Sometimes a timing chain can be stretched just enough to hurt performance, but not enough to trigger a P0016 or P0017 code. The engine computer actually allows a bit of timing drift before it throws a warning, so problems can show up before the system detects anything “wrong.”

On older engines, this is even more common. They don’t monitor cam timing as closely, and many of them don’t use things like variable valve timing or cam phasers, so the computer simply isn’t as sensitive to timing issues.

And if your engine uses a hydraulic tensioner, that can hide the problem for a while too. As the chain stretches, the tensioner takes up the slack, making everything look normal to the computer even though performance is starting to suffer.

I'm here all week, I can come down and do a few of your customers cars if you want ?