[Val Walkinshaw]

Just curious.
Short term and long term fuel trims are running out of range in the negative which is a sign of a faulty MAF along with other potential causes. O2 sensors are next on my list, much before the injectors.

Just curious how many of you have experienced this.

Already bought it for $66 on rock auto but just wanted to get a feel for often folks have trouble with these.

[SomeGeoffGuy]

Generally, MAF problems are seen when you run an oiled filter and you get a little too aggressive oiling it. I have rarely seen them randomly go bad, but I guess that is a possibility.

Back in my Grand National days, the MAFs would go bad, and you could tap on the MAF housing and it would cause a stumble.

-Geoff

[bishopts]

Originally Posted by Val Walkinshaw

Just curious.
Short term and long term fuel trims are running out of range in the negative which is a sign of a faulty MAF along with other potential causes. O2 sensors are next on my list, much before the injectors.

Just curious how many of you have experienced this.

Already bought it for $66 on rock auto but just wanted to get a feel for often folks have trouble with these.

MAF failure without codes is pretty rare. In fact. Ive never replaced a MAF without an accompanying code. I would look harder at other things.
Fuel in the oil from the high pressure pump leaking into the crankcase,
Restrictive air filter,
Repeatedly shutting off the engine before operating temperature,
Fuel quality,
Worn spark plugs.

Im a diag tech by trade. Throwing parts at the problem without actually testing anything is literally the last thing i would do.

[Junction65]

Not camaro related however my GMC 1500 (95K miles and running oe filter) started throwing a code for MAF. Got some MAF spray cleaner and attempted to clean it, albeit no resolution kept throwing code. Ended up replacing just the MAF with the OE part. Took like 5 mins to swap out, didn't even get to finish the first beer. Resolved issue, no more problem.

[Val Walkinshaw]

Originally Posted by bishopts

MAF failure without codes is pretty rare. In fact. Ive never replaced a MAF without an accompanying code. I would look harder at other things.
Fuel in the oil from the high pressure pump leaking into the crankcase,
Restrictive air filter,
Repeatedly shutting off the engine before operating temperature,
Fuel quality,
Worn spark plugs.

Im a diag tech by trade. Throwing parts at the problem without actually testing anything is literally the last thing i would do.

All fair points. If you take a look at the values I have from the HP tuner file you will have a better idea why I threw parts like a MAF sensor at the car. The MAF is reading is high for 600 rpm and the fuel trim is off. Car has 50k but I have spark plugs and wires on hand due to many track days and noticing this stumble/misfire previously. BTW misfire count on cylinders 6,7,8 are all under 10.

Edit fuel quality is top tier premium.
Car is never run for short periods before up to operating temp of 180 or so
Air filter is rotofab cold air intake, non oiled.

Edit 2 have had 2 samples sent to Blackstone for analysis and neither have been anything other than acceptable, no mention of fuel in oil. (I do this with all my vehicles routinely fort good meausre)

[vince3]

What all is done to the car and is it tuned? If tuned, who tuned it? Have you posted a log to HPtuners? Someone with a MAF error % can look at your logs and see if the MAF is on point.

[bishopts]

Top tier doesn't rule out Bad Batch.

Spray a very little bit of starting fluid on the air filter while it's running and see how quickly it pegs out the fuel trim. It will help determine response time and consistency with the o2 sensors. It should move pretty much the same with both sensors, down and back up on recovery.
You can even spray it on a shop towel then put the towel on or near the air filter to control it better.

Clean your throttle plate and rezero your airflow compensation. (Make sure it's not 100% while you're there)

Not even having a p1101 leans further away from MAF. You will get that code for dumb things like a bad dipstick seal so if your MAF is out of range 1101 is almost guaranteed.

Grams per second is easier and more accurate for reading MAF values

Check your coolant temp sensor and back check it with a temp gun. Just to make sure it isn't running rich because it thinks it's cold

[Val Walkinshaw]

Originally Posted by vince3

What all is done to the car and is it tuned? If tuned, who tuned it? Have you posted a log to HPtuners? Someone with a MAF error % can look at your logs and see if the MAF is on point.

No tune
No mods.
It's my my HP module because I was looking at sending off a base tune file to them when I was thinking about a tune.

Maf should be . 2-.9 lb/min. Mine is reading 1.4 lb/min.

Those forums are a bit of a mess in my experience.

I also have used my bidirectional autel to do some snooping hence how I know about the lack of misfires.

My main problem is a rough idle at 600 rpm/stumble, small reduction in power (not proven but it feels that way) and gas mileage that started at 10mpg for some time under gentle driving that has now worked its way up to 18. I didn't drive the car much last year due to unfortunate circumstances so I'm trying to pick up where I left off with this issue.

[Val Walkinshaw]

Originally Posted by bishopts

Top tier doesn't rule out Bad Batch.

Spray a very little bit of starting fluid on the air filter while it's running and see how quickly it pegs out the fuel trim. It will help determine response time and consistency with the o2 sensors. It should move pretty much the same with both sensors, down and back up on recovery.
You can even spray it on a shop towel then put the towel on or near the air filter to control it better.

Clean your throttle plate and rezero your airflow compensation. (Make sure it's not 100% while you're there)

Not even having a p1101 leans further away from MAF. You will get that code for dumb things like a bad dipstick seal so if your MAF is out of range 1101 is almost guaranteed.

Grams per second is easier and more accurate for reading MAF values

Check your coolant temp sensor and back check it with a temp gun. Just to make sure it isn't running rich because it thinks it's cold

To rezero the airflow comp unfortunately I'm not finding idle learn rest under ecm special functions. Not supported.

I removed thr MAF and studied the numbers real time. Fuel trim and O2 sensors responded appropriately. I don't remember the DTCs it threw. Thought I snapped a shot. Will repeat MAF removal to verify 1101 shows up.

[bishopts]

Originally Posted by Val Walkinshaw

To rezero the airflow comp unfortunately I'm not finding idle learn rest under ecm special functions. Not supported.

I removed thr MAF and studied the numbers real time. Fuel trim and O2 sensors responded appropriately. I don't remember the DTCs it threw. Thought I snapped a shot. Will repeat MAF removal to verify 1101 shows up.

Its under special functions in your autel, it might also be in system tests but my autel is at work so i can't help with that right now. Its usually toward the end of the list of special functions. You could probably also try clear learned values.
Idle relearn is a different thing, pretty much useless to do that since it does it itself every ignition cycle.

Using your autel, go into OBD2 generic. Its the top left that looks like an engine light icon in the list of makes. Then go to mode 6 in the next menu. Look at live data and scroll to the bottom it will have a different list for your misfires compared to the one under the camaro specific data. It will show you a more accurate list of current misfires and past 10 ignition cycles. Just to give you a better idea if you need to change the plugs.

[Val Walkinshaw]

The misfires are for the last 10 ignition cycles. I have a diagnostic print out from 2024 and 2026. both read similarly. would you mind taking some screen shots on your Autel so I can follow the tree to find the correct menu? or even take a video. I have two autels. MK 808 TS and the 906 Pro.
I will admit my limitations here as that you are a tech, I am not but I am gearhead with enough experience to follow along.

I would contact HP tuners but those unfortunate circumstances....my brother and I went in on it together. He suddenly unexpectedly died in January of last year and HP has not been kind to me to transfer over the credits or ownership even though we went in half's on it.

[ember1205]

When you say they are "running out of range", what does that mean and how are you measuring? A common thing that a lot of folks to incorrectly is to review these readings at idle and that doesn't tell the correct story.

Drive the car and watch the numbers under load. I have a WiFi dongle that I pair to TrackAddict on my phone. With that, I can record a diag session to play back later. Set it up, press Record, and head out for a drive. You want to be able to capture data accelerating and holding speed at highway speeds (if possible). Flat roads where you can set the cruise control to anywhere from 45 to 65 for a short bit at least will get you some good long term numbers.

It's extremely common for the numbers to be negative... That's ok as long as they don't run way down and stay there solid.

[Val Walkinshaw]

Originally Posted by ember1205

When you say they are "running out of range", what does that mean and how are you measuring? A common thing that a lot of folks to incorrectly is to review these readings at idle and that doesn't tell the correct story.

Drive the car and watch the numbers under load. I have a WiFi dongle that I pair to TrackAddict on my phone. With that, I can record a diag session to play back later. Set it up, press Record, and head out for a drive. You want to be able to capture data accelerating and holding speed at highway speeds (if possible). Flat roads where you can set the cruise control to anywhere from 45 to 65 for a short bit at least will get you some good long term numbers.

It's extremely common for the numbers to be negative... That's ok as long as they don't run way down and stay there solid.

Thankyou, this is a very good thought process. I have run my torque app and brought up all 4 fuel trims and watched it as I drove last summer for a good 100 miles. It stayed -17. I also with the HP Tuner have hard set the RPM to 1000 and let the car run for an hour to achieve the -23/-27 values just yesterday.

ALso it is winter here. keeping the RPMS at 1k-2k for an hour in my garage is the best I can do to obtain fuel trim values.
Edit I love the track addict app. I forgot about that. I will have to reinstall that. THe more data the better

[ember1205]

Originally Posted by Val Walkinshaw

Thankyou, this is a very good thought process. I have run my torque app and brought up all 4 fuel trims and watched it as I drove last summer for a good 100 miles. It stayed -17. I also with the HP Tuner have hard set the RPM to 1000 and let the car run for an hour to achieve the -23/-27 values just yesterday.

ALso it is winter here. keeping the RPMS at 1k-2k for an hour in my garage is the best I can do to obtain fuel trim values.

Good info... -17 is definitely lower than what one would want, but shouldn't trigger any codes (yet). With the RPM's raised but no load on the engine, the other numbers aren't telling a lot. Having the engine under load will naturally require more fuel, and the LTFT numbers should back off a bit from no load (which seems to match with what you're measuring.

When the numbers are far to the negative, something is causing the ECM to determine there's too much fuel. One of a few things is likely going on:

- MAF is dirty or failed. Try cleaning with MAF Sensor cleaner before replacing.
- O2 sensor is failing. Would -seem- unlikely if both banks are experiencing the same issue since a sensor on both sides would have to be failing at the same time. It would be worth at least checking the wiring, though.
- Leaking injectors.
- Leaking High Pressure Fuel Pump. This pump, used on a LOT of GM vehicles over the years, "used to be" a problem where it would develop a leak. Since it sits under the intake manifold, it would leak fuel directly into the engine, unmeasured. The issue would be detected through low LTFT numbers which were found -after- a CEL was set. I had this issue in my 2014 Silverado and the truck set a CEL on me two different times over a few months - that's what pushed me to investigate and I found the problem through monitoring like I described. The newer pumps should not still have this issue, but it's possible that yours may have been built at the end of the period before they knew of the issue.
- Fuel pressure is too high.

Plenty of other things could be off, but this would be the stuff I would start with.