3.6 engine and 87 octane a no-no

[Dr. RGB]

The 3.6L has a very high compression ratio. FCA are trying to control the consequences of that with electronic wizardry. Their software and electronics just do not get it done with 87 octane. On 87 and even on 89 octane when there is some 87 left in the tank, mine consistently stumbles at 1300rpm whether warm or cold. And it is down on power on the highway such as long steady climbs - mine has 35's, so 6th gear is useless on low octane gas. But when I hit a brand like Shell that carries 91 octane, it is perfect. As a result, when I get gas elsewhere, I have to put half 89 and half 93 in which is a pain. Interestly, mine does not seem to benefit from unlimited octane - 93 seems to be more than I need. But 91 does the trick, so that's what I run. Wish I could get away with cheaper, but engine just does not run as well.

My JL would stumble around 2,000 rpm with a steady throttle. Since I switched to 90 Ethanol-Free, I have had no problems at all.

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[Petey]

I take it to mean that maybe the oil vapor going through the PVC was contributing to the pinging and the catch can reduced or stopped it, so the pinging went away. If not the vapor itself, it may have changed a variable or multiple variables enough to stop it. If I had a pinging issue that was difficult to crack, I'd give it a shot. I don't think a catch can does one bit of harm.

I have to add in my experience the engines that do suck in oil into the combustion chamber were the ones that typically didn't have fuel quality issues because the oil would slow down or mitigate the shock of the combustion. This point of view is alien to me, in fact ,contradicts my observations But hey, I could be wrong. The lucas product works on this very idea.

 

[DanW]

I have to add in my experience the engines that do suck in oil into the combustion chamber were the ones that typically didn't have fuel quality issues because the oil would slow down or mitigate the shock of the combustion. This point of view is alien to me, in fact ,contradicts my observations But hey, I could be wrong. The lucas product works on this very idea.

I'm no expert. I'm totally guessing here. I don't even have observations to fall back on. I was just explaining what I think the member with the catch can was implying.

 

[Petey]

I'm no expert. I'm totally guessing here. I don't even have observations to fall back on. I was just explaining what I think the member with the catch can was implying.

Yes, I understand. One more thing came to mind right about now . If u do get in contact with ur buddy please do ask him if the EGR flow is in any way adjustable and if so, can flow from it be matched to the opening of throttle in a linear fashion.

 

[DanW]

Yes, I understand. One more thing came to mind right about now . If u do get in contact with ur buddy please do ask him if the EGR flow is in any way adjustable and if so, can flow from it be matched to the opening of throttle in a linear fashion.

I'll ask him. I"m betting it is not independently adjustable, if it is at all. If it is, I'd guess it would be dependent on other variables. But again, I'm 100% guessing.

He's taking longer to respond because of Black Friday and Cyber Monday. Thier product was featured in Car and Driver, so he's up to his eyebrows in orders right now.

 

[Petey]

I'll ask him. I"m betting it is not independently adjustable, if it is at all. If it is, I'd guess it would be dependent on other variables. But again, I'm 100% guessing.

He's taking longer to respond because of Black Friday and Cyber Monday. Thier product was featured in Car and Driver, so he's up to his eyebrows in orders right now.

Thnx

 

[JeepU4IA]

Wow! Catch can and fuel octane discussions in the same thread. I think this is the first time. Thread should go for another 10 pages at least.

 

[Rodeoflyer]

I take it to mean that maybe the oil vapor going through the PVC was contributing to the pinging and the catch can reduced or stopped it, so the pinging went away. If not the vapor itself, it may have changed a variable or multiple variables enough to stop it. If I had a pinging issue that was difficult to crack, I'd give it a shot. I don't think a catch can does one bit of harm.

Exactly. I'm no engineer, just 30 years of driving many different makes and models of hot rods, trucks and jeeps since the 80's so I somewhat understand mechanical things lol. The new gen 3.6 is a high compression motor (10.9 if I recall?) so any dilution of the intake charge can lead to minor ping, and I do think (and FCA says) the minor ping isn't really worrisome, however the catch can eliminated it in my case.

Ah.. edit:
https://www.cjponyparts.com/resources/pentastar-v6-specs
Increased Compression Ratio
The compression ratio was raised from 10.2:1 to 11.3:1. This was made possible by a few knock reduction measures taken in the design of the engine. One of these was the liquid-cooled exhaust gas recirculation system.

Maybe there's a PCM update/flash I need? Who knows.. FCA never tells me. I probably just need to take it to the dealer for updates every few months. I know every time I take the truck in there's some 'update' and need to flash the PCM.

 

[TheRaven]

It's neat how this same thread exists on every car forum on the net. I've been through GM, Ford, Toyota, Honda, BMW, Subaru...every forum for every model, same thread.

The answer is the same in every case - your owner's manual has the answer. The people who engineered and built your car know the most about which fuel grade is best for it.

