loud engine knock, need help

ok, heres the deal.just replaced alternator ,battery,serpentine belt,and belt tensioner on my 97 ex sport with 155,000 miles.engine is an overhead cam 4.0 v6.drove great for about a week,and then the trouble began.my wife took it to work,and by the time she got it home, the engine was making a extremely loud knock at idle that would get faster as the rpms increase.it sounds like it was coming from the passenger side top end of the motor,but i could be wrong.i was thinking maybe a rocker arm,valve,rod or something like that.i went ahead and parked the truck for now because i dont want to risk any more damage.the truck holds good oil pressure,there are no lights on in the dash,its full of oil ,and doesnt leak any fluids.anyone who can help diagnose this problem would be greatly appreciated,as this is our only vehicle.im hoping its not trying to blow up on me!!!

found the problem

had a mechanic come by and found out it was just the idler pulley was worn out and rattling around.quick $50 fix.

You did the right thing. Glad that's all it was. When you said knock, I thought the worse.

i never thought in a million years that an idler pulley could cause that much racket.it sounded like a broken rod,or like a death rattle from the mains or something.the idler pulley was so worn out that you could grab the top of it and pull it out about a half an inch.it was wobbling around like crazy.sooooo glad thats all it was.

Did you try to start the motor with the belt off? The problem you described sounds just like mine. My idler pulley isn't turning. But the only problem I have with mine, is the noise continued with the belt off, and I was curious about yours.

after i replaced the idler pulley,there have been no more noises at all.as far as yours goes,if your idler pulley isnt turning,you will definitley have to replace it.the noise your hearing sounds like the dreaded timing chain issues.this is caused by worn out timing chain guides.its also a very expensive repair if you take it to the shop.most of the shops around here wont even work on the ohc engines due to having to pull the motor and special tools are also required to keep the engine in time.hopefully your problem is something more simple.you could probably find another engine for the same price that it would cost you to have the timing chain repaired.i also would not recommend running the engine with the drive belt off.your best bet would be to find a mechanic and let them check it out before you decide to do anything.if its a rod knocking,the knock sensors should kick on the check engine light.if no lights are on i would think its the timing chain.is the truck missing or anything?

No check engine lights, the knock is the same in idle and increases with rpm's. Oil pressure, water temp, all gauges are good, no changes at all. It came on all of a sudden, kind of like a light switch, no there, fix the coolant temp sensor wire after the rat got thru with lunch(chewed thru) replaced the intake gaskets, accounted for all tools and hardware, started it up, there's the knock. Sounds like it comes from the whole motor, front back, left, right, top, and bottom at the same time. My husband is a mechanic and he can't tell where it's coming from even using a stethoscope. I am hoping for an easy and pretty much cheap fix. If not, the sohc will be pulled and a pushrod 4.0 from a 92 with 54,000 miles will be put in along with the obd1 set up in it. Lots of time, little money.

Sorry to bring up an old thread but just today my 98 explorer just started knocking
i hope mine is only a 50 dollar quick fix I am trying to diagnose the problem now Which one is the idler pulley?

The idler pully is the only one that isn't attached to an accessory (not the alternator, not the water pump, power steering, A/C, etc.)

You use a 3/8 drive ratchet (with no socket attached) to loosen the belt by fitting into the square hole in the idler pulley bracket. Once hte belt is off you can remove the idler pulley mounting bolts (bracket to motor bolts).

Thanks russ

I have the knocking sound you are describing in my 1999 explorer XLS 4.0 ohv. I put a new timing chain kit on it, checked all my pulleys, pulled the oil pan and checked my rod bearings and riss pins. Everything looked great. The sound I have resembles more of putting a baseball card in a bicycle spokes. Is there a possibility that it could be a bad torque converter or cracked flywheel?

yes, could be flywheel or torque converter. Does it sound like its coming from up front, or down below?

You say you checked your 'pullys'. You mean idler pully, alt, power steering, etc? The sound you describe could be any of those. Easy enough to temp remove serp belt and see if noise goes away. If it does, you know its one of those belt driven accessories (or the idler). If it doesn't go away, you quickly & easily ruled that out.

Engine knock at idle

I had a problem with my 98 explorer sport 4.0 knockin at idle speeds. It was driving me crazy. It sounded like a diesel when idling. I researched this site and found it could be carbon deposits built up in my motor causing this problem. I didnt really believe it but figured i should try somthing. I went down to my auto parts store and asked for a top end engine cleaner. they brought me a kit by Berryman. It came with 3 cans of chemicals and an adapter kit to hook a can to the motor and suck it through the intake. after going through the 3 step process the knock went away. Im very pleased with the info from this site.
Anyway , good luck.

rod bearings?

MUSTANG1978 said:

I have the knocking sound you are describing in my 1999 explorer XLS 4.0 ohv. I put a new timing chain kit on it, checked all my pulleys, pulled the oil pan and checked my rod bearings and riss pins. Everything looked great. The sound I have resembles more of putting a baseball card in a bicycle spokes. Is there a possibility that it could be a bad torque converter or cracked flywheel?

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i have the same problem with my 1997 xlt sohc, it almost sounds like a diesel engine, but my problem was the connecting rods, let me know if this helps

Hi, slight divergence here , sorry, but I have a 2001 x Eddie Bauer 5.0 v8 that started knocking this afternoon and has me very concerned. It sounds as if it is coming from the front right end near the alternator and towards the bottom of the engine. No check engine light and the idler pulley feels pretty good to me. One strange thing about this is that it is more constant when the x is idling rather than when I put it into gear. When idling it is more of a knock.knock.knock but when in drive it is more like a knock..knock (period denotes a second) basically just knocks with a higher frequency when in idle. It is also not a very loud knock and can only hear it when under the hood or pulled up next to an object that echoes. Anyways I'm no mechanic but I actually do not think it is a rod but I don't know for sure, and I really hope it is not the timing chain ($$$$) Any thoughts?

Sam

P.S. First post btw wooo, wish it was on better terms haha

pps, haha it also runs fine and doesn't miss at all whatsoever, still get around 23 mpg on the highway

I

jamienjason said:

i never thought in a million years that an idler pulley could cause that much racket.it sounded like a broken rod,or like a death rattle from the mains or something.the idler pulley was so worn out that you could grab the top of it and pull it out about a half an inch.it was wobbling around like crazy.sooooo glad thats all it was.

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I have a 99 explorer that has a loud knock when started in the morning and can not find out what it is.. very frustrating