It's a stock 84 L69 motor with the coil-in-cap dizzy. The dizzy is ALL rebuilt, but I suspect the module may had been otherwise(EBay piece).

I disconnect the brown wire to set the timing, and it is absolutly positivly rock solid. However, when the wire is reconnected, it'll wander randomly. According to the ECM log, the advance moves ~.5 deg. On the light, ~10 deg.

QUESTION: If the timing chain is worn, wouldn't the timing wander regardless of the advance amount?? And regardless of whether the ECM is in control or not??

I'm trying to rule out mechanical problems as the cause.
Wouldn't this indicate a problem at least with the Ignition Control Module, or maybe my ECM??

 

i would think the timing would wander a bit if the timing chain was shot, but also a wore knock sensor would cause a large amount randomization

 

Agreed, but it would show up in my log if it was the knock sensor.

But wouldn't it still wander even with the brown wire disconnected if it were mechanical slop?

 

What happens when you open the throttle and hold it at other RPMs? Does teh timing still wander?

I dont know how MS handles the timing, but maybe its doing something funny at idle. The fact that its stable with the EST disconnected suggests that it may be ok mechanically.

 

Thank you dimented24X7,

I know the board isn't really knowledgeable about MegaSquirt...that's why I was only asking about the mechanical aspect of it.

Yeah, it wanders during all rpms. The ADV table of the Megasquirt is flat at idle. I'm not sure if the issue is the MS, the control module, electrical interference, or mechanical slop. When cruising, I'll see the afr jump up 2 points occasionally, and the timing jumping around sounds like it fits these fluctuations. And it's NOT fuel issues...trust me, I've been through that.

I figured it wasn't mechanical, considering it's perfect when the EST is disconnected. Just needed some outside opinions. I'll wander(pun intended) to the Megasquirt forums now that it's a signal issue.

Thanks for the help!

 

If the timing stays rock solid throuout RPMs with the ESC wire disconnected you are OK on the mechanical end.

I would suspect the module, or maybe possibly a bad wire/connector somewhere...

 

It's a long shot..but it was worth it for me.
-Buy a new cap and rotor. Use the old one and cut slot at the #1 post wide enough so you can see through on each side of the post. You need to do this so you can see the rotor as it sweeps past the post with the engine running.
-Install the slotted cap and start the engine with the timing electrical plug disconnected.
-Shine your timing light in the slot. The timing should fire directly on the post
If it's not then you have an out of phase issue between the reluctor and the magnet. The reluctor is the star with 6 points on it. The maget connects to the module by two wires.

or.... Pull the distributor out and look at it closer...if it's off at all, you will be able to see it

 

Mines doing the same thing. Bad ESC module or bad electronic module in the distributor?
GW