Tach Issue
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
Tach Issue
Like the majority of you with a 90 my tach doesn't work. It reads alot higher then it actually is. My oil pressure guage also doesnt work.
So I bought a cluster from a member to swap out thinking it would fix my problem but it didn't. The weird thing is that on the new cluster my tach doesnt work at all, and my oil pressure guage still doesnt work.
I thought maybe it could be the wire from the distributor to the dash, so I ran a new one. The tach still reads way to high. I tried a new ground, but that didn't work either. I've tried with and without the tach filter but it doesn't make a difference. I figure both clusters can't be bad because they both don't work, so it must be a wiring issue. Does anyone have any insight on this? I would greatly appreciate any help! Anything I'm missing? I don't think I need to have my cluster rebuilt.
So I bought a cluster from a member to swap out thinking it would fix my problem but it didn't. The weird thing is that on the new cluster my tach doesnt work at all, and my oil pressure guage still doesnt work.
I thought maybe it could be the wire from the distributor to the dash, so I ran a new one. The tach still reads way to high. I tried a new ground, but that didn't work either. I've tried with and without the tach filter but it doesn't make a difference. I figure both clusters can't be bad because they both don't work, so it must be a wiring issue. Does anyone have any insight on this? I would greatly appreciate any help! Anything I'm missing? I don't think I need to have my cluster rebuilt.
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
In a way I don't think it can be a ground issue either because the other 3 gauges work just fine! I've read of guys installing a MSD distributor, removing the tach filter and not having any problems. Do you think that would solve my problem?
Last edited by jimmers; Apr 15, 2008 at 08:47 PM.
Team Owner
Joined: Sep 2003
Posts: 25,366
Likes: 2,733
Are both clusters the same part#? The tach is calibrated with resistors on the mainboard. If both clusters are the same part# I believe I'd swap the mainboard and give it a try. The tach should read something other than what it did with the original mainboard but still might not be correct! Post both part#'s
The oil pressure gauge I would guess requires more diagnostics. I'd start at the OPS with a FSM for that.
The oil pressure gauge I would guess requires more diagnostics. I'd start at the OPS with a FSM for that.
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
Are both clusters the same part#? The tach is calibrated with resistors on the mainboard. If both clusters are the same part# I believe I'd swap the mainboard and give it a try. The tach should read something other than what it did with the original mainboard but still might not be correct! Post both part#'s
The oil pressure gauge I would guess requires more diagnostics. I'd start at the OPS with a FSM for that.
The oil pressure gauge I would guess requires more diagnostics. I'd start at the OPS with a FSM for that.
Drifting
Joined: Mar 2002
Posts: 1,251
Likes: 2
From: Thomson Georgia
Hello Dave
The 90 clusters are noted to be inaccurate.
The easiest thing to do is update to a later cluster and be done with it.
I've posted a bunch of times on the 90 cluster, I've got 93 clusters in both of my 90s, just swap the LCD from your 90.
Johnny
The 90 clusters are noted to be inaccurate.
The easiest thing to do is update to a later cluster and be done with it.
I've posted a bunch of times on the 90 cluster, I've got 93 clusters in both of my 90s, just swap the LCD from your 90.
Johnny
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
So do you suspect that both of my clusters are bad?
Drifting
Joined: Mar 2002
Posts: 1,251
Likes: 2
From: Thomson Georgia
I've seen three (3) good (aka accurate) ones, they all had been rebuilt.
Let's see how many jump on and say theirs is fine.
I have gone thru and replaced every component that controls the tach on the printed circuit board and without exception, except for 1 which had a bad resistor, 5 so far, the tach itself was bad.
I put a 94 tach in a 90 cluster, with no other changes, and the accuracy returned. It was 2k high at idle.
The driver chips for the LCD boards is basically the same, newer revision, the difference is the pin outs of the LCD itself.
You can use a 91 tach and a 92 - I think, without having to replace the LCD.
Let's see how many jump on and say theirs is fine.
I have gone thru and replaced every component that controls the tach on the printed circuit board and without exception, except for 1 which had a bad resistor, 5 so far, the tach itself was bad.
I put a 94 tach in a 90 cluster, with no other changes, and the accuracy returned. It was 2k high at idle.
The driver chips for the LCD boards is basically the same, newer revision, the difference is the pin outs of the LCD itself.
You can use a 91 tach and a 92 - I think, without having to replace the LCD.
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Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
In a way I think it could be the clusters. It's hard to believe it could be a ground or wiring issue when the other 3 guages work. Its weird that the oil pressure guage doesn't work either. If I plug in a aftermarket tach under the dash at the tach wire, it works fine. Just thinking out loud!
Last edited by jimmers; Apr 16, 2008 at 01:30 PM.
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
Are both clusters the same part#? The tach is calibrated with resistors on the mainboard. If both clusters are the same part# I believe I'd swap the mainboard and give it a try. The tach should read something other than what it did with the original mainboard but still might not be correct! Post both part#'s
The oil pressure gauge I would guess requires more diagnostics. I'd start at the OPS with a FSM for that.
The oil pressure gauge I would guess requires more diagnostics. I'd start at the OPS with a FSM for that.
Le Mans Master
Joined: Apr 2002
Posts: 5,726
Likes: 46
From: Waukesha WI
St. Jude Donor '15
Same problem here. A year or so ago, I switched to a different cluster (from a forum member parting out his car) because the LCD in mine started losing segments. The tach in the replacement was even farther off than mine so I just swapped the LCD. Now, mine has decided to read even higher and is basically useless. My stock engined 90 now magically idles at almost 3k, apparently.
I've thought about sending it in for a recal/refurb to an 8k tach. I'm not sure if that would fix the problem or only band-aid it for a short time.
Racer
Joined: Apr 2006
Posts: 378
Likes: 0
From: Whitby Ontario
'90 and '91 uses a filter unique to those years. I ordered a used filter as no one was making replacements for '90 - '91 .
Once installed ,my tach with the false reading worked fine and still does 3 years later.
Advanced
Joined: Feb 2005
Posts: 77
Likes: 0
From: N. Tonawanda NY
I have a 90 with the same issue. If there is a tach filter on this car I would like some to tell me exactly where it is. I have looked countless times and never saw it. The factory service manual doesn't show one. Red C4 if you got a picture of one in the car I really would like to see it.
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
I had the same problem with my '91 . Did some research and found that the Tach Filter was a common cause. Located in engine compartment between the Distributor and Firewall on Mine.
'90 and '91 uses a filter unique to those years. I ordered a used filter as no one was making replacements for '90 - '91 .
Once installed ,my tach with the false reading worked fine and still does 3 years later.
'90 and '91 uses a filter unique to those years. I ordered a used filter as no one was making replacements for '90 - '91 .
Once installed ,my tach with the false reading worked fine and still does 3 years later.
I already replaced the tach filter. I also tried without the filter.
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
I have a 90 with the same issue. If there is a tach filter on this car I would like some to tell me exactly where it is. I have looked countless times and never saw it. The factory service manual doesn't show one. Red C4 if you got a picture of one in the car I really would like to see it.
http://forums.corvetteforum.com/show...ht=tach+filter