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Anything I can look for in my datalogs that would tell me I got some bad gas? (supposed to be 93 octane). I got a etune from a reputable tuner a couple weeks ago. My car has only a midpipe. I took a few datalogs when I first started running the tune, he looked them over and said all looks fine and I didn't see any knock sums that were more than a couple hundred. I ran about a tank of gas through it. Last night I filled up at a exxon station I had never been to. Looked like a brand new station but not in a "great" part of town. I went to visit a friend, we did a couple quick pulls and I didn't notice much different. I drove about 50 miles home and took the long way and did some pulls on the way back. My boost gauge flashed quite a few times. I didn't have my AP with me so I couldn't log. Fast forward to tonight, had kind of a stressful day and wanted to do some pulls. Did some logs and got some crazy high (low) knock sums. I saw a friggin -1800 at one point. After a while it started flashing when I wasn't even in boost. I can't think of anything much different between now and then, the weather was about the same (high 60's with high humidity) except for the gas. I sent the logs to my tuner and would rather not post them until I hear back from him, but is there anything I can look for in particular?
 

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Probably bad gas

I have a 93octane tune and my father once filled up the car with 91octance by mistake

I got about -1000 knock on low boost

Drained the tank and filled up with fresh 93 octane and the problem went away
 

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it is an electronical problem. another member posted something similar in the R35 section.

If your car had a real knock with a log count of 1800+ you would easily hear it. Do you reckon hearing pinging noise coming off the engine?

Is your car USDM 2010?
 

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The gt-r electronic system seems to have a tendency to trigger knock control in many occasions. once i was getting knock signals due to some water soaking into the ecu sockets. it freaked me out lol
 

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With just midpipe and how aggressive tuners tune the car it is not uncommon to get knock. It is even worst if you do a hard pull from dead stop. On your next tank of gas, log it and drive how you normally drive on this pulls. Sent the log to tuner as he might need to back out some timing. Good luck
 

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If your car had a real knock with a log count of 1800+ you would easily hear it. Do you reckon hearing pinging noise coming off the engine?
This is incorrect! Stop posting misinformation. Seeing -1800 on a Cobb datalog is not real knock. It's still pre-knock. You WOULD NOT hear it. The car will go into limp mode at around -3800 or so and you STILL would not be hearing any knock.
 

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Bad fuel. Refuel it at the same petrol station, do some logs then retune if needed.

This is incorrect! Stop posting misinformation. Seeing -1800 on a Cobb datalog is not real knock. It's still pre-knock. You WOULD NOT hear it. The car will go into limp mode at around -3800 or so and you STILL would not be hearing any knock.
My car used to get -1800 ( on cobb ) and i heard some ticking, and sometimes it would reach -2200. All on 91 octane / 95 RON.
 

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This is incorrect! Stop posting misinformation. Seeing -1800 on a Cobb datalog is not real knock. It's still pre-knock. You WOULD NOT hear it. The car will go into limp mode at around -3800 or so and you STILL would not be hearing any knock.
if you can't hear a knock that gets a count higher than 1000 with stock knock sensitivity you need to get your ears checked. i'm talking based on my experience, the car starts detecting knock in vacuum conditions (even during idle) randomly. Would take more than gas to make the car knock in such conditions so its obviously a phantom knock.
 

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Discussion Starter · #12 ·
I'm not gonna go back to the same station, it's nowhere near my house. I'll just run it as low as I can ona conservative tune and then fill up with my local Shell. The pump was really slow and the hose was unusually cold. Just making me think the gas was suspect.
 

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if you can't hear a knock that gets a count higher than 1000 with stock knock sensitivity you need to get your ears checked. i'm talking based on my experience, the car starts detecting knock in vacuum conditions (even during idle) randomly. Would take more than gas to make the car knock in such conditions so its obviously a phantom knock.
Speak with any tuner and they will back em up. If you hear knock your engine is being damaged severely.

Achenator, DO NOT go back to that same station ever again. I have no idea what that other dude was talking about.
 

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if you can't hear a knock that gets a count higher than 1000 with stock knock sensitivity you need to get your ears checked.
No way. You will not hear audible knock in the cabin of the car at -1000.

Bad gas definitely can make the car knock.

Although "phantom" knock is a possibility, I would stay conservative and assume it is real.
 

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I heard if your bell housing is going bad it can create false knock at low RPMS with all the rattling....

If you have a 09-10 I would check that out as well.

Just giving back to the community! ;)
 

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Discussion Starter · #16 ·
I heard if your bell housing is going bad it can create false knock at low RPMS with all the rattling....

If you have a 09-10 I would check that out as well.

Just giving back to the community! ;)
Yeah< I thought of this as well but it seems like that it would be consistent and not one second show zero knock and the next show -1000
 

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as stated.... Gas would be the first thing I attribute to abnormal knock sums...especially since the car was run with low sums previously and then suddenly exhibits high sums....
 

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Call your tuner and ask him to put a low boost map on your wheel switcher, that way if this happens again you have the option to dial down the cylinder pressure during situations such as this.

I would agree that the first thing you should do is run that tank of gas out and fill again to see if the problem goes away.

However, going from 1-200 to 1800 is still a pretty big jump just for bad gas, that would be like going from 93oct to 89ish.

Hope you get it all sorted out, first thing I would do is get a conservative map from your tuner and load it, it would be very easy for him to do.

~Cicio
 

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OP states that he gets knock flashing even while he's not boosting. Correct me if i'm wrong but it would take more than just gas quality to get the car to knock while its in vacuum, if it happens at all.

Also as far as i know ~ -1800 is the max amount that Cobb registers as knock sum so it might be a higher number and still cobb might be registering only 1800 which is why i said he would hear it in cabin if that was a real knock.

I feel like in some occasions once the car filters a real knock, the sensitivity for listening starts getting lower and lower up to a point where it starts reading the normal noises from the cylinders as knock (in which case you start seeing knock counts under vacuum conditions). I saw this happen with couple of cars and i wasn't able to hear anything via det can. Car was driving with 0 counts after a hard ecu reset by disconnecting the battery.

To OP, this might not be the issue for you so your best bet is to get a new tank of gas from a trustable source as above posts suggested before me.
 

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i would think knock in vacuum would not be a Fuel issue either... you'd have to have some really really miserable fuel lol. I highly doubt that.. More then likely if this is occurring at idle its phantom. New Gas, verify you don't have the bell housing issue. Get those 2 things out of the way and work backwards. But i do agree if knock was bad enough to cause damage chances are you would hear it or the car wouldn't be running so great.

Mark
 
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