1990 G20 Van Stopped running - Need Help

Just bought a 90 G20 van. When I bought the vehicle I noticed it had a slight knocking noise almost like something was loose under the van.

I started it up and looked under it and saw nothing that would be making the noise. I removed the engine cover and started it and tried to pin point the sound in the engine and still couldn't isolate where the sound was coming from. I would listen to each head and it sounded like the noise was coming from more the center of the engine, I thought perhaps it may be the water pump toward the front.

The van would run fine, no loss of power, tranny was shifting smooth, the only problem was an audible knocking noise at times. At idle it wasn't that audible, more so when I would give it more gas. So, I also thought it could have something to do with the throttle body injection.

Anyway, took a little road trip over very mountainous roads. 100 miles one way and 100 miles back. And I was thinking how well it was running and how good of a purchase I made, and then it happened.

As I was ascending a mountain the knocking noise changed from the normal sound to almost a sound where your muffler blows a whole in it. Almost like the internal knocking noise became an external rattling and grinding. Needless to say the power I had going up the mountain dropped off considerably, almost to a creep. I pulled over as much as I could with cars behind me and decided I had to go a little farther. I got up the mountain a little more (maybe 50 feet) and then I had no more power. I had to pull off the road and it shut off on me. I let it cool off some and checked the radiator and it had coolant in it, the temp gauge was not reading hot. As we were rolling it up on the roll back, engine oil started pouring out onto the bed of the rollback. So I guess I have a hole somewhere in the block or head or a seal is blown out.

I tried to start it again and nothing, the engine wouldn't turn over at all, and still won't. Any help of what this sounds like and what I should be looking for when I get around to tearing it apart is greatly appreciated.

Thanks

Can you get under and look for any holes in the block or pan? That oil pouring out sounds like it may have thrown a rod and punched a hole in the block.

But whether it has a hole in the pan or not - I imagine the next step is to remove the engine and rebuild it. And since this makes it much easier to reach the tranny - I would think about rebuilding that too. When you rebuild a tranny that is just worn, and has eaten its frictional surfaces - I find its a fairly easy rebuild.

Heres an update on whats going on.

I removed the head covers to see what might be going on with the push rods and valves and everything is there, the push rods are tight and none are broken. The valves and springs are all there too. I even took a flashlight and looked down into the head to make sure the push rods went the whole way down through the head and they do. So, its not them. As I stated, I didn't hear the tapping coming from the heads, it sounded more internal or more toward the center of the engine.

I drained the oil and found some very small metallic pieces in the oil, none stuck to the drain plug, not sure if its magnetized or not. Pulled the flywheel cover off, because the oil that ran out onto the rollback was coming from a hole in the bottom of the flywheel cover. I noticed some oil on the flywheel. I guess this oil is coming from the rear crankshaft seal.

There are no holes in the oil pan or engine block.

Could the problem be the oil pump itself? would the oil pump make a tapping like noise if its about to go? Next I will try to remove the oil pan to inspect the oil pump and inspect what I can see of the crankshaft. Also as I stated, the engine seemed to be seized up after what happened. Could damage to the oil pump or the oil pump not working cause this?

I believe the problem is not in the heads but in the bottom end of the engine. So if anyone has any ideas what to look for any help would be greatly appreciated.

Thanks.

As you noted, the next step is to pull the pan and inspect the bottom end.

And pulling the pan may be a pain in the neck, if you have to undo the motor mounts and jack the engine up a couple of inches, to get the pan to clear the space between the oil pump pickup strainer and the subframe.
I think of knocking noises from inside the motor (that arent valve train related) as being the dreaded 'rod-knock'. In other words, a rod bearing has failed, and there is enough slop between the bearing and the crankshaft, that the combustion pressures are slamming the piston/rod down onto the crankshaft journal. This will distort/melt the rod bearing fairly quick, as well as resulting in very low oil pressure for the remaining crank bearings.
If that is what happened, it will be obvious enough when you unbolt the bearing caps. I would say it would be obvious by wiggling the bottom end of each connecting rod - but that rod may be seized onto the crankshaft journal.
I never heard of an oil pump making noise you could hear in a running engine. A rod knock you would easily hear from inside the vehicle.
If it was a rod knock - you will very likely need to get the crankshaft ground to an undersize, replace at least one cod rod. Probably the oil filter wold have stopped the metal particles from getting scattered into the oiling system. If you remove the oil filter and hacksaw the bottom off, I think you will find plenty of metal particles inside. The metal 'facing' on the crankshaft & con-rod bearings is non-magnetic.