CCKen

cruiser54

I know Renix is 12* BTDC but that ain't gonna help ya.

CCKen

Thanks 54. If I find out I'll let you know what it is.

cruiser54

Just gonna throw a light on it?

CCKen

There has to be a published number somewhere.

I've Googled it and came up with nothing. I thought about the 'Ask A Jeep Mechanic' thingy but that cost money - I think.

XJ.89.Limited

I know the timing is factory set. Not sure how you would even check it with a timing light. I remember my dad spending hours tweaking the timing on his old chevelle, but that had markings on it to check. Check the jeep manual maybe?

Radi

Ken, I don't think there is such a number.
Back in the old days if you set your idle speed and capped off the vacuum advance, you'd be running at the initial mechanical timing advance. That was a repeatable set of baseline conditions.
That carried through to the early generation computer-controlled systems that only considered engine RPM and load to calculate timing- at idle both were still repeatable.
There is no equivalent to that with a JTEC controlled dynamic system, it considers everything from coolant temp to O2 readings to calculate instantaneous timing. You'd need the programming info to create a table...under X Y and Z conditions the timing should be X.
Since there is no way to set it up for repeatable "baseline" conditions, a published initial advance number would be meaningless. I've never seen one, even the FSM merely states it is not-adjustable, lol.
Plug a live scanner in, you'll see what I mean. Timing isn't even static at idle. Anywhere from 10-14 BTDC just sitting there, generally lower when it's cold and increasing as it warms up. I think the timing and the IAC are chasing each other around, lol.

odgreen

As said above... Can't adjust timing.

CCKen

I understand how the system works, and I've seen the PCM adjusting the timing on my scanner - what I was curious about is what "base" timing is. Below is an exerpt from the '99 FSM concerning the PCM control of the 'base' ignition timing and all timing advance. Is the base timing programmed in the PCM "Dynamic". I don't think so.

"The distributors on both the 2.5L 4-cylinder and the 4.0L-6 cylinder engines do not have built in centrifugal or vacuum assisted advance. Base ignition timing and all timing advance is controlled by the powertrain control module (PCM). Because ignition timing is controlled by the PCM, base ignition timing is not adjustable on any of these engines.

The distributor is locked in place by a fork with a slot located on the distributor housing base. The distributor holddown clamp bolt passes through this slot when installed. Because the distributor position is locked when installed, its rotational position can not
be changed. Do not attempt to modify the distributor housing to get distributor rotation. Distributor position will have no effect on ignition timing. The position of the distributor will determine fuel synchronization only."

Radi

I guess the point I was trying to make was that "base" timing isn't what it used to be. The name "base timing" is still used because that's the terminology that's familiar, but it really no longer exists per-se.
The PCM may start off with a fixed number of degrees retard, but modifies that starting point almost instantly.