And as for the "it may not be required, but it's still better" crowd - for the past 16 years, on every new car my wife or I get, we have run 3 tanks 87, 3 tanks 91 on the same daily drive for the first couple months...and we have NEVER seen a tangible difference in performance, fuel mileage, or manners on a vehicle designed for 87. I'm sure there are exceptions, but they are exceedingly rare...despite the fact that every single forum for every single vehicle in existence has this thread that claims you need to run 93.

 

[Rodeoflyer]

Why I refuse to run anything other than 87 octane, and the catch can allowed it with much reduced pinging.

 

[Petey]

Exactly. I'm no engineer, just 30 years of driving many different makes and models of hot rods, trucks and jeeps since the 80's so I somewhat understand mechanical things lol. The new gen 3.6 is a high compression motor (10.9 if I recall?) so any dilution of the intake charge can lead to minor ping, and I do think (and FCA says) the minor ping isn't really worrisome, however the catch can eliminated it in my case.

Ah.. edit:
https://www.cjponyparts.com/resources/pentastar-v6-specs
Increased Compression Ratio
The compression ratio was raised from 10.2:1 to 11.3:1. This was made possible by a few knock reduction measures taken in the design of the engine. One of these was the liquid-cooled exhaust gas recirculation system.

Maybe there's a PCM update/flash I need? Who knows.. FCA never tells me. I probably just need to take it to the dealer for updates every few months. I know every time I take the truck in there's some 'update' and need to flash the PCM.

If I understand correctly , ur saying that too much oil was being directed into the intake thru PCV? \
Did this happen all the time or while maybe offloading at a certain angle?

 

[Rodeoflyer]

If I understand correctly , ur saying that too much oil was being directed into the intake thru PCV? \
Did this happen all the time or while maybe offloading at a certain angle?

That's correct, oil was being pushed through the PCV into the intake. It's much worse after a trip so yes, high angles exacerbate it. I have much more oil in my catch can after an offroading trip than regular driving but I'm always driving up and down angles daily.

 

[zakaron]

@Petey Do you notice any oil burning or having to add much oil between changes? I ask because oil mist in the intake will lower octane when it mixes with gas in the cylinder. Something like a stuck PCV (check the valve and any cracks in hoses) can increase oil consumption. Not only does the additional oil lower octane, but if enough is ingested, it will start causing hot spots to build up on the piston tops and spark plugs. These hot spots will ignite fuel before the spark event causing detonation. If PCV looks intact, a catch can may help by filtering out a lot of that oil mist and allowing it to condense in the can before reaching the intake and combustion chamber.

I still find it impressive that (for the most part) FCA has been able to tune a non direct injected engine with 11.3:1 compression on 87 octane. So it is possible that yes, unfortunately, you may have gotten a sour Pentastar that due to manufacturing variances is more prone to pinging. Of course this is why tuners have had good success with the PUG Pentastar - such high compression on 93 with much more aggressive timing can yield noticable results.

 

[Petey]

@Petey Do you notice any oil burning or having to add much oil between changes? I ask because oil mist in the intake will lower octane when it mixes with gas in the cylinder. Something like a stuck PCV (check the valve and any cracks in hoses) can increase oil consumption. Not only does the additional oil lower octane, but if enough is ingested, it will start causing hot spots to build up on the piston tops and spark plugs. These hot spots will ignite fuel before the spark event causing detonation. If PCV looks intact, a catch can may help by filtering out a lot of that oil mist and allowing it to condense in the can before reaching the intake and combustion chamber.

I still find it impressive that (for the most part) FCA has been able to tune a non direct injected engine with 11.3:1 compression on 87 octane. So it is possible that yes, unfortunately, you may have gotten a sour Pentastar that due to manufacturing variances is more prone to pinging. Of course this is why tuners have had good success with the PUG Pentastar - such high compression on 93 with much more aggressive timing can yield noticable results.

Just did my first oil change about 1000 miles ago. . there was absolutely no sign of oil consumption, it was actually a bit overfilled .I've had the vehicle since I rode it off the dealers lot with like 40 miles on it. The exhaust burns clear, no oil to be smelled from the combustion exiting the tailpipe.. I don't think the engine is preigniting .. I just think the spark advance might be too aggressive with the 87. In my view it doesn't necessarily mean the pinging is caused by the engine itself when things like this happen. Engine controls could be at fault too.. I never did put a vacuum gauge on it but frankly , never heard any leaks and the engine seems to idle fine . No rev hang to indicate this either. The hoses still look new there is nothing that would indicate loss of vacuum. I'm happy this thing isn't direct injected it just adds to complexity.

 

[Rodeoflyer]

I just think the spark advance might be too aggressive with the 87.

I also think the tune is bit aggressive. As far as oil consumption, I've been using the oil life monitor (past two changes) and notice zero consumption on the dipstick. I drain about 2-3 oz out of the catch can every 2k miles so.. there's def oil being pushed though the PCV system but you won't notice that amount on the dipstick between 7500 mile oil changes.

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