I have a g35 with some bolt ons and a uprev tune. Before when I got on the gas around 3500 to 4000 it would feel like vvt kicks in and you feel it pull harder. I had 2 cel on the other week when it hit 95° one was for small evap leak (changed gas cap went off) second was p0328 knock sensor high input. I reset lights it's been like 2 weeks still no light but sometimes I no longer feel that vvt pull like I did before. Just feels sluggish other times feels fine. Could knock sensor cause this even though light never came back on. Any other thoughts. I have new air filter and sparkplugs were done few months back. Any help would be appreciated.

 

Are you using premium gas? I wonder why you aren’t getting codes again.

 

Using the best gas 93

 

Knock sensor code will kill power yes, basically it turns off your cam advance if there's a knock sensor issue.

Typically the problem with the KS is the sub harness, not the actual sensor itself. There's ways to do a contortionist act with a metal coat hanger to replace the thing without removing the intake plenum. I've never tried but this guy made a VERY detailed video that lays everything out perfectly.

 

So even with the code reset no cel on and not reading when I use a scan tool would still cause this issue and thanks for the responses

 

Not if you're not throwing that code. However it could be intermittently throwing the code, then self-clearing once the connection is reestablished. If you threw the knock sensor code AT ALL then you really should replace that sub harness.

That code won't always turn on the CEL either, it could be picked up, logged as a hidden code, then self-cleared immediately after the harness connection is reestablished. Some codes will self-clear REALLY fast, like the fuel level low input code from intermittent connection with the fuel level sensor. I suspect the knock sensor might be one of those too.

 

Check your intake tube accordion connections. If they tear, they can cause they car to sometimes feel normal, other times down on power because there is additional airflow after the MAF.

 

Ok while I'm there I'll look into my spacer bolts have not checked in awhile maybe it's loose as well. I bought a spacer off Amazon when I first got the car 60 buck vs the name brand ones for closer to 200 could that be it as well cheap spacer. It fit good but is plastic or something similar to plastic.

 

This is spacer I bought about a year ago

 

When you're checking the spacer make sure you didn't pinch the rubber collar on the oil filler tube between the spacer and plenum. It's a somewhat common oversight, and will produce a vacuum issue.

 

Thanks I'll keep that in mind I'll let you know what I find I'm going to run car and spray either water or something to check for leaks I use to do that on scooters and bikes

 

Checked for vacuum leaks couldn't find any seems better some days then others

 

I would remove the upper plenum and thoroughly inspect that plenum spacer for cracks. Typically the plastic ones start to fracture around the screw holes and it will be a really small vacuum leak that's hard to chase down because it will happen usually when cold but not when hot, or in certain specific situations.

I like using throttle body cleaner for chasing down vacuum leaks, it will lower the engine rpm if it's sucking cleaner.

 

Yea I always used carb cleaner on bikes around the intake I could check plenum spacer I did spray around didn't notice any leaks. I'm going to get my hands on a obd2 reader that has live data seeing that I have a tune will that throw off my fuel trim numbers

 

Ok so the better odb2 reader is saying only one code but its pd so no cel on atm but it's pd 0328 knock sensor high imput I think it said. I have new harness been raining on my days off so i didn't change it. Short term fuel trim is about -1 to 4 some times 7 for a second when giving it gas it moves between -5 and 10 depending on how much throttle is used. Long term is about 5 ish at idle and and goes up toward 9.7 to 10.2 ish while driving. Spark timing advance is about 9 at idle and only goes up to 25 under full throttle when I let off the the throttle it goes upwards of 37 40. Is all that normal or does the show a small issue idk what the normal range is for all that info. Also mass air flow reads 5 gs or less at idle and upward of 90 at full throttle. The mass air flow numbers I didn't watch as closely so that what I noticed