So I picked up a 2.8 t5 sweet deal. Previous owner replaced dizzy and told me that timing might be off a bit. Car takes a few seconds to start. My 3.1 starts in half a second so I know that's a retarded timing symptom. Yesterday I took it out for a spin and ran pretty good. Was running a little hot but nothing to be concerned about I hope. So I checked timing today by disconnecting timing wire, and it was at 4 degrees btdc. Timing mark is solid and doesn't bounce around. Was wondering if running timing so retarded can damage the engine as I don't know how long previous owner ran it at 4 btdc. I know timing has to be 10 btdc.

 

I tried to set the timing today..... man there is no space whatsoever . On my 3.1 I have plenty of room but on this 2.8, no go. A.i.r. system pipe is in the way. I'm gonna tackle it this weekend. I'm sure someone has removed the air pump and the pipes that go to the manifold. How did you plug the holes and did it affect driveability??

 

4 degrees BTDC isn't THAT retarded, and won't cause any damage. It'll just make the engine a bit lazy.

 

Well I decided I'm gonna leave it all stock . I made a simple tool to reach the dizzy bolt. I cut a 15 mm wrench with my grinder like 3 or 4 inches long from the head. Works great. Got the timing set right.

 

I have wondered about this myself.

Certainly retarded timing is what it is during open loop, or whenever the ESC is unplugged.

But, once the ECU switches to closed loop, and with the benefit of the O2 sensor reporting during closed loop, does the ECU have the ability to add ADDITIONAL timing-advance to compensate for the retarded distributor position?

At the risk of exposing my very limited understanding of what is going on in the ECU, my perception is that the ECU directs timing-advance from the "base timing." The amout of timing-advance is determined by the load on the motor. Am I right so far?

Load is determined by airflow measurement (MAF or MAP) signal, in combination with engine RPM. The ECU then uses that signal data to figure out where on the fuel map the ECU should look to determine the amount of fuel (injector pulse duration?) to deliver.

Now, here is where I ask my question, and try to sound clever. Also hoping that the ECU is equally clever. While the ECU is slavishly following the fuel map based on load/rpm numbers, does the O2 sensor detect an anomaly in the O2 levels of the exhaust gas (I assume increased O2, because the retarded timing caused lesser fuel and lesser O2 to be consumed)? Provided that RPM is sufficient, does the increased O2 level in the exhaust gas trigger the ECU to advance timing a little extra, to compensate for the retarded base-timing, and in effort to try to achieve a more complete burn?

 

That was a lot bro, Im not sure how to answer but all I know is the ecu goes off the base timing to properly calculate all of the above. If the base timing is off, ecu's calculations will be off. I read this detailed post on timing explains alot.

 

Closed and open loop has no effect on timing.

The ECM takes over timing control at about 400 RPM (all bins I have looked at have been set at 400 RPM from GM, though there may be some other value used in applications I haven't looked at). This is separate from open and closed loop qualifiers.

There are timing modifiers, separate from the main SA table, but these are usally based solely on engine temp, and a couple other variables. At no point does the timing control ever get disabled from the ECM, unless the engine is below 400 RPM.