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2018 - Odd starting problem - struggles to start, sputter, then dies? - Updated!

('14-'18) 
6K views 15 replies 8 participants last post by  SoobADoob 
#1 · (Edited)
I have just under 25K miles on her and experiencing an odd starting problem:

My office is at 11,000 feet.

Even with temperatures as low at -14F and as high as 25F when I leave from work to drive home, the car has started just fine.

Yet, during the past week here -- and only here -- the car has struggled to start. It'll turn, sputter, then die. Usually on the 2nd or 3rd attempt, it'll finally start. Drives well, idles well. Typically, this problem will occur in the high 20s to 37F but starts right up at temps lower.

Everywhere else I drive to, park, and start the car, leave the car overnight as I sleep then go out to start my day, she starts right up. These spots are at lower elevations, about 8,800 - 9,100 feet.

I did experience this same problem about a year or so ago: The engine filter was so dirty (from me driving US Forest Service roads, typically), that once I swapped out the engine air filter, she was back to normal.

I replaced the engine air filter at 24,000 miles, over a month ago. As I mentioned above, this starting problem has only started to occur within the past week at ONLY my office location.

So, if it isn't the air filter this time, what is it?

I'm wondering whether the battery is struggling, but the car starts easily everywhere but at 11,000 feet.

(Stats of car in signature below)
 
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#2 · (Edited)
I've lived at or below sea level my entire life so can't speak from any experience but air density is less so I'd imagine your air is significantly thinner so maybe the car runs richer. I'd imagine it would make adjustments automatically, tho..
Edit: This is pure conjecture, but maybe, since it lives at 'normal' elevations, the starting algorithm uses the parameters it learned at those elevations. After all, the car doesn't know its elevation so doesn't know to make adjustments until it is running. Kind of a chicken and egg thing..
It is weird it is happening only recently so something clearly changed..

Do you have an OBD2 reader that is able to show live data?
 
#4 · (Edited)
If you have the Subaru battery an upgrade to one with more CCA is a good idea. I live at 8,200ft and have never had a cold starting problem after getting a different battery, before that there were many.

If the air filter was that dirty last year, possibly take a look at the MAF sensor, if dirty it could cause many issues like rough starting.

I highly doubt the air density or fuel octane is the culprit, higher altitude reduces the propensity for pre-detonation which is the key feature of high octane fuel. These cars have sensors to detect air density, and temp, and adjust mixture accordingly, symptoms point to one of those sensors like the MAF giving poor signals to the ECU.

Good luck!
 
#5 ·
"It is weird it is happening only recently so something clearly changed .. Do you have an OBD2 reader that is able to show live data?" (I don't have this reader.)

"Octane of fuel potentially causing problem?"

I thought about these two points last night as I walked to my car to leave work (car started on 1st attempt. ugh. really!.). The only thing different was that I filled up my gas tank. I filled it up at the same station I always use. Maybe the fuel tanker added the 85 to the 87 underground tank by accident? ¯\(ツ)

"If the air filter was that dirty last year, possibly take a look at the MAF sensor, if dirty it could cause many issues like rough starting."

I'll check MAF sensor out. I have an appointment at the dealer this Saturday.

Thanks for the input guys!
 
#6 ·
UPDATE: So, after I took the car into the dealership, they replaced the battery (warranty).

Car started well since. More of a sluggish start, but started on the first time -- regardless of temperature and location.

BUT ... Last night and this morning, the same starting problem occurred. Once after my 10-hour shift and again at home after I woke up to run errands. Took about 3 times each before finally catching. Check Engine light is not coming on.

Car idles/runs well and smooth once it's started up. Even when I run errands and make stops, the car starts up rather crispily -- better than it does when left alone for a long time.

* So it seems engine temperature is playing a role, and problem is only with the starting after left along for prolonged periods. *

Made an appointment with the dealership again tomorrow.

(Annoyed how a new-ish car is having this problem.)
 
#8 ·
Quick list of what I would expect the dealer to do next:

1. Check the battery: check voltage, charge if necessary, and load test it if they have the means to do so. They might have pulled a super-old battery from the back of the rack when you came in for warranty work. This battery might have come to you with reduced capacity due to sulphation and under-charged.

2. Check if any ECM updates: a very similar issue to what you describe was resolved for me with an ECM update or two. The final update resulted in zero issues in the fast few years.

3. Crank position sensor: this seems to be a common cause of cranking, but no start.

@asphaltaddict33 mentioned that it might be the MAF sensor. I've started vehicles with the intake removed and with the MAF sensor disconnected, so I'm not sure if a dirty MAF would cause the sputtering starts and no-start condition you're describing. It should be easy enough for Subaru to hookup and see whether your fuel trims are within range, though. This will just tell you that the MAF and O2 sensor are matching up well enough to usually rule that out as an obvious problem.

You can buy a cheap Bluetooth OBD-2 reader and pay for an app to view these parameters on your own if you're curious enough. A long-term fuel trim of around +/- 4% is great, though I've seen it fluctuate double that without any noticeable issues whatsoever. I can't recall what max fuel trim capability is, but I want to say it's somewhere around +/- 16-20%. Something is seriously wrong if you see numbers anywhere near that high.

Note: short-term fuel trims will be all over the place. I don't even pay attention to them. Long-term fuel trims will take a bit of driving after the ECM loses its memory (e.g., after swapping out a battery) to populate, so don't take a low initial LTFT as a good sign; drive a bit.
 
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#9 ·
As Gathermewool said, agreed!

DItch the stock battery, they are barely sufficient in warm weather at sea level, bought an Odyssey gellcell battery for mine before the stocker failed, much better starting, way more reserve capacity, and no corrosion at terminals/cables due to zero acid leakage. I don't believe this is the root cause, but a great battery goes a long ways towards reliability. :)
 
#10 ·
@jdac85 Thought about it, but I'd rather not take a chance with messing with the warranty since this car requires a specific oil type

@gathermewool I did think about the crank position sensor; only saw it brought up a very few times but seemed to hit the mark of what might be happening with my starting.

@Natedog Seriously considering a better battery. Hard to do so, though, with it under warranty and all.
 
#11 ·
Clean your Mass Airflow Sensor (MAF). If your filters are getting fairly dirty, then there’s a good chance that the MAF is too.
NOTE: only use MAF cleaning spray from auto shop, it’s not that expensive. Anything else ‘may’ cause damage to sensor.

Also the O2 concentration in the air at your work is possibly different to everywhere else. When you start the car, the ECU is going to be using the last known good values (just before you switched off). So if the air pressure and temp has changed significantly (in conjunction with a dirty MAF sensor), it may be taking the ECU a few attempts to get the correct tuning values.
 
#12 · (Edited)
UPDATE:
Picked up the car today from the dealership. Their diagnosis: low-octane gasoline is the problem (even though I put in 87 every fill-up).

I don't know how to feel about this. Part of me is like "Cool". Another part of me is like "Maybe I'll take it to another dealership to see what they come up with".

(I was given a loaner, a new Ascent. Loved the paddle shifters! If I knew how fun these were, I would have probably bought an XT.)
 
#16 ·
Well, second dealership held onto the car for a couple days and was unable to replicate the problem. sigh

Had a couple warmish days up here since, with starting problems at both 36F and 37F, on separate days after sitting for a prolonged period.
 
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