Torn MAF boot causes interesting symptom

Bob Owner/Technician Massachusetts Posted   Latest   Edited  
Tech Tip
Driveability
2009 Nissan Altima S 2.5L (QR25DE) (RE0F10A)
No Acceleration
No Codes
Intermittent

Ok, you know what was broken from the description but I thought the failure mode was interesting enough to post. I'm sure we have all diagnosed torn MAF boots that cause a hesitation, bucking, stumble etc. This symptom however was much different than I have experienced before and I have now seen 2 different vehicles with exactly the same fault symptom.

Customer stated that sometimes the car would not accelerate from a stop. A system scan found no stored codes, so I took a road test. It took me a few tries to duplicate the symptom but I found that if I accelerated with just the right load, the power would drop off and then there was no further response from the accelerator pedal. It was like a flat spot and I could keep pushing the gas pedal with no response from the engine. No bucking or jerking, just no acceleration. A couple times when I hit the flat spot I would hold the gas pedal steady and after a few moments the engine would suddenly take off.

The way this manifested itself had me a little perplexed at first and I was not even thinking about a MAF issue. When I looked at scan data I noticed that during the fault the throttle opening would flat line and stay fixed while the APP continued moving. I also saw the the fuel system went lean at the same time. I thought I was dealing with some crazy type of failure strategy.

Here's how I figured out the first one. I had the car in the parking lot and tried power braking the engine in drive. When I hit the flat spot I heard very loud spark knock. I immediately thought of spark timing being too advanced. I know a dirty MAF usually causes spark knock due to advanced timing but the vehicle didn't have a fueling problem except at that one certain load.

Next I power braked the engine in reverse. There was NO flat spot and NO spark knock. I immediately knew what I needed to look at and sure enough, the boot has a tear. The other vehicle I just had with the exact same symptom was a Nissan Rogue. I had that one diagnosed in about 5 minutes.

I marked up a scan data capture of me power braking the engine in Rev first and then Drive. You can clearly see what's happening when the tear opens and allows a big gulp of pirate air. I believe the symptom difference has to do with whether or not the engine has a throttle cable or drive by wire. I'm not sure why the throttle opening becomes fixed. I would love to hear your thoughts on this.

Now that I have experienced two of these my 2 big diag tips would be to 1) Power brake the car in Drive and Reverse and 2) Listen for spark knock. Watch for the flat spot to only happen in drive and keep you ears open for spark knock.

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Justin Mobile Technician
Utah
Justin Default
 

What do us deaf guys do? lol

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Bob Owner/Technician
Massachusetts
Bob Default
 

Turn up your hearing aid? Just kidding you.

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Justin Mobile Technician
Utah
Justin Default
 

If only a hearing aid would work for me. Nerve damage is still not anything they can repair yet.

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Ken Owner/Technician
New Jersey
Ken Default
 

That car might come back soon. 2008 to 2015 those cars had made read issues where a flash is needed to completely erradicate the problem. Most of the time a new boot and maf was installed and p0101 or p0106 would pop back up after 100 or so miles. There is more to this than a busted boot.

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Bob Owner/Technician
Massachusetts
Bob Default
 

The MAF was not replaced, just the boot. I doubt there is anything else wrong but if it comes back I will definitely update this.

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Tommy Technician
Georgia
Tommy Default
 

Every time i have had a vehicle with torn boot the fuel trims do the opposite of what you would think they would do for a vacuum leak. Like you mentioned the power brake method seems to work pretty good, I have found a couple of them that way.

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Hollis Technician
Colorado
Hollis Default
   

I think you're on to it, the difference between throttle by wire or cable. As I'm seeing it, when MAF rate drops, maybe the ECM by design strategy may or obviously inhibits throttle opening irregardless of APP input, kinda-sorta ? The last time I experienced this scenario was on a FWD Toyota with a throttle cable with the classic symptoms and that was close to twenty years ago, but guess what I…

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Ray Diagnostician
Ontario
Ray Default
 

Thank you for the post. I've found over the years that a torn MAF boot is usually caused by one or more broken or worn out transmission or engine mounts. A cracked and leaking front exhaust flex pipe is usually caused by the same issue.

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David Technician
California
David Default
 

There is some confusion on your labeling , the first peak you label as D at the AAP and A/f alfa is the second peak ,I'm bit confused . thanks

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Bob Owner/Technician
Massachusetts
Bob Default
 

There was a mistake in labeling. In hindsight I should have lined up the APP and TPS graphs on top of each other to see the relationship easier.

