I have a 2.6 with A/C, so I have the 3-groove pulley. I cannot, for the life of me, find a timing mark on the pulley. I even set up an inspection camera and rotated the crank by hand so I could see the entire circumference - still can't find a mark!

So, I decided to tune the old-school way (which is how I learned to tune engines): with a vacuum gauge. I loosened the distributor bolt so I could advance and retard the timing, and found something odd: on most other engines, when you reduce or advance the timing too far, the engine will drop RPM. In this case, as I advanced the distributor the revs just kept climbing until I reached the physical stop of the bolt in the slot. So I have no idea how far "too far" is in advance.

Engine has 149k on it and has been well taken care of. I don't suspect a timing chain tooth jump, because it's not off enough to account for that. I thought perhaps the previous owner had installed the distributor one tooth off, but a quick check showed the rotor is indeed pointing at the #1 cylinder wire when at TDC. That's obviously not the problem.

Any thoughts? And any idea where that timing mark might have gone?