ST Knock with hotter weather

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West27

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I have noticed now in the summer 80+ degrees that I am getting 1-4 st knock under moderate to heavy acceleration and when the engine is under load. Has anyone else had this issues? Never use to get any st knock when the weather was cooler and using same tune and 91 octane gas. Going to switch to a different brand of gas next tank and see how that goes.
 

shane1981

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do you have a 180 or 170 thermostat? do you have a tune of some sorts?

tuned by jay greene
 
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West27

West27

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I have 180 therm with a custom 91 HF tune with the electric fans turning on at 190 and the clutch fan removed. Sean thinks it is the fuel so we will see next tank but I'm kind of thinking it is just because of the hotter air temps.
 

shane1981

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its possible i could be the fuel. maybe go down to an 89 or 87 tune and see if it does it. if it does on the lower tune then you have something rattling or touching somewhere if not then i could be the fuel

tuned by jay greene
 
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West27

West27

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its possible i could be the fuel. maybe go down to an 89 or 87 tune and see if it does it. if it does on the lower tune then you have something rattling or touching somewhere if not then i could be the fuel

tuned by jay greene

What do you mean something rattling or touching?
 

Hemi395

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Had this same problem and pretty much the same convo with Sean about this. Did about 4 logs for him and he tweaked the 93 tune 3 times. I ended up going to his 89 tune with 93 octane gas and my ST knock is 0 unless I'm lugging the engine at low rpms. During the winter I didn't have this problem at all and ran his 93 tune with very little ST knock.

Honestly I don't really feel much of a difference between his 89 and 93 tunes so I may just leave the 89 tune. Truck still pulls hard and has crisp throttle response.
 

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My guess would be bad fuel as well. Did you put name brand in, or grocery store gas? With a tune I'd steer clear of the latter. If better fuel doesn't solve it, then it could be mechanical knock. The rattling or touching. Something hitting something else and getting picked up by the knock sensor. If it's mechanical and you can't find it, your tuner can desensitize your sensors, but that's a last resort. Better to find and fix the problem.

Good luck!

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shane1981

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What do you mean something rattling or touching?
heat shield ,loose bolt etc it could be a number of things . the sensors are picking up a rattle somewhere either a detonation rattle or a metalic rattle from something being loose

tuned by jay greene
 
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West27

West27

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This last tank was from Costco but usually I run Shell or Chevron. I am going to switch back to shell this next tank.
 

shane1981

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This last tank was from Costco but usually I run Shell or Chevron. I am going to switch back to shell this next tank.
costco is a cheaper fuel. i would change to a softer tune with the same fuel ans see what it does then go back to shell or chevron andcreload the other tune then you will know if its fuel or something else

tuned by jay greene
 

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This last tank was from Costco but usually I run Shell or Chevron. I am going to switch back to shell this next tank.

I suspect that's the culprit. It's what I call grocery store gas. Not really good for a high compression engine, especially if your tuner bumped the timing up. But I'd try Shane's test to eliminate mechanical knock. It can be harder to find.

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This last tank was from Costco but usually I run Shell or Chevron. I am going to switch back to shell this next tank.

That is probably your problem, Costco. I wouldn't run that in a lawn mower.
 
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West27

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Yea I was on a road trip and had to stop there so figure I would give it a shot since I figured it should be similar to other brand gas but maybe not....
 

Hemi395

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FWIW I've been using Shell 93 and have the same problems
 

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Yea I was on a road trip and had to stop there so figure I would give it a shot since I figured it should be similar to other brand gas but maybe not....

Here's a shocker. All gas is the same. Regardless of where it comes form, it all gets mixed in the big holding tanks at the terminal. If a Conoco and Shell tanker pull up at the same time, they get filled with the exact same gas. However the Conoco truck will get the Conoco additives, and the Shell truck will get the Shell additives. The additives are what makes gas brands different. The name brands have high dollar chemists and testing facilities to develop their additives. The guys that sell what I call grocery store gas don't. Makes a huge difference, especially in preventing knock. With cheap gas, you get what you pay for...

Also some states have what they call winter and summer formulations. The winter stuff up here usually sucks vs what they provide in the summer.

Just wanted to get that out there...

A couple of things I watch for when I get gas. Is the station really busy? They're the ones I fill up at. Slow stations with stale gas are more likely to accumulate water in the gas. A bad thing. Also I never fill up if the tanker is there filling the station's tanks. It stirs up any sediment in the tanks. I don't want that crap in my fuel system.

I always use name brand gas from busy stations. Been running Conoco for years in my Jeep. But Shell is good too. That's all we have up here. Exxon and the other big names pulled out long ago.

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FWIW I've been using Shell 93 and have the same problems

Could be stale gas, or mechanical knock. You could get your tuner to back off the timing a few degrees and see if it clears up. If not, it's probably mechanical.

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West27

West27

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Here's a shocker. All gas is the same. Regardless of where it comes form, it all gets mixed in the big holding tanks at the terminal. If a Conoco and Shell tanker pull up at the same time, they get filled with the exact same gas. However the Conoco truck will get the Conoco additives, and the Shell truck will get the Shell additives. The additives are what makes gas brands different. The name brands have high dollar chemists and testing facilities to develop their additives. The guys that sell what I call grocery store gas don't. Makes a huge difference, especially in preventing knock. With cheap gas, you get what you pay for...

Also some states have what they call winter and summer formulations. The winter stuff up here usually sucks vs what they provide in the summer.

Just wanted to get that out there...

A couple of things I watch for when I get gas. Is the station really busy? They're the ones I fill up at. Slow stations with stale gas are more likely to accumulate water in the gas. A bad thing. Also I never fill up if the tanker is there filling the station's tanks. It stirs up any sediment in the tanks. I don't want that crap in my fuel system.

I always use name brand gas from busy stations. Been running Conoco for years in my Jeep. But Shell is good too. That's all we have up here. Exxon and the other big names pulled out long ago.

wink

I totally agree with everything you said other than filling up if the tanker is unloading. I am betting that they have filters between the pump and the tank for this reason to eleminate sediment and any water. I could be wrong but I would be very surprised if they didn't.
 

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I totally agree with everything you said other than filling up if the tanker is unloading. I am betting that they have filters between the pump and the tank for this reason to eleminate sediment and any water. I could be wrong but I would be very surprised if they didn't.

You'd think so, but I've seen old tanks dug up and new tanks going in. Never saw any filtration. Only access to the tanks I've seen is where the tanker hose connects. So cleaning any hidden filters would probably be difficult. Maybe that's changed, but knowing corp types, additional costs cut into their bottom line...

Also a filter can't tell the difference between water and gas, so both would squeeze right on through. I got water in my SeaDoo tank once. Never got it all out. Never ran right again either.

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Hemi395

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Could be stale gas, or mechanical knock. You could get your tuner to back off the timing a few degrees and see if it clears up. If not, it's probably mechanical.

wink
Yeah I went back to my custom 89 tune. No more knocking.
 

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Yeah I went back to my custom 89 tune. No more knocking.

Looks like you eliminated mechanical. Did it always knock with the other tune? Same fuel? How much ST KNK are you seeing in your logs?

wink
 
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