I can't find any open plug at the cap area (like the older HEI), but I do have a white wire coming from the coil not plugged into anything...is this the tach plug?
Rene
Rene
Last edited:
CK5
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Factory Tach in a VSS cluster, vids added.
- Thread starter tRustyK5
- Start date
bp71k5
3/4 ton status
yep!
Thanks man!
Rene
Rene
OK, I tried to post this earlier and had some puter issues I guess.
I have the factory tach and small fuel guage in the 90 VSS cluster. Having a good look at each one I figured it was the easiest way. I traced the circuits on both PC sheets for the fuel guage and found enough similarities that I took a chance and wired the guage directly. It worked, I had the small fuel guage wired by itself to the wires i identified and it read what it should read.
I did some creative hacking on the cluster body for the small fuel guage, and also for the tach so the wiring for the tach could come in from the rear. It's a seperate 3 wire harness. Ground, keyed hot and tach signal.
The donor truck I got this from was all hooked up and I didn't see any splices...except on the tach signal wire where there is what looks like a condenser. I "assumed" it was a noise filter.
So here is what it does when the engine is running. It reads higher than my ear tells me it's revving. High cold idle the tach shows about 2800 rpm, eventually settling at 1700 rpm after 5 minutes. My ear says roughly 700 rpm after 5 minutes.
Rev it up and it gets weird. Steady increase in throttle watching for full range of the tach. Tach goes up to 4000, then drops down to 3000 (as R's are still increasing) and then continues upward to 4200 or so...at this point my ear says true revs are between 4000 and 4500 rpm. As I let off the throttle it does the reverse.
I'm going to remove that condenser/filter and see if things change at all.
Anyone have experience with these old factory tachs? I'd sure love to have this work somewhat correctly.
Rene
I have the factory tach and small fuel guage in the 90 VSS cluster. Having a good look at each one I figured it was the easiest way. I traced the circuits on both PC sheets for the fuel guage and found enough similarities that I took a chance and wired the guage directly. It worked, I had the small fuel guage wired by itself to the wires i identified and it read what it should read.
I did some creative hacking on the cluster body for the small fuel guage, and also for the tach so the wiring for the tach could come in from the rear. It's a seperate 3 wire harness. Ground, keyed hot and tach signal.
The donor truck I got this from was all hooked up and I didn't see any splices...except on the tach signal wire where there is what looks like a condenser. I "assumed" it was a noise filter.
So here is what it does when the engine is running. It reads higher than my ear tells me it's revving. High cold idle the tach shows about 2800 rpm, eventually settling at 1700 rpm after 5 minutes. My ear says roughly 700 rpm after 5 minutes.
Rev it up and it gets weird. Steady increase in throttle watching for full range of the tach. Tach goes up to 4000, then drops down to 3000 (as R's are still increasing) and then continues upward to 4200 or so...at this point my ear says true revs are between 4000 and 4500 rpm. As I let off the throttle it does the reverse.
I'm going to remove that condenser/filter and see if things change at all.
Anyone have experience with these old factory tachs? I'd sure love to have this work somewhat correctly.
Rene
bp71k5
3/4 ton status
I can't remember all the details, but i do remember that when i was going to try hooking up my old tach to the tach wire on the coil, I read somewhere that the tach signal from the TBI system is a pure "square wave" rather than whatever other type of signal the old style tachs use. There's a filter or device I've read about that adapts the two and I don't remember it being very expensive.
A new tach was my solution.
A new tach was my solution.
Well, I don't know what to say other than when I removed that condenser looking thing and wired the tach signal directly the tach works perfectly now. It's smooth, no longer does anything weird and reads what my ear says it should be reading. Cold high idle the tach reads 1250 or so and drops to about 850 within 5 minutes. Snapping the throttle it reads smoothly right to 5000+ now.
I'll clean things up a bit and get it mounted properly and take some vid.
Rene
I'll clean things up a bit and get it mounted properly and take some vid.
Rene
I didn't have that filter on my old 87 or my 84, both worked great and was OK far as accuracy goes.
OK, my daughter took some vid for you guys. First is the tach and the guages and stuff, second is the noise filter/condenser looking thing.
This is the noise filter thing that caused the tach to not work properly.
Rene
This is the noise filter thing that caused the tach to not work properly.
Rene
Last edited by a moderator:
Oh yeah, mileage is in kilometers in case you're wondering. 420,067 is what it reads. 
Rene
Rene
Now that is cool.
That's the way GM should have made all of the gauges in the first place, I have no idea why they didn't.
That's the way GM should have made all of the gauges in the first place, I have no idea why they didn't.
