MAF sensor choppy at WOT
MAF sensor choppy at WOT 2002 C5 Z06, mild cam + FAST 90/90. Recently added the fast, trying to get things dialed in again for it.
On dialing in the MAF, I noticed the MAF signal is rather choppy at WOT, sometimes fluctuating as much as 40 g/s. I don't have any old MAF logs to compare with, but I don't think this is normal? Bad/dirty MAF maybe? Air filter is a Blackwing, maf directly behind it. Any chance a vacuum leak would cause it? I'm not 100% the MAP sensor is leak-free as the hole on the FAST is a bit larger than the LS6.
Inserted screen shot of the graph and also copy of the log (3rd gear WOT pull around 21 minutes in)
On dialing in the MAF, I noticed the MAF signal is rather choppy at WOT, sometimes fluctuating as much as 40 g/s. I don't have any old MAF logs to compare with, but I don't think this is normal? Bad/dirty MAF maybe? Air filter is a Blackwing, maf directly behind it. Any chance a vacuum leak would cause it? I'm not 100% the MAP sensor is leak-free as the hole on the FAST is a bit larger than the LS6.
Inserted screen shot of the graph and also copy of the log (3rd gear WOT pull around 21 minutes in)
I've seen gross instability on a MAF that I went nuts on
"porting" (an 85mm, cut out the main airfoil trying to get
it to read like a 75mm). But my descreened stocker 85mm
on a similar sounding intake lineup is not too jiggy.
I suspect that the datalog is at a pretty low rate (from
many PIDs in play). I suggect you pull anpther log with
only a few (like MAP, RPM, MAF freq, MAF airflow, etc. -
stay under 12 altogether) to get a higher sample rate
and more visibility. This may reveal something useful,
like if the "triangular" character of the MAF g/sec is
really mostly a sensible line with some spikes (when
you get to look "closer" (finer) then this could be a
harness EMI problem (as service manual mentions is
a potential issue). Another cut at it is, if you hold a
steady high load point is the MAF steady, or is it
unstable when air mass flow is known stable?
Substituting a known good truck MAF (screened)
and a known good Z06 MAF (descreened) might let
you see if air turbulence or resonance is at play. A
big throat intake can let manifold pulsations bother
the MAF (although high air velocity ought to make
this more of a low-end problem). If you get strong
reversion pulses and they are free to go back and
forth across the sense elements, you may be in
effect "double counting" (in this case, probably only
~10%, but still) some air. Might take off the air filter
and ducting leaving only the open MAF in place, and
see if you hear audible pulsation or smooth suction
(if you can hear anything over fan and exhaust noise).
But what you'd do about this being a problem, I dunno -
probably would involve undesirable restriction (like MAF
screen).
A vacuum leak is unlikely to cause that scale of error (40
g/sec). That's a pretty decent sized leak.
"porting" (an 85mm, cut out the main airfoil trying to get
it to read like a 75mm). But my descreened stocker 85mm
on a similar sounding intake lineup is not too jiggy.
I suspect that the datalog is at a pretty low rate (from
many PIDs in play). I suggect you pull anpther log with
only a few (like MAP, RPM, MAF freq, MAF airflow, etc. -
stay under 12 altogether) to get a higher sample rate
and more visibility. This may reveal something useful,
like if the "triangular" character of the MAF g/sec is
really mostly a sensible line with some spikes (when
you get to look "closer" (finer) then this could be a
harness EMI problem (as service manual mentions is
a potential issue). Another cut at it is, if you hold a
steady high load point is the MAF steady, or is it
unstable when air mass flow is known stable?
Substituting a known good truck MAF (screened)
and a known good Z06 MAF (descreened) might let
you see if air turbulence or resonance is at play. A
big throat intake can let manifold pulsations bother
the MAF (although high air velocity ought to make
this more of a low-end problem). If you get strong
reversion pulses and they are free to go back and
forth across the sense elements, you may be in
effect "double counting" (in this case, probably only
~10%, but still) some air. Might take off the air filter
and ducting leaving only the open MAF in place, and
see if you hear audible pulsation or smooth suction
(if you can hear anything over fan and exhaust noise).
But what you'd do about this being a problem, I dunno -
probably would involve undesirable restriction (like MAF
screen).
A vacuum leak is unlikely to cause that scale of error (40
g/sec). That's a pretty decent sized leak.
2002 C5 Z06, mild cam + FAST 90/90. Recently added the fast, trying to get things dialed in again for it.
On dialing in the MAF, I noticed the MAF signal is rather choppy at WOT, sometimes fluctuating as much as 40 g/s. I don't have any old MAF logs to compare with, but I don't think this is normal? Bad/dirty MAF maybe? Air filter is a Blackwing, maf directly behind it. Any chance a vacuum leak would cause it? I'm not 100% the MAP sensor is leak-free as the hole on the FAST is a bit larger than the LS6.
Inserted screen shot of the graph and also copy of the log (3rd gear WOT pull around 21 minutes in)
On dialing in the MAF, I noticed the MAF signal is rather choppy at WOT, sometimes fluctuating as much as 40 g/s. I don't have any old MAF logs to compare with, but I don't think this is normal? Bad/dirty MAF maybe? Air filter is a Blackwing, maf directly behind it. Any chance a vacuum leak would cause it? I'm not 100% the MAP sensor is leak-free as the hole on the FAST is a bit larger than the LS6.
Inserted screen shot of the graph and also copy of the log (3rd gear WOT pull around 21 minutes in)
Thanks for the responses, even removing more PIDs the choppy ness was there, so I'm glad to hear it's normal. Probably going to pull the intake again anyways and tap the MAP sensor hole to fit a 1/4" brass fitting and do a remote MAP sensor install.
