02 xjr
no codes
No misfiring
Super charger seems to whine a bit less than before. Any suggestions what to check for?

 

intercoolers too hot to touch?

 

Glogged cats ? Dirty maf?

 

Key out, remove the secondary fuel pump relay and jump pin 30 to 87 directly across from each other and listen if the fuel pump hums.

 

Belt slip? How old is the S/C belt? Any aftermarket pulley installs?

 

Exhaust of CAT system clogged?

 

Not any hotter than usual. But I'll double check.
Not sure how to check for clogged cats. Maf is new, Denso oem unit.
New pumps and fuel filter as of April 2020. But when I floor it, the instant mpg does go 4mpg, so I assume the secondary pump is working. But I'll make sure of it with a better test.
No clue how old the belt is. Stock pulleys, for now.
I'll have to see if that is the case.

All that said, I drove it once this week. Pulled great, like usual.

 

Spark plugs? Had an issue with feeling down on power and weird stumbling at mid throttle with no other faults for a long time, eventually traced it to spark plugs. Their gap was a little outside recommended, and they were slightly worn which made it worse. Replaced with new double iridium plugs with a gap slightly under factory spec (.052 spec for my year, think they measured a few thou narrower) and problem went away completely.

 

Go into the data list of your scanner with the key ON engine OFF, floor the accelerator and see what the TPS percentage is at WOT. It won’t be 100% but, it should be in the high 80’s to the low 90’s at best.

 

Yup, I need to check that. Thanks! I did eyeball the TB cable at wot. No slack. But I'll confirm with the scanner.

@nilanium I don't even know if my plugs have ever been done. I'll replace them just as maintenance.

 

Keep in mind because yours is an 00+ engine you'll want to go for the narrower .035-.039 gap range plugs.

 

Sorry guys, I have been really really busy lately. I did verify the TPS% goes to 100. So throttle body is opening fully. Also, IAT temps seem like what I have always seen. Verified both using my scanner.

 

Faulty vacuum actuator of the bypass valve could cause reduced boost.

 

I have recently had a batch of bad "high octane" fuel that caused one of my cars to
show bad coils. Replacing the coils did not help and led me to discover the fuel problem.

 

I think the second fuel pump is not working: see #4

 

It is. Instant mpg at wide open throttle, above 3k rpm goes to 4mpg.

 

Interesting. Thanks I will look into this.