98 Classic 4.0 - While changing a water pump I cleaned the front of the engine down revealing a crusted-over timing mark on the cover. I had never even noticed it before and made a mental note to flash it just to see where it was firing BTC once the job was done. Well, with the belt on there's no way to see it much less put a timing light on it. Kinda odd. Maybe I might have seen it from some weird angle had I tried but without a line of sight I didn't bother.

 

If I'm thinking correctly, the PCM adjusts the timing as long as the distributor is within limits. You should be able to see the actual timing with a good scan tool.

 

Yep, but I'd think with a cap/rotor distributor we're still talking about a pretty close alignment under the cap for the computer to grab it. I don't have a scan tool for timing. I'll look into one. Thanks.

 

Just got out of the service manual for the truck. You're right. No adjustment can be made to the distributor and it suggests timing be viewed via a scan tool.

So, was there a different ignition system originally used on the 4.0 that required the old school timing marks on the timing chain cover?

 

One use would be to use a mirror to find TDC on the timing marks (while Jeep is not running) and index cam sensor if you have a stretched chain