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Cold start idle Warm start rev up


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Hi, I recently bought a ls2 gu patrol with link g4 ecu 

i have 2 problems with tune that need fixing... one being when I start the car cold it fires fine and then slowly drops down in revs untill it stalls. 

The second problem is when warm and I start the car it revs up to over 2 grand and then slowly drops down and stops at 900 rpm and then idles fine. 

Any help would be appreciated.

i do have pc link and could adjust myself with guidance 

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Try to capture this in a log then attach it here and we should be able to make some suggestions.  Here is how to do the log:  https://www.youtube.com/watch?v=_P1LRANeO4A  This video is using a G4+, but you will find the G4 pretty similar.  Start the logger before starting the engine so we record the problem happening.



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  • 3 weeks later...

Ok, so there appears to be two main problems. 

So this appears that this car has not been wired for the proper stepper reset after key off so it has been set to do the reset at key on.  This means you need to first turn the key on, then wait about 5 seconds for the stepper motor to reset before starting.  In your log it looks like you have started the engine before it had reset.

The second problem looks like they are commanding the stepper motor to move further than it actually can which will mean it just bottoms out fully closed and loses position.  The GM stepper motors from memory can only move about 200stepos but your map is commanding 560.  That suggests the throttle blade is probably too far open.

So it is going to need a lot of work, idle control will basically need to tuned from scratch.

I would start by getting the throttle blade in a more suitable position.  To do this, first warm the engine up with the settings as they are now then shut it down.  Close the throttle screw so the throttle can completely seal closed.  Turn power on and change the max clamp to 200 and min clamp to 0, do a store, power off again.  Power back on, give it 5 seconds to reset then start, you will need some pedal to keep it running. Adjust throttle screw so that it idles on its own but say at about 100RPM lower than desired.  With it idling away by itself then adjust the cells around normal running temp in the base position table (smaller number = more RPM), they will be smaller than 200 (max clamp).  Do a store after any changes.

The next day you can do a cold start and adjust all the other cells in the base position table as the engine warms up moving through each cell.


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