Tach issues. Please Help.

[getdowngranny]

The problem is that the little digital tach on the dash and my autometer tach are working intermittently. The auto meter tach is hooked up to the green plug/white wire in the engine compartment. Both gauges work together when they want to. Where should i start chasing the wire down to? Im guessing i should start at the ignition control module, am i right? Where do they both feed from in common to start from there? The rpms work fine on the scanmaster. I took the day off to fix this and would greatly appreciate the help. On another note i had an alarm installed yesterday and since then my knock guage is all out of wack. One of the knock led's stay lit the whole time since the install. Any info?

 

[getdowngranny]

Ok, so i tapped into the white wire coming out if the ignition module which is supposed to be the tach output, well no luck on the tach, tried a known good tach and no good also. I tried to see if maybe it was shorted out by putting the negative lead of the test light on the white wire and the positive on the positive post and no voltage was present so i figured no short. Does that mean that my module is bad?

 

[getdowngranny]

ttt

 

[getdowngranny]

ttt

 

[getdowngranny]

ttt. someone please chime in.

 

[The_Six]

Im not up to speed on the digital dash but I tihnk to use the autometer tach you need a tach signal convertor http://www.casperselectronics.com/store2/product_info.php?cPath=5_6_10&products_id=598.
For the knock Gauge check the conections the guage should be conected to the yellow wire with black stripe going in to the ECM B7. If conection is good there check the ground wire and power wire maybe they tapped in to the same sorce for the alarm.

 

[getdowngranny]

Its not a digital dash, its the analog dash with the little digital tach. I have tapped right into the white wire coming out the the ignition module and nothing. I was just wondering if thats enough evidence to call the module bad.

 

[getdowngranny]

ttt

 

[Joe 1320]

every once in a blue moon, my VDO tach won't register until the engine gets revved. Not sure if it's related but it sure would be nice to find out. It's tapped into the tach feed behind the alternator as well.

 

[GNVenom]

There is not enough signal to drive both the stock tach/boost module and an additional tachometer. You need to use an amplifier to extract the signal for your tach, in order to have them both work.

Otherwise, remove the wiring to the dash LED tach and dedicate that wire to the aftermarket tach.

One note though; the typical tach won't work since the signal is only around 7 volts. Using the amplifier solves that problem.

 

[getdowngranny]

The thing is that when i disconnect my autometer tach off of the feed, the stock tach still doesnt work. Do you thing the amplifier will fix my issue or do i need to keep chasing it?

 

[GNVenom]

The module won't fix a bad tach. You have a common problem with your tach and it needs repair:

http://www.installationinstructions.com/FYI/tachboost.pdf

That should explain it.

 

[jburnsinnj]

I have been using an Auto Meter tach in conjunction with the dash display tach (series of horizontal lights) for twenty years and never needed an amplifier. Auto meter hooked to green tach wire under hood and 12 volt tapped into "ignition on" fuse.

 

[getdowngranny]

So, a bad stock LED tach will cause the white/tach wire not to output any signal? I have tried 2 different known good tachs both off of the white wire with green plug and i also tapped right into the white wire on the module plug. Both no-go's. This has been an intermittent issue, it will work fine for 6 days out of the yaer the rest of the time nothing.

 

[Scott87]

Suscribing.

 

[Turbo Loyd]

How about trying a pull up resister to increase the voltage off the tach wire to drive the aftermarket tachometer.

Borrowed the sketch from another board . . . the "ECM" would be the "CCCC" module on the Turbo Regal

 

[GNVenom]

So, a bad stock LED tach will cause the white/tach wire not to output any signal? I have tried 2 different known good tachs both off of the white wire with green plug and i also tapped right into the white wire on the module plug. Both no-go's. This has been an intermittent issue, it will work fine for 6 days out of the yaer the rest of the time nothing.

No, a bad tach won't take the signal down. What does take it down could be one of two things: 1. Bad connection at pin E of the CCCI Module, or 2. Corroded wire connection in the green connector. I've seen this happen frequently. There are two white wires (or used to be white, probably look yellow or brown by now) crimped together on a 6.3mm male terminal in the green connector housing. Since it's unsealed, corrosion sets in.

My recommendation: If you need to use this connection, cut the green housing and terminal off, strip and sandpaper the wires, then solder them together along with your tap on this wire that goes to the new tach. Be SURE the copper conductors are sanded clean before you solder them because by now, the wiring is very well tarnished and corroded. Solder won't stick to tarnished copper.