how to fix a car running lean ???
Thread Starter
Intermediate
Joined: Dec 2016
Posts: 31
Likes: 13
how to fix a car running lean ???
Hello guys.
I have an 05 ls2 -z51 6 speed.
I have a long tube headers with x pipe(no cat)
my car make 338 hp
but the dyno graph show big power at low rpm (300 HP@3,000 rpm)
i saw other cars make 150HP @3,000rpm ???
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the other wired thing is the Air–fuel ratio
idle shows 14.7
full throttler shows 18.71 ??
is that the reason why my car fell slow ?
I have an 05 ls2 -z51 6 speed.
I have a long tube headers with x pipe(no cat)
my car make 338 hp
but the dyno graph show big power at low rpm (300 HP@3,000 rpm)
i saw other cars make 150HP @3,000rpm ???
==============================
the other wired thing is the Air–fuel ratio
idle shows 14.7
full throttler shows 18.71 ??
is that the reason why my car fell slow ?
Last edited by moh97gt; Mar 15, 2018 at 08:34 PM.
Le Mans Master
Joined: May 2016
Posts: 7,185
Likes: 1,546
From: Florida
First, where did the AFRs come from. Are those calculated or did they come from a WB?
Second, no way of telling at what point you captured the 18:1 AFR, but the way the ECM program works is - after 100% commanded throttle, on the way back to idle, fueling will first turn very rich for a moment which is a cylinder cooling function, then fuel cutoff command will go very lean as rpms and air cylinder mass drop significantly. 18:1, even 20:1 is normal to expect to see on deceleration/coastdown. This is nothing to correct. And cannot believe you would have been at 18:1 under full throttle in PE and still running.
Second, no way of telling at what point you captured the 18:1 AFR, but the way the ECM program works is - after 100% commanded throttle, on the way back to idle, fueling will first turn very rich for a moment which is a cylinder cooling function, then fuel cutoff command will go very lean as rpms and air cylinder mass drop significantly. 18:1, even 20:1 is normal to expect to see on deceleration/coastdown. This is nothing to correct. And cannot believe you would have been at 18:1 under full throttle in PE and still running.
Race Director
Joined: May 2004
Posts: 16,667
Likes: 1,209
From: Raleigh, NC
St. Jude Donor '15
Yeah, if it was during decel then it's not an issue. It wasn't 18:1 during accel, that's pretty much for sure. It'd have been misfiring and running like absolute crap
Otherwise, we basically have nothing to go on other than one tiny bit of data that may or may not be accurate and no idea when it was taken... need more info.
Otherwise, we basically have nothing to go on other than one tiny bit of data that may or may not be accurate and no idea when it was taken... need more info.
Thread Starter
Intermediate
Joined: Dec 2016
Posts: 31
Likes: 13
i got the AFRs from a realtime obd scanner
the 18.7 is continuous during full throttle
~14.7 when cursing at any speed or when the car is stopping
could it be that the fuel pump can't keep up, or the fuel injectors are Clogged ??
the 18.7 is continuous during full throttle
~14.7 when cursing at any speed or when the car is stopping
could it be that the fuel pump can't keep up, or the fuel injectors are Clogged ??
Last edited by moh97gt; Jan 30, 2017 at 11:34 AM.
Race Director
Joined: May 2004
Posts: 16,667
Likes: 1,209
From: Raleigh, NC
St. Jude Donor '15
You can't read actual afr with one of those. You're reading commanded, not actual. The O2 sensors that GM uses are called narrowband O2 sensors. They can only tell you whether it's richer than 14.7 or leaner than 14.7, that's it. Beyond that they are useless in telling how rich or how lean it is.
GM reports commanded EQ ratio inverted from how they're supposed to report it. It's really commanding 0.78 lambda or 11.55 AFR
GM reports commanded EQ ratio inverted from how they're supposed to report it. It's really commanding 0.78 lambda or 11.55 AFR
Last edited by schpenxel; Jan 30, 2017 at 12:40 PM.
