RPM gauge - bouncing
Thread Starter
Instructor
Joined: Jan 2015
Posts: 101
Likes: 3
From: CA; Bay Area
RPM gauge - bouncing
Hi,
I notice that the RPM needle will not start moving until the car is going 40 mph or so then the tach goes to 4500rpm - 55rpm quickly when going 55mph or so. So it's totally not reading accurately. Any idea?
Thanks in advance.
I notice that the RPM needle will not start moving until the car is going 40 mph or so then the tach goes to 4500rpm - 55rpm quickly when going 55mph or so. So it's totally not reading accurately. Any idea?
Thanks in advance.
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Drifting
Joined: Aug 2019
Posts: 1,334
Likes: 225
I would check the distributor tach connection at the distributor(tan wire). also right at the distributor there is a tach filter (I believe it's a white wire). Check to see if that connection is good.
You're getting some kind of activity, so it's not dead. You can buy a tach circuit board(if that's the issue) for like $50 if you do it yourself. But let's eliminate the basic stuff first.
You're getting some kind of activity, so it's not dead. You can buy a tach circuit board(if that's the issue) for like $50 if you do it yourself. But let's eliminate the basic stuff first.
Last edited by Mrvettenick; Feb 26, 2020 at 08:30 PM.
Thread Starter
Instructor
Joined: Jan 2015
Posts: 101
Likes: 3
From: CA; Bay Area
I would check the distributor tach connection at the distributor(tan wire). also right at the distributor there is a tach filter (I believe it's a white wire). Check to see if that connection is good.
You're getting some kind of activity, so it's not dead. You can buy a tach circuit board(if that's the issue) for like $50 if you do it yourself. But let's eliminate the basic stuff first.
You're getting some kind of activity, so it's not dead. You can buy a tach circuit board(if that's the issue) for like $50 if you do it yourself. But let's eliminate the basic stuff first.
Where can I purchase the circuit board and how much work is it to replace? Thanks
Last edited by jvmagic; Apr 12, 2020 at 08:57 PM. Reason: address misspelled words
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
CF sponsor WILLCOX ... their website has many vette troubleshooting aides and they (Ernie) have a on ongoing thread here at CF
https://willcoxcorvette.com/corvette...78-79-usa-made
https://willcoxcorvette.com/corvette...78-79-usa-made
Le Mans Master
Joined: Jun 2019
Posts: 7,649
Likes: 2,466
From: Indiana
I have a 79 as well..
mine did not work when i got it..
Pics help of your filter at distributor etc..many on here can help better..
willcox walked me through mine at ask willcox a question thread.
willcox also backed me up and helped diagnose why my new board fried!!
i changed cap rotor and coil..suggest you may want to as well..since then no issues of burning up boards...
willcox even calibrated my tach..
i bought new board new filter..from him..
if you have a filter try bypassing it to see if that fixes it first.
79 goofy year for tach imo..mine reads perfect til warm the reads low about 3-500 rpm at idle and flops up when starting..oil good too..
other than that works perfect..
mine did not work when i got it..
Pics help of your filter at distributor etc..many on here can help better..
willcox walked me through mine at ask willcox a question thread.
willcox also backed me up and helped diagnose why my new board fried!!
i changed cap rotor and coil..suggest you may want to as well..since then no issues of burning up boards...
willcox even calibrated my tach..
i bought new board new filter..from him..
if you have a filter try bypassing it to see if that fixes it first.
79 goofy year for tach imo..mine reads perfect til warm the reads low about 3-500 rpm at idle and flops up when starting..oil good too..
other than that works perfect..
Last edited by interpon; Apr 12, 2020 at 03:25 PM.