p0328 and running slightly warmer than normal

[Robmnrd]

Hey guys, good ol' engine light popped on the other day, had it scanned and it was p0328. Had them clear the code because I didn't notice (at the time) any signs/symptoms so I figured it was either a one-time weird freak thing or maybe the sensor itself acting up. Drove home watching gauges pretty close, and feeling/listening/smelling for anything to be off and didn't notice anything odd other than coolant temp being *slightly* higher than normal (like 198-208 on a drive that would normally never see above 200).


Next day I was doing a moderate throttle pull in 2nd gear leaving work and engine light pops on again and sudden (significant) loss in power/acceleration. Drove straight home, and the whole way there (only like 3 miles) it was definitely running hotter than normal. Not "overheating", but I do that drive (from work) all the time and never ever (even on 110 degree summer days) see temps over ~200 and this time it was basically 202-216 the entire way. When under lighter load and not giving it the beans I didn't notice any sort of decreased performance.


So I'm guessing I actually have an actual problem (based on the running hotter symptom), but was hoping ya'll could chip in some idea(s) of what it may be.


Summarized symptoms:

-p0328
-Running hotter than normal (never overheated per temp readout)
-decreased power/acceleration under higher load, but not so much under light load.


It's going into the dealer on Tuesday, but obviously appreciate any ideas ahead of time.


Car: 2013 ZL1, CAI, LTs w/hi-flow cats, stock everything else, tuned.
67k miles, all mods and tune done at approx. 18k miles with zero problems or lights at any point before now.

[ZMEnow]

Do you have a record of the antifreeze being changed, dexcool has a 5 year limit before it starts to coagulate.

[Robmnrd]

Originally Posted by ZMEnow

Do you have a record of the antifreeze being changed, dexcool has a 5 year limit before it starts to coagulate.

Coincidentally that was approximately five years ago lol.

My plan for the year was to drive it through the summer and then do a full flush/fill in ~October, along with the next oil change, as well as a visual inspection of plugs/wires.

I am hesitant to blame the coolant for the code though, if I'm honest. Unless you think some kind of buildup has occurred on that side of the engine and is causing hot spots in a cylinder or two. No reason temps within normal operating range should cause a knock sensor code to be thrown in my opinion. Especially since it has run hotter before. These couple drives were hotter than normal, but in Texas summers sitting in traffic after being on the highway for awhile will get it into the upper 220s where the fans promptly kick on and bring it down in less than a minute.

I'm expecting the source of the problem to be fuel or spark related, leading to some actual knock and a cylinder (or cylinders) on that side to run hot.

[Risingson05]

Will state the obvious - have you checked the knock sensor on That bank?

Hopefully it’s that not something internal .

[Robmnrd]

Originally Posted by Risingson05

Will state the obvious - have you checked the knock sensor on That bank?

Hopefully it’s that not something internal .

Not personally, no, but on Tuesday when it goes in I assume that will be the first thing they will look at.

I also hope it's just the sensor, as 67k light-medium duty miles (it's my almost-daily-driver) seems a bit early for something serious to arise.

Curious for more opinions:

When it detects knock (even if it is false knock, or a bad sensor) it obviously pulls timing. Can significantly reducing timing in that way cause it to run a bit hotter? My gut says no, that mildy-hotter temps like what I saw would more likely result from maybe one cylinder running a little hot (like from real knock). But do any of you have experience with a situation where timing was too low or being pulled for some reason and it was just causing very inefficient burn leading to late total-combustion and thus some extra heat running back out the head and headers?

Might be making stuff up but I guess in theory it could happen. Though I would imagine the car wouldn't pull that much timing under pretty much any circumstance. Could be wrong though lol.

[ZMEnow]

Originally Posted by Robmnrd

Coincidentally that was approximately five years ago lol.

My plan for the year was to drive it through the summer and then do a full flush/fill in ~October, along with the next oil change, as well as a visual inspection of plugs/wires.

