Tachometer fails at 2K to 3K RPM

[gordyzx9r]

I'm ready to burn this car to the ground...or turn it into a really bad ass toaster.

I'll start from the beginning.

I have a 6 gauge Stewart Warner instrument cluster that I got from Tom Houser 4 or 5 years ago when he was selling them via his Performance Instruments business.  

It was working fine without any issues until recently.  I had a bunch of work done to the car by Fred's Turbo Performance and the problem manifested after that.

Here's what happens and what I've done so far to try to fix it.

• The tachometer started going to 0 RPM at 2K to 3K RPM after I had a bunch of stuff installed and some work done.
• I took the cluster out, bought a new tachometer, sent off to a place called Williamson's Instruments to have rewired into the cluster like Tom had it (Tom fell off the face of the earth and I can't reach him).  
• I reinstall the cluster, and it still fails, even with the new tachometer.
• I buy a cheap Sunpro tachometer from a local auto parts store and wire it up directly to test out the 'signal' (+ to the fuse box, - to a good ground, and the tachometer lead directly to the pigtail behind the alternator) and it works fine, no failures.  
• I hook the Sunpro up to the auxiliary harness like my cluster is configured and it works fine there too.
• I call Stewart Warner and their tech department is gone (they got rid of it because their tech guys were just calling their distributors for help) and all they can do is send me a free 10K RPM gauge because the 8K has been discontinued.
• So, I get the 10K gauge.  I also buy two VDO modulators from Casper's.  
• Just to test out something, I hook a modulator to one of the old 8K Stewart Warner tachometers and it flat lines at 0 as soon as I fire up the car.  
• I hook up the 10K Stewart Warner with a modulator, and it flat lines too when I fire it up.  I take the modulator off, and it fails between 2K to 3K RPM too.  
• So...the cheap Sunpro tachometer and the Scanmaster signals are never interrupted... but the Stewart Warner gauges seem to be getting interrupted somehow.

How?

Where is the tachometer signal coming from that goes to that pigtail by the alternator?  

How is the signal routed?

Can the signal be weakened by anything and it's just that the Stewart Warner can no longer pick it up (but the cheap Sunpro gauge can)?

I am so lost what to do now, it's been torn apart in the garage since November now...






The following is everything I had installed at Fred's.  I had taken it back to him to see if he could fix it but he couldn't find the problem.  I know allot of this is mundane and not related but if someone has installed something once that had a synergistic effect on something else then maybe they had the same issue I did and can shed some light:

Blistein Gas Shocks, Eibach Pro-Kit Rate Springs, Energy Suspension Bushings, Gbodyparts Tubular Upper Control Arms, Gbodyparts Tubular Lower Control Arms, Gbodyparts 15

[Steve Wood]

Zap handles tech over here!

[gordyzx9r]

Zap handles tech over here!

 I
lol...I'm doomed.  

I guess tomorrow, I'll see if I can trace some wires from the alarm brain.  That is if I can find the damn thing.  If it's just a matter of a few wires that weren't routed properly then maybe I'll be able to swing it.  If the whole damn alarm has to come out...I'm taking it in and getting a whole new system.  I'm so sick of these electrical gremlins.

[Top Speed]

Zap handles tech over here!

You are so screwed.   :rofl;

[87natty]

Send your SW tach to AutoMeter and have them install AutoMeter guts or use your SunPro guts. They'll do funky/fancy things to gauges, but at a price. They're really good with customer service.

[Steve Wood]

He ain't gonna do that.  He is just like me....pissed, and he ain't giving up!

Might just try disconnecting that wire you found spliced into the module and see what happens.

Or find someone else to stick the tach under the hood and connect to the battery and tach test connector and see if the tach works on their car.

[87natty]

Saw the thread on TBs now, I'd just hard wire the motherfucker to the coil module myself, granted if it works that way.

Might be a frequency issue, if the Viper might have anything to do with it. I've seen cars not run right just because the spark plug wires crossed each other wrong. Electricity is a funny thing.

Speaking of frequencies, anyone notice that a GN hums in the key of D at 2,000 rpms?

[gordyzx9r]

He ain't gonna do that.

[Steve Wood]

send me a tach, I will try it on one or both of my cars if you cannot find the problem.

[gordyzx9r]

send me a tach, I will try it on one or both of my cars if you cannot find the problem.

Works for me, I'll send it tomorrow.

Email me an address:

gordyzx9r@hotmail.com

And to rule it out, I'll put the modulators in there too.

[gordyzx9r]

On it's way...

Are we gonna start taking bets that the car is frying tachs or that the tach's are alright?

[Steve Wood]

This tach was/is definitely ok.  It worked perfectly from idle to 4000 rpm.....I am not much on blipping one out of gear any higher.

Worked correctly both at a gradual increase, and with quick blips....

Nice tach, imo.

[Steve Wood]

Sent it back to you this afternoon along with a spare Autometer tach that you can play with.  Feel free to keep it.

As I told you by email, I would guess it is either a module problem, or something you have wired into the module is causing interference.

[gordyzx9r]

Thanks for checking it out Steve.  At least now I know it's car sending discombobulate d signals to my gauges.  I've got a couple of ignition modules sitting around.  First I'll check out those grounds you mentioned in the email.  

I just remembered that I have one these CCCI Ignition Simulators too.

[Steve Wood]

The simulator works well with GM modules, but, not some aftermarket modules.

It will show, on the GM module, that the spark is good but does not check other things like spark bypass, etc.