Verifying RPM signals for tach and ECM from ignition module

[BuickMike]

Would I be correct when I think that pin A on the ignition module (EST) provides the RPM signal to the ECM and pin E goes to the white tach signal wire under the dash?

I am trying to track down an issue where my tach no longer works. I checked my connection to the harness in the dash and it is good. I also tried a spare cluster and that tach does not work wither. This happened not long after I installed a new ignition module and I'm thinking that it is the culprit. I hooked up powerlogger and confirmed that the ECM is reading RPM.

 

[BuickMike]

Ok I just checked continuity and yes pin E goes straight to the tack wire under the dash. Looks like time for me to get my ign module warrantied.

 

[BEATAV8]

You can use a pin or a needle to re-tension the terminals in the stock harness connector. That's super common to lose tension on those.

Bailey posted a vid on youtube showing how to do it.

 

[BuickMike]

You can use a pin or a needle to re-tension the terminals in the stock harness connector. That's super common to lose tension on those.

Bailey posted a vid on youtube showing how to do it.

I will try that. I got another module under warranty and still nothing on the tach. I have full continuity to the pins on the module from the tach connection, so either I got another dud or its not connecting somehow.

 

[BuickMike]

Welp. Turns out somehow both my gauge clusters are bad because I hooked up a autometer tach at the dash and it reads the signal fine.

 

[TurboBob]

This is the vid about the pin tension of the CCCi connector

 

[BuickMike]

Thanks Bob! I'll do that and see what happens. Question, is the signal from the tach pin different from the EST pin? If they are the same signal, I may try jumping the EST pin to the tach input to see what happens. I feel like I lost tach signal after I replaced my ign module with a new one (standard ignition). I warrantied that one out yesterday and no difference. Continuity between pin E on the ign module connector and the connector in the dash is good. The pigtail is not grounded anywhere. No continuity to ground. Then last night I borrowed an autometer tach from a buddy, connected it to the pin in the dash, and it was reading just fine. I'm just having a hard time believing that both my clusters are bad.

 

[TurboBob]

It seems likely that your aftermarket module has a 5v tach output, or even 'open collector' (wants a pullup resistor)

the stock module tach outputs were 10-12v if I remember.

The EST output is the right frequency, but its 5v also.

I'm not sure if the stock dash tachs can be modded to work with a 5v tach, but I would think so.

Bob

 

[BuickMike]

It seems likely that your aftermarket module has a 5v tach output, or even 'open collector' (wants a pullup resistor)

the stock module tach outputs were 10-12v if I remember.

The EST output is the right frequency, but its 5v also.

I'm not sure if the stock dash tachs can be modded to work with a 5v tach, but I would think so.

Bob

I'm kind of thinking the same. I've used borg warner and crappy autozone units (A1 Cardone) in the past with zero issues on the tach. I'm kicking myself because I recently threw all those old ones out. Sure, they had other issues, but at least I could have tested the tach output. I'll call around to some locals and see if they have a spare I could test with.

 

[BuickMike]

Update. So I borrowed an old ign module and coil pack from a buddy. Same issue. Then I realized I do have another cluster laying around. Tach works on that one, so its my tach for sure.

 

[TurboTGuy]

Hey Mike,

Give me a call when you get a chance.