3.6 engine and 87 octane a no-no

[Karlow17]

To my relatively uneducated, poor hearing - yes. After the engine is nice and hot, does it also “diesel“ when you turn the ignition off (continues to sputter and knock after shutdown)?

its hard to tell, sometimes maybe for half a second or so? Like a short jolt or two, almost like a slight sputter as it’s shutting off

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[Guv]

I dumped some of the lucass magic oil in the tank. It took a few miles but now it's mixed in well and a definite difference is felt . Of idle it would have some jerking (torque spikes)and u could hear some pinging . Cant hear it no more ...and finally of idle accel is smooth. 87 octane is definitely not good for our cars . The spark advance is too much and possibly running lean also. So my advice if ur going with low octane pour some octane booster the fuel spark curve will work much better. And yes its bone stock

Nothing but snake oil.
And please explain, how does 87 make a difference in the air/fuel ratio

 

[Wabujitsu]

its hard to tell, sometimes maybe for half a second or so? Like a short jolt or two, almost like a slight sputter as it’s shutting off

If that is the case, sir, you may also have some carbon buildup in your cylinders, creating hot spots, and/or your timing may be off.

 

[Karlow17]

If that is the case, sir, you may also have some carbon buildup in your cylinders, creating hot spots, and/or your timing may be off.

Is the timing controlled through the PCM since it has a VVT system? To me it’s almost like it’s running too lean when it gets up to temperature for some reason. I was thinking it would maybe be a bad rod bearing but I don’t think it’s the same sound and it doesn’t happen when idling. Mind you when it is idling it sounds like a diesel so who knows. I probably have a bad rocker as well but I think that’s a different issue than this intermittent knock when hot

 

[Wabujitsu]

Is the timing controlled through the PCM since it has a VVT system? To me it’s almost like it’s running too lean when it gets up to temperature for some reason. I was thinking it would maybe be a bad rod bearing but I don’t think it’s the same sound and it doesn’t happen when idling. Mind you when it is idling it sounds like a diesel so who knows. I probably have a bad rocker as well but I think that’s a different issue than this intermittent knock when hot

Hopefully a real mechanic will chime-in; I’m afraid your questions are now beyond the scope of my knowledge.

 

[Petey]

Nothing but snake oil.
And please explain, how does 87 make a difference in the air/fuel ratio

ahem..... octane ratings. And it does make a difference in the air fuel ratio depending on how lean you run. you might be new to this game so let me throw a query your way .. would you put straight gas in a diesel.. if you answer yes then u should look up why this is a big no no. I will stand by my Lucas octane booster and stand by its ability to stop pinging.. I got a 1000 bucks saying that it will hold u over till u figure out the reason the engine is running lean or pinging .. if you have this problem and want to run ur vehicle that's fine .... your engine your dime...

 

[Petey]

Hopefully a real mechanic will chime-in; I’m afraid your questions are now beyond the scope of my knowledge.

upon start up engine runs a richer ..this might be the reason one might have the issue until the regular fuel map kicks in after it reaches a certain threshold in temps.

 

[Petey]

Does Amsoil make gas?

Asking for a friend.

we all make gas .... just don't tell anyone

 

[Petey]

This may be be a zombie thread, but it gives an opportunity for those of us who've been running premium since the original post was written to check in. I've been running 91 pretty much exclusively since I bought this unit new in '20. Occasionally I have to fill with 87 when 91 is not available, and the difference in performance is stark.



...and gets better mileage.

With a compression ratio of almost 11.5:1, it seems stupid to not run a fuel that makes the most of that. And for those of us living at high altitude, the difference between non-alcohol 91 octane and the 87 minivan gas is really dramatic.

just got back from Brazil and let say it is stark .. not just here in the states .. rented a three cylinder Hyundai to putt around .. in the southern cone of South America....I tell you no lie it was a lawnmower of an engine.. yet one thing I noticed immediately was that the gas that was made with ethanol would at times almost shut the engine off at idle. I by chance put regular gasoline and immediately the vehicle had composure and quite a lot more horse power..it was a world of difference and don't let anyone tell otherwise .. if they do they're absolutely clueless.

 

[Petey]

