HELP...about to give up on SD open loop
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From: Gainesville, GA
HELP...about to give up on SD open loop Everything has been dialed in. A/F is perfect, timing is there, but the motor acts like there is some kind of governor on it. Pulls hard to 4000, then acts like something is holding it up. Rwtq won't go above 434 ft-lbs or so. Is there anything that the PCM might be doing to keep the motor down on power? Timing was verified with a timing light. Also, MAP reading at WOT is right at 15. Also, we can't get any knock retard. Knock sensors are hooked up, everything seems great in that area. We tried to get knock to verify the timing was there, but no go. Even tried using 93 octane gas at 40 degrees timing. We have gone through edit and tried everything. Is there something that is holding this motor back in the programming area?? 
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From: Gainesville, GA
Total spark advance was showing whatever we told it to. We could hold it at 42 degrees, or 32 degrees. It does seem that fuel or spark has to be it, but we verified timing with a light, and the A/F is perfect on the wideband. Any leaner or richer, and we lose some power. O2s aren't hooked up. We are using the HP tuners scanning program for all of this also.
Gotta be fuel Did you upgrade the injectors and fix the IFR table? Did you upgrade the fuel pump? Did you put a mechanical fuel pressure gauge on to make sure the pressure is not dipping at 4000 rpms. If it is dipping below 59 psi you need to upgrade the fuel pump. Especially with a stroker motor...
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Originally Posted by Taphee6
Did you upgrade the injectors and fix the IFR table? Did you upgrade the fuel pump? Did you put a mechanical fuel pressure gauge on to make sure the pressure is not dipping at 4000 rpms. If it is dipping below 59 psi you need to upgrade the fuel pump. Especially with a stroker motor...
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What can you see for intake airflow? MAF readings
or MAP readings indicate any restriction at the point
of output falloff? Any chance of an exhaust choke
(busted brick in a cat, etc.?) You should see MAF
roughly linear w/ RPM at least up to 5000+ (more
w/ cam & good exhaust) and MAP be flat, near-
atmospheric.
What is the "stops pulling" measured by? Is this a
dyno setup, street driving, ???
or MAP readings indicate any restriction at the point
of output falloff? Any chance of an exhaust choke
(busted brick in a cat, etc.?) You should see MAF
roughly linear w/ RPM at least up to 5000+ (more
w/ cam & good exhaust) and MAP be flat, near-
atmospheric.
What is the "stops pulling" measured by? Is this a
dyno setup, street driving, ???
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From: Gainesville, GA
Originally Posted by jimmyblue
What can you see for intake airflow? MAF readings
or MAP readings indicate any restriction at the point
of output falloff? Any chance of an exhaust choke
(busted brick in a cat, etc.?) You should see MAF
roughly linear w/ RPM at least up to 5000+ (more
w/ cam & good exhaust) and MAP be flat, near-
atmospheric.
What is the "stops pulling" measured by? Is this a
dyno setup, street driving, ???
or MAP readings indicate any restriction at the point
of output falloff? Any chance of an exhaust choke
(busted brick in a cat, etc.?) You should see MAF
roughly linear w/ RPM at least up to 5000+ (more
w/ cam & good exhaust) and MAP be flat, near-
atmospheric.
What is the "stops pulling" measured by? Is this a
dyno setup, street driving, ???
Any chance that you have (say) dual valvesprings
but one of them is "getting by on the backup"?
Something that would "float" at higher RPM? Don't
know what the distinguishing signs would be,
there. Maybe check the logger for misfires-current
on all 8 cylinders and see if somebody's dropping out?
but one of them is "getting by on the backup"?
Something that would "float" at higher RPM? Don't
know what the distinguishing signs would be,
there. Maybe check the logger for misfires-current
on all 8 cylinders and see if somebody's dropping out?
One other thing - I suggest looking at your spark
and your VE tables (whichever ones are active,
that varies by year) in the 3D view, just eyeball
the surface for any freaky spikes or potholes that
could be "sticky". Might as well check the PE line
and the open loop fuel/air table similarly, just for
luck. Not clear on how you are looking at mixture
with open headers. It might be worth the effort to
put a couple of feet of pipe after them to eliminate
any fresh air reversion that might corrupt any
readings (?). I presume COT is disabled (prone to
come on at mid-high RPM and really over-enrich)
and you have all engine and transmission torque
management features disabled, or set to their
clip limits?
and your VE tables (whichever ones are active,
that varies by year) in the 3D view, just eyeball
the surface for any freaky spikes or potholes that
could be "sticky". Might as well check the PE line
and the open loop fuel/air table similarly, just for
luck. Not clear on how you are looking at mixture
with open headers. It might be worth the effort to
put a couple of feet of pipe after them to eliminate
any fresh air reversion that might corrupt any
readings (?). I presume COT is disabled (prone to
come on at mid-high RPM and really over-enrich)
and you have all engine and transmission torque
management features disabled, or set to their
clip limits?
Originally Posted by LOnSLO
Yep, COT is disabled, and we have a header extension to measure A/F. I'm beginning to think it's the valvesprings.
What is your A/F reading above the drop off point.
13, 12, 11, 10?
