2015 Captiva randomly misfires low MPG difficult startup
 

I have a 2015 Chevy Captiva LTZ 2.4L, and have been working on diagnosing a random misfire issue while driving, or a minute right after startup, usually on a cold morning. The biggest issue is that the computer is not throwing a trouble code anymore, and I was told by a tech at Paradise Chevrolet that they cannot do anything until there is a trouble code. I have replaced coil packs and spark plugs for a P0301 code, and the bank 1 O2 sensor for a P0132A code. Replacing those parts have reduced the severity of the issue immensely, but about once a month (on regular gas), I can be driving up a curvy hill at 35MPH (with nowhere to pull over), and the engine will begin to misfire for a few seconds before recovering it's self.

A most recent issue happened a few days ago. It was 35 degrees F outside, my car took a few extra turns by the starter to get it to startup (probably because I am running e85 in cold weather), after about a minute, I felt a misfire, the engine began to sputter REALLY bad, and blew out a lot of white, and dark gray smoke out of the tailpipe before stalling out completely. After that, the engine started up again just fine, and ran like normal.

I have also noticed that the issue tends to happen most often while running regular gas, and almost never happens on e85. I have recently purchased an OBD II scan tool and the Torque app for my phone, and began looking at the fuel trim numbers. I have noticed that at idle (I haven't tested at 2,500rpm yet), the fuel trim is reading at -20% or greater while running pure e85 ( I honestly can't run regular gas anymore, it's simply not safe to drive). If I understand correctly, e85, being between 50 to 85% ethanol should require an injection of MORE fuel, as pure ethanol has 25% less energy content than regular gasoline... so I am wondering, how is it, that my cars computer is trying to reduce the fuel injection by around 20%?

I am wondering if anyone knows if this is normal... I am suspecting a faulty fuel injector. I honestly need to collect all of the facts before I can bring my car in to the dealer again... I cannot get them to do anything to remedy the situation, at least if I have all the facts, I can debate them, and make claims etc...

Could be a bad coil pack too. Maybe you got one that has a defect?

Thanks for the reply. I am not entirely sure what is going on... I could probably swap around the coil packs, and possibly read the resistance on each one. One thing which is confusing me now, is on last Friday, I bought Torque Pro, and kept a glance on the LTFT, and STFT, and the whole time while driving and idling, the two numbers always stayed within +5 and -5, and even both reported 0 at 40MPH. I assume now at the very least, there isn't a major problem with the engine mechanically, however, I am now more confused than ever.

I forgot to mention, a few months ago I did a leak-down test on each cylinder, and they all reported the same numbers with only -5psi after 60 seconds. (which is fantastic btw).

The only thing I can think of at this point, is to drive with the torque app every day, and wait for the event it has another misfire, and watch the graphs...

Thats what I would do as well. I wish I could be of more help but to be perfectly honest I havent studied duel or flex fuel motors enough to know, having only a 5 percent difference in compression between your cylinders is indeed a very good sign. Maybe the E85 is helping with that good news? I know most states have 10 percent ethanolin the pump gasoline, but I dont see any savings which that at all. 100 percent ethanol only has 2/3rd's of the power of 100 percent gasoline, but E85 is cheaper then gasoline at the pump, so its a bit confusing as to which can save more money to me. I do know one thing about ethanol however:

That 10 percent ethanol/gasoline gas-pump mix can raise hell with small engine motors like chainsaws and the like. My Husky 241 saw quit working one day. The fuel lines were as hard as a rock and broke so no fuel to the carb, and I had to tear it down and replace them all, as well as rebuild the carb. Found out it was the ethanol that cuases that issue, so I pour the gas back in the small containers I have for my chainsaws and other small air-cooled engines after I am done.

I am sure that the flex-fuel motors don't do that, since you are running at 85 percent ethanol, but buying pure gasoline with no ethanol is expensive in my state and many others.

As far as I understand so far, there are some interesting characteristics about e85. I know that most of the rubbers have to be upgraded, jetting or injection must be increased by 25%, and you can get more horsepower by adding more timing, and compression if it's an option. Another issue is, you don't really know what kind of grade of e85 your getting, as it varies between 51% to 85%... If I could find out if it acts up depending on the percentage of ethanol, that would help pinpoint the issue.

You could actually be onto something though, there may be some quality issues on our E10 - E85 over here. California rapidly changes laws on restrictions and formulations on virtually everything over here.

Maybe I should research a bit more into how the Flex Fuel sensor works?

I wont hurt. I intend to study it myself. The ECM''s in those vehicles has to have much different programming to change from E85 to gasoline, then a gasoline only vehicle.

Hey, I have to say thanks for helping so far. Last night I forgot to plug in my obd2 tool with the torque app running, and of course that was the moment my Captiva started having some issues, although it was more subtle than usual.

It first started 5min after startup, then engine was about 163*F, I was at a stoplight, and the engine began to act as if it was misfiring again with an unstable idle. When the light turned green, I lightly gave it gas knowing exactly how it would respond due to experience with this issue, and it began to once again act as if it was misfiring as I slowly approached a steep hill with an overpass. I always drive my Captiva in manual mode, so I let the rpm's rise gracefully, and when it reached about 2k rpm's the issue immediately went away and ran perfectly normal.

That same night, while driving on the curvy road all the way home, I noticed that every time I took my foot completely out of the gas while I approached a curve, and put my foot back into the gas after going 3/4 of the way around a curve, the engine would hesitate at first and then pull. I began to experiment, and sure enough, even in a straight line, if I took my foot completely off the gas, and went back onto the gas, no matter how hard or lightly I wanted to accelerate, the engine would at first hesitate, and then accelerate. After doing this about 10 times, the issue vanished completely, and I could not repeat the issue. This morning, I still could not repeat the issue.

Btw the air temperature outside was 54*F. I'm taking a wild guess that maybe my air intake temperature sensor may be reading incorrectly, maybe the throttle body is dirty or worn out, or maybe a sensor for the throttle position may be worn... I'm not sure...

One thing I noticed, that I forgot to mention, when I drove with the Torque app last, I noticed that every time I completely let my foot off the gas, the STFT would surge to +25 and drop back down to almost 0 for about one second. I thought this might have been normal, because it would repeat perfectly to the exact same value, every time I let my foot completely off the gas. The engine did not respond negatively, and I noticed no issue in performance.

In this situation, isn't the STFT basically pointing out that the computer, or bank 1 O2 sensor thinks the engine is running lean for a second after I take my foot completely off the gas? Or is this just a pre-programmed procedure that triggers automatically by default (for reasons I do not understand yet)?

I think I will do a throttle body cleaning this weekend, I haven't done it yet, as I know you have to do a whole re-learn procedure which seems like a pain.

Still... no check engine light triggered, and no pending fault codes...

https://cimg9.ibsrv.net/gimg/chevrol...afc7a0806a.jpg
Finally got a screenshot app installed, so I can show you guys some of the diagnostic data. Misfire count of 16 today on Cylinder 2... very interesting.

I tried to contact the orignal sales person who sold the Captiva to me:

The original message was received at Fri, 11 Jan 2019 12:41:55 -0800
from m0096558.ppops.net [127.0.0.1]

----- The following addresses had permanent fatal errors -----
<brandondeangelis@dchcjdoftemecula.com>
(reason: 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [[url=http://BN3NAM04FT038.eop-NAM04.prod.protection.outlook.com]BN3NAM04FT038.eop-NAM04.prod.protection.outlook.com])

----- Transcript of session follows -----
... while talking to dchcjdoftemecula-com.mail.protection.outlook.com.:
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554 5.0.0 Service unavailable

"mail.protection.outlook" ...hmmmm... protection from what? LOL!

Anyways, now with the scan tool data, I have been able to finally score an appointment with Paradise Chevy. To tell the truth, I think I have been a bit harsh on Paradise, they take my calls, they actually talk to me, but when I try to make contact with Dodge, where I bought the car from... no help.

Got my Captiva back from the Chevy dealer the day before yesterday, they did an induction cleaning service on the injectors, rail, and intake/throttlebody. It improved the symptoms quite a lot, and I now have a very noticeable improvement in acceleration and performance in general.

I was greeted by a GM tech at the dealership who was actually very straight forward and honest with me, and I actually really respected that, and wish that more mechanics would be even at least half as honest.

In his opinion he was thinking that the issue didn't have to do with the timing chain or tensioner as I thought, and he was leaning more towards the fuel injection system, specifically a bad injector.

I noticed that there are less misfires across all cylinders now, however, cylinder 4 still seems to be stubborn with 21 misfires on the way to work. I also noticed that the Catalytic converter temperature has decreased from 1300*F to 1150*F, which may be due to a more efficient running engine now.

I have one question though, would it void my powertrain warranty, If I swap the #4 injector, with the #3, and see if the misfires follow the injector? (assuming I use a fresh o-ring, and torque to spec.)