Cylinder four misfire, low compression

MICKEY98

MEMBER
2019 HYUNDAI ACCENT
1.6L
4 CYL
2WD
AUTOMATIC
35,000 MILES

Short story. While driving the car uphill it started to shake, smell of gas, and engine light flashing. Took it to get checked. Cylinder 4 misfire turned out no issue with spark plugs but compression test was at about 150 for #4 bad fuel injector. It was not checked internally. Does a bad fuel injector cause the issue or more internal problems? Thank you.

9 Replies

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Hi,

I looked up the specs on compression, and it indicates 156.4 is the minimum. See pic 1.

Now, if you had a fuel injector sticking open and dumping fuel in that cylinder, it will cause the oil on the cylinder walls to get washed away. That can cause compression to drop. Is that what they told you?

Also, if there was that much fuel being sent into the cylinder, there is a good chance it mixed into the engine oil. If you haven't, I would suggest checking the oil for a fuel smell and changing it if there is one.

Let me know.

Joe

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Saturday, March 27th, 2021 AT 10:22 PM

MICKEY98

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5 POSTS

Hi Joe. No, they did not tell me but recommended to take it to the dealer as they did not go further. They looked into the misfiring and stopped at #4, low PSI, and bad fuel injector but no straight answer to the problem as no further work was done.

To add: At first the car took few cranks to start but later it started from one crank.

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Saturday, March 27th, 2021 AT 10:34 PM

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Was the injector replaced? If not, do you still have the misfire? If you do, I wouldn't drive it because it could lead to damaging the catalytic converter.

As far as the lower compression, if the injector was stuck open so that it was dumping fuel all the time, that could have been the cause of the lower compression. Once the motor oil is washed off the cylinder walls, the rings can't do their job properly.

Actually, when I have a cylinder with low compression, I check it both dry and wet. Dry means I check it as it sits. A wet test is done by adding a small amount of motor oil right into the affected cylinder. If the pressure goes up, then it's a ring issue. However, your issues sound related to the injector as I mentioned.

If it still has a misfire, I wouldn't recommend driving it until that is fixed. The engine is under powertrain warranty (10 year/100,000 miles), so even if it is mechanical, it will be fixed. If it is the injector, I believe there is a 5 year/60,000 basic manufacturer warranty that covers nearly everything except maintenance items. A faulty fuel injector should fall under that warranty.

Let me know if I can help or if you have other questions.

Take care,
Joe

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Saturday, March 27th, 2021 AT 10:47 PM

MICKEY98

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5 POSTS

Thank you for the reply Joe. They did mention the PSI is at a minimum level of a functioning engine. They did not replace the spark plugs nor the injector. I looked at the notes and it says #4 fouled out and #4 bad fuel injector. Did ask for cost to repair it but they do want to touch it. Possibly it is not something they do there or maybe it is time consuming. Was told that replacing the spark plugs will not solve the problem. Per the check oil and coolant level are okay. I do remember now seeing darkish smoke come out when stepped on gas.

Thank you for your response as I now know there are more steps needed to take a look at the issue.

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Saturday, March 27th, 2021 AT 11:25 PM

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Hi,

There is a chance what I described is the cause of the problem. If you decide to do the repair yourself, I attached the directions below for injector and spark plug replacement. However, I would contact the dealership and ask if it is covered. It should be.

Let me know if there is anything I can do to help.

Take care,
Joe

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