In Australia our octane level is calculated differently which gives us 91, 95 or 98 octane fuel ratings. Our jeeps are recommended to run on our 91 octane which I believe is equivalent to the US 87. Our JL Overland Unlimited was bought new in 2019 & I definitely noticed the rattling/ping but only at low speeds/revs & only after the engine was well warmed up. It seems to be especially prominent & worse when 4 wheeling at low speeds & climbing. I went looking for threads on this issue as it seemed to be getting worse & tried the highest octane fuel to remedy the problem. My observations after a couple of months using our 98 octane fuel from BP are - pinging/rattle is very much reduced with normal street driving & barely noticeable but when offroading in 4wd it is still very prominent & at it's loudest & worse. Fuel economy appears to be a little improved but marginal & not enough to make a big song & dance about (maybe half a litre per hundred kilometers better) but it does seem to run a little smoother & have slightly more get up & go & a bit more responsive to pedal input but again nothing to write home about by itself but all combined it does add up to an improvement overall with power, economy & smoother running even if it is only marginal, but using the high octane does considerably reduce & almost eliminate the pinging/rattle for normal street driving. So overall I will continue to use the higher octane fuel because personally I notice enough difference overall in my JL to think it's worth the few extra dollars each time I fuel up especially since the thing set us back 70k.But of course this is my own personal experience & observation with our JL & for others their experiences could be different because one thing I've learned about cars over 30+ years of driving them is that like people they can be temperamental & one doesn't always behave like another. 2 cars off the same production line built minutes apart can be completely different, 1 an awesome build with little to no issues & the other a lemon with every issue you can imagine. Enough people across enough forums & threads are describing the exact same issue which means it exists & is common enough to spawn countless threads on the problem so it is obviously a common enough problem to warrant Jeeps attention to finding the problem & rectifying it. The higher octane fuel clearly does not rectify the problem completely by any means but it's a short term alleviation of the issue that people can easily do themselves which won't affect or void warranties or do any damage until such time as Jeep addresses it with a fix. If you are one of the many who have no issues with your Jeep pinging then consider yourself lucky but bare in mind that many of us do have this issue & until Jeep comes to the party these forums & discussions are all we have to communally discuss these issues & try to find solutions & I for one find this forum to be an awesome tool for finding info & fixes for bugs & faults especially ones that Jeep themselves are denying the existence of or have not yet found a fix for. Our JL is auto 8spd & has done just over 32,000klms.

Check fuel pressure if not use a octane booster in the meantime it might hold u over till u get a chance to figure out the underlying problem.

 

[Guv]

ahem..... octane ratings. And it does make a difference in the air fuel ratio depending on how lean you run. you might be new to this game so let me throw a query your way .. would you put straight gas in a diesel.. if you answer yes then u should look up why this is a big no no. I will stand by my Lucas octane booster and stand by its ability to stop pinging.. I got a 1000 bucks saying that it will hold u over till u figure out the reason the engine is running lean or pinging .. if you have this problem and want to run ur vehicle that's fine .... your engine your dime...

I retired as a senior research technologist in an engine lab 3 years ago. 38 years there, I used to manage a project testing and determining octane numbers and cetane numbers for various fuels.
So, how about you take your $1,000 and invest in some real education, buy some tools, get a job in the industry and then get back to me with how OCTANE affects A/F ratio.
Rich A/F ratios will reduce knock and enrichment is used to cool exhaust gases which also help reduce turbo boost.
Engines going richer than Stoichiometric (14.7:1) under load has been used to keep engines safe under high load forever.
No amount of increased octane will change the air fuel ratio but it will effect the knock limit.

 

[Guv]

I suppose that if your knock sensors failed and you were using too low of an octane gasoline the knock events could create engine misfires that would cause the O2 sensor to read some strange numbers. This would be a perfect storm of engine control failures and pretty unlikely unless purposely done.

 

[Petey]

I retired as a senior research technologist in an engine lab 3 years ago. 38 years there, I used to manage a project testing and determining octane numbers and cetane numbers for various fuels.
So, how about you take your $1,000 and invest in some real education, buy some tools, get a job in the industry and then get back to me with how OCTANE affects A/F ratio.
Rich A/F ratios will reduce knock and enrichment is used to cool exhaust gases which also help reduce turbo boost.
Engines going richer than Stoichiometric (14.7:1) under load has been used to keep engines safe under high load forever.
No amount of increased octane will change the air fuel ratio but it will affect the knock limit.

Ur telling that rich A/F ratios are used to cool exhaust gasses but clearly that’s not what I even mentioned . So what happens when you run lean and there is no enrichment . Ur gonna run on it just the same..???

“No amount of increased octane will change the air fuel ratio but it will affect the knock limit.”

Kind of self own here bud because fuel curves and maps do exist. They deviate a bit its not a one shoe fits all .. of course not by too much if predetonation is detected its there to make adjustments this is how octane changes it… it clearly won’t change the air fuel ratio by it self..

and please don’t hold the armchair joystick too hard its going to give u tennis elbow.

 

[Petey]

I suppose that if your knock sensors failed and you were using too low of an octane gasoline the knock events could create engine misfires that would cause the O2 sensor to read some strange numbers. This would be a perfect storm of engine control failures and pretty unlikely unless purposely done.

No codes showing even from a code reader that dealers use.. I did find out today though that my ground terminal was a bit lose . Hoping this was it.. so far it’s not showing the hiccups I would typically feel during acceleration.

 

[ASSFROW]

ahem..... octane ratings. And it does make a difference in the air fuel ratio depending on how lean you run. you might be new to this game so let me throw a query your way .. would you put straight gas in a diesel.. if you answer yes then u should look up why this is a big no no. I will stand by my Lucas octane booster and stand by its ability to stop pinging.. I got a 1000 bucks saying that it will hold u over till u figure out the reason the engine is running lean or pinging .. if you have this problem and want to run ur vehicle that's fine .... your engine your dime...

So you're saying the difference in octane rating between diesel and gas are the reason a diesel won't run on gas?

BTW octane does not affect air/fuel ratio.

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