A/F super lean - dyno results...ideas?
#1
A/F super lean - dyno results...ideas?
Ran the first dyno on this combination today and found a very lean condition.
See below for the results.
This is a 8.1 Vortec with a Comp HR270 cam, magnum tip rockers, long tube side mount headers with CAI mated to a Richmond six speed manual in a 69 Vette.
While warming up the combo the a/f was 18:1 - By 4,150 RPM it was around 17.
He shut down and talked me out of any more runs until this is resolved.
Fuel pressure comes from a 255 GPH in tank pump - routed through stock injectors. Stock these motors run 340 hp and 455 ft lbs at the crank.
See below for the results.
This is a 8.1 Vortec with a Comp HR270 cam, magnum tip rockers, long tube side mount headers with CAI mated to a Richmond six speed manual in a 69 Vette.
While warming up the combo the a/f was 18:1 - By 4,150 RPM it was around 17.
He shut down and talked me out of any more runs until this is resolved.
Fuel pressure comes from a 255 GPH in tank pump - routed through stock injectors. Stock these motors run 340 hp and 455 ft lbs at the crank.
#5
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Even if you aren't entering PE (GM does tune in a 60 second PE delay on the HD trucks), you're AFR should still be 14.6:1, not 18:1. I'd check fuel pressure at the rail on the intake.
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#9
I'll test the fuel pressure at the rail tonight. I figured since it was so lean at cruise and actually got richer during throttle that it wouldn't be a f/p issue.
I didn't tune it, but I'll be working with that. It is a mail order tune.
I'll post up the fp numbers tonight. I'll test that from idle, mid point, and WOT to see what kind of swing I see. It is a fixed regulator with a C5 fuel pressure reg/filter between the 255 pump and the rail.
I didn't tune it, but I'll be working with that. It is a mail order tune.
I'll post up the fp numbers tonight. I'll test that from idle, mid point, and WOT to see what kind of swing I see. It is a fixed regulator with a C5 fuel pressure reg/filter between the 255 pump and the rail.
#10
Can't rule it out...but for our discussion that is all I can add about that.
Also...the way the power curve shows a ribbon on (up down flutter) - this appeared to be the PCM taking timing out on knock retard during the run due to the lean condition - Has that been your experience when you see that?
#12
This is a single line fuel rail like the 1999 and up Corvette.
It is running a 1999-2004 Corvette filter regulator.
The last LS build I did we ran it the same way on an LS2 in a 1985 Corvette.
There is no regulator on the fuel rail - it is a feed only.
It is right by the tank with a short return line:
It is being fed by an intank (custom fit) 255 GPH pump:
It is running a 1999-2004 Corvette filter regulator.
The last LS build I did we ran it the same way on an LS2 in a 1985 Corvette.
There is no regulator on the fuel rail - it is a feed only.
It is right by the tank with a short return line:
It is being fed by an intank (custom fit) 255 GPH pump:
#16
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Sounds like a WB issue to me. You can have the best WB available, but if the pump is acting up, or the filters are stopped up, you'll get crazy lean readings.
You should be able to verify with your scan data, and NB O2 sensors. If it's that lean, the NBs should be flat lined near zero.
You should be able to verify with your scan data, and NB O2 sensors. If it's that lean, the NBs should be flat lined near zero.
#17
Going to take it to straightline performance Friday. He had me weld another O2 bung in the header for his wide band.
I don't have tuning software - will learn more through this process.
I would think if it is that lean I'd have a lean trouble code popping up.
I don't have tuning software - will learn more through this process.
I would think if it is that lean I'd have a lean trouble code popping up.