Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Tachometer not working. Steps to diagnose?
#1
Hi all,

The rev counter has never worked since I've owned the car and I think it's about time I figure it out.

It's currently sat at 5000rpm. That's with the car running and also when the car is off and battery disconnected.

I do remember that at some points it will shift to another value and sit there instead (e.g. 3k). It's never gone down to 0.

So what should I check and in what order?

I reckon it's the tachometer itself. Either have to get it repaired or buy a replacement
#1373 - Black, Manual, Gas Flap

"Marty: Wait a minute, wait a minute, Doc, are you telling me that you built a time machine out of a delorean?

Doc: The way I see it, if you're gonna build a time machine into a car why not do it with some style..."
Reply
#2
Probably a mechanical breakdown inside the Tachometer as you've suggested.

Although you could check the integrity of the supply/gnd line at the Tachometer (Pin 9 on the 16 Pin Binnacle Plug for the 12V supply - Green and Pin 13 on the 16 Pin Binnacle Plug for the GND - Black) and the White/Slate stripe wire between all parties it connects to:

Tachometer (Pin 12 of the 16 pin connector)
Ignition COIL
Bulkhead connector (The pin 3rd up on the right hand side of the yellow plug)
Ignition ECU (Pin 7)
RPM Relay (Pin 31b)
Idle Speed ECU (Pin 12)

Another train of thought could be a dodgy Idle Speed or Ignition ECU (what ultimately drives everything else on that line). Would obviously help at that point to have a known good example of each to test with.
Rissy
Chris M. Morionem qui loquitur multus sine cogitatione.
(Forum Member 288)
(DOC Member 663)

May 1981 vin#1458
"LEX" aka "Wonkey" - Officially used in Britain's Greatest Machines (80's episode) with Chris Barrie.
Grey Wheels
Grooved, flapped Bonnet
Black Leather Interior
Chassis: #1073
Engine: #2839

Main Car(s):

2005 BMW M3 E46 Shape 3.246 Straight Six in Velvet Blue
1999 Honda Civic MB6 Shape 1.8VTi VTEC in Pirates Black
Reply
#3
Thanks Rissy!

Looking at the wiring diagram fo the white/slate stripe wire, I can see that multiple places it goes to, but I thought the only one I am worried about is the link from the coil to the tachometer?

Are all those other items also receiving the signal from the coil? If they were faulty why would it impact the connection between the coil and the tachometer?

Cheers!
#1373 - Black, Manual, Gas Flap

"Marty: Wait a minute, wait a minute, Doc, are you telling me that you built a time machine out of a delorean?

Doc: The way I see it, if you're gonna build a time machine into a car why not do it with some style..."
Reply
#4
That's why i said it's most likely a mechanical issue at the Tacho. But to be fair, i'm not an expert at that circuit, so i'm not sure if a dodgy ECU (either idle or Ignition) could have an outside influence on the Tacho. It's a negative terminal connection to the Coil, so i'm not sure how this becomes a "pulsed" signal for the Tacho to be energised by in order to convey that as a speed. Maybe someone more expert in that area could enlighten us all....?
Rissy
Chris M. Morionem qui loquitur multus sine cogitatione.
(Forum Member 288)
(DOC Member 663)

May 1981 vin#1458
"LEX" aka "Wonkey" - Officially used in Britain's Greatest Machines (80's episode) with Chris Barrie.
Grey Wheels
Grooved, flapped Bonnet
Black Leather Interior
Chassis: #1073
Engine: #2839

Main Car(s):

2005 BMW M3 E46 Shape 3.246 Straight Six in Velvet Blue
1999 Honda Civic MB6 Shape 1.8VTi VTEC in Pirates Black
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)