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Geoff Diagnostician
Hawaii
Geoff Default
 

Not that you would waste the time....(however the customer base here only goes to a shop as a last resort)....I wonder.... if you induced the issue enough times, if the ECM would admit defeat and set a DTC and go into limp. It sounds like it was "thinking" about going into limp but wasn't quite sure. Here's a pic of a Honda I looked at a couple weeks ago that wouldn't idle, can you guess what…

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Bob Owner/Technician
Massachusetts
Bob Default
 

That's a good possibility Geoff. I'm thinking that the ECM sees a rationality error and fixes the throttle position for safety reasons. Is that a piece of rubber from the air filter? Mouse chewed?

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Geoff Diagnostician
Hawaii
Geoff Default
 

That's a piece of "rib" from the intake tube. That's how long they waited to bring the car in. Not when it started cracking....

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Scott Manager
California
Scott Default
 

Thanks for sharing this Bob, can you share the Snap-on data log file with us?

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Bob Owner/Technician
Massachusetts
Bob Default
 

Just uploaded it

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Scott Manager
California
Scott Default
 

Thanks, It appears that the pid list is the same as what's offered at the OEM level. Generic OBDII would have likely delivered the PIDs I was after. I would have loved to have been able to plot out cyl/air and spark like so in order to illustrate the spark table reference.

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Interesting
Dmitriy Analyst
Ontario
Dmitriy Default
 

Hi Scott, I took the values from the pids file Bob posted for the Murano (6 cyl), got something like this. Does this look reasonable? diag​.​net/file/f5f3mk5rb… ​

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Scott Manager
California
Scott Default
 

Ah, I didn't look at the Murano file (yet) but what you did looks great, I'm almost afraid to ask how you did that though... ;) I was hoping that his other log had the MASS AIR so I could see the delta air charge from reverse to drive.

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Dmitriy Analyst
Ontario
Dmitriy Default
 

The pids for Altima have MAF voltage with precision of only one digit after the point... And assuming exponential function to convert voltage into g/sec... here goes nothing: diag​.​net/file/f4yk140k9… ​ P.S. For this dataset I just used Linux buddies (grep, sed, awk) to extract column data, then used Octave to plot. Would not be hard to make an online tool, but is there demand for…

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Hollis Technician
Colorado
Hollis Default
 

Hi Dmitriy. Interesting, I've been searching for a way to convert data to graph form. I'm not very computer savvy. Can you point me in a direction to convert the data format in this link / file, if that's even the correct terminology ? docs​.​google​.​com/spreadsheets/d…

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Dmitriy Analyst
Ontario
Dmitriy Default
 

Hollis, Google says: no permissions to access the file...

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Hollis Technician
Colorado
Hollis Default
 

Yeah, me and Google got this thing goin' security, security, security, dear valued customer, ect :O) Thanks, I'll dink around with it with and the other bazillion things I got going on and when I figger it out you'll be the first I share with. It's 'Live Data' from a Blue Driver Bluetooth Scanner that when the 'Share' function is selected and emailed shows up as a long data list. I was hoping…

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Bob Owner/Technician
Massachusetts
Bob Default
 

Do the timing data points come from a selected part of the graph or is it an average of the whole capture? BTW, I uploaded another Murano capture that has a series of normal accelerations and then at the end it has 2 or 3 significant flat spots. I notice during a normal accel the timing is around 15 deg and when the fault is occurring the timing is about double that in the 30's. I also added…

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Dmitriy Analyst
Ontario
Dmitriy Default
 

For the table I calculated, Ignition Timing data points come from the whole dataset. Do you expect the ignition timing map to change when the issue occurs?

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Bob Owner/Technician
Massachusetts
Bob Default
 

I'm thinking the answer to the question is yes if i'm understanding it right. I'm guessing the timing map is programmed into the ecm according to load, rpm, tps and air mass. When the fault is happening there is a rationality skew in the data pids causing the wrong timing output. Am I on the right track?

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Scott Manager
California
Scott Default
 

Hi Bob, The spark table is primarily driven by RPM over Cylinder air mass. What's happening is that the engine controller thinks that there's less air mass at a particular RPM when in fact there's a higher mass. The spark table at that lower mass is calling for advanced timing, more than it needs and therefore you have detonation. That's the way I see it. Since we cannot see the actual…

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