Multiple random cylinder misfire

Tiny
SOHAIL TARIQ
  • MEMBER
  • 2009 INFINITI G37
  • 3.7L
  • V6
  • 2WD
  • MANUAL
  • 98,000 MILES
A vq37vhr engine was brought to my attention after it was throwing a multiple random misfire code.

Here are the details:

1. Engine was just rebuilt after a porcelain spark plug shattered and bits of it fell down the combustion chamber.
2. The spark plug bits were retrieved and the engine was put back together.
3. A faulty angle wrench was used and may have thrown off the actual angle torque on the head bolts, along with a possibility of one bank to be only tightened to 95° instead of the full 190°.
4. Spark plugs on cylinder one and five (passenger side bank 1) are black and smell like burnt oil.
5. According to OBD readers car is running lean.
6. Milky white residue found at oil filler cap, even after wiping off and running engine again.
6. A bubble every three to four seconds seen coming from radiator filler cap. May be possible car was not bled all the way and radiator still releasing air but coolant level did not seem to go down as bubbles came up.
7. Leak down test was also performed while engine was cold.

Any suggestions on possible causes of the lean mixture and two black spark plugs?

Thank you
Tuesday, November 14th, 2017 AT 1:18 PM

1 Reply

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,512 POSTS
Hello,

You hit it when you said the head bolts were not tightened correctly which will cause the head gasket to fail causing the black plugs and the coolant in the engine oil. Here is a guide to confirm the failure.

https://www.2carpros.com/articles/head-gasket-blown-test

and

https://www.2carpros.com/articles/coolantantifreeze-in-the-engine-oil

Please let us know what you find. We are interested to see what it is.

Cheers, Ken
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Friday, November 17th, 2017 AT 1:59 PM

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