2018 with PRX93 tune engine stuttering at altitude

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eclou

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I have a 2018 with PRX93 tune, 80k miles, had cam phasers done x2. Just replaced the vacuum hoses and check valve for the front hub engagement. Newer motorsports plugs in the last 5k miles.

Driving up to Colorado from Houston started getting some stuttering from the engine on medium throttle at highway speeds. Thought it might be related to octane as only 91 was available in West Texas, NM, Colorado. I have been adding octane boost and fuel system cleaner. No codes thrown on the NPT gauge but at one point trying to pass on the freeway it stuttered badly enough to throw a CE service light and said "cylinder 1 misfire". I cleared it and engine ran ok again but still stutters under higher throttle load.

Now if I manually downshift to 7th gear and ease into the acceleration it doesn't happen as much

Anyone got any ideas of what's up?
 

TwizzleStix

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Without data logs, guesses are the best you’ll get. With the misfire event it could be the plugs/gap. If running 91 on the MPT 93 tune, I recommend NOT pushing it, AT ALL. Set the cruise and let it work. At altitude the turbos must work harder to meet the tuned higher Load/Torque targets, so the boosted air temps run hotter, so the cylinders are more prone to knock and misfire.
 

smurfslayer

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fiction.
"the US ain't Germany, where the left lane on the Autobahn is kept clear for the fastest drivers."

Anyone who’s been on the a-bahn in the last 25 years knows that the left lane is just as hogged in the much touted Germany as it is in the USA. Same class of SUV piloting, self absorbed cell yakkers too.
 
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eclou

eclou

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Happy to say I flashed the truck back to the 91PRX tune on my way back to Texas and all of the shuddering is gone. Runs smooth as silk with no issues. Proper Octane is no joking matter!!! Ambient temps for the issues were around 30F at 7000-10000 FT elevation, and coolant temps were 220-230 F
 

Badgertits

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Happy to say I flashed the truck back to the 91PRX tune on my way back to Texas and all of the shuddering is gone. Runs smooth as silk with no issues. Proper Octane is no joking matter!!! Ambient temps for the issues were around 30F at 7000-10000 FT elevation, and coolant temps were 220-230 F
I’m not surprised at all, these engines are super sensitive to octane rating period, in stock form on stock tune you’ll pickup 30whp on 93 octane va 87 & you’ll never hear any knock/ping

BTW The hp rating for the truck is based on the min recommended octane - 87, so running 93 bone stock is basically a “performance mod” kinda like my ‘14 5.3 Chevy truck that could run on E85, picked up like 40-50hp
 
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