Engine stumble/piston rock?
This is a discussion on Engine stumble/piston rock? within the General Help forums, part of the LSx Technical Help Section category; ive been having a problem with my car for a few months now. its not getting any worse it doesnt ...
10-29-2008, 09:27 PM #1
Engine stumble/piston rock?
ive been having a problem with my car for a few months now. its not getting any worse it doesnt seem but its still quite annoying.
it doesnt do it at startup but after it gets up to 110 or so degrees it starts making a knocking sound, BUT only at idle! it almost sounds like one of the pistons is rocking around inside the cylinder, i hope its not that but thats sure what it sounds like. it does it constantly, but the second i give it a little gas it quits. but comes right back at idle, doesnt do it while driving. The engine also stumbles a little when it does it, doesnt wanna die but kinda rocks back and forth. Maybe could be a rocker problem too.
i will see if i can get a video of it soon.
im using 5w30 penzoil platinum, carquest filter. im soon gonna switch to 10w30 and maybe a quart of lucas?
Any idea what it might be? i know its very vague but its extremely hard to describe.
There is 80,000 miles on my car so i dont know if the previous owner did the plus and wires or not. im going with msd 8.5 super conductors and ngk tr55s soon.
10-30-2008, 11:46 AM #2
Sounds like you might have a bad rocker arm. The stock rockers have been known to have issues with the needle bearings wearing out and coming loose, although it is not that common. That would create the knocking sound you hear at idle. It could also have a stuck lifter, which would create excessive clearance between the lifter and pushrod, but the noise probably wouldn't go away when you increase the RPM.1998 Trans Am WS6 SGM
Lid, Pro 5.0, WS6 Short Stick, LS7 Clutch, TB Bypass, Detroit TrueTrac, Poly Mounts, Bilstein Shocks, LS6 Intake, SFCs, CTS-V Brake Upgrade, STB, Nitto 555's. SS Longtube Headers and True Duals w/ H pipe and Magnaflows. Tuned by Harris Speed Works. 341.4WHP/346.1 lb/ft.
10-30-2008, 03:32 PM #3
I was thinking rocker or lifter also. Use a long handled screwdriver as a stethoscope and listen to the end of the handle while putting the tip on the valve covers and narrow down where it's at and then pull the valve cover and give it a look.
I almost wonder if it isn't a lifter and when the oil gets thin as it heats up is why it shows up at idle and as oil pressure increases with rpm's it goes away??? Just a thought and could be off track.
10-30-2008, 07:17 PM #4
11-30-2008, 12:50 AM #5
did plugs and wires and its completely cleared up and runs great now!, went with the PP 10w30 instead of the 5w30 , and used a quart of lucas just to try something new. and it runs like a champ!!!! better than it ever has
had the stock plugs in it and the number 5 was chipped, hence the sound.
11-30-2008, 04:32 AM #6
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