MAF and O2 issues?
Thread Starter
Joined: Mar 2002
Posts: 5,778
Likes: 4
From: SW Chicago, IL
MAF and O2 issues? Stock LS1 motor with a P1SC-1 Procahrger and long tube headers. No cats. 60lb injectors.
At idle my MAF only reads 4-5g/sec. Goes to 8g/sec at 2,000rpm.
Both front O2 sensors read 900 at idle and stay there. If I give it throttle it will go down to 70 and then stay back at 900.
What do these readings tell you? I am trying to get this car tuned, but they want me to fix these issues 1st.
At idle my MAF only reads 4-5g/sec. Goes to 8g/sec at 2,000rpm.
Both front O2 sensors read 900 at idle and stay there. If I give it throttle it will go down to 70 and then stay back at 900.
What do these readings tell you? I am trying to get this car tuned, but they want me to fix these issues 1st.
Last edited by MadIceV8; Jul 10, 2012 at 07:26 PM.
The MAF is reading crazy low. I'm pulling 8-10g/sec at
warm idle. Of course you do have the blower load that
will add to that.
Look at how MAF compares to dynamic airflow g/sec.
I think you're not really running off the MAF at idle, a
fraction blended in perhaps. With as lean as it's reading
for you to be showing such high O2 voltages, says to
me you may be in PE / open loop mode (enriched above
stoich due to high MAP w/ blower load?) and using the
dynamic airflow for fueling - otherwise you'd need an
opposing bit of crazy on the injector flow side to make
it up (and then some, to get pig rich).
Now being pig rich is also going to elevate idle MAP
more, perhaps leading to additional enrichment, on and
on.
warm idle. Of course you do have the blower load that
will add to that.
Look at how MAF compares to dynamic airflow g/sec.
I think you're not really running off the MAF at idle, a
fraction blended in perhaps. With as lean as it's reading
for you to be showing such high O2 voltages, says to
me you may be in PE / open loop mode (enriched above
stoich due to high MAP w/ blower load?) and using the
dynamic airflow for fueling - otherwise you'd need an
opposing bit of crazy on the injector flow side to make
it up (and then some, to get pig rich).
Now being pig rich is also going to elevate idle MAP
more, perhaps leading to additional enrichment, on and
on.
Thread Starter
Joined: Mar 2002
Posts: 5,778
Likes: 4
From: SW Chicago, IL
jimmyblue - I have a feeling it is in open loop but not sure. Unfortunately I do not have HPT. Just going off what I was told from FLP and the readings I get off of a MAC OBDII scanner.
SMOKINV8 - Only knew of these symptoms from FLP when I attempted to get the car tuned. I ran LT headers for ~20,000 miles and had Speed Inc do a basic tune by handing them the PCM. Then I put the Procharger, injectors, and other supporting modifications (pushrods/springs) all at once.
One issue I have is that I really have no idea what Speed Inc and then FLP did to my PCM. I would have expected FLP to override everything Speed Inc did when they allowed the car to run on the 60lb injectors. I would have also expected them to ensure the settings on the PCM were correct since they did have it on the dyno at one point. FLP says it is not a tuning issue?
One issue I have is that I really have no idea what Speed Inc and then FLP did to my PCM. I would have expected FLP to override everything Speed Inc did when they allowed the car to run on the 60lb injectors. I would have also expected them to ensure the settings on the PCM were correct since they did have it on the dyno at one point. FLP says it is not a tuning issue?
Thread Starter
Joined: Mar 2002
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From: SW Chicago, IL
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Seems pretty odd. I'd be willing to bet there's some sort of vacuum/boost leak somewhere. I'd also be willing to bet your injectors aren't setup correctly in your tune. The high voltage in the O2 sensors is likely due to the injectors bottoming out on the minimum pulse width. If ALL of the minimums haven't been adjusted properly, then you'll be idling rich (as indicated by a high mV reading on the O2s).
If you can, post a copy of your tune and someone will take a look at it. But, check for mechanical issues as well...
If you can, post a copy of your tune and someone will take a look at it. But, check for mechanical issues as well...
Thread Starter
Joined: Mar 2002
Posts: 5,778
Likes: 4
From: SW Chicago, IL
Seems pretty odd. I'd be willing to bet there's some sort of vacuum/boost leak somewhere. I'd also be willing to bet your injectors aren't setup correctly in your tune. The high voltage in the O2 sensors is likely due to the injectors bottoming out on the minimum pulse width. If ALL of the minimums haven't been adjusted properly, then you'll be idling rich (as indicated by a high mV reading on the O2s).