I am hesitant to blame the coolant for the code though, if I'm honest. Unless you think some kind of buildup has occurred on that side of the engine and is causing hot spots in a cylinder or two. No reason temps within normal operating range should cause a knock sensor code to be thrown in my opinion. Especially since it has run hotter before. These couple drives were hotter than normal, but in Texas summers sitting in traffic after being on the highway for awhile will get it into the upper 220s where the fans promptly kick on and bring it down in less than a minute.

I'm expecting the source of the problem to be fuel or spark related, leading to some actual knock and a cylinder (or cylinders) on that side to run hot.

Tried for the easy option, I don't guess on internals, its easy enough to take a drive and do a data log..

[Robmnrd]

Shoot man I know, I hope it is a 'KISS' thing honestly.

I've kept it near-stock all this time for reliability. If this ends up being something more serious than just the sensor or a crap plug or something I may finally just pull the trigger on a second round of mods and take it up to DMS and have them sort it all out at once hahaha

[Tomtom87]

Just a thought… Could high IAT set off knock sensors? Have you checked your heat exchanger pump to make sure its working and theres no air in the system?

[Robmnrd]

Update: Knock sensor wire harness fell on the header and melted. Obviously a problem, and hopefully the only problem. I'm still mildly skeptical that whatever amount of pulled timing was resulting from the "knock" it was detecting would cause it to run hotter than normal, but tbh I don't know tuning well enough to say for sure. So..hoping tomorrow when it is returned it runs well and back to normal Temps.

They've estimated an absurdly high cost of labor for this job though. Said yes to it because I don't have the ability to do it myself. But you better believe when I get there I'm gonna have them put it up on a lift and let me look to make sure the harness is tied as strong and as far from the header as possible lol...

[ZMEnow]

Interesting I don't have any harnesses close to my headers..

[Robmnrd]

Yeah my knowledge of knock sensor location and harness routing is that the pigtail on that side leads to harness hugging the block pretty well and shouldn't (keyword) easily come into contact with the header, but with some digging I did find other reports online of this happening with aftermarket headers... just on very rare occasion. Unknown reason why it kind of all of a sudden happens. If I can convince them to let me get under the car today while it is up on a lift I'll try to take some pics of spacing between the sensor itself, wiring, and the header on that side.

[Robmnrd]

Final Update:

They finished work on it this morning before I could get there, so couldn't see it up on the lift with the belly pan off to see routing.

They did save the old pigtail and wiring to show me though, and sure enough it had been completely melted through lol.

On the drive home everything drove/acted normal again. Obviously no engine light or decreased power, and I put it through it's paces to make sure.

Engine temp back to normal as well. I even repeated my work -> home drive (this time with the engine starting out fully warmed up already since I drove there from the dealer) and temps are exactly what they usually are/should be.

So, for anyone curious, the answer seems to be "Yes, when timing is pulled due to (fake) knock, it can potentially raise running temps".

Although I couldn't see the routing myself, the tech said he A. Routed it even further from any/all heat sources compared to stock routing, and B. Added additional insulating tape just to make extra sure. They are warrantying their work for 2 years (even with my headers), too. So I'm fine with the higher-than-expected labor cost.

[Robmnrd]

Final Update:

They finished work on it this morning before I could get there, so couldn't see it up on the lift with the belly pan off to see routing.

They did save the old pigtail and wiring to show me though, and sure enough it had been completely melted through lol.

On the drive home everything drove/acted normal again. Obviously no engine light or decreased power, and I put it through it's paces to make sure.

Engine temp back to normal as well. I even repeated my work -> home drive (this time with the engine starting out fully warmed up already since I drove there from the dealer) and temps are exactly what they usually are/should be.

So, for anyone curious, the answer seems to be "Yes, when timing is pulled due to (fake) knock, it can potentially raise running temps".

Although I couldn't see the routing myself, the tech said he A. Routed it even further from any/all heat sources compared to stock routing, and B. Added additional insulating tape just to make extra sure. They are warrantying their work for 2 years (even with my headers), too. So I'm fine with the higher-than-expected labor cost.