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Old 03-07-2012, 09:39 PM   #1
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Ethanol or Premium

OK,, here's the math. Regular = 3.64 per gallon 10% ethanol.. Premium= 3.94per gallon. No ethanol... Regular = 15mpg
Premium = 18 mpg
This translates into .24 cents per mile reg
.22 cents per mile pre

Without the ethanol blend my jeep also has much more power, with no need to downshift for headwinds or slight grades. I've been testing this now for a few months, and my data is accurate, and averaged, with very little city driving. Mostly, country roads, and interstate.
So, my question? Is running premium going to damage my engine? Common sense tells me no. At worst I'll have to change my plugs out more often but that's about it... The first time I tried premium grade gasoline without ethanol, I was blown away by the difference in power and MPG gains.. I do understand today's engines are designed to run on regular, except for high compression, high performance engines.. the 4.0 is neither. So what do any of you knowledgable people think? Thanks.

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Old 03-07-2012, 09:50 PM   #2
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I see no problem with running Prem. My tj has so much more power and better fuel Milage with it.

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Old 03-08-2012, 10:53 AM   #3
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Another consideration is that premium fuels tend to have better/more detergent packages in them and this would be an advantage.
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Old 03-08-2012, 10:57 AM   #4
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My tj has so much more power and better fuel Milage with it.
No it doesn't. Octane's sole job is to resist knock and make the fuel harder to ignite so it doesn't self-detonate from excess engine compression. That is octane's sole job... octane itself does not add power. Do a search here for octane and you'll see a lot has been written about it. Here's a recent post on it... http://www.wranglerforum.com/f5/89-o...ml#post2090022

In fact, running a higher octane gasoline than the engine was designed for can actually cause deposits to form and the engine to run worse due to the fact higher octane fuels are harder to ignite (true) and burn slower (true).

In fact, many higher octane fuels actually contain less energy content per gallon than lower octane fuels do.
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Old 03-08-2012, 10:57 AM   #5
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Another consideration is that premium fuels tend to have better/more detergent packages in them and this would be an advantage.
It used to be that way but now all grades have detergent packages.
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Old 03-08-2012, 12:32 PM   #6
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If you are losing power with lower octane or ethanol gas, then it is likely because your knock sensor is signalling the ECU to retard ignition timing due to detected knock (pre-detonation). As ignition timing is pulled, decreased power & efficiency results. However, if your engine is not performing optimally with 87 octane then carbon buildup, etc. is interfering.
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Old 03-08-2012, 12:34 PM   #7
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If you are losing power with lower octane or ethanol gas, then it is likely because your knock sensor is signalling the ECU to retard ignition timing due to detected knock (pre-detonation).
The 4.0L engine does not have a knock sensor.
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Old 03-08-2012, 12:46 PM   #8
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No it doesn't. Octane's sole job is to resist knock and make the fuel harder to ignite so it doesn't self-detonate from excess engine compression. That is octane's sole job... octane itself does not add power. Do a search here for octane and you'll see a lot has been written about it. Here's a recent post on it... http://www.wranglerforum.com/f5/89-o...ml#post2090022

In fact, running a higher octane gasoline than the engine was designed for can actually cause deposits to form and the engine to run worse due to the fact higher octane fuels are harder to ignite (true) and burn slower (true).

In fact, many higher octane fuels actually contain less energy content per gallon than lower octane fuels do.

Yep, in our Jeep motors, 87 will produce the most power. I think people get confused thinking that if they pay more for 89 or 92, they are getting "go faster" additives. My 110 Race gas ($10/gallon) would make my Jeep motor become a dog worse that it is already is.
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Old 03-08-2012, 12:47 PM   #9
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The 4.0L engine does not have a knock sensor.
Doh!! I'm still new to TJ's... should have posted a "noob" disclaimer...

But definitely not new to tuning motors. Before posting I did a quick check and found knock sensors on sale for TJ's. Are they only for the 2.5L? How do our ECU's handle ignition timing? Or do they at all?

