Attempting to Fix Factory Tach & Gauges

R

RGBody87

Apprentice
Jan 7, 2018
92
19
8
#1
Good evening,

I have a 1987 Monte Carlo SS with a 454 BBC swapped into it. It's running an HEI distributor. I am having a hard time getting an accurate RPM reading inside the car because the gauge is reading really far off from what it should be. For example. When the car is idling at probably 700 RPM the car is reading close to 2,000RPM. What should I look at or buy or modify to get this to start reading accurately.
Additionally. The OEM wiring harness has been hacked so many times... I am having a hard time finding the OEM wires that were used to power the Water Temp Gauge and the factory Oil Pressure gauge. Currently I only have a working Fuel Tank gauge and Volt Meter.
I'm not concerning myself with the Speedometer until I swap the T56 in and know that I have a working transmission /sending unit set up.

Any help you can suggest would be great! Thank you!

Ryan
 
buick7332

buick7332

Greasemonkey
Oct 21, 2014
126
107
43
N.E. Philadelphia area
#2
Good evening,

I have a 1987 Monte Carlo SS with a 454 BBC swapped into it. It's running an HEI distributor. I am having a hard time getting an accurate RPM reading inside the car because the gauge is reading really far off from what it should be. For example. When the car is idling at probably 700 RPM the car is reading close to 2,000RPM. What should I look at or buy or modify to get this to start reading accurately.
Additionally. The OEM wiring harness has been hacked so many times... I am having a hard time finding the OEM wires that were used to power the Water Temp Gauge and the factory Oil Pressure gauge. Currently I only have a working Fuel Tank gauge and Volt Meter.
I'm not concerning myself with the Speedometer until I swap the T56 in and know that I have a working transmission /sending unit set up.

Any help you can suggest would be great! Thank you!

Ryan
If you're tach has a jumper bar it could be loose. The remedy is to solder a wire in its place.
 
TURNA

TURNA

Comic Book Super Hero
Jul 24, 2009
4,940
2,915
113
Socialist NY
#3
Do you still have the tach filter in place?
 
R

RGBody87

Apprentice
Jan 7, 2018
92
19
8
#4
If you're tach has a jumper bar it could be loose. The remedy is to solder a wire in its place.
I have never actually taken the gauges out or looked into anything yet, and if I'm being totally honest I do not know what you mean by a jumper bar. I have the factory GM manuals... but I have not looked at all the options for repair.

I noticed that the distributor has the 4 wires coming off of it, and one of them go to what looks like a small capacitor on the firewall. I was wondering if the difference in the ignition requires something that is not stock to the car or something of that nature.
 
R

RGBody87

Apprentice
Jan 7, 2018
92
19
8
#5
Do you still have the tach filter in place?
What is a tach filter? Where could it be found? I've never played with anything like this before.
 
pontiacgp

pontiacgp

Canadian Prime Minister
Mar 31, 2006
23,515
4,237
113
Kitchener, Ontario
#6
When I upgraded to an aftermarket tach I sent my defective stock tach to Bonnewagon who fixed it. Maybe if you contact him he can help you out.
 
GuysMonteSS

GuysMonteSS

G-Body Guru
May 21, 2011
906
384
63
Kentville,Nova Scotia,Canada
#7
I have never actually taken the gauges out or looked into anything yet, and if I'm being totally honest I do not know what you mean by a jumper bar. I have the factory GM manuals... but I have not looked at all the options for repair.

I noticed that the distributor has the 4 wires coming off of it, and one of them go to what looks like a small capacitor on the firewall. I was wondering if the difference in the ignition requires something that is not stock to the car or something of that nature.
That small capacitor looking thing is the tach filter.Try bypassing it and see if that helps.
If that dosent help,here is a write up that may help;
http://www.montecarloss.com/community/ubbthreads.php?ubb=showflat&Number=646206#Post646206
If you don't want to do that,call Mike at Mike's Montes;
http://www.mikesmontes.com/
Mike has new and rebuilt units.He might also be able to help if you need a harness or other gauges.
A great guy to deal with,he knows G Body's like the back of his hand.
Guy
 
R

RGBody87

Apprentice
Jan 7, 2018
92
19
8
#8
When I upgraded to an aftermarket tach I sent my defective stock tach to Bonnewagon who fixed it. Maybe if you contact him he can help you out.
Thank you, I might send him a message or reach out. I actually was unsure if it was the gauge itself or if it could have been something else associated with the wiring. I have a hacked rats nest of wires that are going to need some attention. Thank you!
 
R

RGBody87

Apprentice
Jan 7, 2018
92
19
8
#9
That small capacitor looking thing is the tach filter.Try bypassing it and see if that helps.
If that dosent help,here is a write up that may help;
http://www.montecarloss.com/community/ubbthreads.php?ubb=showflat&Number=646206#Post646206
If you don't want to do that,call Mike at Mike's Montes;
http://www.mikesmontes.com/
Mike has new and rebuilt units.He might also be able to help if you need a harness or other gauges.
A great guy to deal with,he knows G Body's like the back of his hand.
Guy
That is exactly what I'll do to start off. Than you!
 

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