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6-spd w. 35" tires: engine valve knocking sound issue

coolcj7

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Hello Experts! I really need some help solving this strange problem with my new JL. I have a 2-door, 6-speed MANUAL transmission, 3.6 engine, Rubicon with 4.10 gear ratio. I added 35" Milestar Patagonia tires. I did NOT change the speedometer settings in the internal computer after the new taller tires installation. Problem is that when I accelerate I hear this ringing (pinging, knocking, or whatever) sound from the valves. I try to keep the car above 2000 rpms, but it is not easy. I tried 89 octane fuel, but it didn't really help. Does anyone have a solution or a suggestion how to make the engine valve rattle sound go away? If I calibrate the internal computer with the new tire size, will that help? I know that is the solution with automatics, but mine is manual, so the car doesn't shift my gears. I tried riding on lower gears to keep the RPMs higher, but then my fuel mileage goes down the drain: it was 11 mpg when I looked at it yesterday! Horrendous!! Any help would be greatly appreciated. As a side note, yes, the 6th gear is non-existent with the 35s, I can barely get to 5th if ever.
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mwilk012

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How certain are you it’s the valves? The 3.6 is bad about rocker arms and lifters crapping out. Does it tick, or knock? Do you mean pre-ignition knock?
 

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Sounds like spark knock (pre-ignition or dieseling). Can be caused by poor fuel or lugging the engine. If you are shifting, under load, around 2 k my money would be on lugging the engine. Try raising your shift points to 3.5k or so and see if that doesn’t resolve the issue. If you go to accelerate and you are down around2k, downshift and gets there s up. If that doesn’t solve the issue try running a tank or two of 93 octane through it and see if that helps. Good luck!
 

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is it happening more when you step on it harder?
 
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Thanks @mwilk012 , @Oldbear , @Karnak for your replies. To answer your questions... after I changed the tires to 35", it is harder for the car to get to higher rpms but I am indeed trying to keep it at or above 2000. The car only has ~1000 miles on it so I hope no real failures yet. This "diesel" thing is sounding when the rpms are below 2000 especially when shifting between 1 and 2 gear. When driving at 40-50 mph, I am on a third gear mostly and rarely on 4th since the rpms would drop below 2000. When I am over ~2000rpm, all is fine, but it's the thing around shifting at slow speeds. I will try a different gas station further down the road and see if the "neighbor" station is selling me water instead of gasoline. In my previous Jeep (a CJ7 with a lousy 2.72 ratio) when I went to a taller 33" tire from a 31" I simply lost lots power, but never had weird noises from the engine. This one sounds indeed like a diesel when I shift and then goes away when I get a higher rpms. I do try to keep the RPMs up, but it is eating my fuel economy (like a 1972 Caddy!) so any advice and help would be appreciated. Again, many thanks for your replies.
 

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mwilk012

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You ever drive a TJ with the weak 4 cylinder engine and manual tranny? Sounds like you’re just dropping RPM’s too low for the load on the drivetrain.
 

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Thanks @mwilk012 , @Oldbear , @Karnak for your replies. To answer your questions... after I changed the tires to 35", it is harder for the car to get to higher rpms but I am indeed trying to keep it at or above 2000. The car only has ~1000 miles on it so I hope no real failures yet. This "diesel" thing is sounding when the rpms are below 2000 especially when shifting between 1 and 2 gear. When driving at 40-50 mph, I am on a third gear mostly and rarely on 4th since the rpms would drop below 2000. When I am over ~2000rpm, all is fine, but it's the thing around shifting at slow speeds. I will try a different gas station further down the road and see if the "neighbor" station is selling me water instead of gasoline. In my previous Jeep (a CJ7 with a lousy 2.72 ratio) when I went to a taller 33" tire from a 31" I simply lost lots power, but never had weird noises from the engine. This one sounds indeed like a diesel when I shift and then goes away when I get a higher rpms. I do try to keep the RPMs up, but it is eating my fuel economy (like a 1972 Caddy!) so any advice and help would be appreciated. Again, many thanks for your replies.
Thats maybe not you want to hear but I'll be honest now that you mentioned you didn't even have 1000 miles on it when you switched your tires, I would be tempted to tell you, put back those stock tires for now until you can break in your engine properly and let you computer learn your drive style. Lugging a motor thats not broken in by having large tires on it and not adjust the gearing and/or computer settings is not something I'd want to do personally. Your computer is probably still trying to figure out everything and setting its parameters and adjust itself to you and yet you just put these tires on making it harder for the whole engine and computer to work efficiently when its not fully broken in. Its like putting boots on a baby when he's just starting to get up on his back legs to start walking, i don't think its helping...;)

Keep the tires and after your first oil change, you can swap them in, you'll also see if the noise goes away when you swap them out to the stocks which if the noise doesn't go away, thats your indication if could be your engine itself.
 

