[Gmecm] Engine is not smooth at steady cruise

[squelch at ix.netcom.com]

Dermot:

It sounds like it's in lean cruise.

You can add some fuel to the VE table, but you are correct the ECM will pull it back out.  You would need to modify the desired o2 table instead, however..  it's going to effect your lean cruise fuel mileage.

If you have some logging hooked up (I believe that you do) take a look at the o2 voltage and comparie it to the A:F 
The A:F is the ECM's desired A:F not what is actually running, it may be up around 14:5 or even higher.

You could always just shut off the BLM


John Welch



 

-----Original Message-----
From: Dermot O'Hare <dermot.ohare at chemistry.oxford.ac.uk>
Sent: Oct 20, 2005 10:31 AM
To: gmecm at diy-efi.org
Subject: [Gmecm] Engine is not smooth at steady cruise

I have heavily modified 4-cylinder Lotus Esprit Turbo,  runs on a GM  
1228708  using a speed density system.

In 5th gear,  trying to hold steady 85 mph,  3500 rpm, MAP about 
100-130 kPa,  ECU is in closed loop.  O2 cycling between 0-0.65 V. 
The engine is lumpy, like a slight hesitation. It feels like a very 
slight misfire,  press the throttle and it goes away as it richen up 
the mixture and accelerates  under power perfectly.

Could it be a lean cruise condition,  the other suggestion I have 
been told is that  the ECU may be reacting too quickly to the O2 
swings?   When the ECU is reset it is not so bad but gets worse as 
the ECU learns the fuel trim,  BLM values are way  down.

If a change the VE table will the BLM values not bring it back down 
anyway,  in closed loop the ECU is not running on them.


What am I missing here....

Dermot