Erattic Tach

[goes2fast]

I'm wondering if anyone has had this problem, and has a solution? I got my dash together and installed recently, and everything worked great for the first few days. Now at random times my factory tach starts reading eratticly. It seems to be worse when the engine is under load, but the engine is running fine, I'm hoping someone has a fix for this, Thanks in advance. :huh:

[datto510]

Check your ground wire.

[datzenmike]

My '70 dart had points and when they were worn the tach acted up. If you have points check them carefully. If EI dizzy look for loose wires on the matchbox or coil and the back of the tach..

[goes2fast]

I guess i should have stated, it's in a 79 620 and is plugged in to the factory wiring harness, all fresh connections. :P

[Braden]

dude this is happenging to me too and its damn annoying when im winding it out!!! mine didnt act up untill i installed a matchbox dizzy.

[danfiveten]

Sometimes its just when tachs get old ie noticed. My 510 never had problems, but over the years he tach has been getting worse and worse. If i hit it it decides to work correctly for a certain time, and in really hot water it works perfectly.

[DISLEXICDIME]

is it jumping or spinning back words? if its jumping ground better check the connection at the coil if its loose it will jump. if it spin's back words its your alt.

[Braden]

hey i actually installed the matchbox and the satrun alt at the same time, if i wired up something wrong could it be the cause of my tach jumping up? if it was getting two signals maybe?

[ggzilla]

Datsun tachometers work fine with matchbox distributors. Most likely it is the wiring... there is a loose wire someplace. Happened to me too.

[dat521gatherer]

i just googles this yesterday cause mine jumps around when cold but not as much when warmed up. I have a l16 with matchbox. most sites say to checking wiring and grounds. plugs and plug wires. coil and ignitor.

 

i havent found my problem yet. truck runs fine when it's jumping though.

[zed]

I have this problem with my aftermarket tach on my L18. I'm also running an Ignitor and Magfire coil. All my connections are tight. I even bought another tach and tried it - same problem. The same tach does not jump on my Toyota truck, which also has an Ignitor and Magfire 40kv coil

[DISLEXICDIME]

I have this problem with my aftermarket tach on my L18. I'm also running an Ignitor and Magfire coil. All my connections are tight. I even bought another tach and tried it - same problem. The same tach does not jump on my Toyota truck, which also has an Ignitor and Magfire 40kv coil

 

when my coil was getting old it did this then i changed the coil and it stopped.

[imtb]

Mine was doing the same thing. Do you have it wired to the coil? I wired right to the Black box dizzy and it works fine now. Maybe give that a try.

[Braden]

is the trigger wire on a 77 620 solid light blue color? mine is wired to the coil when it used to be wired to the ballast resistor

[ggzilla]

Did you put the condensor back on the coil? That is for reducing EMI.

[Braden]

there is no condensor on the coil, never was, i guess it was always internal? somebody clarify this? i am running msd blaster 2. i notcied earlier my tach only acts up at rpms above 3000,after that its is all erratic

[ggzilla]

The condensor is not needed. With a points distributor it is required. But with EI, not required, but they are fitted to reduce electromagnetic interference, for example so the radio doesn't pick up electronic noise. I dunno may it affects the tachometer?

[imtb]

Did you try hooking it straight to the negative side of the black box? Mine was acting up above 3000rpms and when I hook it up the black box, it worked perfect!

[john510]

The factory tach in my 510 was erratic with inconsistent readings for years,it finally died.I hooked up an aftermarket tach just to make sure it wasnt wiring or a bad connection somewhere.The aftermarket worked fine. I took the factory tach to a repair shop and had it tested,it was shot.I ended up buying another factory tach on E-bay.

[goes2fast]

Thanks for all the suggestions, for now it has stopped acting up, so it will do no good to try them, I think since it is connected to the factory wiring harness and plug, the most likely cause is that the coil may be getting tired. I'm planing to upgrade to a multispark ignition in the near future. If the coil holds out til then, the coil will get replaced along with the new system. I wish Pertronics made the Igniter III the Datsuns, then I would get a points style distributor, and convert it, and have everything under the distributor cap. They are the coolest tech, I have one in my 57 Chevy, looks like a stock distributor, but has the latest tech hidden underneath. The only one they make for Datsuns is the Igniter I, which is just an electronic conversion. :cool:

[hang_510]

the rotor(not the part that contacts inside the cap) on my dizzy had a small chip in it, was very hard to see.

that shit pissed me off for months.

i replaced it, prob gone! :)

[zed]

I moved the tach trigger wire from the positive to the negative post on the coil as someone suggested here - it works much better! thanks

[ggzilla]

Glad to hear it is working... another success story.

[Braden]

if i could get my truck runnig i would try and fix mine

[jun]

I'll add that relocating my coil to the core support, next to the radiator (in efforts to clean up the engine bay) didn't fare well. I got erratic tach readings after my engine warmed up, and affected the running some. Maybe the heat off the radiator was causing it, or some interference with other wiring. I moved it back to the stock location and all is fine. Something to consider if you've moved the coil elsewhere.