89' Tachometer install
 

Ok, started by reading the sticky's and there is a ton of information, but I didn't find where anyone has done what I want to do so I'll start a thread that covers these specific things.
So this is what I want to do and I'll try to explain how I intend to achieve my goals. I fully realize there are many ways to do things and my approach is only one of them.

I want to use the Stewart Warner Deluxe Series Tachometers 82620 0-3500 rpm. I feel this has the look and function I like. Plus it has a dip switch that can be set for 2ppr which would support the stock OEM harmonic balancer of a 90.5-93. This harmonic balancer is held on by four bolts and is interchangeable with the 89 balancer. This would then allow the use of the Cummins pickup and bracket. Two knowledgeable forum members have posted that the sensor is excited by 8vdc and this can be supplied by a 12vdc supply using a 8.2 vdc zener diode (1 watt) and a 300 ohm (1/2 watt) resistor. These are readily available although my local RS doesn't carry components any longer. If that works out to be too difficult I could switch the pickup for this one that actually is the recommended pickup, but that would make everything way too easy as I wouldn't need to mess with the zener and resistor. (Stewart Warner Performance Replacement Senders 82646)
I have a 90.5-93 balancer on the way and I may just go ahead and cut some more grooves in it before installing it. (option)
As for mounting, I want to use a cup and mount it in the corner of the dash on the pillar.
I'll continue to post up results as reality intervenes. As a added note the egr and boost gauges I'm thinking of installing in the dash itself.

Thanks, inputs are always appreciated.

Parts arrived, need to experiment a little..

http://imagizer.imageshack.us/v2/xq90/537/ro7ldK.jpg

I bought a tach a while back off a 1990. My truck is a 1993, so it's different in the way it picks up its signal. I'm looking forward to how all this goes together, sounds like you have it figured out.
Attachment 51504

Clifford, that looks exactly like what I'm trying to do. Question is that a OEM pickup? Was it used on a notched harmonic balancer?

Yes, to my knowledge this is all OEM and did use the notched HB. The plug on the tach is different than the 92's and 93's as well.

Do you know what voltage was used to power the sensor? 8 vdc is what I'm being told is OEM voltage, just wondering what might have driven yours.

Gotcha, thanks

Installed the notched harmonic balancer today. It was a bit of a PIA had to remove the fan and the bolts are torqued to 92 ft/lbs. Someone mentioned the belt pulley was smaller, but I did not find this to be true with the parts I used.
http://imagizer.imageshack.us/v2/xq90/661/ez1zoD.jpg

Ordered a few electrical parts needed to drive the pickup sensor. 8.2vdc zener and some resistors.

Gauges are on the way.. Going to use the SWW-82620 tach. It has dip switches that go as low as 2PPR.

Here's the diagram you asked for. There's a band on the zener diode. It denotes the cathode and goes to the top in the diagram.

300 ohms will supply from 0 to 13 ma to your sensor. If the voltage is low, use a lower value resistor. This should work, though.

Attachment 51489

Martin,
That was exactly what I was looking for.
I have a 270 ohm and several 10 ohm's resistors to adjust voltage with.
Thank you.

The voltage is pinned by the zener diode. It bypasses current not used by the circuit to maintain the voltage at 8.2V. 300 ohms disipates about 0.055 watts. About .1 watt is distributed between the zener and the load. If there's more load than that, the voltage will drop below the zener voltage and cease to be regulated.

The Zener voltage is nominal. It can vary by 5% or so.

Don't try to fine tune the voltage with resistors. The zener is what you get, live with it.

Gotcha, I bought several spares, so I can try others if the initial doesn't work the way I want it to.

Thanks,

Made a little progress, sensor is mounted. Anyone know the color code of the wires coming from the sensor itself?
Thanks,
http://imagizer.imageshack.us/v2/xq90/661/PB35l1.jpg

Pin out and color codes should be on this page.

Attachment 51430

That's great. I have the 89 service manual but that didn't help me with this.
YL- 8vdc
BK/LB - GRD
GY/PK- CKP pickup

Thanks,

This install is going really slow. I keep getting side lined. I have all the bits and pieces I need. Got the Tach physically mounted, had to get another longer cup to fit the tach and then modify it. The 25 year old plastic molding is brittle and I had to be very careful not to break it. I couldn't locate a female plug so I guess I'll cut off the plug and simply splice it together. Any way I'm getting it done slowly, heres a picture of the mounting.

http://imagizer.imageshack.us/v2/xq90/910/MMdL0e.jpg

I like the Tach...has a bit of a retro feel to it.:cool:

Thanks, I too like the retro look, especially in the old girl...

