Misfire

Tiny
TOM.FEOD
  • MEMBER
  • 2003 NISSAN SENTRA
  • 2.5L
  • 4 CYL
  • 2WD
  • MANUAL
  • 191,000 MILES
Took car into garage for a misfire. Already changed the spark plugs, coils and the valve cover as it was getting oil in the spark plug tubes. I don't understand why they would do a compression test or a coolant pressure test for a misfire. After $691.00, all they did was put in some older coils we still had in the glove box from when we put the new coils in. They wanted $120.00 per coil plus labour to install. I can get coils from NAPA for $75.00 and my son and I can put them in in 15 minutes.
Please see invoice.
I'm thinking we got ripped off big time.
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Thursday, April 15th, 2021 AT 10:46 PM

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Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning,

According to there story, they did a good though diagnostic test. Compression is always part of a diagnostic and from there results, you have 3 cylinders that are out of spec when cold. They all should be 140-160. 115 is low and that alone could cause the misfire.

https://www.2carpros.com/articles/the-reasons-for-low-compression

The one thing they did not do that I would have done is a fuel pressure test to be sure the fuel pump is working correctly. That is the most common reason for the misfire codes.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Fuel Pressure
Fuel pressure at idle .................... Approximately 350 kPa (3.57 kg/sq.cm., 51 psi)

I attached the procedure for you below if it is the fuel pump that is the failure.

Roy
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Friday, April 16th, 2021 AT 4:01 AM

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