Intermittant tach

[Turbo Brian]

Trying to track down an intermittant tach. I have switched in a known good dash cluster and it too was intermittant. I checked the wiring diagrams on the turbo regal web site and think I have the circuit figured out, but any input would be helpful.

It seems that the signal for the tach starts at the ignition module and output is to the white wire in the ignition module plug. It seems that the signal travels thru the white wire to the bottom row on the bulkhead connecter and then travels into the car. The diagram then shows a path to the diagnostic connecter and then to the actual tach in the gage cluster. Is there anything missing in this description?

Does anyone have any tips on tracing down this problem?

 

[Turbo Brian]

ttt

 

[Turbo Ryan]

When you say it is intermittant do mean just that, or does it not work at all? I know when I got my car the previous owner had plugged the white wire with the green connector into the wire with the black connector. These are down by the alternator. Good luck.

Ryan

 

[Turbo Ryan]

I should add, those two wires should not be plugged to getter. The black one activates the fuel pump when 12Vs are applied, and the green is a signal wire for an after market tach.

Ryan

 

[Turbo Brian]

It will work when it feels like it. The previous time that it quit, it began to work about 3 weeks later and was normal for months. It recently has been inoperable until the car has been driven for 5-10 miles and then will work properly for a while and then quit. It seems like it gets finicky when I do any work under the dash or near the driver's side valve cover wiring. The slightest movement of the wiring bundles seems to cause the problem. That is why I hoped that someone had experienced the same thing and had traced back the tach circuit so that I could confirm that I am looking for the right wiring.

 

[GNVenom]

Take a good look at the green connector behind the alternator, it has two white wires going into it. This is a "daisy-chain" hookup that contains your tach signal, and frequently, the unsealed male terminal in the connector becomes corroded, breaking the wires from eachother. This can cause an intermittent tach reading. Best bet is to just completely cut off the green connector, strip both wires, clean and solder them together, then tape them up and insert the pair into the engine harness conduit.
-John Spina
http://www.casperselectronics.com

 

[Turbo Brian]

I will try that. Thanks.

 

[87 Pete]

Originally posted by Turbo Brian
It seems like it gets finicky when I do any work under the dash or near the driver's side valve cover wiring. The slightest movement of the wiring bundles seems to cause the problem.

I had a similar problem after I had a guy fix my my DS header. The problem was that the wires in the engine harness got pinched near the lower front DS valve cover bolt, as this bolt also secures the black plastic channel containing the wiring harness.

In my case, the pinch resulted in the wire actually breaking.

I would advise removing the upper plastic channel and inspecting the wires in this area. The tach signal is provided by a white wire.

If all else fails, you can cut the white wire that comes out of the ignition module, and wire it directly to the input of an aftemarket tachometer.

Pete

 

[Turbo Brian]

Another great tip. I will have some time to troubleshoot this weekend. I will check this area out. Thanks.