Ignition timing question

[Diz]

I grounded the ignition timing pigtail on my '90 Talon and checked the timing. I was expecting the mark to be steady as a rock, but it was moving from 2-degrees to around 8-degrees as the idle speed changed. I thought there might be a wiring problem so I grounded the timing wire (#12) at the ECU and it made no difference.

What's the deal? I obviously can't set the timing accurately like this. Is this something that can go wrong with the ECU? A bad crank angle sensor? Am I doing something wrong? Am I a buffoon?

Thanks.

 

[pneumo]

Did you have a logger plugged in while doing the test? You have to unplug the logger to check the timing.

There are two check terminals on the firewall. Make sure you get the right one.
A loose or worn timing belt idler pulley might cause a variation in the timing. CAS might be going bad, too.

 

[Diz]

Logger cable was plugged in. Drat!

Thanks for the help!

 

[Nautica985]

Are you sure you grounded the right plug? The first time i tried to set my timing I had the same problem because i was grouding the wrong plug. you need to ground the bigger plug that has a white plastic circle thing on each side of it. I was grouding the small plug and it did not work

 

[kpt4321]

His logger was plugged in, that was probably the issue.