I have a 99 k1500 with a 5.7 350. I recently put a brand new crate motor in from Jeggs. (Same motor) Got it in and let it run for a few minutes and shut it off. Finished up a few miscellaneous things and ran it again. Slowly drove around the block and it stalled out. Motor wouldn’t even turn over. Found out I had a bad injector that was dumping gas down into the cylinders. Got it drained and broke free and replaced the injectors. Now with the plugs out, distributor out and torque convert unbolted from the flywheel, it turns over just fine. As soon as I put the plugs back in, it lopes and struggles to turn over. If I put the fuel pump relay in with the plugs in it turns over a time or two and then acts like it’s locked up again. If I pull the plugs and the relay it rolls just fine. The only reason the torque converter is unbolted is because I was told it might be jamming up with the flywheel. That was before I realized it rolls over without the plugs.

it has a brand new starter and a new battery. I have two new starters and two new batteries and none of them change anything.

 

If the leaking injector caused a hydro-locked situation it’s possible one of the connecting rods is bent.

Install the spark plugs one at a time - or if they’re already installed, remove them one at a time.

Use a jumper wire at the starter relay (jump pin 30 to 87) to crank the engine after each plug is installed/removed.

If the engine cranking speed changes with one particular cylinder, that’s the suspect, but make sure to check all the cylinders before going after one in particular.

 

With the plugs out it has no problem. With the plugs in, it gets to one spot and tries to hang up but most of the time will slip past. When it does get completely hung, I can take the plugs out and it will act like there was never a problem. So if it’s a bent rod would this still happen?

 

It depends on what’s actually damaged. A bent rod was the first thing that came to mind but there’s other possibilities.

Being able to remove the plugs and obtain even cranking speed indicates compression is a factor - in other words, the starter is under more load.

The uneven cranking speed with the plugs installed indicates a mechanical problem with the rotational motion of the engine - one or more cylinders is creating increased resistance to motion. This could be any component from the crankshaft to the valves.

So, the next step is to determine what cylinders are causing the excessive load on the starter.

This could also be achieved by doing compression testing on each cylinder, but using the plugs and your ears is a short cut to narrow down the problem cylinders. Once you have suspect cylinders identified, further diagnostic tests can be focused on them.

 

Just a thought. You said you had the distributor out, is it possible when it was put back in it is off a tooth or two?

 

I don’t think it was, but yes it is possible. Even with the distributor out, if I put the plugs in it still has a sticking point. Once I get off work I’m going to go through my push rods and valves and check them. Then I’ll drop the oil pan and see if I can see any issues with the pistons.

 

Were you able to figure out the problem on your truck? Just wondering.

 

no not yet. Haven’t had much time. Came back from vacation Saturday and it’s been 12 hour shifts since then