Tach wire shutting down my engine - Team Camaro Tech
Electrical & Wiring Troubleshooting electrical.

 
LinkBack Thread Tools Display Modes
post #1 of 14 (permalink) Old Apr 24th, 12, 08:50 PM Thread Starter
Tech Team
CHOPS
 
Join Date: Dec 2011
Location: La
Posts: 58
Tach wire shutting down my engine

I can't make this crap up. So after my 4 month ordeal with my 6 speed trans I finally get it out for a cruise with my daughter and I broke down. The distributor cap broke (torque made it hit the firewall) and tore the rotor all to hell. Fine, I throw another one on and make my way home and it starts to run like crap. I pull over, mess with the cap, get it to start again and make it home. I go to start it and nothing. Long story short after replacing the cap, rotor, coil, module, and a whole new distributor I got nothing. Finally trouble shoot it to the factory tach wire going to the cap. Ohmed it out and it reads 0.3. Is this normal? If I hook it up the car won't start. Why will the tach wire shut the car off if it's grounded? Did I fry my tach? How do I test it? I did install a DIY tach filter and everything did work for over 100 miles. This car is going to give me an ulser.
BUFFDRIVER is offline  
Sponsored Links
Advertisement
 
post #2 of 14 (permalink) Old Apr 25th, 12, 04:42 AM
Super Moderator
Jake-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 29,444
Re: Tach wire shutting down my engine

I would suspect the filter 'bit the dirt'. The filter blocks the DC voltage but passes the AC component, the tach pulses, to the tach input coil and you are reading the primary winding of the coil circuit.
Time for an aftermarket tach.........

Give a man a rescued dog for the health of both their souls.
'With age comes wisdom, but then wisdom ages you even more.'Other Stuff' CUBS - 2016 World Series Champions
Everett#2390 is offline  
post #3 of 14 (permalink) Old Apr 25th, 12, 02:06 PM
Senior Tech
 
Join Date: May 2004
Location: Southeast PA
Posts: 8,303
Re: Tach wire shutting down my engine

Yup. When I was trying to troubleshoot if my OE tach was completely dead or just needed a signal filter, I made an adjustable one as described in the thread, to make sure I made one with the right components. When I turned the knob trying to find the setting needed to make the tach move, I found I could shut off the engine with the knob. So I gave up on the filter idea and set the tach out for rebuild (which it needed anyway, because it was completely dead). But I had never experienced such a small circuit killing the whole ignition like that.

Eric
69 'vert project big block/TKO 600 RR
68 'vert driver RS clone -- gone!
Eric Kammerer is offline  
post #4 of 14 (permalink) Old Apr 25th, 12, 05:39 PM Thread Starter
Tech Team
CHOPS
 
Join Date: Dec 2011
Location: La
Posts: 58
Re: Tach wire shutting down my engine

I'm wondering if when the rotor let go the metal could have shorted something out under the cap.
BUFFDRIVER is offline  
post #5 of 14 (permalink) Old Apr 26th, 12, 10:03 AM Thread Starter
Tech Team
CHOPS
 
Join Date: Dec 2011
Location: La
Posts: 58
Re: Tach wire shutting down my engine

GOOD NEWS! It was the filter. The tach works fine without it.
BUFFDRIVER is offline  
post #6 of 14 (permalink) Old Apr 26th, 12, 08:13 PM
Senior Tech
Jim
 
Join Date: Jul 2005
Location: MA
Posts: 1,915
Send a message via Yahoo to go2fast
Re: Tach wire shutting down my engine

We used to use the tach line for kill switches at the Chevy dealer I worked at many years ago.
go2fast is offline  
post #7 of 14 (permalink) Old Apr 26th, 12, 10:15 PM
Senior Tech
Steps
 
Join Date: Dec 2005
Location: New Zealand
Posts: 13,315
Re: Tach wire shutting down my engine

Quote:
We used to use the tach line for kill switches at the Chevy dealer I worked at many years ago.
That is a bit of useful information....
Thoughts on that Everett any issues that could arise?
Steptoe is offline  
post #8 of 14 (permalink) Old Apr 26th, 12, 10:41 PM
Senior Tech
Steiner
 
Join Date: Mar 2009
Location: Lyman, SC
Posts: 8,349
Re: Tach wire shutting down my engine

Probably isn't an issue unless ignition power is left on for awhile with the kill switch engaged. Otherwise it's like leaving the key on in a points system with the points closed although the points will about always give it up first.

