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Old 06-04-2020, 07:05 PM   #1
Mini-Skoolie
 
Join Date: Jul 2019
Location: Asheville, NC
Posts: 42
Year: 1988
Coachwork: GMC
Wiring up dash gauges? (Tachometer)

Hey all, trying to install a 4 wire tachometer today. Got all the wires hooked up properly except that funky green wire, which is supposed to go to the distributor.

Every single YouTube video on the subject shows every distributor shown as having a “tach” port specifically made for that wire.

These are all most likely newer model cars. I’m working with an ‘88 GMC Bluebird with the 8.2L Detroit Diesel “fuel pincher” engine.

I certainly couldn’t claim to be an engine expert, but I believe I found what certainly appears to be the distributor. This distributor of course does NOT have a tach port. So, I ran the green distributor wire to the negative side of the ignition coil, which is the only other thing I’ve seen people do.

When started up, you can tell it has power because the needle moves upon startup, and I tested the power with a voltmeter as well.

But the issue is that I’m not getting a reading at all from the distributor.


What would be your next plan of action in this situation?


I’ve attached some photos for reference. One is a photo of the engine, and there are a few of the distributor, the ignition coil as currently wired, as well as a wiring diagram.


Thanks for your input! It’s always appreciated.
Attached Thumbnails
596AB571-05E3-49F8-930C-4CB78D84054E.jpeg   0B29FD8A-65FF-4C60-8709-BE420F76BCC3.jpeg   BC70DABC-BD61-462A-B66F-1F996F80510F.jpg   02962286-C2E7-416C-95FC-6EB2A07C0ABD.jpg   A8A3E472-80BC-4945-8E9E-52727A7D341F.jpg  


silvermachine is offline   Reply With Quote
Old 06-04-2020, 09:17 PM   #2
Bus Crazy
 
Join Date: Jun 2016
Location: Orange County, CA
Posts: 1,356
Year: 1990
Coachwork: Crown, integral. (With 2kW of tiltable solar)
Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
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Diesel engines don't have distributors or ignition coils! It appears you bought a tachometer for gasoline engines - you need a tach for diesels. Their signal inputs are different: diesel tachs get their signal either from the alternator's W or S terminal or from a separate dedicated signal generator. In addition, most diesel tachs will have a scale that reads to a lower maximum RPM than gasoline tachs. See if you can exchange your tach for a diesel one, and get one with only as much RPM scale as your engine needs, i.e. don't buy a 5000 RPM tach for a 2100 RPM engine!

I just finished replacing my old Teleflex 4000 RPM tach that was beginning to have spastic twitches - I got a VDO 3000 RPM tach which has much better resolution, and a new Leece-Neville alternator because my old one had weak field windings that wouldn't have lasted much longer. It's better to change it now than to be stranded on the road with a dead bus.

Good luck, John
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Old 06-05-2020, 01:57 AM   #3
Mini-Skoolie
 
Join Date: Jul 2019
Location: Asheville, NC
Posts: 42
Year: 1988
Coachwork: GMC
Well...! That sure explains it. There seemed to be an extreme shortage on information on diesel distributors, and now I can see why! Oh well, I suppose I’ll leave this thread up for others to learn from my mistake.

For any wondering, this is the wireless diesel tachometer I ended up buying from AutoHack. It’s wireless which is definitely a plus. It’s rather hard to find a decent diesel tach and corresponding sensor for cheap. This one seems to do the trick!

https://autohackguys.com/shop/black-diesel-gauge/
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Old 06-05-2020, 07:25 AM   #4
Bus Geek
 
Join Date: May 2014
Location: West Ohio
Posts: 3,660
Year: 1984
Coachwork: Bluebird
Chassis: International 1753
Engine: 6.9 International
Rated Cap: 65
Or, if you like the tachometer you have, you can use an interface from dakota digital that takes an rpm signal from your engine and converts it to a signal that can be read by your tach.

https://www.dakotadigital.com/index....rod/prd128.htm

On my bus, it had a factory option for a tach, but all the NOS ones that I could find were for gasoline engines. So I installed a gas engine tach, the box in the link above, and a crank sensor reading the teeth off the ring gear on the flywheel.
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