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1999 3.3L 4wd. Have had a periodic service engine light. Got it checked yesterday and got codes for knock sensor and running rich on
Bank 1.

Any idea whether these could be related and if replacing the knock sensor could fix the other? Gas mileage has been suffering as of late for sure. Used to be able to squeeze 20mpg out of her, but now I struggle to get 17-18 mpg. Is it possible that I'm losing that much by running too rich.

Engine seems to have gotten pretty boggy.

Thanks.
 

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Generally, running rich will reduce knock so its unlikely that running rich is the cause of a knock sensor code. Knock sensor codes are pretty typical on a 3.3 liter engine. I'd attack the running rich problem first. Running rich will affect the gas mileage.

First, the simple stuff. Is the air filter clean? I'd also check the PCV valve function. How many miles on the truck? I'm not a big fan of fuel injector flushing but, if you have high miles it may be a help or cure.

The best solution is to attach a code reader that can read the engine "trims". This requires a more sophisticated code reader, e.g. the Nissan CONSULT system and a good technician who knows how to use it (not the typical parts installer). The advantage of looking at the trims is that the technician can look at the various sensor values and pinpoint a sensor that is out of the norm. The other approach, beyond basic maintenance is to start replacing parts. I'd probably target the oxygen sensor first as a cause, but like I said, you're taking your best guess.

Steve

Steve
 
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