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Jairek
11-21-2010, 04:11 AM
so i have a 3.1 has ignition coil today i decided to look at the timing and when the light flashes it hits the mark but the mark on the engine is there and the mark on the crank pulley is like a inch above that mark what would i do to change this in my 94 Oldsmobile cutlass ciera s 3.1 engine code m

turbokinetic
11-24-2010, 12:24 AM
The computer controls the timing on this, constantly making adjustments while the engine is running. There is no adjustment other than re-tuning the ECM chip.

The actual point of timing is the machined notches in the crankshaft passing the crank position sensor. Everything is calculated based on this reference point. The crank notches and CPS sensor take the place of the distributor pickup coil or breaker points. Since you can't move the sensor like you could a distributor, there is no way to manually adjust the timing.

With a digital-advance timing light, you can actually see what advance the ECM is producing, but a standard timing light is useless on these.

David

85_Ciera_Rebuild
11-27-2010, 11:57 PM
With a digital-advance timing light, you can actually see what advance the ECM is producing, but a standard timing light is useless on these.


You mean you can read a meter to see these changes? From reading this tidbit here (http://www.ground-z.org/electronics/vehicle/timing-light.html), I must assume computer changes timing very quickly back/forth, so you can NOT see actual changes with plain old timing light, yes?

85_Ciera_Rebuild
11-27-2010, 11:57 PM
Delete; duplicate

turbokinetic
11-28-2010, 01:04 AM
Well - here's what happens. I've tried both and will describe it here.

When I hooked up a "normal" timing light to my DIS-equipped car, the light flashed and I could see the mark I made on the balancer. The mark was stationary (firing at a steady advance degree). When I revved the engine, the timing advanced smoothly as the RPM's came up, and fell back smoothly as the engine slowed back down. It moved exactly like a distributor engine's timing mark. You could see the advance working just as plain as day. The only problem is, there is no way to tell EXACTLY HOW MANY DEGREES it was advancing, because the engine has only got a TDC timing mark, not degree marks. It gives a "qualitative" check telling you that the computer is in fact contreolling the timing.

With the digital advance timing light, you can turn a dial on the light, and the timing mark will "move" until you have used the timing light to "dial the TDC marks together." Then you look at the digital advance timing dial, and it shows the degrees of advance you added to the light. This is your actual spark timing, relative to TDC.

With the engine idling at a steady stable rate, with the timing mark not jumping around, you can get the "real world" timing advance the engine hardware is seeing. Then you connect the laptop to the diagnostic port under the dash, and pull up the ECM's "Spark Advance Relative to TDC" variable. It should equal the timing advance you measured with the timing light.

This is a check you would do if you were re-tuning an ECM and making a custom setup, OR thought the crank trigger ring had slipped on the balancer, or had some other reason to beleive the ECM was creating an incorrect timing advance. There is a timing offset setting in the ECM calibration that is used to make sure the ECM's desired timing actually equals the engine's actual timing. If you has pieced together ECM's and igntion parts from different engine families, you would use this constant to set the base timing; just as you turn the distributor to set the base timing on an older engine.

Hope this makes sense! It really only comes into play when setting up calibrations or troubleshooting really oddball timing issues.

But you can definately see the computer advancing and retarding the timing.

Later,
David

85_Ciera_Rebuild
11-28-2010, 03:21 AM
If you has pieced together ECM's and igntion parts from different engine families, you would use this constant to set the base timing; just as you turn the distributor to set the base timing on an older engine.

Hope this makes sense!

Bingo...yes, it makes sense, been there, done that on point-vacuum pot distributors......but, the above may explain why a shop mechanic could not "piece together" engines/etc from other vehicles...he always said, they don't run right when you install other engines/etc.

Timing table is messed up, may be the reason...thx