Testing a tach sensor and/or gage & harness?

[helidiesel]

Well it's been 2 years and I'm having the same issues are we still standing by. The fourm will not make it if we as poster don't finish the thread. Damn.

 

[93blklightning]

I'd really like to see your results as my tach doesn't work either . Only when I turn on a lot of other stuff like radio, headlights , defrost or ac , and windshield wipers . Then it only halfway works . I'm very interested in fixing mine also

Sent from my XT907 using Tapatalk

 

[rhkcommander]

loose wiring and bad grounding, corrosion, could be loose probably by the firewall. I haven't chased mine down to it yet but a lot of the stock wiring is crap.

My gauge with no tach sensor will "read" up to 800 or so RPM and go back down to 0. And it would work 50/50 when I did have the sensor on there. Still haven't had time to chase the problem out.

 

[OLDBULL8]

Well it's been 2 years and I'm having the same issues are we still standing by. The fourm will not make it if we as poster don't finish the thread. Damn.

Don't be so impatient, thread is only 2-1/2 years old.

If I waited that long to get info, and really wanted to fix something I would start my own thread. But since I ran into this thread, here is some info to try and fix your tach.

Now this info is from a 89 Ford manual, but should lead you to the fix.

Sorry this new computer, is screwed up as far as scanning, you'll have to print the pics out.

 

[jaluhn83]

What voltage you measure is going to be highly dependent on how good for meter you're using. At idle you're putting out about a 300 hz signal, going up to about 2.5 Khz at 3k rpm.... some cheap meters woln't pick up that high of frequency very well. I would say as long as you're getting a measurable voltage, the sensor is *probably* in decent condition. Certainly wouldn't worry too much about too high of voltage.

One thing I'd try would be checking the sensor output at the tach instead of the sensor - should be able to clip leads on the 2 screws on the back of the tach pretty easily.

One of these days I'll get a chance to play around with an o-scope on the tach sensor and see if I can see what actually comes off these things - something with the tach system on these trucks isn't designed very well.

Also worth noting that when you tighten the sensor be careful not to overtorque it - you can put the sensor apart if you do that.

 

[helidiesel]

ok men thanks for the info. here is the update so far
-tested old rpm/cam sensor OL replaced with new sensor that show 2.5 resitance (i think thats mega ohms..cant remeber without the meter infornt of me)
-with motor runing i could not get a reading on my crappy meter as stated above the numbers would jump but nothing stedy...
-at the sensor plug I tested for gound to the enging block and tested good
-rang the other sig wire all the way to the fire wall and it tested good..

so next the cluster will be removed and i will test the wiring there. my guestions are
-is the tach replacable its self?
-the rpm/cam sensor is pulse width modulation correct? meaning the out put of the sensor should be AC voltage
I have the injectors out right now so im not able to turn the motor over at this point to test the tach.... soon the new injectors will be here and i hope to get this pig smoke free and on the road....