Duramax7man7 506 #1 Posted November 7, 2016 Is there a way to test a tachometer at all? Mine is not working... It seemed to be almost moving backward... lol I know odd. Murphy's Law though over here... I swear. Share this post Link to post Share on other sites
gwest_ca-(File Mod) 11,246 #2 Posted November 7, 2016 This will likely not be of any help Garry 2 Share this post Link to post Share on other sites
cleat 7,030 #3 Posted November 7, 2016 About all you can do besides reading the guide above is to check all the connections. Remove all the wires one by one from the gauge then clean and reinstall. Check the connection at the voltage regulator making sure the tach is connected to the rear lug on the voltage regulator. Also the grey wire in the 9 pin. Actually clean all the connectors in the 9 pin. I am assuming you have a 520 at this point. 1 Share this post Link to post Share on other sites
Duramax7man7 506 #4 Posted November 7, 2016 (edited) Thank you both for the recommendation and link. I have that and shouldve looked in that first. smh. Yes it's the 520 and I completely removed the 9 pin molex, and replaced it with individual male to female pins one by one so I didn't mix up the colors. Everything is working fine (other than my high speed surging rpms) so hopefully this is my issue because the piggy back connector I have is connecting the grey wire on the stator lead on the front side of the rectifier. But I like keeping forum conversations going. I'm on other forums and facebook seems to be attracting other people. Seems like more of the narscisistic types though. "look at me"... Any I will try this and report back. I did place the grey wire on the rectifier lead that the original connection was. Figuring that it was the rectifier that was doing it. So I'll will switch them and see if that fixes. I already cleaned all connections and checked through the wiring harness before wrapping to pressure wash the frame. Edited November 7, 2016 by Mastiffman Share this post Link to post Share on other sites
Duramax7man7 506 #5 Posted November 7, 2016 Okay, so I did switch the leads and that did make the tach respond, but it's not coming down past 1500-1700 Rpms and takes a couple of minutes to get back down. But when I bring up the throttle it raises the tachs rpm to 3500-4000rpms.... Bad Tach? Share this post Link to post Share on other sites
cleat 7,030 #6 Posted November 7, 2016 Are you sure the engine is not running at that RPM ? What does it do when you turn the key off ? What does it show with the key on but engine not running ? Just asking because any tach's I have ever had either work or not, never half work. Share this post Link to post Share on other sites
Duramax7man7 506 #7 Posted November 8, 2016 Yes. It stays at the lowest that it will go if I let it idle down to that. If I shut if off after letting it idle down for just 20-30 seconds, the rpms will stay at 2800+ Same thing if I just turn the key on and no running. It's like it's gummed up inside or something. One thing I've noticed is that the new lamp and socket still doesn't illuminate the tach as well as the other gauges. Not sure if that's even relevant or not. I'm telling you, all of my conscious life I have experinced the most odd things. Abnormal from everyone else. Along with stuff that others experince. I'm not surprised when it happens at this point. Share this post Link to post Share on other sites
RubyCon1 63 #8 Posted November 8, 2016 (edited) I know I read about this on another post on this forum. I think SOI replied to a few posts regarding the electronics in this style gauge. The tach gauge you have is not a voltmeter that returns to zero thru mechanical action. This tach is based on air core technology used in airplanes. There is no mechanical zero only an electrical zero. Air core gauge pointers can span a full 360 degree rotation and tends to rest wherever the pointer is when the electrons inside the gauge loose voltage and shut off internally. . . . . there it is - lots of good info here and some examples of how the tach circuitry self destructs at times Edited November 8, 2016 by RubyCon1 1 Share this post Link to post Share on other sites
Duramax7man7 506 #9 Posted November 8, 2016 Thanks! Good info. I will recheck all connections again and potentially pull the tach for inspection and report back . Share this post Link to post Share on other sites
Duramax7man7 506 #10 Posted November 12, 2016 Okay., SO I tested everything and I'm still getting the same result. Tested the G, S and I. S and I were good. The ground was horrible. Like 78ohms. So I cleaned every ground that I could. All of the guage grounds. The grounds from chassis to hood stand. Hood stand to side panels and side panels to guage panel. Then I cleaned the ground post, nuts and washers on the tach and then put it all back together. My ground ohms matched the battery to chassis. Still the same result. Idles at 2500- 2800rpms and then goes higher to 3600 and 4000rpms is what it's reading. I'm guessing new tach? Share this post Link to post Share on other sites
RubyCon1 63 #11 Posted November 12, 2016 what are the actual RPM's of the engine when the tach is reading 2500 ? Share this post Link to post Share on other sites
Duramax7man7 506 #12 Posted November 12, 2016 Idle... Share this post Link to post Share on other sites
RubyCon1 63 #13 Posted November 12, 2016 the point I'm trying to make is maybe the engine is actually at 2500 rpm when the throttle control is at idle. Maybe the tach is telling the truth. Do you have an optical tach to act as a referee so we know what rpm the engine is actually at? Share this post Link to post Share on other sites
Duramax7man7 506 #14 Posted November 12, 2016 I have ears... lol- It's not running at 2500 rpms. No offense or anything. Share this post Link to post Share on other sites
RubyCon1 63 #15 Posted November 12, 2016 no offense taken since i'm not there to confirm your observation, we will all have to go with your judgment the tach is bad 1 Share this post Link to post Share on other sites
Duramax7man7 506 #16 Posted November 21, 2016 I've done everything that I can with this tach and it partially works. SO that says to me that its connections are working but it's not working properly. I have a used one coming in the mail tomorrow and that will be the tell all for the answer.... Share this post Link to post Share on other sites
Duramax7man7 506 #17 Posted November 21, 2016 Okay. So I got the new (used) tach in the mail today and all is well. And cool enough it's good to know that I can trust me ears still. The engine idle RPMs were just about dead on! I would say about 950-975 rpms... One thing I noticed about this new gauge once I even picked it up was that the needle moved freely and moved when I would turn the tach. The old tach wouldn't do that at all. So I pulled the old one apart and found that I was right. It's like the needle, which is ran off of some coils on the inside of its case but the way, is gummy somehow. Not sure of the bearings/ bushings are dirty or just melted somehow. I'd like to pull that apart and check it out. But the other thing I noticed was that these two coil looking pieces of metal were almost touching. One seemed to be dark. Like it was burned. There was a piece of thermal insulation between them but it was burn through. They were really close so I gently pried the outside one Way to create space between them... I'm wondering if this could fix it if eliminating any type of short. All of the rest of the components look good. There IC are all in tact and no burned areas in the Circuit board itself.... Some pics... Share this post Link to post Share on other sites
