Engine Knocking!!! Please Help!!!

[gmcsierra93]

I own a 1993 GMC Sierra 1500 2WD 5.7 350 V-8 with 177,000 miles. Brought truck to repair shop to have rear main seal fixed and the intake manifold gaskets replaced. When I got the truck back I had a real bad knocking sound coming from my engine.

Next I had the oil pump replaced along with a new oil pan gasket and had the main bearings replaced hoping to fix the knocking. STILL NO LUCK!!! The truck has low oil pressure now for some reason and runs a little hotter than usual. Somebody please help. I'm running out of patience and money!!

[embflyr]

Are you getting a check engine light with the knock, and is the knock more pronounced when at high idle? If so, probably a bad rod bearing, or main. The other scenario is a bad lifter. If this is the case, you will experience a strong knock at cold start-up, but will decrease or in many cases disappear with an increase in rpm and temp.

[gmcsierra93]

I had the main bearings replaced and the problem did not go away. When I push the gas, the knocking gets faster and faster. I have really low oil pressure and the check gauges light flashes on and off at times. Every now and then the "service engine soon" light will come on but thats only if I'm on the interstate. Its a really weird situation. I also had the oil pump replaced to see if I could increase pressure but it didn't.

In the mornings when I crank it up, my oil pressure is fine and it doesn't knock, but after I drive it a few minutes is when the problems continue. The mechanic I use said it sounded like a main bearing and not a rod bearing so I had those replaced. Thanks for your feedback.

Stephen

[mjgjr72]

did he check the torque converter bolts maybe the bolts loosend up or flyweel bolts or possibly cracked the flywheel.
miain bearings usually do not make knocking noise, although if they are worn or spun they with effect oil pressure, it is usually rod bearings knocking as the piston and rod reverse direction, oil pumps usually due not go bad they are the best lubed part of the motor, and usually only fail if dirt or metal get in them with 177,000 miles i would bite the bullet and put in a rebuild, if its a bearing problem usually stuffing in new bearing will only get you another 20K if lucky.

[surfacerider]

Hey there....just registered and saw your plight.

There's a few things I need to know to give you my input...........I'm going to assume you have throttlebody fuel injection and the first guess will be the intake gaskets,they have 4 ports to allow coolant to circulate 2 at the front and 2 at the rear.on GM's throttle body the 2 rear ports are blocked off,and the 2 front ports are to allow coolant to flow throught the area under the throttle body to preheat the fuel before it enters the cylinders to assist in the atomization process.

If the intake gaskets are installed wrong there will be no coolant flow and possably airlocks in the upper part of the engine.Higher engine temperatures will also cause lower oil pressures

Your knocking could be caused by a number of reasons........the first thing to do is narrow the possabilities down,when does it knkock,during idling could be caused by depending on the condition of the engine..........a piece of carbon from the exhaust crossover (a passage that goes under the intake for the EGR) that accidently entered one of the intake ports and embedded itself in the piston not a serious problem ,remidied with some combustion chamber cleaner............only at higher engine speeds under load or on a float situation depending on the pitch of the noise possable rod or main bearing,which could also acount for the low oil pressure,or improper bearing instilation, as bearing clearances are responsable for oil pressure.

If the knock can be produced by quickly snaping the throttle then dissconnect sparkplug wires one at a time repeating the snap throttle and when you get one that either makes the noise change or dissapear then you have narrowed the noise to a particular cylinder.

another way is to use a long piece of metal or a long screwdriver and place it on each exhaust port where it connects to the head and putting it to your ear,this will act like a stethniscope and allow you to hear only the cylinder you have the tool on.

So give me some more information on the knocking and we can pin this little puppy down.............

surfacerider.........