Hi, guys. I have a 2004 XJ8. I ran into an issue a month or so ago where I changed out my engine air filter and inadvertently misinstalled the plastic air box, which led to a Restricted Performance error. After some troubleshooting, I was able to figure out what I had done wrong, and it's driving just fine again.

However, in the process of doing that research and troubleshooting, I plugged in my Launch scanner and took the readings for the MAF and fuel trim levels. They are not close to 0 for the fuel trims and the MAF is giving a value above the 4ish level I read was normal at idle. My understanding is that if the MAF is wrong, it can lead to premature wear on the catalytic converter or other problems. The fuel trim values have persisted for over two weeks.

I have the $90 Denso MAF sensor in hand. Am I wasting money to install it given these images? My 2004 has 145,000 miles on it and is running great at the moment, but I don't want to cause a problem if installing a $90 sensor will help matters in some way.

Please let me know what you think! Thanks!

 

I am no expert on fuel trims but have you tried cleaning the MAF?

 

Non-expert thoughts - MAF is reading excess flow yet O2 sensors have said to cut back on fuel. Cleaning MAF would usually cause it to read more air flow, which would seem to make the two conflict more. So the MAF may be giving incorrect high reading. Possible the MAF connector needs cleaning. Then since you have one in hand it would be good to swap them out and see if the problem goes away. Keep the old one or put it back in if the values do not change.

 

OK, I will have a go at it with the replacement sensor and see what happens. Thanks!

 

I swapped out the Mass Air Flow sensor today. It was just 1) unclip the plug; 2) remove two screws with a torx bit.

I thought it might be interesting to post side by side pictures of an old and new sensor. I've only had the car about three years, but I have to think this sensor is not original to the car (2004). If you look at the little wire thing, you can see that the old one has some dirt or carbon build up on the little bulb thing at the bottom, but only on one side, while the new one is shiny/clear on both sides.

I will collect some new readings after I run it for a while. The initial readings I took do not look markedly different from what I had before. The value for the Mass Air Flow was in the 4.8 to 5.2 range vs. somewhat higher before. The fuel trim numbers were actually FARTHER away from zero than the old sensor, but we'll see if those change with a bit of exercise and a chance to recalibrate.


Left: Old Right: New

Left: Old Right: New

 

Cleaning it just may solve the issue