Disable Ignition Advance

[landtoy80]

I am wanting to lock the motor into "service mode". I know I can short out the E1 and TE1 terminals but I would like to leave it in "service mode" for a while (emissions testing). My thinking is there must be a wire I can unplug from the distributor that will disable the ignition advance (thinking if I retard the timing and locking it so the ECU cant advance the timing, my NOx will be lowered).

Will this hurt anything mechanically? I know the engine is forgiving as somehow I bumped the timing and ran it that way for a long time. It ran fine but it cause excessive oil consumption. I was getting oil and some other goo/sludge from the PCV system. Discovered this when i installed a catch can. Fixed the timing and sludge problem when away. I dont think there was any damage done, the motor still runs.

 

[jonheld]

Ignition timing is adjusted through the ECU. There is no "advance" wire on the distributor. Pulses from the pick up coils are retimed by the ECU and sent to the igniter and on to the coil.
Shorting the 2 pins on the diagnostic connector is your only real option here, but you'll be running less efficiently as the ECU adjusts timing for various conditions.

If you're not passing emissions then something is wrong and you'd be better off fixing the issue.

 

[Howard705]

How about just retarding the timing with the distributor?

 

[landtoy80]

Was thinking retarding the timing but the ECU still advances the timing. If left in test or service mode then the timing will be retarded even more. How does the timing work in driving mode? Does the ECU send a signal to the distributor (via a wire) to change the timing? Wouldn't unplugging the wire make the 80 have no auto advance?

Retarding the timing reduces NOx, wouldn't there be less NOx if it was in service mode so the timing cant automatically advance? Or will the little bit that the ECU advances the timing not make that much of a difference?

How much can you retard the timing to see a reduction in NOx?

Only reason I thought of this was I was reading a post about a guy struggling to pass emissions, the tech (in CA of all places) took a paper clip and put the timing in "test/service mode" and he passed the emissions test for NOx.

 

[jonheld]

Does the ECU send a signal to the distributor (via a wire) to change the timing? Wouldn't unplugging the wire make the 80 have no auto advance?

Again, there is no "advance wire". The ECU receives pulses from the pick up coils in the distributor. It then performs an internal adjustment and sends out a pulse to the igniter which in turn fires the ignition coil.
There is no timing adjustment within the system other than the static setting of the distributor.

The ECU has a limited window of adjustment.

 

[landtoy80]

Thanks. Wondered how it worked. Was thinking it was like a vacuum advance on older distributors. Remove the vacuum hose and no more advance.

 

[Howard705]

Think the ecu has a programmed map and does the same type of advancing as the vacuum and centrifugal used to but much more precisely and able to adjust for more conditions. I have no idea how the vehicle is run or checked in the test but losing all advance is bound to make it run bad and may change another part of the test negatively. Been years but think NOx is formed at peak combustion temps. Retarding overall should get you the same results and not be obvious while testing. Don't the tests need to be done with no CEL? Maybe the jumpering that you saw was a quickie for just a minute?

 

[landtoy80]

Colorado doesn't care about the CEL. Its a good thing as my wife's Camry has the CEL on all the time. There is a short in the transmission wire from ECU to trans. It cant be fixed without replacing trans (via Toyota). I ran jumper wires and replaced ECU and its still on.
All the wire is for is shifting into OD. When the problem does show up, all you have to do is shift with the shifter and OD switch. Anyhow, it works 99% of the time there is no issue. It would suck if I failed the test just because I have issue shifting.