Did Scotty Kilmer just quickly diagnose our LS460 hesitation mystery?


Timing tensioners, cam and crank intermittent confusion leading to hesitation? I don’t think I’ve heard that explanation in all the years I’ve been following this issue, and it makes some sense.

 

Interesting video, though it does not explain why hesitation goes away after certain time.

 

Yeah, and I’m starting to wonder if the hesitation actually ever really does go away, maybe it’s just a little more pronounced directly after an oil change.

 

Chain stretch and tensioner issues are real....but that's to be expected if you don't use a belt or single cam V8. Not sure why if that is the actual issue why it depends at all on oil changes since the those are hard parts.

I still lean toward LSPI or noise in the sensors combined with low tension oil rings. My car doesn't have the issue and I can immediately after changing oil do limiter runs or rolls without anything strange happening. My engine is very quiet though, if I do have the issue develop I'll add resistors to the knock sensors to see if that is indeed the issue.

If anyone local has a car with the issue and is willing to let me mess with it I may also be able to figure it out.

Ill add that this is why I prefer a belt if the engine has more than one cam, I have replaced too many chains to trust them. They just never last long or under hard use. I still don't fully think the issue is the chains though since oil that is new should have an easier time pumping though t he engine and into the tensioners.

 

I’m not sure if oil would have a direct effect on those tensioners or not. Are they hydraulic tensioners? If so, maybe. Not sure.

I found the video interesting because the car does have a driveability issue with ZERO actual codes. Something a lot of us have experienced - I know I did with my 2007 - and it was a hesitation that would happen from time to time (sometimes more frequent than others, or at a bad time). I never really gave it too much thought, just kept on driving it, and I just figured it was a update or reflash that needed to be done...or bad fuel, timing, transmission, perhaps valve guides causing the knock sensors to activate, whatever. In the video he does mention the heads, but the freeze frame data allowed him to diagnose the tensioners...which I actually found impressive by him - because I usually don’t think of this guy as a solid tech - more like a YouTube guy that has a big following, big opinions, and useful basic stuff people look for. I didn’t expect to see a LS460 sitting behind him in one of his videos. And I’ve got to say, I like how practical he was with his suggestions (just drive it, not worth repairing). I agree with what he said.

 

Pretty weak if you ask me. I usually like his videos, but since when does he just say, "that's a $2000.00 job, no sense in doing it." Come on, tear it down and show us how you fixed it. Maybe it's not premium fuel? Scotty is mega-rich now so maybe that changed him. Come on Scotty, you gotta do better than this.

 

Another miss from old Scotty. Disregard him in this matter.

 

The slight ignition timing moving around at idle is not abnormal if it's a small amount like that and you have ANY varying load like AC or even alternator, that's why I don't think the hesitation is from chain stretch since if the engine is on the tensioners are receiving oil and also are designed to not allow themselves to compress when the engine is off.

Sure stretch is possible and bad but if it has happened the cam crank relation will always be wrong no matter the RPM. It wont just disappear since you rev up, it will actually become more of an issue since at higher speeds the window for each event to occur is smaller and lack of precision is amplified. Same way a misfire shakes worse off you push harder.

On the 4 460s I've dealt with via looking, owning one, and fixing two none have had the relation "pending" codes or the hesitation issue. Two of them where over 200K as well and one was beat to hell. Pending codes like that are usually the case of something acted odd in the last drive cycle for whatever reason but has since corrected into the acceptable range. These cars are insanely quick at setting permanent codes if something acts up even slightly more than once.

 

Chain stretch can be caused by the soot in oil (dirty oil, extended oil change interval, direct injection dumping fuel/soot). The soot gets between the pins/rollers on the chain and causes them to stretch. And worn guides obviously could be oil related (or maintenance abuse).

And I agree...chains aren’t quite as trouble free as people make them out to be, because when they go wrong, they go very wrong $$$

 

I think towards the end of the video he focuses more on the tensioners than the actual chain (if I remember). And are you sure a stretched chain would always vary in relation from cams to crank? Other brands that would be a sign the chains or tensioner were starting to fail (intermittent timing codes). When throttled I’d think the tension would increase and level out the reading, no? If it were a tension/stretched chain. But I agree, it’s strange a hard code wasn’t stored - maybe previously there was - but I think you have a point...these cars would set a code pretty quickly I would think. Although depending on the system OBDll needs a certain number of consecutive failures before it sets a hard code (think it’s 15). And needs a certain number of passes before it resets. Think it’s 15. But it’s been a while since I’ve had to think about this stuff.

 

Im fairly sure yes, it's the same as permanently mechanically putting the camshaft one tooth off and adding in an extra link.VVT in some cases can cover for it in theory but it's literally longer point to point (timed sprocket tooth on crank to timed sprocket tooth on a cam) than it's supposed to be.

Spinning it up would only add oil volume to the tensioners (volume creates psi when it hits a restriction) and correct chain slop/rattle on the non-driven side of the cam and crank. The crank "pulls"on the cam like a rope to a load and the return side is where slop occurs and where the tensioner is. It's kinda hard to describe but if you look at the directions for a common Honda 3.5 timing belt it shows VERY clearly you must start at the crank and then to the front cam and make totally certain there is zero slack or play from the crank to the last cam. The slack is intended to end up near the tensioner because the distance between the crank and cams on the driven side must always be the correct number of links or teeth.

If the chain stretches you effectively added a link or two. Every car with true chain stretch I've repaired (mostly utter trash GM 3.6s (seriously, one of the worst engines of all time) and ford 5.4s and some other ford chain V8s and the horrible cyclone engine family) then you will get a misfire at minimum and cam/crank relation codes. The cars with VVT have a worse time in my experience with this in terms of missfire.

Plus I would be very surprised if Lexus has chains that pull a ford/GM. They are generally much much much better about that.