Ok guys, need your help brainstorming on this one. 2000 2.5L 188k, have this very odd rattling/tapping sound coming from the engine that I can not for the life of me track down the source. It sounds like marbled bouncing around. I’ve watched all the videos and **** about rod knock, piston slap, wrist pin knock, etc. plus remembering all of my experience over the years and that is NOT what my engine is doing. This is happening under LIGHT TO ZERO load. Under load, the sound goes away. If I’m accelerating or driving down the road, no sound. If I put the truck in gear, hold the brake with my left foot, and give it gas with my right foot, the sound goes away. As soon as I let off the gas, the sound starts again. Engine uses almost NO oil. It literally used 3 OUNCES of oil in 3,000 miles. Oil pressure is perfect and is up within 2 seconds of engine start, EVERY time. This truck has a TON of power for a stock, high mileage 2.5L. I’m running a 3.55 gear right now because I had to swap the axle and I put an 8.8”
from a 4.0L in it. It actually does pretty well even with that gear. This is the STRANGEST thing I’ve ever heard. I JUST replaced the head with one from the junkyard because I had the oh-so-lovely recessed valve seats and mine was FAR worse than the average case. My cylinder 1 exhaust valve seat was AT LEAST 0.100” recessed causing it to have absolutely NO compression and cylinder 4 wasn’t far behind it. Even 2 and 3 were recessed with 3 being the “best”. Before I installed the new head, I installed 8 BRAND NEW lifters. 4 Sealed Power from AutoZone and 4 Melling from Advance because that what was in stock. I used the Sealed Power for all of exhaust valves and Melling for the Intakes, that way all of the like valves were at least balanced. I also replaced all of the valve stem oil seals. I felt all of the guides and inspected all of the valves while I was replacing the seals. Nothing felt strange or worn. There was only slight side to side movement of the valves indicating normal oil passage clearance and I had no bent or pitted valves. I thought maybe it was from the wrong grade of oil because I used 5W-20 instead of 5W-30 like the sticker on the core support says. So, today I changed the oil again using 3.5qts of 5W-30 and a qt of Lucas standard oil stabilizer. Did NOT affect the rattle AT ALL. ALL of the videos I’ve seen about engine noises show and all of my experience says that the noise level INCREASES under load and decreases when load is removed. Mine is EXACTLY OPPOSITE. Am I chasing a ghost here? It’s kind of annoying and I’m a mobile mechanic so I show up to customers houses with the engine sounding like this. They don’t know any better and are probably having negative thoughts about my abilities due to this rattle in my engine! This is NOT good for a professional image. I DESPERATELY want this sound fixed! Does ANYONE have any ideas as to what this could be?

 

I didn't read where you took off the fan belt and started COLD engine to see if sound was gone so a pulley issue, but if noise is still there you can often localize it better with no fan noise
You can run a COLD engine without a water pump for 90seconds or so, and you can repeat this every time engine is COLD again

 

If its an auto trans check the torque convertor nuts

 

I think it’s one of the new HLA’s I installed or I have a clogged oil passage for the HLA’s on either intake or exhaust. The sound significantly decreases after a long highway drive and the oil temperature has gotten good and hot. The sound actually increased with going from 5W-20 (which everyone’s specs indicated) to 5W-30 (which is on the sticker on the core support) with Lucas. But it decreases once the oil has gotten good and hot/has thinned out. I will double check the torque converter nuts though just to say it has been done.

 

Long shot here ..how about the oil pump loosing pressure to the top end.... there is two large O rings that fit to the pump... they seal the pressure

 

I suppose that’s always a possibility, but my oil pressure gauge is pinned perfectly right in the middle. Although I think it MIGHT be possible that the IDIOT previous owner replaced it with the SWITCH for the LIGHT rather than the SENSOR for the GAUGE. Also, I doubt there are any issues in that department because I did just change the head due to the exhaust valve seat recess issue and I had a SEVERE misfire on cylinders one and four due to the HLA’s holding the valves off their seats. That would indicate I am getting plenty of pressure to the head otherwise the HLA’s would not have pumped up enough to hold the valves off their seats. Where exactly are those o-rings for the oil pump? I’m going to put a KNOWN sensor in the oil pressure port to make SURE my oil pressure is correct because I wouldn’t put any retarded move passed the previous owner of this truck. He was a COMPLETE MORON and I could VERY easily see him installing a switch instead of a sensor in that port.

 

picture of pump O rings

 

Ok, but if that was my issue, wouldn’t that cause the sound to get WORSE as oil temperature rises rather than DECREASE as oil temperature rises? Right now the sound is WORST when the engine is cold which is when the oil is thickest and LEAST likely to squeeze passed leaking o-rings. The sound gets QUIETER as the temperature increases and the oil thins out which would be when it WOULD get passed leaking o-rings and cause a pressure loss. My sound is increasing with higher oil pressures and decreasing under lower oil pressures. Everything with this sound is a$$ backwards which is why it has me so stumped. EVERY engine noise I have ever dealt with INCREASES with load and when the oil thins out. This one is doing exactly the opposite

 

The only way is to fit an oil pressure gage at the oil switch back of the cyl head ..... but pain in the **** to get at .... could be barking up the wrong tree on the oil pump lol.... with age them O rings get hard and brittle pressure does not hold when engine is cold ..as engine warms up the O rings get softer holding pressure ... as i said its a long shot .. pressure gage is the way to go... i got my O rings off my pump, replacing them with rebuild...

 

It is DEFINITELY only ONE HLA making the noise. I need to identify which one it is because I need to get a replacement under warranty and they can replace my throttle body and valve cover gaskets under warranty as well. I definitely just tested it again right now and the heavier the load, the quieter the noise is. And actually it does get to a point where the noise is completely gone. Simply doing a “power brake” and loading the engine up shows that. Barely giving it gas makes the sound get quieter and giving it more to the point where the truck tries to creep, it is completely silent. If that was a rod, wrist pin, or piston slap, that noise would be loud as can be when I load the engine like that.

 

So the noise was only a lifter lol

 

That’s really all I’ve ever thought it was but it’s weird because it DOES go away with engine load. It does NOT go away when you rev the engine without a load. But what I’m p!ssed and concerned about is the fact that they are BRAND NEW lifters. I JUST replaced them when I swapped my head due to the valve seats recessing. They have LESS than 4,000 miles on them and this one was making noise as soon as I started the engine with the replacement head.