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Tuning Question - Knock

mjscar

By mjscar,
in Engines & Forced Induction

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mjscar Enthusiast

mjscar

Posted
Posted

Hey guys,

I just got a quick question in regards to a knocking issue on my car. The car is basically a 25DE+T with std turbo, injectors, fmic, and powerfc and a few other bits and pieces. It's currently running 10psi and have been running for the past month with no problem. Anyway, in that month, I've pretty much been taking it quite easy on the engine. I tried to look for the problems and whatnot in that period before I went full bore with it.

So last week, I started to push the engine a little bit more and more. I started with going full throttle in 3rd gear and that gave me no problem whatsover. The car pulled hard and everything is still good. However, 2 nights ago, I tried to push it in 2nd gear and I got the engine light flashing. First I did this at 100% throttle, and then 80% throttle. Now, I will take it back to the tuner to get it fixed, but before then, I want to get a little bit more knowledge as to what could be the main cause. Here's a jist of my thinking:

The knock sensor started going off around 4000-5000RPM all the way to redline. This is to would suggest

(1) It's not a boost spike because I don't think boost "spike" would go for 2000RPM long. Or could it???

(2) It's more likely to be an issue with timing because, if I'm not mistaken, 4000-5000RPM is where advanced timing usually kicks in from the VVT.

So what do you guys think? Is that a fair assessment of the issue? or can a boost spike really occur for over 2000RPM? Is it even possible for the advanced timing to affect the 2nd gear that much more than 3rd gear to cause a knock in 2nd but not 3rd gear?

I do apologise for my noobness in tuning but it's something I really want to learn. So thanks for all your help guys. Much appreciated.

NOTE: I don't have the handheld for the PFC.

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TiTAN Grand Master

TiTAN

Posted
Posted

there are a couple of things that make the check engine light flash. you need the hand controler or a laptop interface for the ecu to check if its the AFM voltage or its picking up knock, either way dont keep making it do it untill you can check what it actually is.

mjscar Enthusiast

mjscar

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  • Author
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there are a couple of things that make the check engine light flash. you need the hand controler or a laptop interface for the ecu to check if its the AFM voltage or its picking up nock, either way dont keep making it do it untill you can check what it actually is.

Nah I haven't been pushing it again ever since then. I only did it the 2nd time to make sure that it really was occuring. As for the AFM voltage, is it possible for it to cause an engine light flash only in 2nd gear? What would be the reason, if it was the AFM voltage, to cause it to only occur in 2nd and not 3rd?

Sorry for the many questions

TiTAN Grand Master

TiTAN

Posted
Posted

if the AFM voltage gets close to maxing out by default the PFC will flash the check engine light.

generally it will happen in every higher gear as well (as they put the engine under more load) rather than only in one specific gear if it is over a large RPM band

paulr33 Grand Master

paulr33

Posted
Posted

without the hand controller it is all guess work

get a hand controller and check the peak values and ETC, SENSOR SW CHECK when it occurs

it's not VVT, it's VCT and the changeover point is 4700rpm

mjscar Enthusiast

mjscar

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  • Author
Posted (edited)
without the hand controller it is all guess work

get a hand controller and check the peak values and ETC, SENSOR SW CHECK when it occurs

it's not VVT, it's VCT and the changeover point is 4700rpm

Alright. I guess there's no other way to find out for sure other than take it back to the tuner or find a hand controller. Thanks for all the help.

On a side note Paul, I saw in one of your links about the fake Z32's. Considering the ambigous tell-tale sign of a fake, would my tuner have noticed a big difference while tuning my car if it was a fake? And also, I read in a thread on SAU about the fake Z32's that you talked about idle issues. What kind of issue are we talking about here?

Just curious because I'm hoping that mine isn't a fake :S

Cheers.

Edited by mjscar
D_Stirls Veteran

D_Stirls

Posted
Posted

What are you using for boost control?

Cold nights cause higher boost due to cooler denser air, and a cooler intake charge also means higher cylinder pressures. So if it is Knock that could be what was causing it. As said above though, at this stage it's only guess work.

PaulosECR33 Community Regular

PaulosECR33

Posted
Posted

this is a bit off electronic side of the topic but i had major problems with boost creep on my stock turbo, only saw it in 3rd and 4th gear at full noise. i had the boost set to 10psi but i would see it creep up to 15 at about 5000rpm. it ended up being my wastegate. the shaft for the wastegate flap was binding up on the exhaust housing, causing it to not open fully. i have since gone onto bigger things for the car so i never tried to fix it but I'm just putting it out there.

A few other guys i know have had this problem to.

mjscar Enthusiast

mjscar

Posted
  • Author
Posted
What are you using for boost control?

Cold nights cause higher boost due to cooler denser air, and a cooler intake charge also means higher cylinder pressures. So if it is Knock that could be what was causing it. As said above though, at this stage it's only guess work.

Just using a manual boost controller. I might wait for a "hotter" day and give it another run. It is highly plausible that it is the very cold air because when I called the tuner, he was pretty puzzled considering how conservative he tuned my car.

yeah with a fake Z32 once you bring the car on power it runs like ass and the signal would be all over the shop

ie i dont think you could get a good stable tune from the fake z32

Ohh ok. Well when it was tuned, the tuner didn't comment on anything whack with the how the car was running so I am assuming that it's not a fake. But my car is just having idle issues, although I don't think are detrimental, that I can't put my finger on.

hadnt recently put a lower octane fuel in it?

Not at all. My tuner actually told me to use ONLY BP ultimate for some reason and not Vortex98 and that's what I've done. Not really sure with the difference is but can't argue against my tuner I guess.

Adriano Grand Master

Adriano

Posted
Posted

It could be the timing, as in a lower gear it can spike more than a higher gear, due to the ramp rate. It may then hit a cell which causes it to knock, and once an engine starts knocking they tend to keep knocking till you back off. However it could be injector warning, what injectors are you running?

mjscar Enthusiast

mjscar

Posted
  • Author
Posted
Sorry i see standard injetors, are they turbo injectors, what fuel pump?

DEt injectors and bosch 040 fuel pump. I highly doubt it's the injectors though because the tuner said it was only running 75% duty cycle.

Anywho, I really am starting to think it might be the cold weather. I might try to wait for a hot day close to the temp my car was tuned at and see if that gives a warning light. If not, then I might turn down the boost and do it again in the cold night. Fingers cross that a hot day is on the way and the cold temperature is the main problem.

Just getting a general idea here from those who know, how much of an effect would a, let's say, 10-15 degrees drop in temperature affect the tuning? Is this a common issue for those who have had their cars tuned or is it something the tuners would have accounted for?

Thanks for all the response and help guys. I really appreciate all the help!

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