3.6 Cam Self destruction

[JeepingJohn]

I have a Magnuson Supercharger on my 2020 JTR 3.6. A few weeks ago I was heading out to go wheeling and as my rpms hit 4000, I got a Cylinder 6 misfire and an awful shake in the engine. I stopped and turned off the Jeep. After letting it sit for a bit, I cranked it up and it drove fine until rpms hit 4000 again and then it went into limp mode. I disconnected the battery to get it out of limp mode and then took it to the dealership nearby. The construction of the cam/lifters is such that above 3500 rpms, the outside lobes of the cams ride on the rollers on either side of the lifters. One of the rollers on the Number 6 lifter (Driver Side) broke and carved out a big chunk of the cam lobe. Photos attached. While working on it, they also found out about the TSB to correct coding for the passenger side Cam(odd # Cylinders). I got the passenger side replaced for free, but was out of warranty for the driver side and it was not included in the TSB for one of the reasons described above.

I had to off load the new dealer code and email it to Magnuson along with the information from the dongle and VIN, etc. Within 4 hours, they sent back a new tune file. I loaded it onto my Jeep and it drove great leaving the dealership. Halfway home it went into partial limp, which I think limits rpms to 3000. Took it back to dealer and it showed a PCM Communication error. Dealer cleared it and again it drove great halfway home and went back into the partial limp mode. No engine lights either time. Remembering how @DAVECS2 suggested disconnecting the battery overnight when we had a similar issue on initial install, I just unhooked the battery. Hopefully when I reconnect in the morning it runs fine. I just hate they had to reflash it and cause me to have to redo the tune. Otherwise, the supercharger was running great.

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[JeepingJohn]

BTW: 75,000 miles with all oil changes at 5k mile intervals done at dealership so they have records.

 

[Lunentucker]

These engines seem marginal with normal aspiration. I'm sure forced induction isn't doing them any favors. I'm pretty amazed that the dealer warrantied anything. That's a one in a million dealer.

 

[Lunentucker]

BTW: 75,000 miles with all oil changes at 5k mile intervals done at dealership so they have records.

I just saw that you're in Oxford. What dealer are you using? Might be something good to know in the future. It's not much drive for me from Southern VA.

 

[ShadowsPapa]

The construction of the cam/lifters is such that above 3500 rpms, the outside lobes of the cams ride on the rollers on either side of the lifters.

Actually, the outside rollers are the low lift mode and under 2800 RPM.
High lift mode is above 2800 RPM and on the center of the rocker/follower.

So going over 2800 rpm you are not on the rollers, you are on the center section.

 

[JeepingJohn]

I just saw that you're in Oxford. What dealer are you using? Might be something good to know in the future. It's not much drive for me from Southern VA.

Superior Chrysler, Jeep, etc. in Henderson, NC. They have done me a solid on a few occasions.

 

[JeepingJohn]

Actually, the outside rollers are the low lift mode and under 2800 RPM.
High lift mode is above 2800 RPM and on the center of the rocker/follower.

So going over 2800 rpm you are not on the rollers, you are on the center section.

I am just repeating what the mechanic told me, which makes sense given the issues only presented at around 4000 rpms and the damage to the lifter is a broken roller and the corresponding gouge in the cam lobe. I am no engine expert, just trying to make sense of the problem based on info the mechanic who fixed it showed me. You may be right. he may be right. Either way, my junk was broken.

 

[Lunentucker]

Superior Chrysler, Jeep, etc. in Henderson, NC. They have done me a solid on a few occasions.

Thanks and noted. I'll go to Hendo in the daytime

 

[ShadowsPapa]

I am just repeating what the mechanic told me, which makes sense given the issues only presented at around 4000 rpms and the damage to the lifter is a broken roller and the corresponding gouge in the cam lobe. I am no engine expert, just trying to make sense of the problem based on info the mechanic who fixed it showed me. You may be right. he may be right. Either way, my junk was broken.

No, what he told you makes no sense and he doesn't know what he's talking about.

At over 2800 rpm, the follower (rocker) is on the center section. Not sure where he got the 3500 RPM or whatever. That's way off.
Granted, the low lift outer lobes are worn, but that's the low lift, and what it's using at lower RPM.
I'm showing you a picture from MOPAR STAR tech training documents. I have a feeling I know more than that tech does, but then, that's no surprise, either.

Low lift used at lower RPMs is the purple colored outer lobes.
The inner lobes are the high lift - over about 2800 RPM.

Outer lobes are low lift, low speed operation.

Inner lobe = high lift for higher engine speeds.

I get it- the mechanics are tasked with trying to find explanations or to explain to customers even if they themselves don't fully understand.

Why you saw the misfires and errors at high RPM - especially above 3500-4000 rpm, is interesting.
I wonder why it took out the low lift portion of things - that's been pretty solid on these for the most part.

 

[Lunentucker]

 

[ShadowsPapa]

LOL - for that, and I have to laugh when I hear/read some of the explanations for things coming out of the mouths of mechanics.

My concern would be in this case - what caused the low RPM, low lift rollers to fail like that.......... that's not the weak spot in these. Oil issues?
OTOH, 4,000 RPM seems like high RPM for ordinary driving, not towing, and it's a 2020, the year of the cam issues. I only hit 4,000 RPM when trying to maintain speed while towing in the hills.

