Another spark knock thread... sorry

[dstrahm]

Well, well, well. 2021 JLUR with around 25,000 miles. Been hearing a bit of spark knock (Preignition) on slow pulls at low rpm’s. Mentioned it during several service visits and dealers just shrugged their shoulders and claimed ignorance.
Took it in for several items before end of warranty and they found a TSB mentioning the spark knock issue. The number is 09-012-22. Based on a customer complaint (failure code CC) of hearing spark knock they are supposed to remove the heads, clean the heads and top of pistons and reassemble with an updated PCV, part number 686019110AA. It’s a 10.5 hour job so I’m glad I’m under warranty still. I’m not fond of taking apart an engine that has otherwise been running well, but the sound you hear with spark knock is the piston skirts hitting the cylinder walls. Eventually they may break off!!
Apparently the original PCV design let too much raw oil pass into the intake causing buildup and carboning. The TSB applies to 2018-2022 JL, 2020-2022 JT and 2018-2022 Grand Cherokee models all with the 3.6l standard and e-torque engines.

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[m3reno]

What is the down side of allowing less oil through the pcv valve by installing the new valve? Also, What is the down side of the elevated pressures in the crank case? Looks like your giving up one problem for another.

 

[Willys41]

I assume that you will still have the same air movement through the PVC system put the new 686019110AA will do a better job at separating the liquid oil from the air stream
Basically the same thing my UPR catch can dose

 

[dstrahm]

I assume that you will still have the same air movement through the PVC system put the new 686019110AA will do a better job at separating the liquid oil from the air stream
Basically the same thing my UPR catch can dose

perhaps, but there are more than a few instances where the contents of a catch can was sucked into the intake on a significant angle. One thread here documents a few hydrolock situations and at least one thrown rod. I’d rather fix the problem with a revised PCV valve.

 

[dstrahm]

What is the down side of allowing less oil through the pcv valve by installing the new valve? Also, What is the down side of the elevated pressures in the crank case? Looks like your giving up one problem for another.

The downside of leaving the flow the same is that engine oil continues to get into the intake and therefore into the combustion chamber. This causes carbon buildup on the valves, heads and piston which leads to preignition (spark knock) problems. Spark knock can likely result in broken piston skirts and require an entire rebuild!
A properly functioning PCV valve just keeps a slight negative pressure in the crankcase to prevent crankcase vapors from escaping into the atmosphere. Too much vacuum and you can pull in contaminates from outside into the crankcase which bring on other engine life shortening problems. Thank the EPA for all this fun and games.?

 

[Willys41]

dstrahm

Your are right
That's why I doubled the capacity of my UPR catch can
I ran a 4ft 1/2in. hose from the bottom of the catch can to a lower area on the jeep with a drain valve
I drain it every 1000 miles simply by opening the valve
I have yet to see any oil in the can itself. Its all in the 4ft hose eliminating any chance of oil getting sucked into the intake

 

[dstrahm]

This is what they found when they performed the TSB repair. So far so good but it hasn’t been in the trails yet.

 

[UncleJimmy]

This is what they found when they performed the TSB repair. So far so good but it hasn’t been in the trails yet.

That is awful. What was the mileage and how long did you have knocking before the service? How is it running now?

I had LSPI develop on mine at 40k and did some Seafoam treatments with WOT (crankcase, induction, fuel), followed up with Techron and catch can and haven’t had any more knocking.

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