Test Start?

[C.I.Blazer]

I have put a lot of time and money swapping this motor into my Blazer and I am a little nervous that I am going to do all this work and the motor will not run. The motor I am installing is out of a wrecked Yukon. The seller did send me a video of it running before he pulled it, but of course I have no idea if that was the actual car or not. The motor is very clean, spins freely, and passed a leak down test I did. The shop that swapped the output shaft on the transmission said it looked like like it was in great shape.

I would love to do a test fire of the motor and see if it runs even for a few seconds before I continue putting everything back together. At what point is it safe to do that? The motor and trans are installed and by this weekend I should have the wiring all connected albeit not a super neat installation at this time. No front accessories (water pump, alternator, power steering pump) and no core support/radiator. Exhaust manifolds will be installed this weekend but at some point I will have to tow it to a shop to have the exhaust done. Finished the fuel system last night.

Would it be safe to fill it with oil and transmission fluid (no cooler lines yet) and give it a test fire? I would do my best to prime the oil first. Obviously I would not run it for more than a few seconds so I am not too worried about overheating. Do I risk anything with the PCM. It would not have o2 sensors, the alternator, or the MAF hooked up.

What do you think? Try to start it or just keep installing everything?

[ls1nova71]

If your fuel system is hooked up, and the VATs has been programmed out, then just hook up the harness, directly to a battery if you have to, and start it, it wont hurt anything. I start them on the garage floor when I get them, just to hear them run. Make sure it has oil in it, and unhook the torque converter bolts so it doesn't pump trans fluid all over, unless you have the lines already run, then just loop them with a short piece of hose. I always put an oil pressure gauge on them too, to see if they have pressure, but don't get worried if you don't build pressure by just cranking it with the starter, it usually isn't enough to get an engine that has been sitting for a while to prime up.
https://www.youtube.com/watch?v=08fM5HY3Azc

[Wgesnerjr]

Your engine sounds like mine.

I got mine out a Yukon too. Only problem was that it hit a tree, really hard! So hard in fact, that the starter broke in half. The wrecking yard gave me a 1 year exchange warranty so I was under a deadline to get mine fired and checked.

Took me about 4 months of test fitting and wiring. The had to have the VATS programed out and buy a new starter.

Finally hooked up a temp fuel line to a gas can and fired up. There was no Coolant or Trans fluid, but the motor fired right up and sounded great. Let it run for about a minute then shut it off. Really helped motivate me to keep going.

I would put the manifolds on and fill with oil before starting.

I have about 8000 miles on the set up and it runs great. These motors are really rock solid.

[Steve Cole]

Similar situation that may help C.I. Blazer - I am doing a LS swap and my motor has sat for 2.5 years. (I know) I changed the oil pump, water Pump, and every seal and gasket I could. I also replaced the oil pan so pretty much all the oil was removed from the engine. I attempted to build oil pressure today- I disconnected the coils and the fuel tank is bone dry. I tried cranking over the motor while watching a oil pressure gauge I connected. The needle never moved. I motored it multiple times, 5-10 seconds at a time. The needle never moved. They say to prime the oil pump when you install it but I can't remember if I did that. So my question is, should I worry about building oil pressure under these conditions, or should I just put gas in it and go for it? Sorry if this is a hijack.

[C.I.Blazer]

It's alive! I hooked up some temporary wiring, primed the fuel, then primed the oil. Turned the key and it fired right up. Only ran it for a few seconds, but gave me confidence that the motor is in good shape.

You were exactly right. What great motivation to keep working. Now I can't wait to actually drive it!

Thanks for the support!

[LS short box]

It is so cool when they fire up. Congrats.