Mike:

Car: 1991 Corvette with automatic transmission, completely stock
Problem: Tachometer reads zero, rest of gauges in cluster appear to work properly

I've recently acquired a C4 vette (last night) and was told that the tachometer doesn't function properly. Although the car is an automatic it's something that would bother me.


I've pulled the cluster, soldered in a 300K ohm resistor as shown in another post for high reading tachometers. The tach now only goes to zero vs. before when it would go to full rpm range and then to zero. I removed the added resistor and am now back to stock. It seems as though it is only getting ignition power and not signal from the tachometer, which I believe should be from the distributor but that appears fine.

I've read about the tachometer chip but don't have access to a working one.

Any thoughts?

kimmer

I'm no expert on this but could it be the tach filter or connections to it?

Mike:

Alright and that is the one wire plug by the distributor? Appears to be intact and going to factory wire loom.


I'm going by a local speedometer shop tomorrow to see if I can get a quote.


Any way of getting a new LCD screen while its out? The display is weak and the contrast is nonexistent. I'm looking at LED bulbs to replace the original faded ones if I can find the right size

aboatguy

Do a search on polorizing film.

vetteoz

White tacho wire at dist goes to the tach filter then back into the main harness

corvetteronw

I have a used tach filter for my 91 that I never installed. I got it from Vette2Vette. He says he tests all his electronics and guarantees that they work correctly.
I decided to go with the repair that you tried but have not done so yet.
$25 shipped (much less than I paid for it). PM me if you want it.
Corvette Central charges $54 plus shipping for a new one if you want to go that route.

Mike:

Thanks for the offer and I will surely keep that in mind. I called a few local shops and was honestly surprised at the number of shops with parts and more importantly experience. My cluster is at a local speedometer shop and I'm waiting on a quote but the shop recently bought all stock from a closing corvette shop so we'll see where that goes.

Mike:

Just got it back from the shop, tachometer works great however the lcd doesn't. The tachometer circuitry was replaced and a new 'bread board' was installed along with a new lcd screen. The screen turns on with the key in and everything appears fine and then when I turn the car on the letters and numbers don't fully appear. I think it wants to read GAS but only reads something resembeling Jh6. I'll be taking it back to the shop but any ideas here. Would a bad signal from the car give a bad readout on the display. I know if I take the cluster back they'll hook it up to there tester and everything will display correctly.

WVZR-1

LCD display was functional and working correctly when you removed the cluster from the car?

You don't mention where you're located or maybe what the charges were to do the tachometer aspect of the repair. Care to share?

Mike:

I was told the LCD display functioned correctly but because of the dim lighting "I" couldnt see it. The new LCD is much brighter, everything displays clearly at ignition but in run the display numbers/letters aren't complete. The battery also won't hold a charge, previous owner allowed battery to die several times and I think its done, but he will replace as it is still under warranty. He drove the vehicle without the tach working but said the lcd, however dim, did work.

I'm located in South Florida and paid a discounted rate and total cost was less $250.

I pulled the battery and previous owner who took the cluster into the shop will replace the battery and speak with the shop about my current condition. I guess I just wanted to know what specifically gives information to the LCD display in a 91' my Chilton manual doesn't seem to acknowledge that there is even a digital display in the vehicle.

WVZR-1

Since it's going back to the shop anyway you might want to attach a scanner to the ALDL and confirm the accuracy of the tach. If it's appreciably off it could likely be corrected while the cluster is there. It's part of what you paid for!

Mike:

The tachometer shows the idle right under 1000rpm. I changed the plug wires, and that got rid of a slight surge in idle. All other gauges work except the LCD so I can only presume it is a problem with the LCD or else all other gauges wouldn't function properly for instance if the main plug wasn't seated fully into the back of the cluster.

I already gave the battery to the previous owner(my neighbor) so I wont be able to start the car till Monday.

Pictures are from 3 different start-ups

kimmer

Damm that's in Arabic.

WVZR-1

Since it worked previously theres a connector behind the LCD that is maybe loose/mis-pinned or what-ever. It shouldn't be an issue with the shop to check but if there's a voltage problem I believe the LCD get's "stupid" also. Never had the problem. I see a "check gauges" light also. Was that there previously or is it new? If they check the cluster in the local shop see if they'll do a "show me" it works and then you know you might have ground issues. No bent pins on the primary cluster connector?

Try the new battery first!

Mike:

Previous owner degreassed the engine bay and I can only think a sensor got wet, a good deal of the plastic plugs are fragile and/or somewhat broken and something got wet. It is a "new to me" LCD screen possibly never been used, I'm not sure. Primary cluster connector appears to be fine and making good contact as all of the other gauges work. I'll be getting a new battery and talking with the shop tomorrow and I'll check back in.

Mike:

Slight update

Display will change with the vehicle moving, still does not display speed and I'm really not sure what its trying to show, just a bunch of vertical and horizontal lines thrown together

Mike:

Update: I dont drive the car and its been sitting for a while

Cluster was removed, cluster's circuit was visually checked and all seems well. The main press-fit connection for the cluster was pulled, snaked under the dash and pressed into the cluster for a visually secure connection (cluster was beneath the steering wheel). Car was started with no improvement to the LCD display, the car remained in park.

Trip Settings unit was removed and green electrical mold like residue was removed and the unit was reassembled.

Battery was pulled to access nylon grounding strap from bellhousing with the wires on both ends, tight and secure but had buildup and were cleaned.

I will hook everything back up tomorrow and hope everything goes well.

But If i wanted to run new wires (temporarily) from the source for each of the LCD wires to the cluster, where would I start?

Mike:

I got it all back together, minus the dash trim and I have a slight improvement over the above photos but it is still not functioning properly. The trip function buttons don't seem to work so the unit will be pulled and checked for continuity.

But If i wanted to run new wires (temporarily) from the source for each of the LCD wires to the cluster, where would I start?