[Diy_efi] Lumpy engine in closed loop cruise

Becker, Damon Damon damonb
Thu Oct 20 15:46:54 UTC 2005


It's hard on the turbo to hold boost for a long time like that.  FYI.  
 
You shouldn't be in closed-loop at that high of a manifold pressure.  At
the very least you are giving up power, and probably detonating.  
 
If you didn't rechip that GM ECU, then my theory is you are misfiring
and sending unburned O2 down the exhaust and it's being picked up by the
O2 sensor and registered as a momentary lean spot in an otherwise rich
situation.  There's no way that GM ECU would allow the engine to be lean
at that high of a boost.  

  _____  

From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
On Behalf Of Dermot O'Hare
Sent: Thursday, October 20, 2005 9:35 AM
To: diy_efi at diy-efi.org
Subject: [Diy_efi] Lumpy engine in closed loop cruise




I have 4-cylinder Lotus Esprit Turbo. ECU is 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. The target A/F ratio in cruise is
14.7. 

Are there any obvious causes of this,  over lean ?  etc...


Dermot




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