1999 GMC 2500 5.7 Knock from Hell....

Hey guys trying to help my buddy out here he’s got a 1999 5.7 gmc 2500 2wd 8 lug,he uses it as his work truck (we are both 19-20 and have Landscaping & lawncare businesses)he bought the truck about 6-7 months ago long story short the guy he bought it from screwed him over and the trans went out the same week he bought it and just recently he took it to a shop and had EVERYTHING fixed all the oil leaks,new front end,a ton of motor work new head gaskets,rear main,oil pan gasket,new intake manifold gaskets,new timing cover gasket,water pump,injectors and bunch of other stuff the shop checked over the motor and confirmed it was in good condition and had definitely been replaced before (which lines up with the story of the previous owner) but today 2 weeks after he gets it back from 4,500$ worth of work he’s sitting at a red light and it cuts off,said that the starter barely turned it over to crank back up and as soon as it fired off it starts this god awful knock that’s loud as hell basically to me sounds like a thrown rod but it’s not leaking any oil,no shavings in the oil either...so now what? Give me your guys thoughts just trying to be a good friend and help my buddy out.

If it were mine, I'd start with pulling the spark plugs to see if the end of one is destroyed.

i would look closely for signs of silicone sealant. being as it was just in the shop and resealed. some folks take shortcuts for profit and use sealant on gaskets and that sealant turns loose and gets sucked into the pickup for the oil pump.
letitsnow has great point too. i have seen the ol broken plug do lots of damage, especially champions.

sounds very similar to the problem I had same thing just died barely crank and god awful noise.if when they put distributor back in if they did not use a scanner (I hate to admit it)to set the CMP/CKR correlation it can cause a crossfire condition that can do what yours is doing.not saying that is the cause but it was in my case after ignoring advice from churkey a member on here a large amount of money and time later.it was a brand new cap (2 months)no warning just died.garage after having it towed finally replaced cap and set(timing)cured I am old school and thought it was bullshit setting CMP but an old dog learned a new trick.worth asking them.I can not believe it is a rod out of the blue.in meantime you may change cap for ***** and giggles as there have been posts about problems with the newer caps

Have him pull the transmission inspection cover and check the torque converter to flywheel bolts. If they back out, they can strike the block and make a noise that sounds like a rod knock. Also, they could potentially cause a stall and hard start. Not a guarantee, but with so many parts of the truck taken apart and worked on, anything is possible.

I bought a Vortec 5.7L short-block that was pulled from the truck because of a "rod knock". Once they had the engine out and hanging on the engine hoist, they discovered that the flexplate was broken--the entire center section that bolts to the crank had a 360-degree, irregularly-shaped crack. The center would move separately from the main part, but didn't fall out.

However, if the truck stalled and was hard to re-start, it sounds more like internal damage.

1. What is the oil pressure?
2. What does the filter media look like when you cut the oil filter apart?
3. Cranking compression test results?
4. Cylinder-balance test results?

$4,700 for all that work? I'd take back to the shop. Didn't they give some of warranty? I would think a 30 day would be reasonable.

I mean, that's a lot of money. Surely they will take a look at it. Maybe it's something simple wasn't put back together?

I would definitely take it back to the repair shop and turn it over to them. That's almost as much as a totally remanufactured engine.

The shop who did the work is coming to get his truck tomorrow with a trailer.They are going to put it on their lift and figure out what happened,however I agree with you all because even with the problems the truck had before it was at the shop for all that work...it was very reliable and never had any problems other than the trans going on and then 2 weeks after a supposedly revamp the motor may have blown....something ain’t right here

Shop came and got truck today...motor is blown something in the bottom end has turned loose