OK, so I picked up this 97 Old Bravada this afternoon and took it down to my shop. The short history with the vehicle is it was driven from a town about 50 miles away to a ball game in our town. When the folks arrived, the engine started knocking. It has 98K on it, in near perfect condition, they took it to the local GM dealer and proceeded to trade it in as is. The GM dealer, which I do a lot of business with as they do not have a body shop so I do all the GM warranty work plus any damage that they may trade for, let me have the car to inspect down at my shop. After getting it to the shop, I did a little investigating and I'll be darned if I can tell if the engine knock is at the top or bottom. It is actually best heard right through the grille. I thought it was more towards the drivers’ side, so I decided to start pulling plug wires, one cylinder at a time, to see if the noise changed at all. When I pull the number 1 cylinder plug wire, the knock practically doubles. When the plug wire is installed, the knock sounds like a knock on both an up and down stroke, with one end of the knock being deeper in sound and the other end being lighter in sound. With the plug wire removed, it simply knocks to beat the band.

It carries between 40 and 80 PSI on the oil when cold, once warmed up, it drops below 40. Usually around 20 at idle, and revving up to 2 grand gets the pressure back above 40 slightly.

I think I'm going to buy the vehicle and plan on a new engine is needed but was curious what anyone thinks that it might be something such as a lifter, push rod, or rocker arm. I was under the impression, and 4.3 W engine of this year would have roller lifters, anyone know if this to be true?

One thing I did notice about the engine is that is has recently, and I mean probably within the last month, had a new water pump installed along with the intake plenum removed. The new water pump was obvious enough, but apparently the water pump and the front of the intake received the same type of gasket sealer. I could see a small bead of gray sealer around the water pump mount, and a whole bunch of gray sealer squeezed out the front of the intake manifold (was wondering if perhaps some sealer may have come loose inside the motor and block an oil passage or caused a lifter to go a little crazy). Of course I couldn't be for sure without pulling the intake and valve cover.

I'm going back to the shop and take my scanner to see if there have been any stored codes from prior problems. Other than the Water pump and Intake work, the EGR valve looked like it had been replaced recently and the AC compressor looked brand new as well. I put it up in the air and run it in drive, all four wheels turned, assumed that was normal for the smart track. It did appear the differentials, and transfer case had been serviced recently and often.

The dealer wants 2 grand for it but I think I could get it for 1500. Does that seem reasonable, taking in account I would most likely need a new motor?

 

I'm betting on a broken piston skirt or possibly a way worn cylinder, but piston skirt is my final answer!

 

Ok, but there is no prize for the correct answer, just so you know.

 

As a PS Swartlkk, I see what all the talk was about on getting to the flexplate/torque converter bolts. Looks like fun since there isn't a shield to remove like most have.

 

Sorry... Didn't read down through the whole post first before blurting out my diagnosis...

For $2k, grab it! You could pull the motor, pull the pan, heads, and crank, then check the block. I'm betting you'll find a peice of the #1 cylinder in the pan. What seals the deal is that when you pulled the wire off, the knock got worse. Its either a broken piston or reall bad piston slap...

Heck, you might even be able to salvage the block and just do a rebuild with a cylinder overbore. You'll already need new pistons. Bore the block and have the crank checked and polished. While you're at it, lap the valves and put in new valve seals. Then everything should be good to go!

 

DAMN... Come on, why not??? LOL!

Yeah, that's what I noticed while down under mine. Not too fun.

 

Well, for the prize I suppose I could send the broken piece.

I'll probably clean out a spot in my barn (yeah, barn, I live in the country), and park it there and tinker with it as I have time. I'm not in a hurry to get it going, so I could take my time tearing it down. Although I did find 2 4.3 Vortecs in two local salvage yards, one for 550 and the other for 400, complete. Pretty high mileage (104K and 142K respectively), but both were reported as good running before being pulled.

Your diagnosis makes sense. I was stumped when the sound was worse when I pulled the plug wire. I was really expecting (if it were a rod bearing) for the noise to quiet a bit. Other than the work I mentioned, the oil had been changed about 400 miles prior to the mishap according to the oil change label. Apparently they had it serviced at the local GM dealer in their area.

 

Well, I got it for 1750.00. Still at the shop, got it washed up and ready to put in the barn. Will start by tearing the top end off, then pull the block. I got a price from the machine shop I used to use in my younger days and it is a little less than 700.00 for all parts (inlcuding pistons should it need bored) and labor to bore the block, and grind the crank. Would be cheaper if it turns out to be just a rod bearing as I probably won't have the cylinders bored.

That price doesn't include cam and lifters, but I get the impression since it is a roller cam, that generally isn't necessary. It is another 310 for lifters and cam.