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3.6 - For Those Running Premium Fuel

TheRaven

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I don't care what anyone else says. I know for a fact that my Jeep runs like absolute dog shit on 87, and so I switched to 91. World of difference.
This is exactly it - and I want to make clear that I am not calling you out at all, you need to be happy with your vehicle and i'd feel the same way in your shoes because i'm very OCD - but having said that, mine runs beautifully on 87. No loss of power, no problematic knocking or pinging, nothing. Even more importantly, I already did the "premium test" and got absolutely nothing out of it. My 3.6l averages 20.5-21mpg on both regular and premium, and power and smoothness is the same.

We need to understand that everyone is different and every situation is different. There are differences between vehicles built in different runs, weather and climate differences, altitude differences, terrain differences, differences in the way we drive (i.e. my wife gets an extra 1-1.5mpg out of any vehicle she drives in comparison to me), that explain why some of us feel the need to run premium and others don't. We need to get away from this "YOU NEED TO RUN PREMIUM OR YOU'LL BLOW UP YOUR ENGINE YA'LL!!!!!". It's a long debunked myth.
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iboostgti335

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I have been filling up with 93 for nearly a decade in other cars, so I followed suit with my 3.6. I have no idea if it runs better on premium vs regular, its just what I am used to using.
 

TxJeepers

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I have been filling up with 93 for nearly a decade in other cars, so I followed suit with my 3.6. I have no idea if it runs better on premium vs regular, its just what I am used to using.
Thank you
Sincerely,
Big Oil
 

iboostgti335

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Thank you
Sincerely,
Big Oil
Well yes, but they were all modified forced induction cars that I could never get away running regular in. One was actually 100 octane only. Plus, fuel is cheaper than replacing fuel injectors.
 

TheRaven

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Plus, fuel is cheaper than replacing fuel injectors.
Is it? This claim made me wonder, so I did some math. Up here, premium fuel costs $0.60-1.00 more than regular. That works out to an additional $560 per year in fuel costs for a standard 15k mile per year life. Your injectors will last at least 100k miles even with crappy fuel, so at 15k/year that's over six and a half years or $3700 in additional fuel cost. Injector replacement should be in the $600-800 range.

So for me at least, injectors are way cheaper. Seems to me like just dumping in a bottle of injector cleaner with each oil change would be the best of both worlds.
 

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iboostgti335

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Is it? This claim made me wonder, so I did some math. Up here, premium fuel costs $0.60-1.00 more than regular. That works out to an additional $560 per year in fuel costs for a standard 15k mile per year life. Your injectors will last at least 100k miles even with crappy fuel, so at 15k/year that's over six and a half years or $3700 in additional fuel cost. Injector replacement should be in the $600-800 range.

So for me at least, injectors are way cheaper. Seems to me like just dumping in a bottle of injector cleaner with each oil change would be the best of both worlds.
Not try argue here. I wasn't speaking towards Jeep fuel injectors, as I stated. The fully built motor on 36psi of boost and methanol injection in my Subaru needed new injectors every 20k miles. Again, completely different car, completely different scenario.
 

AnnDee4444

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Is it? This claim made me wonder, so I did some math. Up here, premium fuel costs $0.60-1.00 more than regular. That works out to an additional $560 per year in fuel costs for a standard 15k mile per year life. Your injectors will last at least 100k miles even with crappy fuel, so at 15k/year that's over six and a half years or $3700 in additional fuel cost. Injector replacement should be in the $600-800 range.

So for me at least, injectors are way cheaper. Seems to me like just dumping in a bottle of injector cleaner with each oil change would be the best of both worlds.
See those two BMWs in @iboostgti335's signature? $3700 probably didn't even break even.
 

TheRaven

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Not try argue here. I wasn't speaking towards Jeep fuel injectors, as I stated. The fully built motor on 36psi of boost and methanol injection in my Subaru needed new injectors every 20k miles. Again, completely different car, completely different scenario.
Me neither, but that's insane. Also why i've learned to stick with big motors for big power.

See those two BMWs in @iboostgti335's signature? $3700 probably didn't even break even.
For fuel injectors? BMW isn't out of line. Maybe a tad more expensive but nowhere near $3k. I had a 2004 M5 back in the day and aside from the inordinate amount of time it spent in the shop and and horrifically bad electrical system, it wasn't especially expensive to fix.

Nonetheless, we're talking about Jeeps here, not BMWs.
 

iboostgti335

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Me neither, but that's insane. Also why i've learned to stick with big motors for big power.
Bigger is better. Its the Murican way.
 

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AnnDee4444

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For fuel injectors? BMW isn't out of line. Maybe a tad more expensive but nowhere near $3k. I had a 2004 M5 back in the day and aside from the inordinate amount of time it spent in the shop and and horrifically bad electrical system, it wasn't especially expensive to fix.

Nonetheless, we're talking about Jeeps here, not BMWs.
I know, I forgot to indicate my sarcasm.
 

rob377

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Then it never left long term knock status.

The JL, as with most chryslers, will learn repeated knock situations and apply "long term knock control" where it pulls out timing no matter what. The MOAB we have was pulling out 6* of spark almost everywhere with 93 in it after the last tank was 87. with 87 it was 6* plus another 1-2. The point was that unless the ECM says that it's safe to start adding more timing back in, it won't. no matter how many tanks of 93 you run. You would need to meet the load/speed requirements to get it to start learning timing back in.

OR, disconnect the ECM, and it will revert on it's own. but the JL heavily knocks on 87 octane, and should be on 91+ for all engines. that's why they audibly spark knock with 87.
Sorry to resurrect this, but how long is the learning process for the ECM?

Or put another way, how repeated does the "repeated knock situations" have to be to register as a long term knock control value? E.g. I've been using 91 or have a ECM with freshly reset adaptives, and then put in 87, what criteria move a short term retard value into the long term knock control category?


On the flip side, if I've been using 87, how long does 91 need to be run (or what load/speed requirements need to be met) does the ECM need to stop pulling timing?

Thanks for the information you've posted so far, it's been educational!
 

Bikemobile

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Pretty sure the vehicle runs a set timing map and Paul’s timing when it sees necessary. I don’t think it learns to advance more timing than the map allows, or learns to always pull timing.
Just run 87 and it will be fine. Unless its tuned. I run 85 and its fine.
 

Rodeoflyer

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Says the guy nearly 8,000 ft. above sea level...
I'm around 6000ft and had some pinging issues since I purchased the jeep. Started running 91 octane and installed a catch can to decrease some of the combustion contamination and it stopped. Since gas prices went off the chart, I started using 87 and it's not pinging at all now. I did have to disconnect the battery to clear the start/stop error/top gear relearn after installing 5.13 gears so maybe the fuel maps re-adjusted(?) Not sure but for whatever reason it stopped...
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