My 2000 4.0 makes a light knocking sound at idle only. It sounds like a very quiet diesel. Had a malibu once that made the same noise. They said it was "piston slap". Has anyone heard of this? Is it common with the 4.0? Will it hurt anything? Is there a cure?

 

How many miles on your truck? being a 2000, I would'nt think you have enough miles to have piston slap.the noise could be accessorie related. you could remove the fan belt and start it for just a second and see if it still knocks,and while you have the belt off check the harmonic ballancer to see if its loose or moves at all.

 

44k miles. it sounds like a quiet diesel. this is the best way i can describe it.

 

Piston slap should only happen when it is cold, once it warms up the sound should go away.

 

I don't think its the pistons,I've got 186,000 on my 2.3L and it humms like a new one.As I said before,I would suspect a bad bearing in the accessories,like water pump,altenator,A/C,or idler pully.Maybe even the power steering pump. removing the belt for a minute will prove this or rule it out.

 

I flagged my new, "special ordered", 99 4.0L push rod engine for this diesel noise, at delivery.

A month later the noise was much worse cold & didn't disappear after warming up.

I explained to the dealer, I've owned Fords since my first one, a 53 flat head & NEVER had an engine problem, nor one that knoked & if I had been able to test drive this vehicle off the lot, before I opted to purchase it, I would NEVER have considered buying it.

Yah I know, I could have refused this "special order" delivery & maybe I should have, but they were't giving me any grief or runaround, so I opted to take it & see what happened. This dealer has been around since Hector was a pup, has a very good reputation, so I decided to test it.

The dealer's best Tech & Ford said replace the engine for "bad wrist pins", one month after delivery. They did so.

Afterward TSB 15226 "4.0L OHV Marble Noise", was issued, that said, "Some 1998~2000 Ranger/Exlorer equipped with a 4.0L OHV engine may exhibit an engine noise that may be percieved by the customer as a "Diesel" type noise & is known as marble noise. Marble noise is clearly heard when the vehicle is at idle, under 2000 rpm or under very light load. High mileage studies of the condition show no adverse effect to engine life or performance. Cleaning carbon from the combustion chamber, will have no effect on the marble noise condition. Marble noise is a characteristic of this engie and cannot be serviced with an engine exchange."

All that said, seems I just squeeked in under that TSB. I know one thing, mine sounded like a diesel, at idle & under light load & it was getting worse & no way would someone want to buy a vehicle with an engine that sounded like that.

The dealer service manager told me the problem really lay in this engine's long stroke & short skirted pistons, such that if not carefully enough toleranced, would "wobble" in the bore, causing the racket.

He said this has all come about over the years, as this engine evolved through various mods, one of which shortened or did away with the skirts on the pistons.

My replacement engine, over time, developed a cold knock that disappeared after warm up, that fits the sound definition of "marble noise", but it's been proven to be caused by carbon deposits, called CCDI (Combustion Chamber Deposit Interference).

By decarboning the heads & piston crowns, during head removal, for new "revised" head gaskets, to cure a water leak. After the mechanical decarboning, it was as quiet as a church mouse for 18 months.

This CCDI, can be cleared up by decarboning the engine & holding those deposit build up's at bay, by using top tier gasolines & switching between the two best performing brands, in your vehicle, at say, every oil change, or twice a year, or maybe as soon as every 1000 miles, as it takes that long for one fuels detergents to clean the others deposits.

I control my CCDI by switching between Chevron & Texaco, as they perform the best for me, in my engine, in my area, for my type of driving. Chevron gives me about 4 more mpg, Texaco about 2 more mpg, than the others available in my area. Previous to my CCDI problems I had used niether of them.

Also, not all fuels detergents will clean COMBUSTON CHAMBER DEPOSITS, some will clean the intake side, only to add deposits to the combustion chamber.
This happened to me last summer, after I used three tanks of new formula Shell. My 4.0L just can't tolerate it, 3 tanks & the CCDI was back, took about 3~4 tanks of Chevron to cure it. My engine is VERY sensitive to any combustion chamber deposit buildup.

So all that said, seems to me there may be as many a three conditions at play, that may cause the percieved,"diesel" knocking sound. Bad wrist pins, "piston slap" from slightly undersized pistons & CCDI.
Only the CCDI problem will lend itself to improvement by "decarboning" the engine. Don't know which one you have, but if it's CCDI, there is a cure, DECARBON THAT PUPPY.

A good read on fuels, additives, deposits, ect, can be had at Chevron's web site on fuels, at http://www.chevron.com/prodserv/fuel...techback.shtml

 

glad to know i'm not going crazy. when my malibu made this sound, that is exactly what the chevy dealer told me. your description is spot on. i'm glad to know this sound doesn't hurt it. thanks.