Black smoke from exhaust?

Tiny
INFINITIANDBEYOND96
  • MEMBER
  • 2019 INFINITI QX60
  • 2WD
  • AUTOMATIC
  • 76,000 MILES
Infiniti service said a dirty engine air filter could be the cause of it running rich, so I replaced it and did an engine performance service, but the black smoke was still there. I took it back in and this time they test drove it aggressively and adjusted the fuel trim so it’s back within specifications which seems to have worked because the black smoke is mostly gone. My concern is that they only temporarily fixed the problem and did not find the main cause such as a faulty sensor or part that can lead to engine wear or other issues. Should I get another diagnostic test before my warranty expires at the end of this month?
Friday, May 12th, 2023 AT 6:58 AM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

The fuel trims are controlled by the powertrain control module (PCM) and other sensors. They couldn't have manually adjusted it.

A rich fuel mixture can be caused by a couple of things. For example, excessive fuel pressure due to a regulator issue, a failing fuel injector, or even an engine coolant temperature sensor. By any chance, do you have access to a live data scan tool? If you do, when the engine is cold, check the coolant temperature signal to confirm it is close to the ambient temperature.

Also, let me know what the short-term fuel trims are at idle and the engine at operating temperature.

Let me know if this is something you can do or have done.

Take care,

joe
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Friday, May 12th, 2023 AT 9:06 PM
Tiny
INFINITIANDBEYOND96
  • MEMBER
  • 3 POSTS
Thanks Joe. I’ve taken my QX60 in 6 times for the same issue (black smoke from the exhaust). They’ve replaced the engine air filter, done an engine performance service and throttle body cleaning, and reprogrammed the ECM after the check engine light came on with a P0101 code for the MAF sensor. Today they told me the cause of the black smoke is excessive sludge buildup at the intake and exhaust valves. They likely won’t cover it under warranty because I only did oil changes every 6 months but drove 9000 miles between each oil change. The car has 47000 miles on it. Can an engine flush remove the excessive sludge? Or a mechanical clean? How much will this cost me? Thanks!
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Wednesday, June 14th, 2023 AT 10:53 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

If you do an engine flush, it won't reach the intake or where the valves are sludged. You know, neither of those things makes sense to me. Black smoke is a sign of too much fuel reaching the engine. Did they replace the MAF?

If they didn't, try cleaning it.

Here is a link that explains how it's done:

https://www.2carpros.com/articles/mass-air-flow-service

Also, the manufacturer recommends changing the oil at 7,500-mile intervals. I would hope they wouldn't hold that against you.

Let me know.

Joe
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Thursday, June 15th, 2023 AT 10:38 PM
Tiny
INFINITIANDBEYOND96
  • MEMBER
  • 3 POSTS
They refuse to clean or test the MAF sensor. Their final solution is to walnut blast the carbon buildup off the valves and hope the black smoke goes away. They claim carbon buildup is the cause of the black smoke, but I think it’s the reverse. What do you think?
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Thursday, July 6th, 2023 AT 10:07 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
If there is a carbon issue, I would think it would cause the vehicle to react differently. Do me a favor. Disconnect the MAF and see if the smoke is gone.

Disconnecting it will force it into a predetermined setting to allow the engine to run. However, it shouldn't cause smoke.

Let me know.

Joe
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Friday, July 7th, 2023 AT 6:30 PM

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Black smoke be­ing pro­duced from the ex­haust sys­tem of is a sign of too much fuel be­ing processed by the en­gine.