthe tach is the culprit???
yes.. it jumps around because of a loose or shorting connection

Been thru this and I run a GM HEI.
Quote:
As Al said the male spades sticking down from the distributor will be marked. Mark each wire and then pull off just the TACH wire. My suspicion is that this will not change your erratic running.
The chances are you have an aftermarket spade connector on the tach wire...If u push it straight up, 9 times out of 10 it doesnt slide on to the blade, but rather between the blade and wall.....make sure the connector clamp part is tight, and the connector isa firm on the blade...use long nose pliers and the mirror as suggested above.
AND do the same for the BaTT as suggested above....
If both are not located and grip well and not sleeved its possble to get an induced current across the 2...causing the tach to jump and a miss.

RJ is right on the money ....

I chassed this down for months years go...it was intermitant.

My Spelling is not incorrect...it is creative

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Old Apr 30th, 11, 06:22 AM Thread Starter
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Re: Can a bad tach make an engine run poorly???

Thanks, all!! I will work on this today!! Keep you posted!!! D
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Old Apr 30th, 11, 07:46 AM
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Re: Can a bad tach make an engine run poorly???

It could be the other way around too. The tach may be faithfully showing whatever is causing the engine to miss.
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Old Apr 30th, 11, 10:28 AM Thread Starter
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Re: Can a bad tach make an engine run poorly???

Quote:
Originally Posted by Moonpie View Post
It could be the other way around too. The tach may be faithfully showing whatever is causing the engine to miss.
Excellent point. Thanks!
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Old May 1st, 11, 06:27 PM Thread Starter
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Re: Can a bad tach make an engine run poorly???

Mickey was right! The tach proved that there was an electrical problem. See the culprit here: http://i1130.photobucket.com/albums/...CamaroWire.jpg

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Old May 1st, 11, 11:37 PM
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Re: Can a bad tach make an engine run poorly???

There's your problem. lol
Also, since it's an HEI, it does not need to use that wire, that is a ballast resistor wire, it knocks down the voltage for a points style ignition, splicing it won't change the voltage.
Run a wire from the fuse box that has power when the key is in the accessory position and when starting, easy to locate with a test light.
Also, as others said, 9 times out of 10 when you slide the clip in, it goes in between or on the sides of the posts they need to go on, been there done that, my tach jumped around also, and because when the shop replaced the body mounts, they ripped out the ground wires.

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Old May 2nd, 11, 07:10 PM Thread Starter
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Re: Can a bad tach make an engine run poorly???

HAHAHA Thanks, AJ for the input. That is my next step. I didn't know that about the wire. Going to get a 12 gauge wire soon to replace it and run it directly from the fuse box. Thanks!
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Old May 3rd, 11, 02:26 AM
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Re: Can a bad tach make an engine run poorly???

Best take it from the ign source of the ballast wire.....Somewhere in the electrical section is a wiring diagram
But if taking from the box make sure it goes from the ing side...not the side thats live all the time....

My Spelling is not incorrect...it is creative

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