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Discussion Starter #1 (Edited)
Hi all,

Newbie here, see intro

here

I recently acquired a '92 3.8ltr, love it. However the following probs:

Top end rattle of some kind under load at high RPM or above about 40 Mph, keeping in mind my OD is burnt so Rpm's are higher at those speeds driving in D)

The rattle is weird, it's not consistent and was a lot worse because my IAC was busted. Now that's fixed it's subsided some. It's coming from the top middle and sounds like a hammer hitting metal back and forth. A knock if you will.

The engine runs completely smooth and makes no rattle whatsoever at lower speeds/rpm. Accelaration, moderate or quick is sweet up to above mentioned speeds. Then the rattle comes, however if I apply more throttle it will go away up to 60 MPH. Then if I let off the throttle it rattles extra on release, and extra on reapplication of my foot on the pedal, but as long as it keeps accelarating up to a point, it's fine.

I know diagnosing sounds without hearing it is almost impossible. But any ideas would be apreciated.

TIA

David
 

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Maybe it's spark knock (pinging). When was the last time it had the plugs and wires changed? Fuel filter?

If these are all good, maybe try running some Seafoam through the motor.

Jay
 

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+1 on the spark knock. Might be time for a tune up or maybe cleaning your MAF sensor (there's a write up in the tech articles on how to do that) Pinging is bad on your motor, so try to get it fixed soon :) Welcome to the community by the way :D
 

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Discussion Starter #4
+1 on the spark knock. Might be time for a tune up or maybe cleaning your MAF sensor (there's a write up in the tech articles on how to do that) Pinging is bad on your motor, so try to get it fixed soon :) Welcome to the community by the way :D
Thank you all,

Tune-up it is.

I've read about Seafoam, wonder if I can get this side o' the ocean, maybe through the UK.

I haven't replaced the bad IAC yet... it's still sort of 'bypassed' and manually set to idle. Could this have an effect also?

TIA
 

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Discussion Starter #5 (Edited)
All tuned up, mild difference.

Any other ideas? Should I put a vid up on Youtube to give some idea of the sound?

Also can't buy Seafoam over here. Any idea what it's made of or alternative products?
 

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cam bearings

I have had a knock like you are describing when the cam bearings are getting loose....is the oil pressure low when idling---I don't mean zero but lower than a comparable engine----it may not be since the oil pressure sender is below the cam bearings so it may not see a problem.......................Dan
 

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Discussion Starter #7
I have had a knock like you are describing when the cam bearings are getting loose....is the oil pressure low when idling---I don't mean zero but lower than a comparable engine----it may not be since the oil pressure sender is below the cam bearings so it may not see a problem.......................Dan

I'll check the pressure, it's not tripping the dummy light in any case.

Cam bearings eh, how labor intensive was the fix?
 

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The engine will most likely have to come out of the car. A mahine shop will have to remove & replce them.

If the cam bearings are bad it's time to rebuild the engine as the rod bearings will be next to go.
 

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Discussion Starter #9
After an oil change and tune up it only knocks/rattles at WOT and when I let off or get on the throttle. All other times it's smooth as hell. Not even valve chatter... WTF!?

I've got a decent offer from a guy to take it off my hands and I get to strip it for headlights, taillights, mirrors and a few other things.

Should I just cut my losses?
 

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i have a knock that had me worried for a bit, i first thought it was rod knock but here are my symptoms.........maybe similar to yours idk.

On start up its fine i can Rev and hear nothing, after running for a while i can hear a knocking that starts at around 2.5RPMs and gets a tad louder as the RPMs climb, ive had 2 ppl look at it and they all say its normal lifter arm noise so maybe thats it idk. If not someone tell me what the hell is up with my car. (Have had the car for almost 4 years now and have had the sound since ive owned it).
 

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Discussion Starter #11
Yeah I still haven't found wtf is up with mine, prolly gonna sell it for parts,

Mine does about the same, an oil change did help a bit but it's a pretty loud knock. Is yours sensetive to when you get on/off the throttle, min rattles at top RPM's above 60mph (I have no OD) and when I get on or off the throttle it will rattle a bit on the way on and off....
 

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Does she rattle when parked? Get it warmed up a bit then put it in park and rev it up see what happens, if around 2Gs you start rattling and then goes away after you get off of it, it may be what mine is.

Ive had two Mec. listen to it and they both told me that its a noise that i shouldnt be worried to much about. Now if your worried about a rod knock let the car sit for a few days and start it up ( the oil will settle so all noises will be intensified). Now how loud is this knock though?
From 1-10 1 being dropping a pen 10 being womans heels in a hall way lol.
 

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If it's rattling when you're letting off the throttle, I'm going to bet that it's a spun rod bearing. A quick/simple check would be to remove the oil filter, cut it open, and check the filter media for metal shavings.

This is what you don't want to see:





-Rod
 

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I have a similar rattle in my 3.8 cougar, it almost sounds like a fluttering metallic sound, but not valve tapping. Mine happens when Im heavy on the gas but eventually it mostly goes away. Im afraid to cut open my oil filter because of what I may find. I have a new maf, freshly cleaned IAC that looks new now lol. I have done sea foam with not much success. If you figure it out let me know.
 

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another thought it the timing chain---if its stretched and/or the tensioner is worn you could be getting some timing chain noise...................Dan
 

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Discussion Starter #16
Thanks Dan,

I'll keep it in mind for future reference, I sold the car last week as I have my hands full with a '93 5.0 and 95 4.6 ;)
 
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