2015 Infiniti QX50 stall when starting sometimes

Discussion of Infiniti's amazing (and underrated) sport-luxury crossovers, the EX35 and EX37. For 2014, the EX series will be renamed QX50, in line with Ininfiit's new naming conventions.
rjkoop
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2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Sun Nov 15, 2020 5:57 am

Have a 2015 Infiniti QX50 Journey with about 50,000kms.

Noticed that sometimes when I start the engine (especially when cold) the RPMs will come up like a normal start, and then drop to below idle and the car will stall. Pressing the button again it will then start fine and the RPMs will stay high like it should with a cold start and then come down to normal idle when it warms up a bit.

Anyone seen this before? Maybe I should clean the MAF sensor (I assume there is one... haven't checked), check for any loose hoses (maybe a small air leak?), clean the throttle body (looks like they may get dirty quickly on these cars), change the air filter, etc... Haven't done much with this car other than oil changes since I bought it at 38,000kms.

Richard


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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby PapaSmurf2k3 » Sun Nov 15, 2020 10:07 pm

Yeah that sounds like either a lazy throttle/idle, or fuel pump. I'd start with the throttle body like you mentioned.
Are there any codes/check engine light?

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Mon Nov 16, 2020 4:41 am

Nope. No check engine lights. Mileage seems fine and no other issues.

Did the easiest thing 1st. Cleaned the MAF sensor.

Richard

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby sev » Thu Nov 19, 2020 12:04 am

This is a tell-tale sign your throttle actuators are dirty and need cleaning and recalibration. There's a bunch of youtube videos on how to do it, should be about an hour tops to do if you take your time. Let us know if it worked!

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Tue Dec 08, 2020 4:23 pm

Throttle body cleaned. No change. Argh! Guess I'll look for a vacuum leak. It only has 54,000kms. Not sure what else is easy to check.

Once again, cold starts and idles fine. Warm start... sometimes RPMs go up and then down below idle and stalls. Only about every 1 in 5 times.

Richard

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby sev » Tue Dec 08, 2020 4:26 pm

rjkoop wrote:
Tue Dec 08, 2020 4:23 pm
Throttle body cleaned. No change. Argh! Guess I'll look for a vacuum leak. It only has 54,000kms. Not sure what else is easy to check.

Once again, cold starts and idles fine. Warm start... sometimes RPMs go up and then down below idle and stalls. Only about every 1 in 5 times.

Richard
Did you do the throttle re-learn procedure after cleaning the throttle bodies? It will do that if you dont have it relearn.

https://www.youtube.com/watch?v=TZJfWQLGUZI

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby VStar650CL » Tue Dec 08, 2020 4:47 pm

The re-learn could be the whole issue. The characteristics of a MAF can change with age, like any silicon device. I've seen before-after differences in indicated airflow of as much as 30% on 5-10 year old cars that never had IAVL since the factory. It's very often a cause of poor fuel mileage as well as stalling. Our dealership encourages techs to do IAVL as part of any standard tuneup, but not every repair shop does. It's especially critical on Nissan products, because with few exceptions, Nissans have no MAP sensor to allow the ECM to double-check the MAF. The ECM has to trust what it sees, so If the MAF is lying, bad things happen with no codes to indicate a problem.

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby PapaSmurf2k3 » Tue Dec 08, 2020 6:44 pm

VStar650CL wrote:
Tue Dec 08, 2020 4:47 pm
I've seen before-after differences in indicated airflow of as much as 30% on 5-10 year old cars that never had IAVL since the factory.
WOW!!!

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby VStar650CL » Tue Dec 08, 2020 7:28 pm

PapaSmurf2k3 wrote:
Tue Dec 08, 2020 6:44 pm
WOW!!!
Yah, what a little proper experimentation will reveal. Our own '13 Altima was a perfect instance, we bought it with 63K in '16 and it was serviced at a different dealership, records were good but showed no engine work ever. Average mileage in the cluster was horrible for an Altima, just 21 at an average 35 mph. Before-and-after MAF was 23%, average mpg went from 21 to 26.5 at about the same average speeds. That's why milspec (the purchasing code for military products) generally insists on "aged" silicon. Stuff in the electron-world changes just from being used.

