Hey guys so I'm having an issue with my truck. It's a 2000 xlt with the 2.5l. When I got the truck it had a blown motor so I sourced a used one and did a tune up on it and put the motor in. The problem is the used motor has a knock coming from it on cold start up for a few seconds and then goes away. Once its warm taking off from a dead stop it makes a knocking sound until it gets moving and then stops. This is the only times when the knock can be heard. If I go under the hood and slowly blip the throttle I can hear it make the knock. It almost sounds like it's coming from the valve cover but I've never heard a knock from a valvetrain. I replaced the timing belt before dropping the motor in and I'm wondering if the timing was off by a teeth or two if it would cause a knock like this.. driving around town of I try giving it more than half throttle it pings like crazy so this leads me to think it might be timing.. I dont think it has a vacuum leak as it pulled 19inches of vacuum.. I'll try to get a video tomorrow of it making the knock.

 

1st thing to do is determine if this is the same knock or different knocks.
2nd what is the frequency?

A knock for the 1st few seconds of cold starting is usually a bearing in the bottom end. If it *doesn't* knock during a hot re-start... I'd definitely lean towards a bearing in the bottom. which btw can usually be mitigated by using a slightly more viscous oil w/high mileage additives and a higher quality filter w/anti drainback valve. M1 high mileage has been good for me.

If your hearing a heavy knocking sound from the top end.. that's not good. Return the engine.
If it's lighter from the top end, more of a "ticking", and 1/2 the frequency of the engines RPMS... take a hose and listen to differing areas. You'll narrow it down to an area quickly. COuld be an injector if your lucky.
also, you might have to pull the valve cover, turn the engine over by hand, and just feel for loose parts.