If you can, post a copy of your tune and someone will take a look at it. But, check for mechanical issues as well...
If you can, post a copy of your tune and someone will take a look at it. But, check for mechanical issues as well...
Makes sense about the tuning issue. Frustrating since the tuner shop says the tune is setup fine.
Thread Starter
Joined: Mar 2002
Posts: 5,778
Likes: 4
From: SW Chicago, IL
Here is 1 of 2 photo's I attached. See below for other one:
Did a boost leak test. Found a few leaks and fixed them all. Unbolted the rockers and pressure tested the manifold, as well as the entire setup back. No leaks at the manifold or injectors. After fixing the leaks the O2s still read at 900mV. The MAF still reads low at 4-5 g/sec.... ???
Seems pretty odd. I'd be willing to bet there's some sort of vacuum/boost leak somewhere. I'd also be willing to bet your injectors aren't setup correctly in your tune. The high voltage in the O2 sensors is likely due to the injectors bottoming out on the minimum pulse width. If ALL of the minimums haven't been adjusted properly, then you'll be idling rich (as indicated by a high mV reading on the O2s).
If you can, post a copy of your tune and someone will take a look at it. But, check for mechanical issues as well...
If you can, post a copy of your tune and someone will take a look at it. But, check for mechanical issues as well...
Last edited by MadIceV8; Aug 2, 2012 at 06:18 PM.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
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From: So.Cal.
it could also mean the MAF is too close to the throttle blade (the bottom opening blade distorts the airflow to the lower part of the MAF).
Last edited by joecar; Aug 1, 2012 at 04:39 PM. Reason: s/od/of/
Thread Starter
Joined: Mar 2002
Posts: 5,778
Likes: 4
From: SW Chicago, IL
Also to note. The tubes that I had disconnected and saw the rise in g/sec were the two tubes going into the polished plenum box. So the MAF to TB was the same in that respect.
What Joe is saying is that the air isn't going throught the center of the MAF - where the actual sensor is located... It may have to do with the blower causing the airflow to be different. However, as long as it is consistent, it can be tuned around and you shouldn't be running that rich at idle... Personally, I say it is all the more reason to go to a 2 Bar speed density Custom Operating System and ditch that MAF...
You might consider relocating the MAF even to before
the blower; air mass is constant if your leaks are fixed.
Maybe put it all the way up at the inlet. There might be
some transient inaccuracies but then the thing would
be falling back to SD anyway during unsteady-MAP.
Just find some section somewhere that has a straight
or straight funnel kind of geometry (seen blower setups
with a K&N cone type filter and the MAF at the base of
that - not an oiled filter fan, but the plain plumbing
looked kind of right).
the blower; air mass is constant if your leaks are fixed.
Maybe put it all the way up at the inlet. There might be
some transient inaccuracies but then the thing would
be falling back to SD anyway during unsteady-MAP.
Just find some section somewhere that has a straight
or straight funnel kind of geometry (seen blower setups
with a K&N cone type filter and the MAF at the base of
that - not an oiled filter fan, but the plain plumbing
looked kind of right).
Thread Starter
Joined: Mar 2002
Posts: 5,778
Likes: 4
From: SW Chicago, IL
Changed my setup to a front mount. Saw a few improvements in boost (now 8psi) and my MAF g/sec. But the MAF still seems low. My O2's are still reacting the same. Here's the new setup and new numbers I took from the scanner.
MAF Freq ~2260Hz
MAF g/sec - RPM (Done in park)
Front O2s, both banks = 955mV
MAF Freq ~2260Hz
MAF g/sec - RPM (Done in park)
- 5.75 g/sec @ 600
- 8.50 g/sec @ 1000
- 19.30-22 g/sec @ 2000
- 35-45 g/sec @ 3000
Front O2s, both banks = 955mV
Have you cleaned it anytime recently? Any chance that the
blower's lost oil has coked it up over time?
Ever swap in another, right-reading screened MAF from
another vehicle, just to see if it's the piece or its
environment?
blower's lost oil has coked it up over time?
Ever swap in another, right-reading screened MAF from
another vehicle, just to see if it's the piece or its
environment?
Sounds like the min pulse width isn't low enough and possibly they took fuel out of the maf table to try and fix it but didn't work. You really need to get someone with hptuners to pull the file and post it up so we can see what it going on in the pcm.
