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87 v10 350 tbi tach going crazy
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Topic: 87 v10 350 tbi tach going crazy (Read 1528 times)
buzzman351
Newbie
Posts: 50
Newbie
87 v10 350 tbi tach going crazy
«
on:
August 31, 2022, 03:08:17 PM »
Hey guys, new here. I installed a aftermarket tachometer on my 87 350 tbi and when I turn the key the tach buzzes and jumps around 0 for a bit and same at initial startup then goes to the rpm it’s running. Any ideas
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bd
Global Moderator
Senior Member
Posts: 6459
Re: 87 v10 350 tbi tach going crazy
«
Reply #1 on:
August 31, 2022, 03:16:52 PM »
Some possibilities: 1) bad tach head, 2) where it's connected, 3) how it's connected, 4) poor ground.
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Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)
buzzman351
Newbie
Posts: 50
Newbie
Re: 87 v10 350 tbi tach going crazy
«
Reply #2 on:
September 01, 2022, 12:45:23 PM »
I’ve checked everything numerous times. It’s some sort of interference. I’m going to install a resistor on the signal wire
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bd
Global Moderator
Senior Member
Posts: 6459
Re: 87 v10 350 tbi tach going crazy
«
Reply #3 on:
September 01, 2022, 01:17:16 PM »
Tach Filter
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Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)
buzzman351
Newbie
Posts: 50
Newbie
Re: 87 v10 350 tbi tach going crazy
«
Reply #4 on:
September 01, 2022, 08:27:25 PM »
Yesir
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buzzman351
Newbie
Posts: 50
Newbie
Re: 87 v10 350 tbi tach going crazy
«
Reply #5 on:
September 04, 2022, 07:39:21 AM »
my buddy had a sylvania led load equalizer he said would possibly work. i wired it inline with the signal wire. still have the problem. do i need to branch off to ground coming out of the equalizer or it just wont work?
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bd
Global Moderator
Senior Member
Posts: 6459
Re: 87 v10 350 tbi tach going crazy
«
Reply #6 on:
September 04, 2022, 08:47:59 AM »
If the problem is a dirty signal, a resistor by itself won't work. You need a resistor in combination with a capacitor to filter the signal. See my subsequent post or try the tach filter linked previously.
«
Last Edit: September 04, 2022, 06:40:00 PM by bd
»
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Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)
buzzman351
Newbie
Posts: 50
Newbie
Re: 87 v10 350 tbi tach going crazy
«
Reply #7 on:
September 04, 2022, 04:14:35 PM »
my truck is an 87 with the 350 tbi, i have the signal wire running from the ignition coil lead that didnt have anything plugged into it. that is correct right? i dont believe it goes to the distributor cap on this year model
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bd
Global Moderator
Senior Member
Posts: 6459
Re: 87 v10 350 tbi tach going crazy
«
Reply #8 on:
September 04, 2022, 06:32:27 PM »
The tach connects to the white coil lead. Copy the filter configuration below and wire it in as shown...
«
Last Edit: September 04, 2022, 06:38:50 PM by bd
»
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Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)
buzzman351
Newbie
Posts: 50
Newbie
Re: 87 v10 350 tbi tach going crazy
«
Reply #9 on:
September 09, 2022, 05:15:02 PM »
So I got the tach filter and same problem. Unhooked my signal wire and problem still exists. Could it be noise on the 12v keyed side?
Sent from my iPhone using Tapatalk
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bd
Global Moderator
Senior Member
Posts: 6459
Re: 87 v10 350 tbi tach going crazy
«
Reply #10 on:
September 09, 2022, 06:57:43 PM »
The only way you are really going to know the cause is to use an oscilloscope. Outside of that, it's guesswork. Try unplugging the alternator regulator to see if the symptoms disappear.
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Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)
buzzman351
Newbie
Posts: 50
Newbie
Re: 87 v10 350 tbi tach going crazy
«
Reply #11 on:
September 09, 2022, 07:21:38 PM »
Will do. I switched the 12v keyed from the ignition source to the accessory source and it calmed down some.
Sent from my iPhone using Tapatalk
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87 v10 350 tbi tach going crazy