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Discussion Starter · #1 ·
The 2006 4.0 with 147K miles is blowing black smoke under acceleration. I believe that means it is too rich, but it is not throwing any codes. A few months ago we removed the 2nd set of cats and replaced the primary ones with Nissan parts. Could this be the issue?
Also, this truck has burned 3 quarts of oils over 5,000 miles. That seems excessive to me, but I never see any blue smoke or odor.
Any recommendations are appreciated.
 

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PCV valve changed? Leakdown compression test?
 

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The 2006 4.0 with 147K miles is blowing black smoke under acceleration. I believe that means it is too rich, but it is not throwing any codes. A few months ago we removed the 2nd set of cats and replaced the primary ones with Nissan parts. Could this be the issue?
Also, this truck has burned 3 quarts of oils over 5,000 miles. That seems excessive to me, but I never see any blue smoke or odor.
Any recommendations are appreciated.
You are correct, black smoke is a rich mixture but this would be on top of the oil issue. Mt bet is that the rich mixture is covering up the blue smoke that is all your oil consumption.

When you say not throwing any codes, have you actually checked for codes or are you basing that off that there is no CEL on?

Are all of the sensors connected that you disconnected when you changed/deleted CATS?

You need to get a handle on the oil consumption. It is very excessive. Bad rings, valve seats, valves, valve seals, cracked block or oil galleys, etc... Anything that will allow oil into the cylinder.
 

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Was the catalyst substrate damaged in the upstream cats? There have been a few VQ40DE's that have had an upstream converter break apart and the bits got sucked into the combustion chamber during the EGR process, which is done through the variable valve timing rather than via a more conventional EGR valve system. The bits of substrate score the cylinder walls and cause poor ring sealing, resulting in an oil burning engine. It might be worth doing a compression test on the engine.
 

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Was the catalyst substrate damaged in the upstream cats? There have been a few VQ40DE's that have had an upstream converter break apart and the bits got sucked into the combustion chamber during the EGR process, which is done through the variable valve timing rather than via a more conventional EGR valve system. The bits of substrate score the cylinder walls and cause poor ring sealing, resulting in an oil burning engine. It might be worth doing a compression test on the engine.
My thoughts as well, seen it happen to lots of different engines over the years.
 

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Discussion Starter · #7 ·
Thanks guys. Yes, the upstream cats fell apart and clogged the second set. I changed the PCV valve last weekend. It went through 3/4 of a quart in 600 miles. I'm going to monitor it weekly to see if there is any difference. If it is an extreme engine issue, my stepson doesn't have the money to put into it and I already have $5K in it. He's 23 and I'm trying to teach him to be responsible.
 
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