mwilk012

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Thats maybe not you want to hear but I'll be honest now that you mentioned you didn't even have 1000 miles on it when you switched your tires, I would be tempted to tell you, put back those stock tires for now until you can break in your engine properly and let you computer learn your drive style. Lugging a motor thats not broken in by having large tires on it and not adjust the gearing and/or computer settings is not something I'd want to do personally. Your computer is probably still trying to figure out everything and setting its parameters and adjust itself to you and yet you just put these tires on making it harder for the whole engine and computer to work efficiently when its not fully broken in. Its like putting boots on a baby when he's just starting to get up on his back legs to start walking, i don't think its helping...;)

Keep the tires and after your first oil change, you can swap them in, you'll also see if the noise goes away when you swap them out to the stocks which if the noise doesn't go away, thats your indication if could be your engine itself.
There isn’t any learning to do, it’s a manual transmission. The learning is on the driver.
 

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There isn’t any learning to do, it’s a manual transmission. The learning is on the driver.
The computer still adjusts your fuel injection curves based on driving behavior (how much the little right pedal is pressed ) and based on precedent temperature, air ratio, ambient air, humidity, gas pedal position sensor, values taken at different rpm levels etc etc.

Unfortunately for a motor that is not broken in where the temperature values, friction levels and many more are not fully "stable" yet or the computer hasn't properly created its best curve yet., lugging the motor can have detrimental effect on that self-adjustment the computers have and it may have a hard time adjusting correctly because some variable's amplitudes are getting out of their boundaries too much while the engine is "finding its good wear pattern/spot".
 

SargeRubicon14

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Is it a 2021? Is it knocking or misfiring? You might take it to the dealership and see if it fits the TSB for replacing your spark plugs. There have been a few of us with 2021 models with the 3.6L and manual transmissions. The sound you are describing and when it occurs is very similar to what my issue was, they replaced all the spark plugs and solved the problem.
 

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So, @mwilk012 , @Oldbear , @Karnak, @SargeRubicon14. Just an update. I finally caved in and got the Flashcal JL and set my tire size to 34.25 (my actual size). The valve noise is all gone! It seems like no matter what transmission type is there, the computer regulates the fuel intake and whatever else and the tire size setting DO matter. I test drove on the lowest gear as I possibly could and the engine runs perfectly. Not that I plan to be lugging the engine, but now I can drive in peace and hear no noisy valves. I'm a happy camper now.
 

mwilk012

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So, @mwilk012 , @Oldbear , @Karnak, @SargeRubicon14. Just an update. I finally caved in and got the Flashcal JL and set my tire size to 34.25 (my actual size). The valve noise is all gone! It seems like no matter what transmission type is there, the computer regulates the fuel intake and whatever else and the tire size setting DO matter. I test drove on the lowest gear as I possibly could and the engine runs perfectly. Not that I plan to be lugging the engine, but now I can drive in peace and hear no noisy valves. I'm a happy camper now.
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beaups

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The computer still adjusts your fuel injection curves based on driving behavior (how much the little right pedal is pressed ) and based on precedent temperature, air ratio, ambient air, humidity, gas pedal position sensor, values taken at different rpm levels etc etc.

Unfortunately for a motor that is not broken in where the temperature values, friction levels and many more are not fully "stable" yet or the computer hasn't properly created its best curve yet., lugging the motor can have detrimental effect on that self-adjustment the computers have and it may have a hard time adjusting correctly because some variable's amplitudes are getting out of their boundaries too much while the engine is "finding its good wear pattern/spot".
The adjustments are mostly real time and those that aren’t last only seconds and have nothing to do with the driver.
 

Karnak

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The adjustments are mostly real time and those that aren’t last only seconds and have nothing to do with the driver.
https://carcomputerexchange.com/blog/how-car-computers-work/
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What’s more is that these engine computers are also self-learning devices that have been programmed to adjust for driving conditions and the habits of the driver. This means that the computer will make small adjustments to different parts of the engine and different systems in order to adapt to varying environmental conditions and to the way you, specifically, drive your car.
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And based on my motorcycle tuning experience, if new cars are anything like the new bike computers, they are self-learning so will modify their own "permanent" curve gradually over time and your fuel injection curve at 2000 miles will not look the same as when your car is gonna be at 50000 miles. Albeit there is a preset limit for variation, call it a "limiter" if you will so that the curve never gets too out of wack. some bikes was 15-20% max variation from stock for example and you can't get a good tune for a heavily modified engine unless you unlock the computer to bypass that threshold. So go to back to my statement, I was just stating it wasn't good to use oversize tires without compensating for it, especially when the vehicule is new. OP just confirmed by fixing his values in the computer that it now operates within those "limiter" parameters and it wasn't before.
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