Engine Stalling when tach is hooked up

[erik70rt]

As I'm going through all the electrical issues on my Barracuda, a new one has arisen.  When I hook the tach up to the negative side of the coil, it stalls the engine.  I've never had that before.  Anyone ever have this issue?  Factory tach.

[DAYLEY/CHALLENGER]

Sounds like a ground issue..............short in the wiring...............

My issue is when I hook up mine..............I can go down the road at 35mph and read 8000 RPM!!!

[JH27N0B]

Since I put my T/A back together, the factory tach reads about 2X what I think the rpms really are.  Stock dual point ignition.  Used to be fairly accurate back in the day when I had an Accel dual point distributor and Super Coil on it.
Sounds like we need a E Bodies.org factory tach guru to help all us members with tach issues! 

[A.Gramz]

I seem to remember a no start when tach wire connected thread may want to try a search possibly same issue?!?

[Jay Bee]

I think this is the thread that A.Gramz was referring to.
https://forum.e-bodies.org/electrical-and-audio/11/engine-wont-fire-when-tach-wire-hooked-to-coil/589/

[Racer57]

I've had the tach itself go bad and cause the engine to not start.

[erik70rt]

Thanks, everyone.  I'll get back in the garage this weekend and see if I can find the problem. 

[dodj]

As I'm going through all the electrical issues on my Barracuda, a new one has arisen.  When I hook the tach up to the negative side of the coil, it stalls the engine.  I've never had that before.  Anyone ever have this issue?  Factory tach.

Replace the tach. It is a common issue with the factory tach.....they are over 40 years old....Replace the guts with fresh stuff from rte.com

[1 Wild R/T]

http://rt-eng.com/rte/index.php/Main_Page

[dodj]

Thank you Wild 

[usraptor]

I had the exact same issue.  Took me several months to figure it out.  Below is my solution as indicated in the tread that Jay Bee referred to"

Finally, after 6 months I got the Cuda Tachometer working with the factory wiring.  Stumbled on the problem by accident and still don't know why it made a difference.  The "factory" connection on the back of the tach wire that goes to the coil is a bayonet connection.  There is a male connector on the back of the tach that is held on with the nut and the female connection on the tach wire slides onto that.  In desperation I ran a wire directly from the coil to the back of the tach to bypass the factory wiring.   I took the male bayonet connection off the back of the tach and just used a regular round crimp connection, tightened it down with the nut and the engine fired and the tach worked fine; So even though all my tests showed no shorts in the factory wiring after I had made numerous attempts during the past six months at finding a short, without success, I just gave up and decided to make this direct connection between the coil and tach permanent.   I had to cut both ends off the test wire to thread it through a small hole I drilled in the plastic bulkhead and just decided to put a bayonet connection on the end of the wire that connected to the back of the tach and  connect it to the factory male bayonet connection. When I did this the engine wouldn't start again!?@#$^*%#!!^%*&*.  I disconnected the wire at the coil and the engine fired right up!.  So thinking that the only thing different was the male and female bayonet connection on the back of the tach, I took the male connection off the tach, cut off the female connection from the factory wire and replaced it with a round connection like I had done during the initial test from coil directly to tach.   I reconnected the factory tach wire to the coil and the engine fired right up and my tach works!?  Have no ideal why the bayonet connection on the back of the tach caused it to short out the coil since it was the factory connection, but don't care now as my tach works with the factory wiring and I no longer have to spend hours twisted up under my dash trying to figure it out! 

[erik70rt]

I figured out the tach problem - the fiber washer for the ground was missing so the coil was grounding to the dash. 

I also have another issue with the temp and oil pressure gauges not working.  I pulled the dash all the way out to look at the circuit board and see if I could find a problem.  I am not familiar with the circuit boards on A-bodies, but when I look at this one, I can see that there is one section that is not "connected" to any of the pins that mount the main wiring harness.  There is a plastic cap at one end of this section, and the two gauges both are connected to this section.  Should there be a wire that connects to the post with the plastic cap that completes the circuit?  See pic. The section is on the left side and you can see the cap next to the wire for the fuel gauge limiter.

Thanks!

[erik70rt]

UPDATE:  I found there was a nut missing from under the plastic cap.  Installed one and now the oil pressure works fine, but the temp gauge spikes as soon as it gets power.  That says to me grounding issue.  All of the wiring and board is new and I traced them all to see if I could find the problem.  I didn't see anything out of the ordinary.  Anyone have an idea of why/where this could be grounding?

[73_Cuda_4_Me]

Disconnect at the sensor on the engine, and see if it still spikes... eliminate the sensor being shorted or damaged...

Make sure it's a temperature sensor and not a temperature switch! (you should get non-zero ohms from sensor post to engine ground when cold - something like 80-90 ohms, I think... someone correct me if this is incorrect)

If it still spikes, it's gauge or somewhere between gauge and plug for sensor short...

[erik70rt]

I disconnected the sensor and it still spiked.  Gauge worked fine before I replaced the board, so I'll have to pull it all out again.  Ugh.