Really like the looks of your setup, unfortunately i cant justify not using the isspro tach that i got for free! Maybe somewhere down the road ill upgrade and dig up this thread [cool]

I've received the female end of the plug so I'm going to try wiring it up today.

Wired it up and tested it. It idles at 600 rpm, revs to above 1000-1500 then drops to zero. Let up and it goes back to showing idle. I'm thinking it is losing signal, probably the gap is wrong. Anyone have similar problem?

Reset the gap a couple of times both a little on the tight side and at .050. Voltage is 8.3vdc. Idles at 600 rpm, looks solid. Raise the rpm up and it looks good until 1300 and then loses signal and the tach drops to zero. Lower rpm and it re-sync's. Anyone with any ideas?

What voltage is at 8.3v? If you're using a stock CPS, 8v would be supply, output goes between 5V and near ground (usually about 0.3v).

Does the Tach match the application?

Jim,
This is lashed together from pieces I bought. OEM harmonic hub and pickup. 8vdc supply from a zener and the signal output straight to a SW tach set to two PPR. No pmc installed. I don't have a Oscope so really don't know what the signal looks like. Works up to 1300 rpm and then loses sync.

I suspect the tach is looking for a wider pulse by about 5:1 of what it's getting. It would help to have some specs for the tachometer. Also, what's the supply voltage at rpm when the tach fails? Maybe I guessed the wrong resistor value.

The voltage is stable, I'm guessing you are spot on with the value. The only spec sheet I have found is the setup sheet. But the symptoms looks to me to be signal loss.

http://static.summitracing.com/globa.../sww-82620.pdf

You need to hook up a oscilloscope and watch what the signal is doing.
Have you tried just feeding the cps 12v? It's just a hall sensor. Just a thought.

The stock CPS is normally supplied with 8V from the PCM. I believe internally it's further divided or regulated down to 5V. 12V might burn it out.

Pulled it apart and re-installed everything checking as I rewired it. Found a grounding issue and initially ran separate wires straight from one end to the other. Really thought that would correct the problem. wrong. The signal output is around 5.3 and steady through the rpm range. My meter indicated it was a AC voltage. So the best I can figure is the sensor is bad (used item) or the tach, which is new and works up to 1500 rpm and then loses synch. I followed the ground wires and found a loose screw/connection on the cross member near the negative terminal on the battery. Added a second ground and fixed the loose one. Ordered a universal two wire pickup and should have it in a few days and start the installation over again. Almost hope it is the Tach as I like the ruggedness of the OEM pickup.

You can't tell anything with a meter and the engine running. It is a pulse train.

You can hook up a dc meter to the output and you'll find that the state change from 5v to near ground (or vice versa) as you slowly turn the engine so the notch on the damper goes past the sensor. If it works thus, the odds of it failing at speed are close to nil.

Without confirmation that the tach matches the application, or a definitive set of specifications, this is an exercise in futility.

Yep, without proper test equipment I can't diagnose what is actually happening to know the problem. Will experiment a little to find a workable solution.
Thanks,

Success, Removed the OEM pickup and installed a ISSPO magnetic pickup and the tach works great.

One last thing, I want to power the gauge light, But at something about half as bright as full power. What would be an estimate of resistor value should I use?

Thanks,

What's the part number of the bulb? You could run the dimmed dash lamp circuit to it.

Jim,
It's an incandescent bulb. I'll need to pull the gauge back out to look at it.
Thanks,

If you can put an ammeter (the one in a little multimeter will work fine) in series with the lamp and measure the current drawn at full voltage. That is is what I need to know.

Jim, I can do that, might take a day or two, I'm a little under the weather today.


Thanks,

Name's John, or J. An incandescent light bulb changes resistance drastically as the filament heats up. That's why a simple resistance measurement isn't sufficient.

Back when I was cutting my teeth in radio, that principle was used to stabilize a cathode heater temperature in high end short wave radios. It was called a ballast tube. (1955 or so)