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Wed Dec 09, 2020 12:30 pm

Thanks. Going to give it a try today and I'll report back.

Seems pretty easy...

Make sure the accelerator pedal is fully released. Turn the ignition switch on without starting the engine for at least 2 seconds. Turn the ignition switch off for at least 10 seconds. Again, turn the ignition on for at least 2 seconds. Turn the ignition off for at least 10 seconds. This action will inform the computer on the new release position of the accelerator pedal and the closed position. Now that this is done, we can move on to the next step. Please make sure to follow these next instructions precisely as every action is performed within a few seconds. Turn the ignition switch on and wait 3 seconds. Immediately after the 3 seconds, the accelerator pedal must be pressed and released 5 times within 5 seconds. Wait 7 seconds and fully press the accelerator pedal and hold for approximately 20 seconds until the check engine light stops blinking and stays on. Within 3 seconds after the check engine light stays constantly on, release the accelerator pedal. Now start the engine and let it idle. After 20 seconds, rev up the engine a couple of times to ensure idle speed is within specifications. If the relearn was unsuccessful, turn the key to the off position wait 60 seconds and restart the process.


Richard

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Thu Dec 10, 2020 1:13 pm

Relearn done. Did some initial restarts when engine warm and seemed to fix the issue! Thanks all.

Richard

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby sev » Thu Dec 10, 2020 1:14 pm

glad to hear!!!!

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby VStar650CL » Thu Dec 10, 2020 1:19 pm

You're most welcome, happy to help!

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Thu Dec 10, 2020 1:22 pm

For good measure I already replaced the air filters, cleaned the MAF sensors and cleaned the throttle body. So the entire intake should be good for a while. :)

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby VStar650CL » Thu Dec 10, 2020 1:49 pm

So listen up, other readers, good lesson here and not just for Nissans. IAVL with every tuneup, it matters!

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby PapaSmurf2k3 » Thu Dec 10, 2020 6:17 pm

Good news! Good intel. Thanks Vstar!

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby VStar650CL » Thu Dec 10, 2020 6:19 pm

Y'all are most welcome, as always!

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Fri Dec 11, 2020 12:44 pm

I hate to say this but...

This morning the warm start had the same problem. Revs go up, down below idle and almost stalls.

So not sure what to do next. When I cleaned the throttle body I didn't push the butterfly open. I was told that could cause issues. Maybe the relearn and opening the flap and a better cleaning will ensure I don't have an issue with touching the throttle butterfly? Might be worth a try.

Other than that I'm thinking a very minor air leak after the MAF sensor? Idle is pretty good but does have a bit of a variance when idling (you can see the RPM needle move ever so slightly).

Richard

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby sev » Fri Dec 11, 2020 12:56 pm

are you sure the relearn procedure was successful?

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Fri Dec 11, 2020 1:04 pm

sev wrote:
Fri Dec 11, 2020 12:56 pm
are you sure the relearn procedure was successful?
I'll try it again for good measure. But the check engine light flashed when it was supposed to, went solid, etc...

---

Just reprogrammed again now. Tried after the reprogram is done and started it about 5 times and it was perfect. Let's hope it 'sticks' this time. :crazy:

Richard
Last edited by rjkoop on Fri Dec 11, 2020 1:25 pm, edited 1 time in total.

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby VStar650CL » Fri Dec 11, 2020 1:23 pm

rjkoop wrote:
Fri Dec 11, 2020 12:44 pm
Other than that I'm thinking a very minor air leak after the MAF sensor? Idle is pretty good but does have a bit of a variance when idling (you can see the RPM needle move ever so slightly).
If it's unmetered air then your scanner can tell you. Look at the fuel trim at idle and then at 2000+ RPM. If it's enriching at idle but normalizes at higher R's, the culprit is a small leak. If you don't see any big changes, then don't waste time on leak-hunting, the problem is something else.

