Well, I know some of you guys that have read my threads in the past know that I have been experiencing TERRIBLE gas mileage and thought it was simply due to my performance mods. It so happens to be it may be something deeper than this. I posted up a thread in the 2GS section that just the other day I got a PO325 CEL; it is a bad knock sensor. After reading all particulars about this part it said it causes extremely poor gas mileage and poor performance; exactly what I have been experiencing. It effects timing as well. If left unattended it can severly damage engine internals, valves, pistons, rings etc etc. Now, from what I read symptoms can exist way before a CEL pops up...if this is the case then I should see a MUCH more efficient vehicle real soon.

So, I ordered both knock sensors (eventhough the CEL says it's just bank 1) for bank 1 and bank 2 just because it is a PITA as far as the install goes and I don't want to have to deal with this 6 months down the road to do the other one. I figured while I am at it I ordered all parts necessary for a fuel filter change.

I am hoping that by installing all these items I will get MUCH better fuel mileage (hoping for another 2mpg or better) and I am also hoping that the car will feel more punchy since the timing would be restored back to what it should be after a couple of cycles of normal driving (or "my" driving).

I just figured I'd make a thread for those that would like to follow it. I ordered the stuff from Carson Toyota/Lexus last night; $430/shipped and should get it sometime next week. After the install I will keep you guys posted as far as the results go. This thread may be of some use to someone down the road on these forums (RE: the knock sensors; I know the fuel filter replacement has been discusses extensively). I'll keep you guys posted!

 

dude, knock sensors just dont go bad. They detect knock and put your car in limp mode (flood with gas) in order to save your motor from detonation.


What is "NEO" in your sig? If thats some kind of fuel controller, then your fuel trims are causing detonation and knock.. Fix the problem before you install the new knock sensors, otherwise the new ones will do their job and put your car back into limp mode. For toyotas once they tend to pop, they need to be replaced so you may find yourself replacing them again if you dont fix the root cause.

 

NEO= APexi NEO yes?
Have you programmed your fuel trims with a wideband? Are you on the edge of running lean?

I would comment on the AFR ratio you want to see, but i'm not familiar with the V8 and how it likes to run. I would start there.

 

Thanks man, yes, it was tuned with a wideband on a dyno on a couple of occasions. The tuner said he leaned it out a good amount to extract the most power but still at a safe level. IIRC, I was around 13.1 - 13.2 afr. Keep in mind that my car has been tuned with this NEO for the last 2+ years and I never had a single problem. The car has about 125K miles on it so is it possible that it was on it's way out?

 

Not sure, but as an fyi I was gettin a PO430 for a while, which indicates a problem with the evap canister. The CEL went off on its own on that one. Can the root of my new problem be from a bad evap charcoal canister or even possibly a bad EGR?

 

IF your blowing knock sensors i dont think its EGR/Charcoal can related.


13:1 AFR is very lean and thats coming from a turbo guy who doesnt know a whole lot about tuning lol. Do you have any way to monitor knock or timing? Again, not familiar with the lexus much but if you had the ability to monitor either of those two then you coudl tell right away if your AFR is safe. Most folks i know that get tuned shoot for a ~11AFR. 13 is gernade land..

Take this info with a grain of salt. I know you've had this setup as-is for 2 years, but it sounds suspicious.

You may not get anybody else to chime in, since this forum seems a little lacking on the tech side from what i've seen.

 

Hey man, I really appreciate the feedback. The only reason why I brought up the possiblity of the EGR is because from what I read if the EGR is stuck open it will essentially show a vacuum leak thus leaning out the A/F ratios from my "already lean" tune.

BTW, I was battling a PO171 (Bank 1 too lean) a while back. I changed ALL O2 sensors and it went away. Can my EGR still be the culprit? I'm not even sure where my EGR is on the car. lol FYI, the Knock Sensor that shows the error code is also regarding Bank 1.

 

For a sc'd setup, tune your car on the dyno with a wideband aiming for a 11.2-11.5 AFR. Thats where you'll get the most out of your setup and be safe at the same time. 13:1 AFR for the lexus is no good.

 

I'm not SC'd yet.

 

EGR- Good thought, i like it. The EGR usually connects from an exhaust manifold to an intake manifold with the valve in between. Sorry, havent had a gs400 in a while... Im in the market now ;-)

02 Lean- If this was while your AFRs set to 13's, then the root cause points to the fuel trims like we've been talking about.



I think you should email somebody who tunes these cars for a living so he can offer some free advice. If what we're saying is correct, then that blown knock sensor is saving your motor by flooding it with fuel in its current state. Otherwise it could continue to detonate, increase knock and just overall hurt that nice v8.

 

Again man, great info! So your saying if I change the knock sensor(s) and perhaps the EGR (if it's bad) and not change my tune I could kill my engine?

I was thinking that I was perhaps "riding the line" to extract the most power from my car (still kind of being safe). However, if something should break that could potentially further lean the car out (i.e. something that can cause a vacuum leak) then I would be WAAAYYYY too lean leading to big trouble; maybe this is what I am up against.

 

Our engines do not have an EGR valve. EGR is accomplished with valve timing adjustment on the VVTi.

 

Oh, well, there goes that notion. lol What else could be giving me a lean condition? Besides the tune? FYI, all O2 sensors were replaced and MAF sensor was replaced ~1.5 years ago. Again, I was getting a CEL regarding something having to do with the EVAP system / charcoal canister. I thought it was my gas cap but it wasn't. Somehow it just went away on it's on; could this even be possible? or is it actually still there causing problems? Can these items all be related?

 

Could the stock ECU be battling the Neo, and setting the lean condition? Can you get your car to a dyno and see where your AFR numbers are at?

 

Fix the AFR's man.
Either:
-get it re-tuned
-Add more fuel yourself
-remove the fuel controller (apexi neo)


Leaning out your car to extract the most power possible on a STREET CAR, blowing knock sensors which are saving your **** and then trying to "fix" everything other than the real problem is comical. I'm pretty sure you just dont want to hear it or believe it, we've all been there.