Edit: here's what they claim is a KS for TJ 4.0L...
http://www.partsgeek.com/gbproducts/...-07037601.html
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Old 03-08-2012, 12:57 PM   #10
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If the premium doesn't have EtOH in it then you will get better mpg. EtOH has roughly 33% less energy per gallon. Without knock sensors or tuning its impossible to make more power on higher octane.
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Old 03-08-2012, 01:13 PM   #11
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But definitely not new to tuning motors. Before posting I did a quick check and found knock sensors on sale for TJ's. Are they only for the 2.5L? How do our ECU's handle ignition timing? Or do they at all?

Edit: here's what they claim is a KS for TJ 4.0L...
http://www.partsgeek.com/gbproducts/...-07037601.html
I don't know the TJ's 2.5L well enough to know for sure if it as knock sensor or not but for sure, the Wrangler TJ's 4.0L definitely does not have a knock sensor. Engine timing is controlled by the PCM which takes the engine coolant temperature, engine rpm, intake manifold
temperature, manifold absolute pressure and throttle position position data to know how/where to set the engine timing.

And at least in my '97 FSM (factory service manual), it does not mention a knock sensor anywhere that I can find... which makes me think I read somewhere that only earlier Wrangler YJ 2.5L engines before the TJ had a knock sensor.
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Old 03-08-2012, 05:34 PM   #12
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I know my area does E10 all year. Im not sure if the premium here does E0 or not but It would be interesting to see if there would be a gap in MPGs with it. Most gas companies I know anything about put a lot more cleaning additives in the premium aswell so that could prevent the slower burn from leaving as much deposits. Would be nifty if someone already has tested this to see if the gap in $$ is worth not having the e10 in the gas for areas that do E0 in premium.
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Old 03-08-2012, 05:42 PM   #13
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I say continue the testing. I hope you are using Chevron. Let us know what brand. Good luck
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Old 03-08-2012, 06:02 PM   #14
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Quote:
Originally Posted by sm31
If you are losing power with lower octane or ethanol gas, then it is likely because your knock sensor is signalling the ECU to retard ignition timing due to detected knock (pre-detonation). As ignition timing is pulled, decreased power & efficiency results. However, if your engine is not performing optimally with 87 octane then carbon buildup, etc. is interfering.
Thanks all for your input. It is well known in the gear head/ motor head world that ethanol is our common enemy, as it robs us of precious horsepower, and cuts MPGs by 15 to 20%. Unfortunately there is very little access to 87 octane gasoline without ethanol, even the 89 octane around here has 10% ethanol blended in. Jerry has answered the direct question, "yes, there may be carbon deposits, and later on HP drop off" Once again, it is understood that high octane gasoline blends are for high performance, high compression engines, which the 4.0 is neither... I think I shall start to use my own blending methods, but on long trips, stick with premium, and live with said consequences later on down the trail.. One thing I learned on our last trip to Moab (2100 miles one way ) my jeep ran like total crap while driving through the ethanol states of the Midwest.. with headwinds in Kansas, 3400 RPMs in third gear to maintain 55 mph.. and lucky to see 9 MPG.. All of which makes a very strong case for two things.. Avoid Ethanol, and swap in that LS1- 4.3 ASAP...
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Old 03-08-2012, 06:21 PM   #15
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I say continue the testing. I hope you are using Chevron. Let us know what brand. Good luck
No Chevrons around here.. Darnnit... Used chevron exclusively when I ran high performance VWs back in the late 70s..
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Old 03-08-2012, 06:51 PM   #16
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Early Jeep computer-controlled 4.0L engines did in fact have knock sensors. Any suggestion that a knock sensor is incompatible with digital engine control is quite erroneous.

The knock sensor and EGR valve were eliminated concurrent with introduction of the High Output 4.0L engine in 1991.
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Old 03-08-2012, 06:57 PM   #17
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Thanks all for your input. It is well known in the gear head/ motor head world that ethanol is our common enemy, as it robs us of precious horsepower, and cuts MPGs by 15 to 20%.
Unless you have access to e85. Add larger injectors and pump and take advantage of the 105 octane at the pump! On a knock limited boosted engine it cold easily be worth 50+ hp. You will have to fill up a lot, but who cares!
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Old 03-08-2012, 07:37 PM   #18
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Early Jeep computer-controlled 4.0L engines did in fact have knock sensors. Any suggestion that a knock sensor is incompatible with digital engine control is quite erroneous.

