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Code PO305 misfire number five

Tiny
MIKE PATTON2
  • MEMBER
  • 2000 MERCURY SABLE
  • 3.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
I have a dead miss and that cylinder is obviously not 'firing'. I've replaced plugs, wires, and the injector. The cylinder is getting fuel and the plug is firing. I'm no mechanic and I don't know what else to do. Any ideas would help. Thank you!
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Sunday, March 31st, 2019 AT 1:30 PM

5 Replies

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

This sounds to me like it could be a problem with compression in that cylinder. An engine basically needs three things to start, fuel, spark given at proper time, and compression and it basically has no choice but to fire. If you are only experiencing a misfire in number five cylinder only, that would indicate that the other cylinders were getting fuel and spark at the proper time which leaves us with compression.
I have included a few links for you down below to go to:

https://www.2carpros.com/articles/symptoms-of-low-compression
https://www.2carpros.com/articles/the-reasons-for-low-compression
https://www.2carpros.com/articles/how-to-test-engine-compression

Please go through these guides and get back to us with what you find out.

Thanks,
Alex
2CarPros
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Sunday, March 31st, 2019 AT 2:25 PM
Tiny
MIKE PATTON2
  • MEMBER
  • 3 POSTS
If checking only the number five cylinder, do I need to remove all the plugs, or can I simply do them one at a time across the front of the engine (using the other two for comparison)? It's a transverse mounted v6, and the rear plugs aren't easily accessible.
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Sunday, March 31st, 2019 AT 2:50 PM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

The correct way to do a compression test is with all the spark plugs out and one cylinder at a time. The lowest cylinder shouldn't be less than 10% of the highest cylinder.

Thanks,
Alex
2CarPros
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Sunday, March 31st, 2019 AT 7:07 PM
Tiny
MIKE PATTON2
  • MEMBER
  • 3 POSTS
The issue on that is that I'm having trouble figuring out how to disable the fuel system. I can't seem to find the fuse for the fuel pump. I've looked online and my car has no fuse in the slot where it's supposed to be.
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Monday, April 1st, 2019 AT 8:04 AM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

There are a couple of ways to disable the fuel system. You could unplug all the connectors from the fuel injectors, you could unplug the connector from the inertia Fuel Cutoff Switch located behind the right rear tire in the trunk fender well, or you could take out the fuel pump relay located in the battery junction box behind the radiator. Any one will do the trick. I have included some informational material in the diagrams down below. Get back to us if you need more help or have additional questions please. That's what we are here for.

Thanks,
Alex
2CarPros
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Monday, April 1st, 2019 AT 1:10 PM

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