Brief car history: several engine seals replaced early in the trucks life, oil pump failure at 49,000 miles. It sitidle for 3 months until I bought it, then I replaced thewater pump at 49,500 miles.I then did an engine flush and switched to synthetic oil and swapped out the plugs.It has 50,500 miles now. Fuel economy is in the high teens, temps normal, no smoke, and it's not using oil.

At certain times, I can hear a faint knocking sound coming from the engine compartment. There's no rhyme or reason and it's undpredictable as to when it happens. It makes no difference: start up cold, start up hot, running for a while, etc. It randomly comes and goes on its own.

Unless you were actually listening for it, it probably wouldn't be that noticable. It's very muffled and low and easily lost among the din of other engine noises. Also, it seems to be more discernable from the passenger compartment after all the other noise is filtered by the firewall. From the driver's seat, it's sort of a diesel engine sound. Also, standingoutside the vehicleto the rearof the front tires makes it easier to detect as well.

Earlier today, though, I happened to hear it and stopped off at my local mechanic. He brought out his stethoscope and started listening to various parts of the engine but it disappeared before he could go over it a second time. He seemed to think, though, thatwhatever it wasstemmed fromthe passenger side.

He seemed flummoxed, but when I told him about the oil pump issue he startedleaning toward a wrist pin going bad.

The next time I hear it I'm going to start pulling plug wires to see if it goes away.

Aside from that, can anything think of other possibilities to investigate?

 

Do not up the plug wires.

I have been told that if you do you could blow the ECU.
The people that told me this do work on Rover ECU's.

 

They said to pull the plug off the fuel injector.

 

Thanks for the tip!

 

just wondering, are you using premium fuel to fill up?

 

Have you done a fuel pressure test, cold at idle and 2000 rpm's as well as at operating temp?
You can pull a plug wire, one at a time, to bring out a piston knock with no harm to the ECU.
Vave you ever pulled a valve cover to se how bad the sludge build up might be?

 

it has always been my experience that a "knock" is lower end, while a ping or clicking sound is from the top. so what bests describes the sound??
I think Disco Mike is right asking about the valve covers, it could be a valve tick that can be fixed with a good old fashion cleaning and an adjustment, especially since the oil pump was replaced.

and that premium fuel question... 91 or better!! nothing less :-) ... as much as it pains the wallet now adays, it must be done!

 

Thanks for the help so far.

To answer everyone:

I only use 93 Octane.
I haven't had the valve covers off, but I did the AT flush and what went in as a clear, healty looking pink came out a burnt smelling, ugly, dark purple.
I have not did a fuel pressure test.
It's more a knock.

After I let it cool off a bit, I started it up to check. Initially, it wasn't present but it started coming on as I backed down my driveway. I quickly crawled beneath and noticed that it was louder toward the rear of the oil pan on the driver's side.

The future of my Disco isn't sounding so good

 

I get some noticeable piston slap in mine when it's cold but I consider it normal for the vintage of the engine's design.

 

Regardless of what's happening inside the engine, I'm going to drive it. It's too fun to let it collect dust in the garage!

In any event, replacing a rod and piston or two won't fix my problems. Since it's an '03 the only long term cure is a new short block. It's afflicted by the misaligned oil pump disease and is going to hard fail again at some point in the future.

As I see it, either way I need a block in order to be healthy again. I might as well enjoy it until the day a new engine becomes a necessity instead of an option.