Misfire

2003 NISSAN SENTRA

191,000 MILES • 2.5L • 4 CYL • 2WD • MANUAL

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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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Apr 15, 2021 at 10:46 PM

ASEMASTER6371

CERTIFIED EXPERT
52,796 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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Apr 16, 2021 at 4:01 AM