'69 Camaro
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
500hp/538lbft
www.cmengines.com
'69 Camaro Beater-SFT 327-M20-Moser 4.10-sold
'02 Z/28 vert-stock-sold and totaled
Steiner is offline  
post #9 of 14 (permalink) Old Apr 27th, 12, 04:26 AM
Super Moderator
Jake-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 29,444
Re: Tach wire shutting down my engine

As Steiner suggested, not an issue, if used momentarily.
If ign switch left on and wire still grounded, contacts on point set will 'weld' themselves together.

Give a man a rescued dog for the health of both their souls.
'With age comes wisdom, but then wisdom ages you even more.'Other Stuff' CUBS - 2016 World Series Champions
Everett#2390 is offline  
post #10 of 14 (permalink) Old Apr 27th, 12, 08:08 PM
Senior Tech
Steps
 
Join Date: Dec 2005
Location: New Zealand
Posts: 13,315
Re: Tach wire shutting down my engine

With GM HEI not sure if u guys know this but leave the key on and the module switches off by itself...u cant burn out the coil etc.
And from above...dont understand this
Quote:
The distributor cap broke (torque made it hit the firewall) and tore the rotor all to hell.
How can a dizzy hit the firewall when engine movement is lateral???
Even ripping apart a engine mount and having a wide cap GM HEI it cant hit the firewall.
Steptoe is offline  
post #11 of 14 (permalink) Old Apr 27th, 12, 08:41 PM
Senior Tech
Steiner
 
Join Date: Mar 2009
Location: Lyman, SC
Posts: 8,349
Re: Tach wire shutting down my engine

Yes, that's what a I was referring to and just comparing it to leaving points system turned on. Kill switch should only be an issue on a points system with key left on since it would power the coil to ground. No issue with the points themselves unless they were also closed and still probably not an issue as the kill switch would be parallel with the points and most likely be best path to ground.

With an HEI you'd still have the issue of coil heating up after awhile if using a simple kill switch because you'd still be powering the coil with a ground connected to the negative terminal which is not the same state as when just the key is turned on.

Bottom line is that it's not good for any dc coil to be left with power on the positive and straight ground on the negative for a long time. I reckon you could add an rc circuit or just a resistor to it to protect the coil like the condensor but for a simple kill switch there's no reason to since who leaves their key on and then just walks away from the car? OK, me when I used to listen to the radio in my dad's truck but that's about it.

'69 Camaro
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
500hp/538lbft
www.cmengines.com
'69 Camaro Beater-SFT 327-M20-Moser 4.10-sold
'02 Z/28 vert-stock-sold and totaled
Steiner is offline  
post #12 of 14 (permalink) Old Apr 27th, 12, 08:50 PM
Senior Tech
Jim
 
Join Date: Jul 2005
Location: MA
Posts: 1,915
Send a message via Yahoo to go2fast
Re: Tach wire shutting down my engine

Quote:
Originally Posted by Everett#2390 View Post
As Steiner suggested, not an issue, if used momentarily.
If ign switch left on and wire still grounded, contacts on point set will 'weld' themselves together.

I'm sorry, but this makes no sense. The points ground the coil. So putting a switch on the negative of the coil (to ground) bypasses the points entirely. The coil and resistor wire will draw a little current, but that's about it. Besides, I thought we were talking about an HEI?
go2fast is offline  
post #13 of 14 (permalink) Old Apr 27th, 12, 09:00 PM
Senior Tech
Steiner
 
Join Date: Mar 2009
Location: Lyman, SC
Posts: 8,349
Re: Tach wire shutting down my engine

Quote:
Originally Posted by go2fast View Post
I'm sorry, but this makes no sense. The points ground the coil. So putting a switch on the negative of the coil (to ground) bypasses the points entirely. The coil and resistor wire will draw a little current, but that's about it. Besides, I thought we were talking about an HEI?

You're right. See above. I just mentioned the points as a comparison to what it's like just grounding the igition system...as in you can damage something if left for awhile. I think Everett was just making a quick response that came out wrong.

'69 Camaro
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
500hp/538lbft
www.cmengines.com
'69 Camaro Beater-SFT 327-M20-Moser 4.10-sold
'02 Z/28 vert-stock-sold and totaled
Steiner is offline  
post #14 of 14 (permalink) Old Apr 28th, 12, 07:55 AM
Super Moderator
Jake-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 29,444
Re: Tach wire shutting down my engine

Steiner's right, I reread this AM, and it doesn't read correctly.
I honestly don't know what I was thinking................

Give a man a rescued dog for the health of both their souls.
'With age comes wisdom, but then wisdom ages you even more.'Other Stuff' CUBS - 2016 World Series Champions
Everett#2390 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome