818 MAF sensor failure at track days

[Dave 53]

Earlier in the year, I did a track day at Big Willow Springs. A few miles into my drive home, the engine started running like ****. No check engine light. Turned out to be the MAF sensor. Cleaning it didn't help. Bought whatever brand MAF my local parts store had in stock.

Had a track day at Laguna Seca yesterday. I'd been a passenger there years ago, but this was my first time driving. First session I just poked my way around the track and the car was running great. Second session, I was starting to find my groove, but towards the end of the session, the engine lost power. No OBD codes. Suspected maybe the AWIC wasn't working - it was fine. And I fabricated a card board heat shield between the AWIC and new oil cooler thinking maybe the oil cooler was heat soaking the AWIC. Added a couple of gallons of 101 octane track gas. (The 91 track gas was 70 cents a gallon cheaper than out on the street. Needless to say, we emptied their tank). Third session, I got two powerful laps in, then the engine lost power again. Grasping at straws, I ran into town and got a new fuel filter even though the logic didn't hold up because it would run good a couple of laps before loosing power. Fourth session, two laps in big power drop, but got a MAF check engine light. Reset the code and started in the back for the fifth session and sure enough, 2 laps in, power loss and check engine light. Unlike my Willow Springs experience, the drive home was fine, but of course, that's not track conditions. At least now I know what it is - MAF sensor.

Just ordered a Denso MAF sensor for $115 hoping it's quality and will be more robust than a Amazon $25 MAF. I think Denso is OEM and OEM is just under $200. I'll be adding a spare to my track kit.

My engine guy said it's not uncommon for the MAF sensor to go bad without throwing a code. Any time my engine starts to run poorly without a check engine light, MAF is going to be the first thing to check.

That's 2 MAF sensors gone bad at or very shortly after a track day. Anyone else killing MAF sensors at the track?

[Rob T]

Dave: When I had my engine rebuilt at Yimi Motorsports in LA, Paul Leung replaced the MAF with a speed density tune. I had that tune verified when I was in New Mexico by another tuner who said it was "perfect". No problems since then. On a really hot track day, with SD, I did see the engine pull a bit of timing and my knock readouts on the COBB, which I monitor on the track were not at "optimum". Not sure how SD fits in with the new Cobb "green" rules, etc.

[Dave 53]

It seems with the Cobb Green, I'm pretty much stuck with the tune I have without throwing a bunch of money at it (standalone ECU, retune). Not that I'm complaining. I'm very very happy with the tune as long as the MAF sensor doesn't fail. I'm hoping the MAF failed because it was of substandard quality and a new "quality" Denso unit will me more reliable.

What are you monitoring on track with the Cobb and how do you interpret what it's telling you?

[Rob T]

Here is what I am monitoring on the COBB at the track. In addition, I monitor and log transmission temp, A/F ratio and AWIC supply water temp (different than intake temp) on my Traqmate system. There are many things stored on the COBB unit if I remember to hit the log button when I start. I also have analog gauges for boost, water temp, oil temp, oil pressure and A/F ratio.

[Dave 53]

Here is what I am monitoring on the COBB at the track. In addition, I monitor and log transmission temp, A/F ratio and AWIC supply water temp (different than intake temp) on my Traqmate system. There are many things stored on the COBB unit if I remember to hit the log button when I start. I also have analog gauges for boost, water temp, oil temp, oil pressure and A/F ratio.

How do you interpret Dyn Adv Mult and Fine Knock Learn?

Speaking of intake temp... It is my understanding the intake temp is taken at the MAF sensor. I just reviewed some logs. My intake temp got up to 178*! And timing was being pulled as a function of intake temp. At WOT around 5,000 rpm and intake temp of 106*, timing was 8, but only 1 at 176*. I couldn't break 6,000 rpm with intake temp over 167* or 5,000 rpm over 174*. MAF voltage and other logged parameters seemed to acted consistently regardless of intake temp - only timing seemed to be linked. After about 2 laps, it seems air intake temp had reached critical temperature and the ECU cut power accordingly.

Now I'm thinking it could be a bad thermometer in the MAF.

167720Or more likely, my air intake is in a bad / hot place. What changed is I finally installed a diffuser under the tranny and that might have changed the air flow patterns in the engine compartment. And I've got a new oil cooler blowing hot air into the engine compartment.

I'd like to tape a thermometer in a couple of different engine compartment locations, with and without the diffuser, but this is only an issue at the track. I'd like to get this figured on before my next track day (might be Buttonwillow, but not until the end of July).

I'm interested in seeing pictures of alternate air intake locations / cold air intake solutions.

[Rob T]

As I don’t have a passenger seat, my air filter is right where the head of the passenger would be. My intake temp is measured after the turbo and AWIC. It is typically 10-15 hotter than my awic water temperature. I’ve only seen my car pull timing one time when I noticed the intake temp around 125 or so. Pulling air from around the engine makes it much more challenging to get cool air to the engine.

[blomb11]

You might want to try and get your air filter down closer to the passenger side vent to try and get in the air stream or you can duct ambient air flow from the side vent up to it to help. Having it right up against the rear firewall and short like that I would think there is not good air flow to it and you are probably just sucking in hot engine air.

[J R Jones]

There are two likely influences to a MAF failure, heat and vibration. Heat is not an issue while running due to air intake. Heat soak after running could be a problem, especially from near-by exhaust.
Vibration could be a problem due to solid engine mounts of MAF support. It seems a horizontal wire orientation is more effected by road shock than a vertical wire orientation.
jim

[carnutdave]

Dave 53, here is where my intake filter ended up. It seems to be in a good place right near the side duct. Using the stock piping and a Cobb short ram setup I got off Ebay. I've only driven the car ~450 miles on the street so far but I have IAT up on my Accessport (not logging) and have never seen the temps go too high.

167752167753167754

[Sgt.Gator]

How do you interpret Dyn Adv Mult and Fine Knock Learn?

From the now old Cobb Subaru Datalogging Guide:

Monitor: DAM

What it does: DAM, or Dynamic Advance Multiplier, is a learned correction that adjusts overall timing.

What the numbers mean: For the 02-05 WRX, this number ranges from 0 to 16. For all other turbo model Subarus, this number ranges from 0 to 1 in tenths of a decimal (ex: 0.8). The number advances upwards when no knock is detected and decreases for extreme knock situations. You always want this number to be at it’s maximum value.

Why you monitor it: If you ever see this number decreasing, you have a potential severe knock situation.
What to look for: The starting value will depend on the vehicle and tune, but it should always learn up to the maximum value. This value will reset to it’s starting point after a map Reflash, an ECU reset, or a battery disconnect. If you see this value begin to drop under any other circumstance, you most likely have a severe knock situation. You should immediately analyze the tune and mechanical condition of your vehicle.

<<>>

Monitor: Fine Knock Learning

What is does: Fine Knock Learning is a learned correction that makes small corrections to timing once the DAM has settled.

What the numbers mean: The values are degrees of timing being added or subtracted. An initial correction is typically -1.4, but is learned away in increments of 0.35.
Why you monitor it: When Fine Knock Learning hits extreme values, the ECU may start to adjust the DAM.

What to look for: Occasionally under low loads you might see an initial knock value followed by several values of that number decreasing in the incremental value (ex: -1.4, -1.05, -0.7, etc). This would mean that the ECU is already learning the correction away, and would be nothing to worry about. These values would also immediately go away after an ECU reset. If the ECU is making consistent and multiple knock corrections under load (such as full throttle and full boost) all in a row, you could have a potential knock situation.

<<>>
BTW, if you have a kill switch (required by most racing organizations) that will also kill all of the learning the ecu has done. Whenever you disconnect the battery or flip the kill switch off, then later start the car, it's best to let it idle for awhile then take the first track laps easy so the ecu can relearn before you get on it.

I've uploaded this guide and another to the links below since Cobb has moved away from supporting individuals:

Cobb Datalogging Guide (https://1drv.ms/b/s!AjtLSJvxEnlPmxGWdOJAliPlgemA)


Cobb Accessport Tuning Guide (https://1drv.ms/b/s!AjtLSJvxEnlPmxGWdOJAliPlgemA)

[Dave 53]

From the now old Cobb Subaru Datalogging Guide:

Monitor: DAM

What it does: DAM, or Dynamic Advance Multiplier, is a learned correction that adjusts overall timing.

What the numbers mean: For the 02-05 WRX, this number ranges from 0 to 16. For all other turbo model Subarus, this number ranges from 0 to 1 in tenths of a decimal (ex: 0.8). The number advances upwards when no knock is detected and decreases for extreme knock situations. You always want this number to be at it’s maximum value.

Why you monitor it: If you ever see this number decreasing, you have a potential severe knock situation.
What to look for: The starting value will depend on the vehicle and tune, but it should always learn up to the maximum value. This value will reset to it’s starting point after a map Reflash, an ECU reset, or a battery disconnect. If you see this value begin to drop under any other circumstance, you most likely have a severe knock situation. You should immediately analyze the tune and mechanical condition of your vehicle.

<<>>

Monitor: Fine Knock Learning

What is does: Fine Knock Learning is a learned correction that makes small corrections to timing once the DAM has settled.

What the numbers mean: The values are degrees of timing being added or subtracted. An initial correction is typically -1.4, but is learned away in increments of 0.35.
Why you monitor it: When Fine Knock Learning hits extreme values, the ECU may start to adjust the DAM.

What to look for: Occasionally under low loads you might see an initial knock value followed by several values of that number decreasing in the incremental value (ex: -1.4, -1.05, -0.7, etc). This would mean that the ECU is already learning the correction away, and would be nothing to worry about. These values would also immediately go away after an ECU reset. If the ECU is making consistent and multiple knock corrections under load (such as full throttle and full boost) all in a row, you could have a potential knock situation.

<<>>
BTW, if you have a kill switch (required by most racing organizations) that will also kill all of the learning the ecu has done. Whenever you disconnect the battery or flip the kill switch off, then later start the car, it's best to let it idle for awhile then take the first track laps easy so the ecu can relearn before you get on it.

I've uploaded this guide and another to the links below since Cobb has moved away from supporting individuals:

Cobb Datalogging Guide (https://1drv.ms/b/s!AjtLSJvxEnlPmxGWdOJAliPlgemA)


Cobb Accessport Tuning Guide (https://1drv.ms/b/s!AjtLSJvxEnlPmxGWdOJAliPlgemA)

Gold!!!

Thanks!

[Dave 53]

Old air intake location. This seems to be a pretty common 818 set up.168184

New air intake location.168185

80 degree day driving down the freeway: Old location MAF air intake temp was 122. New location MAF temp was 80.

Recall that at the track, I was getting a MAF temp of 178!

The high temps with the old set up are for two reasons.
1. The MAF is inches next to the hot coolant expansion tank, directly above a coolant pipe and generally over the hot engine. Immediately after my old intake location test run, I measured the top of the MAF sensor at 148. I wouldn't be surprised if the top of the MAF sensor was 200 degrees on track. So, the radiant heat of the engine is heat soaking the sensor giving an artificially high reading.
2. The old location is sucking in hot air. I think adding the diffuser under the tranny made the situation worst.

The new location is 44 degrees cooler than the old location freeway driving at 75 mph. With the new location, the intake is getting cool air from the side vent and the MAF is away from radiant heat.

I thought about fabricating some ducting around the air filter and cutting out the body side vent for more air flow, but since MAF is reading ambient temp, I don't see the need at this point. Maybe it would make a difference on track, so I'll be paying attention to that my next track day.

MAF temp was never a problem on the street. Temps never got high enough for the ECU to cut power. But on track, it was an issue. Even so, on a street car with the intake set up like I use to have and I think most 818's have, I might suggest putting some sort of heat shield around the MAF pipe and MAF sensor. Sensor heat soaking is defiantly adding to the MAF temp reading giving the ECU an inflated read.

I'm fairly confident this fix will solve the extreme MAF temp issues I was having at the track.

I started this thread thinking I had a MAF sensor failure. Turns out, the MAF sensor was just in a suboptimal location.

But now I have a new problem. Gonna start a new post on that.

Update: It's looking like changing the air intake pipe requires that the MAF be rescaled in the tune. Working on that....

[Dave 53]

Quote From Sgt.Gator:
Looking at the pics in your other MAF thread in the general discussion (Hint this should be in that thread IMHO ) ....I'll take a guess that the maf is too close to the filter and the filter is now getting turbulent air from the new location at the scoop. That's gotta be a turbulent location.
If possible, try re-locating the MAF sensor further from the filter where there's a few inches of straight pipe on both sides of the sensor. Or move the filter up away from the scoop, or tape the scoop closed, even if it's just temporary to rule out a wiring issue.
You can also try using a honeycomb maf straightener. Google search "maf air straightener". They are just honeycomb "filters" you install.

This guy has has been making filter plus adaptors that includes a housing along with the honeycomb filter. He makes them in a bunch of intake pipe sizes to fit Subaru mafs. I think I still have one buried in my spare parts storage. What size is your intake pipe?

2.5 OD MAF Mass Air Flow Housing Air Straightener for 02-07 Subaru WRX STI



Sgt.Gator, thank you for introducing me to the world of the air flow straightening grid!

I have the (old) Cobb MAF/air filter housing combo pipe that has a very rudimentary air flow straightening grid. 168300I see on the Cobb web site the current version I think has an air flow straightening screen grid, but they don't show a picture. Intuitively, I think you are on to something about the turbulent airflow passing the MAF sensor caused by the air filter being where I put it inside the side scoop.

One of my goals was to get the MAF away from the hot engine. The Ebay air flow straightening pipe makes sense, but I can't think of a place it would fit except for the same (hot) location that I had the MAF before. Seems the newer Cobb combo MAF/ air filter pipe that DOES have a straightening grid built in might be the solution. Also, I see your Ebay guy sells just the straightening grid for about $20. I think I can just add that to my current Cobb pipe.

No matter what, I think I need the tuner to "rescale" the MAF because it was originally tuned in the old non-air flow straightened location and I've now heard from a couple of tuners that if the air intake design is changed pretty much in any way, the MAF needs to be "rescaled". Waiting to hear back from him if he thinks an air flow straightener grid in my MAF/filter pipe (new $225 Cobb or adding $20 Ebay grid to my current Cobb) is necessary or any other advise he might have before retuning.

[Sgt.Gator]

The scaling has to do with the diameter of the pipe the maf is installed in. If you change the intake pipe diameter, then yes you have to rescale. But bends in the pipe shouldn't cause a rescale.
And I still think throwing some duct tape over the outside of the scoop to stop the airflow is a test worth doing.

[Dave 53]

The question: Is air turbulence across the MAF due to it being so close to the side scoop causing drivability issues?

The test: Drive with the scoop open vs. covered at various loads, RPM and speeds.

The results: Side scoop open, air intake temp 90 degrees. Between 2-3k+ rpm under light load, engine stumbles, all speeds. Horrible drivability.
Side scoop covered, air intake temp 110 degrees. Under all conditions of load, RPM and speed, the car runs like a champ!

Conclusion: With scoop open, the MAF is reading turbulent air flow.

Next test: Install an air flow straightening screen in front of the MAF and retest.

Thanks to: Sgt.Gator!!!168335168336

[Sgt.Gator]

Great, you are on your way!
Years ago I cut a hole in my LGT headlight housing and inserted a filter on the outside, then in a later version on the inside.
168364..168365

And now you know why I know about MAF straighteners!

[Dave 53]

Update and I hope the final chapter...

I added the air flow straightening grid in front of the MAF sensor. In fact, two of them. Drove several hundred street miles. Did several experiments with baffling around the air cleaner to try and reduce turbulence even more. With an uncovered side scoop, the air straighteners improved drivability about 80%, but still a bit of stumbling. Completely covering the side scoop to improve drivability wasn't an acceptable solution.

I've learned from my tuner a built engine with a bigger turbo might be sucking in more air than the MAF can read. This will throw a P0103 code - MAF over voltage. When this happens, the ECU doesn't know what to do and is at its limit. The most common solution seems to be a Speed Density tune which doesn't depend on the MAF (as much). I started getting a P0103 code at full throttle much more often than I did before changing my air intake. Maybe because the intake was getting a bit of a ram air effect in the new location behind the side scoop.

I did as much research and talked to as many people as I could about the need to rescale the MAF after moving it. Some say no need to rescale the MAF (make ECU software changes), others said if you do anything to the air intake, it needs to be rescaled and that I should just get a Speed Density tune. Maybe there are other variables in play that allows a change to the air intake without rescaling the MAF, but in my case, the car just wouldn't run right unless I completely blocked off the side scoop.

Took it to my tuner and he suggested and did a Speed Density tune. This did not require any hardware changes. Now the car runs smoother than ever - case closed (I hope)!! And the new tune found 15 horsepower that wasn't there before. I hope to be at Buttonwillow July 30/31 for a track shake down.

I'm amazed on how much my simple little change to the air intake piping affected the performance of the engine. These are the problems and solutions of a track car. Everything was perfectly fine before on the street.

[Rob T]

I have a speed density tune, for the same reasons. I am sure you will be happy with it. Let us know how it goes at Buttonwillow.

[blomb11]

From everything I have learned and understand (limited knowledge) from looking into tuning via Cobb on a WRX/STI platform, any changes to the intake requires a tune update. You can even see in the Cobb database they have different maps for different intakes (Cobb SF, AEM, etc.) so changing the filter or length could definitely effect this and require a new tune. For higher HP and tune stability I have been told a speed density tune is the way to go. I plan to convert to this down the road....once I get to the road that is :).

[STiPWRD]

Took it to my tuner and he suggested and did a Speed Density tune. This did not require any hardware changes. Now the car runs smoother than ever - case closed (I hope)!! And the new tune found 15 horsepower that wasn't there before.
To maximize your speed density tune, I'd suggest adding a temperature sensor to the cold side of your AWIC. This will give you the most accurate reading of the air going into the engine, which is what all the speed density calculations are based on. Because you didn't change any hardware, your tuner probably used the temperature sensor inside the MAF - this isn't very accurate considering it's before the AWIC. I'm running an SD tune and installed an AEM IAT sensor into one of the holes at the bottom of the AWIC. I had to open up the hole and re-thread it to 1/8 NPT.

[Dave 53]

To maximize your speed density tune, I'd suggest adding a temperature sensor to the cold side of your AWIC. This will give you the most accurate reading of the air going into the engine, which is what all the speed density calculations are based on. Because you didn't change any hardware, your tuner probably used the temperature sensor inside the MAF - this isn't very accurate considering it's before the AWIC. I'm running an SD tune and installed an AEM IAT sensor into one of the holes at the bottom of the AWIC. I had to open up the hole and re-thread it to 1/8 NPT.

Wish you told me that before!

The only thing I really knew about Speed Density before yesterday was that it existed, and several friends were telling me I needed it. When the tuner suggested it, I didn't see that coming and was caught a bit off guard. I would have done a stupid amount of research on Speed Density beforehand had I known that's the direction we would be going. I asked if any hardware changes were needed, and he said we were good to go. Okay then...

At this point, moving the temp sensor to the AWIC would require a whole new tune which I'm not up for $$$ wise at this point. If I need a retune in the future for some other reason, I will give very serious consideration to your advice.

It doesn't make sense to me that intake air temp is taken from the MAF sensor. The temperature is measured, then it runs through a turbo, then an intercooler. There is no way the temp inside the manifold is the same as at the MAF, but more importantly, I suspect the relationship isn't linear. On the normally aspirated EJ engine, air intake temp is taken at the manifold, so why is it taken at the MAF on a turbo version? There must be some logic to it above my pay grade.

[Sgt.Gator]

You want a dedicated air temp sensor close the throttle body in the IC tubing. But not in the intake manifold. The IM is thick aluminum that will heat soak and affect the sensor. You want the sensor responding as quickly as possible to temp changes and as accurate about the actual temp of the air going into the engine as possible, that's why you put it in the IC tube just in front of the throttle body.
When you rewire for speed density you can eliminate the MAF.
You can also go "hybrid" which is a combination of a MAF and speed density tune.

Learn all about it here: https://iwireusa.com/blogs/iwire-university/subaru-speed-density-explained

I use the iWire Kit: https://iwireusa.com/products/speed-density-wiring-kit?variant=41181609033881

[STiPWRD]

Wish you told me that before!

Sorry, I haven't been on the forum in a while. My guess is the stock IAT is measured at the MAF because it is measuring volume flow at that same location. Since air density changes with temperature, knowing the volume flow rate and temperature allows the ECU to calculate mass flow rate of air.

In the future, if you install a dedicated IAT sensor and want to save a bit of $ over the iWire harness, this site sells the connectors and pins:
https://www.corsa-technic.com/item.php?item_id=819&category_id=144
https://www.corsa-technic.com/item.php?item_id=656&category_id=144

[Dave 53]

I've had EVERYONE (not just this forum) questioning using the MAF temp sensor at the air intake on a Speed Density tune, so I asked my tuner how to answer that. He said two things...

1. Since we didn't initially know we were going to switch to Speed Density, he used the intake temp at the MAF because I didn't have a throttle body temp sensor and his software has an offset table to adjust for the temp being taken at the intake.

2. If I added a new temp sensor (to the cold side of the intercooler), he could just email me an updated map that I could flash onto the ecu. This is what I will do.

Thanks Sgt.Gator for the iWire lead on their Speed Density wiring kit. Although, at $80, I'll just splice in a new plug for the temp sensor. I can see from the picture it's the green and brown wires.

Thanks STiPWRD for the lead on the AEM IAT sensor.