Bad tachometer filter ?
Thread Starter
Drifting
Joined: Dec 2011
Posts: 1,439
Likes: 23
From: mesa az
Bad tachometer filter ?
I modified my 1988 engine about 12,000 miles ago. The tach operates normally except when I put the pedal all the way down. The speedomter gauge works fine but my tach will read single digets like 2, 3, and just act crazy until the speed starts to come down and then it seems to catch up to the engine. I have yet to slowly increase speed because I am too scared of geting pulled over. I would be well over the speed limit if I were to gently climb in speed. When and if I do speed it is for a short burst and then off the pedal. I just don't know if this is a sign of the tachmoter filter going bad or something else ? I recently had a guy suggest the filter rmight be the problem and told me its under the distributor. I think 1989 was the last year for this filter ?
Last edited by C4in mesa; May 12, 2014 at 08:47 AM.
Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
I modified my 1988 engine about 12,000 miles ago. The tach operates normally except when I put the pedal all the way down. The speedomter gauge works fine but my tach will read single digets like 2, 3, and just act crazy until the speed starts to come down and then it seems to catch up to the engine. I have yet to slowly increase speed because I am too scared of geting pulled over. I would be well over the speed limit if I were to gently climb in speed. When and if I do speed it is for a short burst and then off the pedal. I just don't know if this is a sign of the tachmoter filter going bad or something else ? I recently had a guy suggest the filter rmight be the problem and told me its under the distributor. I think 1989 was the last year for this filter ?
Thread Starter
Drifting
Joined: Dec 2011
Posts: 1,439
Likes: 23
From: mesa az
I am leery of doing that switch. My concern is my cam is now different and so is my air intake system. What I'm trying to say is since my engine now has power at over 5000 rpm's isn't the Hypertech coil best ? I would also like to hear symptoms of a faulty tachometer filter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
I had a similar problem with mine when I installed an MSD coil, I changed back to stock and it worked again.
Then my coil started to go south I guess, or maybe my tach filter was going out. Whatever it was I fixed it by going to a D.U.I. distributor with D.U.I. coil. When I did that, the tach was still messed up until I installed an MSD6AL2 ignition box and bypassed the original tach filter.
There is a tach filter inside the MSD ignition box which allowed my new coil to function properly with my tach.
If you get an aftermarket coil, you should install an MSD ignition box if you plan on continuing to use the aftermarket coil.
I had to install a $30 Sun-Pro II tachometer because the factory tach does not respond fast enough for my new acceleration.
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Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
Yes. And it works just fine. The stock L98 distributor is much better than aftermarket companies would like you to believe. All the aftermarket coils do is allow you to widen the spark plug gap.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
When my tach filter was going bad the numbers jumped all over the place while driving... If you find out it is your tach filter, below is where I bought my tach filter, get the $20.00 filter at the bottom, that's the one I got for my 89 and it's worked perfectly for over 7 years.The more expensive one just looks like the stock filter, but doesn't work any better.....Read what he has printed at the bottom of the page..........WW
http://my.execpc.com/C4/4A/rodney1/corvette/
...WWhttp://my.execpc.com/C4/4A/rodney1/corvette/
Last edited by WW7; May 12, 2014 at 02:49 PM.
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
When my tach filter was going bad the numbers jumped all over the place while driving... If you find out it is your tach filter, below is where I bought my tach filter, get the $20.00 filter at the bottom, that's the one I got for my 89 and it's worked perfectly for over 7 years.The more expensive one just looks like the stock filter, but doesn't work any better.....Read what he has printed at the bottom of the page..........WW
http://my.execpc.com/C4/4A/rodney1/corvette/
...WWhttp://my.execpc.com/C4/4A/rodney1/corvette/
Melting Slicks
Joined: Nov 2010
Posts: 2,216
Likes: 113
From: Michigan
Upgraded my ignition and the tach works fine for normal driving but at WOT it acts up and jumps around. Still I don't like the factory tach and will be installing a nice 3" autometer I had planned on using in my C3 but didn't have the room and ended up using a bit smaller body 3" sunpro tach. Always liked 3" sweep tachs myself and not the big gaudy 5"ers with shiftlight.