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby PapaSmurf2k3 » Fri Dec 11, 2020 1:42 pm

^Or skip all that and spray something combustible around suspect vacuum leak areas. Make sure you stay away from hot exhaust though.
If you have a leak, it should idle up when the starting fluid (or similar) gets sucked in.
That's the "old school" method. A little more dangerous, but certainly faster and no special tools required.

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby VStar650CL » Fri Dec 11, 2020 1:46 pm

One other thing to check is the IAT (intake air temperature). It's in with the MAF on most Nissans and it's just a balance resistor, but depending on the circuit configuration, an open wire or open sensor will make the car think it's either in the Sahara or Siberia. The former will cause cold stumbling, the latter very poor gas mileage.

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Fri Dec 11, 2020 2:01 pm

I'll have to read up on the fuel trim. But in case this helps here's a few screenshots of Torque lite with the car at idle and steady at 2000 rpms.

Image

Image

Richard
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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby PapaSmurf2k3 » Fri Dec 11, 2020 2:35 pm

Hey Richard it looks like the images to your google drive don't like to post here... maybe some kind of privacy issue.
Your attached image works well though. Any chance you could do the same for your google drive images?

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby VStar650CL » Fri Dec 11, 2020 3:00 pm

Pic came through okay here, weird. The STFT you see there is Short Term Fuel Trim, and +8.6% is pretty enriched for 2K with no load. So if it's a vacuum leak it's a big one and not small (if it's a leak at all, which seems doubtful). That also leaves out the IAT, 26C is perfectly normal. I'll have to think about this, we've gone through all the most likely stuff.

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Fri Dec 11, 2020 3:12 pm

Yep. I could bring it to the dealership or local mechanic but normally they just say replace stuff and we'll see if it fixes it (the Mercedes way!). No thanks! Maybe they could diagnose it for a minimal cost, then I check the report and replace the stuff myself. Much cheaper.

Tomorrow I may take off the intake flexible hoses and ensure there are no cracks and maybe wiggle the other hoses and see if I notice a change in RPMs. But the engine compartment looks pristine and the car only has 54,000kms. I've never seen a air leak with such low mileage. My '81 Fiat Spider... yes... but the car is 39 years old and the rubber has deteriorated.

Richard

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Fri Dec 11, 2020 3:13 pm

PapaSmurf2k3 wrote:
Fri Dec 11, 2020 2:35 pm
Hey Richard it looks like the images to your google drive don't like to post here... maybe some kind of privacy issue.
Your attached image works well though. Any chance you could do the same for your google drive images?
Strange. Should be public.

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Fri Dec 11, 2020 3:15 pm

VStar650CL wrote:
Fri Dec 11, 2020 3:00 pm
Pic came through okay here, weird. The STFT you see there is Short Term Fuel Trim, and +8.6% is pretty enriched for 2K with no load. So if it's a vacuum leak it's a big one and not small (if it's a leak at all, which seems doubtful). That also leaves out the IAT, 26C is perfectly normal. I'll have to think about this, we've gone through all the most likely stuff.
Wow... You're relentless! I'm always amazed at how people I've never met spend the time to help strangers out. Thank you!

Richard
Last edited by rjkoop on Fri Dec 11, 2020 3:24 pm, edited 1 time in total.

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Re: 2015 Infiniti QX50 stall when starting sometimes

Postby rjkoop » Fri Dec 11, 2020 3:17 pm

VStar650CL wrote:
Fri Dec 11, 2020 3:00 pm
Pic came through okay here, weird. The STFT you see there is Short Term Fuel Trim, and +8.6% is pretty enriched for 2K with no load. So if it's a vacuum leak it's a big one and not small (if it's a leak at all, which seems doubtful). That also leaves out the IAT, 26C is perfectly normal. I'll have to think about this, we've gone through all the most likely stuff.
I found the STFT level was steady at idle. But when rev'ing the engine there was a range from 6.5% to 10%. Tough to keep it steady when my foot was on the pedal.

In case it matters I'm in Ottawa, Canada and the temperature is about 5 degrees C.

Richard


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