Hi. I just installed a rebuilt 3.0 longblock in my 1988 pick-up. I marked the distributor location to make it easier to get the timing close when starting up the new engine. After starting it up, I adjusted the idle to 800 RPM, and set the timing at 10* BTDC at idle with it warmed up the the connector jumped as per the manual and the under-hood label. Fine so far. Test drove it, and it seemed a bit sluggish, so I rechecked the timing and it was off by about 6*, so I reset it. Drove it for a few days, and rechecked it. Found it to be off again, this time it was about 23* BTDC (connector jumped, warmed up, at idle, etc.) so I reset it again, but this put the distributor nowhere near my original mark on the distributor. It also ran like crap and the check engine light came on, so I just put it back to the mark. I really honestly do know how to work a timing light! Any ideas out there, and how can I find what code I have and then clear that light?

 

Greetings,
You are checking your timing correctly, but make sure that your p/u is on the #1 s.plug wire, your jumper should be on "te" & "e1", now to check your code just leave the jumper in place with just the ignition on look on your dash and it should flash you a code. For example: 2 flashes followed by a short pause and another flash would indicate a code 21, there will be a long pause and it will go onto another code or repeat the previous one. If it flashes real fast no codes. To clear the code pull a battery cable off for a minute or pull the efi fuse. Your code is caused by your timing advancing or retarding to much!
I read that this 3.0 was rebuilt, it almost sounds like your Timing belt might be off a tooth or two or it's the wrong belt, either case if your t-belt is stretched, off a toothe or too big of a belt it will jump time like you described!
To make sure your close to time, get your #1 cylinder to TDC, take your distributor cap off your rotor should be pointing to the #1 cylinder, by doing this once you put your T-light back on she should be real close to time.

Good Luck!

 

Thanks for the input. Now that I'm back from vacation I have a chance to mess whith it. The timing belt is brand new. I made absolutely sure the marks were all lined up properly before I put it the rest of the way together. I did notice something strange, though. . . . . when i set the ignition timing, I jumped then connector, set it at 10*, then removed the connector and noticed that its still at 10*. Seems like jumping the connector made no difference to the timing. This doesn't seem right, does it?

 

Since I did this myself, I'll give the answer again. It sounds like your TPS is out of adjustment. See here: https://www.yotatech.com/forums/f116/timing-3-0-a-79788/