ld9z24

Car :
1999 Cavalier z24
Mileage:
176,000 miles (possibly less on the engine. Engine has a heat tab on it which indicates that it may have been rebuilt or replaced with a used engine)
Engine:
2.4 ld9 twin cam
Transmission :
4t40e 4 speed automatic

Issue :
Short sharp rattle noise during cold startup

Experiencing a short sharp rattle noise during cold startup lasting for about the first 2 seconds very briefly after startup then it stops. Engine runs quiet and smooth while idling and while driving. It only makes the noise at first cold start up in the morning or after it's been sitting for more than a few hours.

I know there's a TSB for the ecotec engines concerning this same issue and it says that it could be because the "cam phasers" are not "parking" properly. Does the ld9 have "cam phasers" and if so, could this be what's causing the noise at start up ? What are "cam phasers" and what do they do ?

UPDATE : Upon further research, I have read that this may be due to the timing chain tensioner not getting enough oil pressure for the first couple seconds of start up. The tensioner uses oil pressure from the block to tension the timing chain and it takes a couple seconds for the oil pressure to build up and tension the chain. Anybody else heard of this issue or experienced it ?


I just had a brand new timing chain kit from PCI preffered components installed which includes chain, chain guides, tensioner, cam sprockets and a new GMB water pump. It almost sounds like the timing chain rattling briefly at start up, especially cold startup. I'm almost 100% sure that everything was installed correctly as it was installed by my friend who is an ASE certified mechanic. I do not recall it doing this before I had these parts replaced. Could it be the PCI tensioner not performing properly ?

I've heard of people using the older style spring loaded tensioner instead of the 97+ tensioner which is spring loaded and hydraulic, operating off oil pressure, however I have read that the mechaincal tensioner is for 96 models only and not to use it if your car came with the hydraulic tensioner. Should I convert to the old style mechanical tensioner ? If converting from hydraulic to mechanical tensioner, won't oil pour out of the block where the hydraulic tensioner goes or do you leave the mechancical tensioner in place ?

WarHammer Racing

hello. did you ever resolve your noise at start up? we have same issue but ours is also setting a timing code p0017 for exhaust cam. we can clear the code and it wont return until it sits long enough for the noise to return then so dues the code. we replaced timing chain due to this and did find a guide that was worn out and chain was loose but this code returns as does the rattle. its a new tensioner from the kit. I agree if the hydraulic tensioner can be replaced with a mechanical spring loaded one it may solve our problem. let me know if you fixed it