The knock sensor and EGR valve were eliminated concurrent with introduction of the High Output 4.0L engine in 1991.
This is the TJ forum, not the YJ forum, and no 4.0 engines used in the TJ ever had a knock sensor. Since this is the TJ forum, there is no need to qualify an answer as to it pertaining strictly to the TJ.
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Old 03-08-2012, 08:30 PM   #19
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Since this is the TJ forum, there is no need to qualify an answer as to it pertaining strictly to the TJ.
Evidently, there is no need to be consistent, either!

To wit:

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Originally Posted by Jerry Bransford View Post
...but for sure, the Wrangler TJ's 4.0L definitely does not have a knock sensor.
I was hoping to offer some insight as to why so many parts catalogs show knock sensors for 4.0L engines. TJs 4.0L engines never had them, but earlier models did.
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Old 03-08-2012, 08:34 PM   #20
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Dont confuse ethanol with octane. Ethanol has higher octane but 30% less BTU's per gallon. Blended fuels are a pain the ass.
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Old 03-08-2012, 08:39 PM   #21
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Dont confuse ethanol with octane.
Excellent point. Octane isn't the only variable.
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Old 03-08-2012, 08:56 PM   #22
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While on the subject of ethanol, does anyone know if the additive sold in stores that's supposed to eliminate the bad effects of ethanol really work? It's supposed to take just a couple of oz. or so per tank full.
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Old 03-08-2012, 09:20 PM   #23
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That depends on which effect you are talking about and type of motor.

Ethanol blends are likely safe for most cars BUT the percents will likely increase. Also the quality control of how much being added is not very good.

Ethanol blends are problematic for marine engines especially two strokes. They ethanol attracts water and causes fuel phase separation. It will kill a two stroke and even some four strokes.

I used an additive in my outboard and do not buy blends for both my boats at all. It is easy to find as I live in the boating Mecca.
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Old 03-08-2012, 09:51 PM   #24
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While on the subject of ethanol, does anyone know if the additive sold in stores that's supposed to eliminate the bad effects of ethanol really work? It's supposed to take just a couple of oz. or so per tank full.
Illinois has been E10 for 20 years--across ALL octanes--and as far as I know there haven't been any ill effects in vehicles built past the Leaded Gasoline era. Even then I believe it only affects non-hardened valve seals but I ran it in my 1965 Mustang fastback for the 5 years I owned it without any issues.

That being said I still think Ethanol is a rip off. I'm paying for 100% gasoline. Not 90% gas and 10% corn!
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Old 03-08-2012, 11:06 PM   #25
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You'd really be pissed if you knew how many times you're paying for that 10%!
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Old 03-09-2012, 11:32 PM   #26
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Ethanol is a complete mess. A perfect example of a government screw up.
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Old 03-10-2012, 03:45 AM   #27
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I move to SD 4 years ago and didnt pay attention that they add ethanol in almot all the fule here. After being here for a few months I couldnt figure out why my jeep ran like chap, got wose than normal mpg, and had a hard time starting. I started to pay attention and avoid the ethanol, jeep runs fine, better mpg, and starts fine.
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Old 03-10-2012, 10:55 AM   #28
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Fleet Farm out here only sells non ethanol. All the boaters and snow machine folks go there for that reason.
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Old 03-10-2012, 11:40 AM   #29
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You'd really be pissed if you knew how many times you're paying for that 10%!
I do. And I am. Corn farming ain't what it was in 1985 thanks to all the ridiculous subsidies. I lived in the corn-belt and some of the wealthiest folks around were corn farmers.
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Old 03-10-2012, 12:43 PM   #30
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It takes MORE than a gallon if oil to make one gallon of ethanol. Plus food prices have been driven up. Dumb.

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