c4 1990 tack not working

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Oct 3, 2013 | 02:30 PM

tonycorvettes

Thread Starter

Racer

Joined: Sep 2008

Posts: 461

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From: baton rouge louisiana

c4 1990 tack not working

when i turn on the key but not start,the neddle slowly moves all the way up.when i try to start it slams down left and stays there,any shgestions?

Oct 3, 2013 | 02:59 PM

don hall

Safety Car

Joined: Aug 2002

Posts: 3,842

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From: SANTA CRUZ CA

Check out this CF thread on tach filter:

http://forums.corvetteforum.com/c4-g...1990-vert.html

Oct 3, 2013 | 08:00 PM

mechguy79

Pro

Joined: Mar 2007

Posts: 526

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From: San Angelo Texas

Quote:

Originally Posted by tonycorvettes

when i turn on the key but not start,the neddle slowly moves all the way up.when i try to start it slams down left and stays there,any shgestions?

Welcome to my world. That is very common. 1990 was the first year of that dash so we have a bunch of one-off parts. Could be the tach filter. That is easy to change so do it first. I would be you need the instrument cluster serviced. Apparently there is a bank of resistors on the tach driver board that go bad.

Oct 3, 2013 | 08:15 PM

WVZR-1

Team Owner

Joined: Sep 2003

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Quote:

Originally Posted by mechguy79

Forget the tach filter - they're very difficult to find and likely won't correct the issue. At "key on" the tach should park at 0.

Just get it scanned from the ALDL and confirm tach operation from there. If the tach signal seems relatively close at the ALDL then assume your problem is cluster main-board related and you've saved the aggravation of attempting to find a filter.

Scan it and be done with it! No signal at the ALDL - the challenge begins!

Oct 5, 2013 | 09:56 PM

tonycorvettes

Thread Starter

Racer

Joined: Sep 2008

Posts: 461

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From: baton rouge louisiana

scan it?

what exactly do you mean,my son has a ob2 ,dont work connector is different...how can i tell if the tach is good at that point?

Oct 5, 2013 | 11:55 PM

WVZR-1

Team Owner

Joined: Sep 2003

Posts: 25,393

Likes: 2,741

Quote:

Originally Posted by tonycorvettes

what exactly do you mean,my son has a ob2 ,dont work connector is different...how can i tell if the tach is good at that point?

A proper scanning device can check this for you. Your son's is only a "code checker" and not actually a diagnostic device I'd guess. OBD2 code checkers are inexpensive and useful, there wasn't such a device for ODB1 because the ALDL for all the manufacturers were different - OBD2 is a "federal standard".

If you do business with a repair shop regularly they might likely accommodate you for "no charges" -

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