 

[Charles 236]

Actually, the outside rollers are the low lift mode and under 2800 RPM.
High lift mode is above 2800 RPM and on the center of the rocker/follower.

So going over 2800 rpm you are not on the rollers, you are on the center section.

It is very unusual for the low lift rollers and cams to wear. I have repaired hundreds of Pentastar and upgraded Pentastar engines, and have seen this kind of damage only a couple of times. The high lift rocker and cam, on the other hand, is more prone to failure. Even then, the actual percentage of failures is very, very low. If only people could realize how good the Pentastar engines really are.

By the way, I am one of the techs who actually knows how the variable valve lift works, and understands it. I just wish more of my colleagues understood the engines that they work on, instead of just seeking to get the job done as fast as possible. Of course, communication errors can come from the service writer/advisor, who may not have the knowledge to explain these engines to the customer.

 

[JeepingJohn]

The service writer at Superior never tries to explain anything. He leaves it to the mechanic who is working on the car. In one way, that is smart on his part to stay in his lane. But, as you pointed out, the mechanic is backward in his explanation.

Now the new problem is that when I put it under load, meaning trying to maintain speed or conservatively accelerate going up-hill, it goes into a partial limp mode. The stop-start light comes on, making me think it is a voltage sensor type thing. I disconnected the battery overnight and reconnected it this morning and got the same result.

Any thoughts? The dealer had to flash the PCM with the new valve train code. I pulled that flash off and sent it to Magnuson and they sent me a new tune based on the new flash. It installed with no problems. The dealership cleared off any random codes that were still in the system and it drove like a monster half-way home. But the first hill, it limped the rest of the way.

 

[Lunentucker]

The service writer at Superior never tries to explain anything. He leaves it to the mechanic who is working on the car. In one way, that is smart on his part to stay in his lane. But, as you pointed out, the mechanic is backward in his explanation.

Now the new problem is that when I put it under load, meaning trying to maintain speed or conservatively accelerate going up-hill, it goes into a partial limp mode. The stop-start light comes on, making me think it is a voltage sensor type thing. I disconnected the battery overnight and reconnected it this morning and got the same result.

Any thoughts? The dealer had to flash the PCM with the new valve train code. I pulled that flash off and sent it to Magnuson and they sent me a new tune based on the new flash. It installed with no problems. The dealership cleared off any random codes that were still in the system and it drove like a monster half-way home. But the first hill, it limped the rest of the way.

Do you have any means recording live data from it? If not then that may be your next move. An OBD device that logs data as you drive.
Others can chime in, but I think the Tazer does this, and maybe some others.

 

[ShadowsPapa]

It is very unusual for the low lift rollers and cams to wear. I have repaired hundreds of Pentastar and upgraded Pentastar engines, and have seen this kind of damage only a couple of times. The high lift rocker and cam, on the other hand, is more prone to failure. Even then, the actual percentage of failures is very, very low. If only people could realize how good the Pentastar engines really are.

By the way, I am one of the techs who actually knows how the variable valve lift works, and understands it. I just wish more of my colleagues understood the engines that they work on, instead of just seeking to get the job done as fast as possible. Of course, communication errors can come from the service writer/advisor, who may not have the knowledge to explain these engines to the customer.

You said a mouthful there. 100%. On all sentences.

I'd love to meet and have a sit-down with you at some time but we're states apart. (I want to know more - I'm a detail person)

Yes, on the service writer/advisor. Some, like Dan at Stew Hansen's, is top of the line - that guy knows as much as many techs I've dealt with. No communication issues with him. He explains like you are talking to a guy who has the STAR documents memorizes. And what he doesn't know, he quickly looks up.

OTOH, at Dewey - there's a horrible lack of communication between shop and service writers. They really don't know much and things get all twisted in translation.

Anyway it's kind of too bad that high lift section isn't a fat roller as well- heck, we can put roller lifters in a 1973 AMC 360 V8 - why not in these? Yeah, I know - total design change, cam profile change, head redesign to accommodate the space needed by another roller, fatter follower..
Oh, well.

I stick with the oils that I use because of the ability to handle the heat and the extreme pressures these followers operate under. I try to ignore "fan boys", funky colors, and hyperbole marketing and anecdotal proof of things.
I lost contact with my 2020 JT when the Sirius expired on it - otherwise until late January I was still getting reports on that truck I'd not owned since last July. As far as I know, it's still not had any engine work needed or done on it. I traded it at 27,000 miles.

Do you have any means recording live data from it? If not then that may be your next move. An OBD device that logs data as you drive.
Others can chime in, but I think the Tazer does this, and maybe some others.

JSCAN, AlfaOBD........ and the free one that comes with the MX+ adapter does a good job.
You can watch almost anything you want as you drive right on your phone or a tablet.
It's how we found the issue with the 2021 Grand Cherokee we had. Because all conditions were perfect and normal, yet misfires of certain types were recorded - they dug where they might not have otherwise.
Similar to the weird hot misfire I had on my 2022 JT - I had things recorded and logged. (and took notes, too, as far as time sitting before restart and so on) - it led them to the STAR documents seeking information on the vehicles that were behaving that way.
They had it resolved in less than half a day.

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