2005 Silverado 4wd

-5.3L vortec L33

-112,000 miles

- no after market mods other than exhaust work done early in trucks life (headers and true duals)

- regular oil and fluid checks/ changes

En route to work one morning about .25 miles from the house, truck began making very loud, noticeable knocking, I immediately turned around and parked in garage.

—-upon inspection —-

- correct fluid levels

-oil pressure at idle (40lb) and holding

(oil pressure sensor replaced last year )

- sound seemed to be coming from passenger side toward firewall

-no noticeable shavings in oil

-DTCs (cylinder misfire, 02 sensor, fuel evap )



For the DTCs both fuel evap and 02 sensor has been triggered for a year probably.


The cylinder misfire may have been an old code a month prior to this knocking from when my catalytic collapsed inside itself causing horrible drivability and totally restricted exhaust flow on PASSENGER side exhaust. This was fixed a month prior to this most recent knocking.

To remedy :

-removed catalyst

-welded exhaust back where catalyst was removed

- checked exhaust manifold gaskets

—- this may have caused cylinder misfire code to still be triggered



truck drove normally for about a month until knocking

——replaced —-

-head gasket

- lifters (hydraulic roller)

- push rods

- valve cover gasket
-valley cover gasket

- intake manifold gasket

- new IR plugs (gapped)

- rocker arms left alone as were in good condition






upon reassembly and fluids topped off and oil primed through system before fuel pump fuse reinserted.

——

- truck started normal but knocking was still present.
- oil pressure normal


-cylinder compression test
showed 135lb ~1% on each cylinder
(should eliminate the possibility of
spun bearing? right?)

- oil and fluids normal



-all this has been checked at idle



- it seems like the knocking sound seems to dissipate as the idle increases though still noticeable.

As mentioned the knocking is loud, very noticeable at idle rpm. Haven’t driven it any distance and want to try avoid attempting to drive to mechanic (tow truck is an option but want to avoid throwing money away on something I can fix myself. )


- no codes are showing now after top end work I did.

- i checked continuity on knock sensors, but did not replace them.
Could it be something in the wiring harness?? There’s no code showing incomplete circuit.

— I’ve also heard it could be torque converter or flex plate. Trying to avoid pulling motor and bottom end.




Any advice or suggestions on how to diagnose what else i could do to diagnose the problem. I have a code reader but nothing that will give live diagnostic feedback.


New here so hope the is formatted and in correct forum to get some guidance on this problem. Love this truck and the L33 engine in it would love to get this problem resolved without an expense trip to a mechanic.

thanks!

I’ll post a video/sound of engine at idle. Just imagine super loud knocking lol!

 

Go buy a cheap Harbor Freight mechanic's stethoscope and start probing around the engine until you find the approximate area the knocking sound is coming from. You'll be pulling your hair out trying to determine it without one.

 

Like this? You might be able to use a flashlight and small mirror or better yet a borescope to see the flexplate thru the dust cover on the belhousing. It might be a bolt backing out and not a crack

 

Good advice.

You can also cut off the top portion of a plastic jug and insert a long flathead screwdriver to use as a redneck megaphone to aid you in pinpointing the noise.

Maybe remove the belt and make sure it's not the accessories making the knocking noise?

 

compression is good, so probably not piston or rods. \

i am suspecting a bad exhaust leak. maybe something in the top end of the motor. wouldn't hurt to pull the valve covers and take a look.

 

135 lbs isn’t good minimum is like 150-160

 

Maybe your compression tester is bad also that’s pretty common,you said 1% was that leak down ?that would be pretty good.

 

Sorry for the absence, work has been killer and haven’t had time to really dig into engine more till last weekend.

Had a mechanic make a house call with a scanner. Idled for around 45 minutes with it knocking while doing multiple test.
fuel pressure 60lb
In conclusion we saw that 02 sensors reading incorrect voltage when throttled up. Seemed to be telling engine to dump fuel,
2nd- knock sensor wiring harness has possible short,
3rd- a grounding issue somewhere on the block
Also—No misfires we’re detected during 100 enigine cycles
-No, knocks detected
- Live feed reported no inconsistencies
- (not sure what the name of all these engine test we did were) there were a lot of different test ran.
The final test was running engine at idle and computer shuttingoff one cylinder individually at a time to see if change/no change occurred. Again inconclusive.
Guys suggestion was: clean all grounds (3 if i remember correctly)
-new wiring harness for knock sensors (did that and went ahead and put new Knock sensors in it since I had intake off)
-new up and down stream 02 sensors
-check driver side rocker arms again
Completed all of that check list and knocking still there with no change. ( his last suggestion was change oil pump).
Will try to tackle that this weekend. Along with sliding tranny/flex plate/ TrqCnvt back enough and idle engine to see if it’s not flex plate warped and slapping. Earlier in this process I pulled starter and everything looked good on FlxP (teeth, and no bolts loose) but it’s near impossible to get a good check with the small amount of room given.
will update again after that.
Baffling (3 people have came and gave their opinion 2 I trust with mechanical stuff like this and no definite answer yet… all say they think bottom end is good I hope they are right but I see now why shops hear knock and instantly motor swap. I’m only about 600$ in the hole as of now but would love to be back on the road.

thanks everyone for the input all is noted and taken into consideration.

 

I had a set of Dynatech longtubes on a silverado that came with high flow cats. When the cats came apart, the sound of those pieces bouncing around was extremely similar to a bottom end knock, and the headers carried the sound right back to the block. You mentioned one cat coming apart already. Are you sure you got all the pieces out?

 

I have an '06 Silverado and I'll tell you one thing - If you didn't put GM or AC Delco knock sensors in it, you'll have knock sensor codes popping up before too long. Had to redo mine after like 50 miles because the ones I got were garbage. It's pretty much a consensus that any aftermarket LS knock sensors are awful.

 

I think this is true for ANY of the sensors on an LS. Genuine GM/Delco or forget it.

 

A 1% leak down would be nearly impossible. Hell, a 3-4% leak down is mighty good. He said the compression varied only 1% between cylinders. That is also mighty good...

 

Yup, just like lifter trays! Those two items, OEM can't be beat.....