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Discussion Starter #21 (Edited)
If your pinging goes away with using better premium fuel then it very well could be carbon build up on the pistons. But yes we are well into winter gas now which is a killer hell i think there is even a TSB out for poor engine performance while using winter blend gas.

If you halfway know what you are doing i would run a can of seafoam through the motor (great way to piss off your neighbors due to the smoke show it will produce lol)
Two things I hadn't mentionned : master tech did an ECM flash before doing the plugs, thinking that might cure the ping. I haven't checked but this flash may be related to a TSB. It didn't help. And before I had my appointment for plugs, I ran Sea Foam, but in the gas tank not in the oil. No change.

Last year this happened in septembre, before winter blend.

Pretty sure gas has no impact on my problem. New plugs + oil leak into spark plug well fixed = ping gone. Tech who did the plugs thinks the oil leak could be responsible, but he's a relative rookie and had no real explanation as to how or why. Can oil on the outside of a plug cause voltage variations to the plug ?


typo edit
 

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Can oil on the outside of a plug cause voltage variations to the plug ?
Normally it would cause a misfire. If it was the cause of the pinging there should have been noticeable change in color on that plug. In the Taxi's, excessive idle time makes 100k plugs last 60k.
 

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Discussion Starter #23
Normally it would cause a misfire. If it was the cause of the pinging there should have been noticeable change in color on that plug. In the Taxi's, excessive idle time makes 100k plugs last 60k.
They kept it an extra day, waiting for gaskets. I forgot to ask for the old plugs. I did ask the tech a few days after if he had noticed anything way wrong with one or more plugs, and he didn't seem to think so.

I had no misfire, no codes. I searched around, a lot... for similar reported problems with Pentastars and came up empty, basically. I don't idle that much, except perhaps the 5-10 minute warm-ups on winter mornings. Master tech did mention plug color, when he inspected one on the first t-shooting visit...

Knock was driving me nuts. Glad it's gone and hopefully... never again.
 

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Two things I hadn't mentionned : master tech did an ECM flash before doing the plugs, thinking that might cure the ping. I haven't checked but this flash may be related to a TSB. It didn't help. And before I had my appointment for plugs, I ran Sea Foam, but in the gas tank not in the oil. No change.

Last year this happened in septembre, before winter blend.

Pretty sure gas has no impact on my problem. New plugs + oil leak into spark plug well fixed = ping gone. Tech who did the plugs thinks the oil leak could be responsible, but he's a relative rookie and had no real explanation as to how or why. Can oil on the outside of a plug cause voltage variations to the plug ?


typo edit
Seafoam in the gas is good for helping keep the fuel lines clean. But for actual carbon build up it has to be intorduced directly to the chambers via vacuum line that feeds all cylinders. You let it suck up some till it starts smoking then unless they changed the directions suck up a 3rd of the can until the car dies then let it sit and soak the top of the pistons for a good hour then start it up rev it a few to blow out the casrbon then take it for a drive. If its heavy build up it can smoke for a few miles.

The TSB is not for a flash just a note to say that people may complain about poor engine performance and to educate them on winter blend fuels.
 

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Discussion Starter #25
Seafoam in the gas is good for helping keep the fuel lines clean. But for actual carbon build up it has to be intorduced directly to the chambers via vacuum line that feeds all cylinders. You let it suck up some till it starts smoking then unless they changed the directions suck up a 3rd of the can until the car dies then let it sit and soak the top of the pistons for a good hour then start it up rev it a few to blow out the casrbon then take it for a drive. If its heavy build up it can smoke for a few miles.

The TSB is not for a flash just a note to say that people may complain about poor engine performance and to educate them on winter blend fuels.
Thanks. Hopefully I won't need to do that Seafoam technique. I've never had a carbon build-up problem in any of my previous vehicles, but who knows... I run good gas always (high volume gas stations, Shell or Petro Canada only). Never had a problem with winter blends.

My hope is the problem was with one cylinder only, the one with the oil leak into the plug well. Or... bad plugs all around.
 

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Its interesting you bring this up, because since i've been testing/learning on the tuning side of things, the vehicle will create false knock that you don't actually hear (because it's not there) and I can make my 2014 (my 2016 did the same thing) do it on command. At low speeds when throttle is given to accelerate and the rpms are below 2200 or so, the vehicle show knock and pulls tons of timing, leading to a feeling of bogging and not wanting to go anywhere, and then it's like a light switch around 2200rpm and the knock magically disappears timing shoots up and you can feel the vehicle accelerate normally again. This of course can be alleviated with tuning, but this low speed bogging was one of my biggest complaints with both my cherokees.

Here's a video to highlight what I mean


On the flip side this is what it looks like when you do have bad gas...

 

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Discussion Starter #27
Well that's interesting... though I can't really process all those numbers, but that's Ok. So yeah your experience with low RPM bogging, I can relate to. My knocking was very real ; this sound... is worse to me than fingernails on a blackboard... Master tech and service manager both kinda looked at me funny, hinting I was imagining the noise... Nope... They didn't hear it because I only allowed the knocking for a few minutes after fill-ups, before I stuffed a bottle of octane booster to silence it.

I'll try to avoid the tuning route if I can ($$), but I know it exists...
 

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Oh I don't doubt you had knocking, i've had it with bad gas before, you can hear it for sure. This knock I'm pointing out would never be audibly noticed and only shows up with data-logging.
I"ve narrowed it down to this table (well there is more) but for "relatively" easy understanding, when you zero this table out almost all the problem goes away (still some other torque management tables to adjust)



As an example (graphically) after some adjustments this is one of the tables that shows ho abrupt (and crappy) some of the factory mapping is and the torque management that shows the abrupt nature of how the bogging happens then goes away, in the modified state its much smoother.

 

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Discussion Starter #29 (Edited)
Aircharge ??? Okey-dokey... heh. I do see the improvement. Is this crappy coding on some 3.6Ls too ? I have to wonder how an engineer can get away with such "imperfect" programming... and why they won't correct it with sofware updates. Maybe they have TSBs we haven't seen, flashes only a few get...
 

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Aircharge ??? Okey-dokey... heh. I do see the improvement. Is this crappy coding on some 3.6Ls too ? I have to wonder how an engineer can get away with such "imperfect" programming... and why they won't correct it with sofware updates. Maybe they have TSBs we haven't seen, flashes only a few get...
These vehicles are a speed density system. No Maf sensor, Aircharge is one of the values used to measure the air going into the engine along with MAP (manifold absolute pressure)
So when tuning, or adjusting things the spark tables are listed in aircharge and RPM.

If I want to adjust timing at a certain point in the RPM range, or want to make sure the engine isn't pulling timing I reference a bunch of different charts, so as an example



Aircharge on left and rpm on the top.

Since we are talking about fuel and knock I may as well make a post up showing how running anything other than 87 octane in the 3.2 is useless (except if you are trying to diagnose something)
long story short, most people never have to worry about it. OCD people like myself love to play with this stuff.

The other really need thing is monitoring air charge, you can watch how a vehicle with a CAI has more volume of air going into the engine, vs stock. Even though people say CAI's don't do anything :)
 

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Normally it would cause a misfire. If it was the cause of the pinging there should have been noticeable change in color on that plug. In the Taxi's, excessive idle time makes 100k plugs last 60k.
i also thought so
 
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