I am running a '747 ECM in my truck. I have removed the AIR pump because it was damaged (truck is exempt from emissions). I am capable of modifying the UVEPROMs. I remember reading a thread about changing the MIN TEMP FOR AIR DIVERT (address location 562H) in the code to a very high temp (like 290 deg F). But now that I think about it, that does not make sense. Since the setup in my truck only diverts air to the exhaust manifolds when the temp is cold, wouldn't I want to change the MIN TEMP to a very low temp so it does not divert air to the manifold because all the AIR hardware has been removed? My understanding is that the AIR pump diverts air to the exhaust manifold during warmup to help burn extra hydrocarbons. Then when the MIN TEMP is met, the solenoid turns on and dumps air to atomosphere (since my vehicle setup doesn't move it to the cat). But if I make the MIN TEMP 290 def F (which is never met), then the ECM will think the pump (that is not there) is always on diverting air to the exhaust manifold and trying to offset for the false lean mixture reported by the O2 sensor. The original setting in ARPC7509 (the stock program) was 65 deg F! Am I missing something here???

As I understand it from other threads I've read here, the reason that the MINIMUM temp is being set high is so that it never engages. If you set it to a ridiculously high temp, then it never comes into play, hence you have deleted it's action and related consequences out of the system.


If the pump and attendant hardware and pipes have been removed, but you set a low temp, then then are compensations that the ECM is still trying to perform and different +/- equations that are in use, which become erroneous.

By setting a high temp, the system never comes in to play, because the qualifying event(s) or conditions haven't been met for it to do so. Thus you've eliminated it both physically (by removal) and mathematically out of the ECM computations with a high temp condition.


I hope this helps, and others will chime in that the logic of it is sound.

im looking for this in rbobs ebl as well so i can disable it.

No AIR in the ebl, so no need to worry about it.

As for the stock '7747 I can't find any O2 term to offset it when AIR is in port mode. So I don't believe it is an issue as it is on other GM ECMs. I also looked into the code that controls the divert valve. From what I can tell if the engine temperature is below the MIN TEMP for DIVERT, the air system is always in divert mode. Part of the issue with looking at the code is it doesn't show how the actual hardware works.

So comparing the AIR to port during x sec's of PE, to what happens when the engine is lower then the temperature threshold, the status bits are set the opposite. When the PE port mode is active status word L0008 has bit 0 cleared, and bit 2 set.

When below the min divert temperature, L0008 has bit 0 set and bit 2 cleared.

These bits are further translated to drive the hardware.

If bit 0 is set, then pin C1 is driven low (AIR DIVERT)
If bit 2 is set, then pin C2 is released (AIR SELECT)

At this point one needs to know how the solenoid & valve assembly operates.

In the code there is another state where both pins C1 & C2 are driven low, which may be for air to the cat.

RBob.