1999 Suburban Valves Tapping

Replace wires, plugs, dist cap and rotor two weeks ago. Everything was fine until yesterday when out of the blue the engine started making a loud knocking sound. Sounds like valves tapping but could be something else. Checked all fluids and all are within range. It only does this when you are driving. Doesn't do it in park regardless of how high you rev the engine. The engine temp is in range and oil pressure is normal. I was told possibly the water pump but checked and it is not loose. Any help is greatly appreciated.

Check spark plugs for proper torque (maybe one is loose and backing out). Get someone in the truck and with the brakes held on put in gear and add some throttle (not a lot) and see if you can pin point the sound.

Good luck

Replace wires, plugs, dist cap and rotor two weeks ago. Everything was fine until yesterday when out of the blue the engine started making a loud knocking sound. Sounds like valves tapping but could be something else. Checked all fluids and all are within range. It only does this when you are driving. Doesn't do it in park regardless of how high you rev the engine. The engine temp is in range and oil pressure is normal. I was told possibly the water pump but checked and it is not loose. Any help is greatly appreciated.

If this is continuous hot/cold when under load I would say a bad crank bearing...also piston issues....does it sound like one or all cylinders making noise.....?

how many miles ? oil condition ? any other work/useage that may have stressed the engine out prior to this .....

I will check that today. It sounds like it is on the drives side and it sounds like the valves tapping.

Like I said it sounds like the valves tapping. I don't know what cylinder noise would sound like. Oil is changed regularly and vehicle has 131,000 miles. I did have the intake manifold gaskets changed about two five weeks ago.

One can of Seafoam in the oil and 2 cans in the gas and all will be well.

No I don't think the sea foam is going to help. I ran a scan today and it came up with the following codes.

P0102 Mass Air Flow (MAF) Sensor Circuit Low Frequency

P0306 Fault Cylinder G-Misfire Detected (CYL6)

P1351 Ign Coil Ctrl Circ Hi Volts

Any help on these is greatly appreciated.

Like I said it sounds like the valves tapping. I don't know what cylinder noise would sound like. Oil is changed regularly and vehicle has 131,000 miles. I did have the intake manifold gaskets changed about two five weeks ago.

since the intake gaskets were replaced I would check the oil for any moisture/coolant loss also...if this is fine, then I would add 5oz of marvel mystrey oil and run the vehicle for 500mi...then change oil when hot not warm,....this should remove any carbon/sludge that may have contaminated the crankcase...tapping ticking would be the lifters....the knocking would be the pistons....

DO NOT USE MORE MARVEL THAN I STATED...MORE IS NOT BETTER.......

it is possible this noise is the exhaust manifold bolts have broken,so give these a look....

new does not mean ANYTHING ....always measure the plug wire resistance when installing new wires and whenever plugs are replaced...

I don't really care what codes you came up with, these engines are notorious for sticky valves, I had the exact same symptoms. Try what I suggested what do you have to lose.

Check to make sure the plugs wires are on the plugs correctly.
push hard they need to be snug