Tach is... weird.
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Supreme Member
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Joined: Jan 2003
Posts: 1,083
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From: Northwestern Pennsylvania
Car: 1985 Pontiac Trans Am
Engine: 355 with stuffs.
Transmission: 700R4
Axle/Gears: 4.10 Posi
Tach is... weird.
Hopefully someone here has encountered this problem before because it's bugging me.
On my L98 Pontiac, the tach will function normally until the engine warms up. After this, it will start jumping, and stay at almost double what the engine speed actually is for a couple seconds, then go back to jumping 1-2k rpm at a time.
Now, If I'm going about 40MPH, and downshift in to third to bring the RPM up, the tach drops to normal and reads accurately with no jumping needle.
The engine has no misfires or stumbles when the tach jumps, it functions normally.
I've inspected the wire going to the tach, and have not found any problems. The only thing I've changed recently is my ignition module. Can an ignition module cause this type of condition?
Is my tach on its way out?
Thanks for reading.
On my L98 Pontiac, the tach will function normally until the engine warms up. After this, it will start jumping, and stay at almost double what the engine speed actually is for a couple seconds, then go back to jumping 1-2k rpm at a time.
Now, If I'm going about 40MPH, and downshift in to third to bring the RPM up, the tach drops to normal and reads accurately with no jumping needle.
The engine has no misfires or stumbles when the tach jumps, it functions normally.
I've inspected the wire going to the tach, and have not found any problems. The only thing I've changed recently is my ignition module. Can an ignition module cause this type of condition?
Is my tach on its way out?
Thanks for reading.
Thread Starter
Supreme Member
iTrader: (2)
Joined: Jan 2003
Posts: 1,083
Likes: 0
From: Northwestern Pennsylvania
Car: 1985 Pontiac Trans Am
Engine: 355 with stuffs.
Transmission: 700R4
Axle/Gears: 4.10 Posi
Re: Tach is... weird.
ttt. Hoping someone can offer some insight.
Supreme Member
Joined: Jan 2006
Posts: 3,341
Likes: 10
From: Mooresville NC
Car: LOWERED ♦ CRIMSON METALFLAKE
Engine: ► 400 KUBES ◄
Transmission: 765R4
Axle/Gears: EATON POSI 4.56
TACH TALK
It sounds like the tach filter is not doing its job.
Without throwing a scope on it your next best alternative is to rebuild/replace the filter.
Happy Racing!
If People Drove Any Slower They’d Be Going BackwardsFog lights are not driving lights. They look dorky. Turn em off slow pokes.
How bout those dorks too scared to drive without headlights on in the daytime!
.
.
Thread Starter
Supreme Member
iTrader: (2)
Joined: Jan 2003
Posts: 1,083
Likes: 0
From: Northwestern Pennsylvania
Car: 1985 Pontiac Trans Am
Engine: 355 with stuffs.
Transmission: 700R4
Axle/Gears: 4.10 Posi
Re: TACH TALK
Thank you for the reply. My knowledge about this subject is very limited, so I have to ask this: I'm assuming this filter is located on or near the tach. How do I go about repairing/replacing?
Supreme Member
Joined: Jan 2006
Posts: 3,341
Likes: 10
From: Mooresville NC
Car: LOWERED ♦ CRIMSON METALFLAKE
Engine: ► 400 KUBES ◄
Transmission: 765R4
Axle/Gears: EATON POSI 4.56
MORE TACH TALK
You can use a test-meter to determine if the resistors, capacitors and diodes are still OK.
OR
You can replace the board (it plugs in).
However if you use a used one you might just be swapping one problem for another.
Happy Racing!
If People Drove Any Slower They’d Be Going BackwardsFog lights are not driving lights. They look dorky. Turn em off slow pokes.
How bout those dorks too scared to drive without headlights on in the daytime!
.
.
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