Poor gas mileage, questionable coil pack, oil on spark plugs...

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sky201

Short stuff: 2017 Cx-5 GT AWD, ~46,000 miles I"m experiencing poor gas mileage.. struggling to get 20 mpg. Maybe 250 miles to a tank, used to be 300+

Long stuff: Since I've towed a boat about 700 miles from SC to NJ (about a year ago) I've experienced pretty awful gas mileage ranging from 15mpg -21 MAX
I've disconnected the battery on several occasions in an attempt to "Reset" the computer.

Today I decided to take a look at the plugs and I noticed my drivers side ignition coil has electrical tape on the wires leading to it where the others do not... Is this common on these vehicles. I've owned it since new and I've only had it serviced at the dealer or by myself.

Second, it seems that there is oil coming up from my cylinders, there is a film of oil on the threads closer to the cylinder, and become clean as you reach the top of the threads near the valve cover...

I've checked the O2 sensors with a OBD2 reader and they respond quickly so I don't think its them.

At first I thought it was a transmission issue, but the trans shifts fine so I"m not sure.
I was thinking of changing the plugs and seeing if it persists, but the MPG is really bothering me considering when it was new I could get 30-32mpg if I tried where as now I can only get 21.

I searched for MPG issues and didn't find much as well as coil pack issues but these cars don't seem to have issues.
I'm mechanically inclined, and can test anything you guys want, but is some of this common? Or should I just give up and trade it in for a 2020 with a/c seats
 

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That spark plug looks excellent. I would look at all the spark plugs and check for a oiled one. Then do a compression check. Then do an injector leak-down check. Ed
 
Agree, the plug looked great. If the other look the same, all good. I have tape on the wires leading to cyl 4 coil pack as well. Assume factory. As for MPG, does it have good power?

Idle smoothly?

What are fuel trims at idle and cruising?

Is B1S2 02 sensor between .6 and .8v during steady cruising?

Air filter clean?

No dragging brakes? Parking brake completely disengaged?
 
Okay spark plugs are good. Got it.

Wires going to coil 4... odd but factory. so I'm less worried.

Car idles smooth but kinda rough with A/c has anyone noticed a significant mpg loss with the A/c on?

Car has good power, well 187hp power 😅

air filter was recently changed (like a week ago) so thats good too.

As far as I can tell no brakes are dragging. The car seem to drive and handle fine. but just dumps gasoline. Is it possible that since towing the boat it has saved that fuel usage as default and got stuck somehow?

I wanted to take it to the dealer and have them scan everything but they said it would be like $300 and the probably wont find anything. Which is probably true
 
The PCM has multiple strategies to maintain efficient combustion; compares MAF, MAP, A/F sensors, after cat 02 sensor. Fuel pressure or delivery issues, intake temp or coolant temp issues will usually show up in fuel trim offsets.

I also assume you have verified fuel gauge calibration against how much fuel it takes on at fill up?

Also, check the IAT temp sensors and the coolant temp senors against each other after overnight cool off and before startup. They ought to read within 10 degrees F of each other.

When the car is full up to temp, what does the dash temp read? What does the OBD data read?

Unusual tire wear pattern or wear rate; i.e. alignment issues.
 
ill look into all of that tomorrow.
I've been reading a bit about a trans fluid flush, seems as easy as an oil change on these cars. since my problem arose after towing the boat I'm thinking it may be trans related, maybe i cooked the ATF.
My autocross days probably haven't helped much either (mudflaps are no longer on the car btw)
 

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Dirty MAF sensor? Do you use a K&N air filter? If so MAF may have oil contamination.
 
trans shifts fine, little slower than when it was new. ( remember taking a video of how fast it shifted when it was new, now it shifts like any other auto i've driven.

I will look into cleaning the MAF, stock filter tho
 
sky201 said:
ill look into all of that tomorrow.
I've been reading a bit about a trans fluid flush, seems as easy as an oil change on these cars. since my problem arose after towing the boat I'm thinking it may be trans related, maybe i cooked the ATF.
My autocross days probably haven't helped much either (mudflaps are no longer on the car btw)
Click to expand...

You need to read a bit more. Without a custom adapter these transmissions can NOT be flushed. If your dealer tells you that it can be flushed, without a custom made adapter, they're lying to you. Even with said adapter, the trans flush is far from being as simple as an oil change.
 
Sorry, by "flush" I meant drain and fill, measuring how much has been drained and adding new fz ATF back. and repeating this process 2 or 3 times.
 
The last thing I can think of that might impact MPG is intake passage/valve carbon and/or carbon build up on injectors. Drivability issues and rough idle normally show up with that as well, though.
 
"Car idles smooth but kinda rough with A/c has anyone noticed a significant mpg loss with the A/c on?"
This might be significant. I have seen bad A/C clutch bearings make a car run poorly. It can affect the mileage and ultimately stall the engine when the bearings seize. Try averaging your gas mileage without using A/C and see if mileage improves.
 
I ran the car with no A/C yesterday and it seemed to coast significantly better and highway mileage improved to ~25 still not the 30 I used to get but its a step in the right direction.
 
You ran the car yesterday and got a mileage average? How are you measuring you fuel consumption/mileage?
 
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