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Opinions on brief lean out at idle and light cruise

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Norman C Shibley

25 year ASE master tech
Joined
Aug 16, 2013
Messages
48
Good morning boost brothers and sisters. I have a brain teaser for you all. I want to preface by saying, I don't have a powerlogger so I'm just pinging the group to see if anyone has seen this problem, before I dive headlong into this car.

Every so often at a stop light or light part throttle cruise, I will get a lean out condition showing on the wideband of around 17 or 18:1. While cruising, you can actually feel it in the engine, so it's not a faulty wideband and the condition usually clears itself out within 10-15 seconds. Pulls very hard and strong with no troubles. I'm leaning towards something electric or electronic

-newer Turbo tweak 3.5 MAF
-Caspers adjustable cam sensor
-newer crank sensor
-newer ignition coil and module
-turbo tweak chip

Has anyone seen a bad knock sensor or bad ESC module cause this issue?
Possibly intermittent problems with the vacuum brake booster?
The idle never changes so I ruled out IAC

I know Brian Lorenz has told me to get rid of the Delphi 50lb injectors that came with this car but I've never had a problem with them under load.

Thank you all in advance
 

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fan kicking on? Fan turbulence will cause stuff like this
Eric did mention something to this effect with aftermarket fans drawing too much current?. I do have duel fans but haven't compared when they are commanded on with the lean out
 
Raise the base fuel pressure a pound or two and see if it improves?
 
Folks suggesting looking at the fan are giving you a good clue, but not because of low voltage affecting the O2 sensor reading.

You're seeing a misfire, which always hits the O2 sensor as a completely lean mixture... because nothing burned. You state you can feel it when it happens. The engine is stumbling. It's a misfire.

You can see if it correlates to the fans coming on and hitting the electrical system so hard you lose spark, but unless your battery is about done that's probably not it. Double check the ignition first, then check the charging system and battery.
 
Folks suggesting looking at the fan are giving you a good clue, but not because of low voltage affecting the O2 sensor reading.

You're seeing a misfire, which always hits the O2 sensor as a completely lean mixture... because nothing burned. You state you can feel it when it happens. The engine is stumbling. It's a misfire.

You can see if it correlates to the fans coming on and hitting the electrical system so hard you lose spark, but unless your battery is about done that's probably not it. Double check the ignition first, then check the charging system and battery.
This is not a misfire. It feels like a sudden change in timing or a slight change in pulse width. Like someone is clamping down the engine for a brief moment not like a cylinder is dropping in a misfire. Eric had suggested changing the ground location on the dual fans i have and that seems to be a starting point, instead of using the same ground that the PCM uses. Thanks for the input
 
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