Well we finally cranked her up yesterday..this has been a long drawn out process of learning, making mistakes and finger crossing. 1999 2wd 2dr Blazer.
164k miles. First time I cranked it started right up, no crazy noises or anything. I ran it for about 15 secs. I'm still skiddish.
Looked underneath for any leaks and there was oil everywhere.. upon further investigation it was coming from the cooler line connection. Went to store bought more oil and a gasket kit. Installed new gasket and saw that the gasket still moved a little when tight. Long story short , had a longer bellhousing bolt and cooler line bolt in wrong place. Once finished, cranked it up again and let it run for about 4-5 mins. Just looking,listening and observing. I'm going back this morning to run her down the road. Does anyone have any pointers as to breaking her in right? I know I should take it easy ... As of now,. She's just idling high and have a rattling noise from the exhaust pipe . Have a throttle position sensor code and ftp sensor code. Any advice???

 

Running in - my technique:

500 miles not over 3'500 rpm
no kick-down
warm up before starting to push a "little" harder.

500 - 1000 miles not over 4'000 rpm
still no kick-down
running it in locked gears i.e. start at some 15mph manually lock in 2nd gear and gently bring it up to 3'500 rpm
change loading frequently same can go on highway.

Make sure it shifts down on inclines by releasing the accelerator or bring it back to 3rd or 2nd manually.
With the run-in oil after 1'500 miles bring it up to operating temperature gently then start to do accelerations.
First to 3'500 rpm bringing it up to full throttle. After couple dozen miles to 100 miles start accelerating at full throttle
and gradually bring the rpm up to redline over the next 100 - 200 miles.

You may have some 1'500 to 1'800 miles now. Change oil and filter, cutting filter open and having a look.

It will also depend on how the engine has been built. If it is a normal build the above should give good results.
It if is a performance build we usually run them a couple of hours on the dyno. You can assume an average of 50mph which brings it to a couple hundred miles on the road before we start loading it. There as well - gradual loading and only once operating temperature has been reached with gentle driving/throttling.
On the dyno we load it up to around 60 - 70 % of max. Then re-check everything. At this point it has some 8 hours of dyno time some 500 miles.
We then start loading it up to full throttle but limit rpm to 70 % of redline. Then over an hour or so do some pulls up to 80 % of max rpm.

Afterwards we change oil and filters and put the engine in the car. An additonal 200 miles on road testing with O2 sensors for fine-tuning.

Have a look into the user manual. The OEM may have written something about that as well and ask the machine shop. They may have some experience too.

 

Thank you for ur time . And advice...