Erratic tachometer reading? - Ford Truck Enthusiasts Forums



Erratic tachometer reading?

Reply
 
 
 
LinkBack Thread Tools Search this Thread
  #1  
Old 05-27-2006, 05:10 AM
Hellbore Hellbore is offline
Senior User
Thread Starter
 
Join Date: Apr 2006
Posts: 228
Hellbore is starting off with a positive reputation.
Erratic tachometer reading?

I have an Actron "auto troubleshooter" that cost me like 60 bucks at AutoPWN.

Unfortunately, the RPM measurement jumps around a lot. Any ideas why this would be?

My Duraspark module is new, dizzy rotor and cap are new, plugs are new, plug wires are new.

Engine is a rebuilt 360, sounds like it is idling very nicely but the tachometer reading jumps all over the place.

Tach is connected as the manual says to connect it.

I'm puzzled... the multimeter seems to work fine besides the RPM measurement...
Reply With Quote
  #2  
Old 05-27-2006, 10:21 AM
Putt's Avatar
Putt Putt is offline
Posting Guru
 
Join Date: Jul 2003
Location: Colville, Washington
Posts: 2,230
Putt is gaining momentum as a positive member of FTE.
Is it the inductive type pickup(wraps around a plug wire)? It may be that the sensor wire is too close to other plug wires or the coil wire and it is picking up more than one signal. The same thing can happen with the factory tach if the wire is too close to the plug wires.
Reply With Quote
  #3  
Old 05-27-2006, 02:58 PM
Hellbore Hellbore is offline
Senior User
Thread Starter
 
Join Date: Apr 2006
Posts: 228
Hellbore is starting off with a positive reputation.
It is the type of tach that connects one lead to the negative coil terminal, and one lead to ground.


I'll try moving spark plug wires away and see if that helps thanks.
Reply With Quote
  #4  
Old 05-30-2006, 04:18 PM
Freightrain's Avatar
Freightrain Freightrain is offline
Shiftoholic
 
Join Date: Jan 2003
Location: Ohio
Posts: 8,055
Freightrain is a name known to allFreightrain is a name known to allFreightrain is a name known to allFreightrain is a name known to allFreightrain is a name known to allFreightrain is a name known to all
Sounds like poor connection. It just takes the pulse signal from coil and creates a reading from it. If the coil or ground connection is at all loose it will create intermittent loss of signal thus causing erratic needle movement. Ya, sounds simple huh? LOL!!!

Make sure connections are tight, and when needle is jumping around, wiggle wires to see if that makes it better or worse.

Only the "inductive" type would be erractic if around other wires. This would be the clamp on style using the spark plug wire.
Reply With Quote
  #5  
Old 05-30-2006, 05:10 PM
Krewat's Avatar
Krewat Krewat is offline
Super Moderator
 
Join Date: Jul 2002
Location: Long Island USA
Posts: 36,746
Krewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputation
Try it on another vehicle and see if it still does it ...
Reply With Quote
  #6  
Old 05-30-2006, 05:16 PM
Hellbore Hellbore is offline
Senior User
Thread Starter
 
Join Date: Apr 2006
Posts: 228
Hellbore is starting off with a positive reputation.
Hey, I think I figured out what was causing it... It is a multimeter-type tach, and so far I had only used it while my timing light was hooked up. Well, that damn timing light must be a doozy because the tach works perfect when the timing light isn't connected.

I also noticed, by connecting and disconnecting the timing light while the engine was running, that when I connect the timing light to spark plug #1 wire, the engine actually runs worse! Crazy huh? Why would that happen? Does the timing light somehow rob some of the engine's spark?
Reply With Quote
  #7  
Old 05-30-2006, 05:53 PM
Krewat's Avatar
Krewat Krewat is offline
Super Moderator
 
Join Date: Jul 2002
Location: Long Island USA
Posts: 36,746
Krewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputationKrewat has a superb reputation
I take it your timing light has to be hooked in inline with the wire and plug? Your timing light might have a problem, as in, it's sparking internally.

The "engine running worse" is because #1 is misfiring
Reply With Quote
  #8  
Old 05-30-2006, 05:55 PM
Hellbore Hellbore is offline
Senior User
Thread Starter
 
Join Date: Apr 2006
Posts: 228
Hellbore is starting off with a positive reputation.
Well it's funny you mention that, I do think the light was sparking internally because when it was turned off (trigger not pushed) it was making a ticking noise inside.

Would that internal sparking cause the cylinder to misfire or does a timing light always make it misfire?
Reply With Quote
  #9  
Old 05-31-2006, 01:43 PM
Freightrain's Avatar
Freightrain Freightrain is offline
Shiftoholic
 
Join Date: Jan 2003
Location: Ohio
Posts: 8,055
Freightrain is a name known to allFreightrain is a name known to allFreightrain is a name known to allFreightrain is a name known to allFreightrain is a name known to allFreightrain is a name known to all
Depends on the type of timing light. The clamp on style WON'T create problems.

The other variation, that makes you insert it between the plug and the plug wire MIGHT create issues.
Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Tachometer Problem ericpbarnett 2009 - 2014 F150 0 10-24-2016 12:45 PM
Tachometer Install connection to Electronic Ignition BGF100 1973 - 1979 F-100 & Larger F-Series Trucks 10 10-15-2016 10:58 AM
Instrument Panel/Tach Help TheBlahMasta 1997 - 2003 F150 4 09-23-2015 07:20 PM
2004 F250 RN Tachometer reading high Little Mick 1999 to 2016 Super Duty 7 07-17-2015 10:03 AM
Tachometer Problem Toplait 1987 - 1996 F150 & Larger F-Series Trucks 1 06-08-2012 09:36 PM


Go Back   Ford Truck Enthusiasts Forums >

Tags
auto, coil, engine, erratic, f150, incorrect, induction, inductive, iradic, misfire, reading, readings, tach, tachometer, timing

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not 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

Forum Jump


All times are GMT -5. The time now is 07:07 PM.


This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. FordŽ is a registered trademark of the Ford Motor Company.