Engine rattle
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Freshman User
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Engine rattle
Hi all,
My 85 Bronco has at 351w, C-6 powertrain and I am getting a strange noise at steady highway speeds with light throttle. It is a rattle that can be heard loud and clear under light steady throttle. if you let off or accelerate it goes away I thought it was the timing chain being loose that was causing this so I replaced it and the cover. the cover has a rub mark in it because the chain was that loose. The new chain and gears are much tighter but after I got it back together it still makes the noise. Any Ideas?
Thanks in advance for any advice
My 85 Bronco has at 351w, C-6 powertrain and I am getting a strange noise at steady highway speeds with light throttle. It is a rattle that can be heard loud and clear under light steady throttle. if you let off or accelerate it goes away I thought it was the timing chain being loose that was causing this so I replaced it and the cover. the cover has a rub mark in it because the chain was that loose. The new chain and gears are much tighter but after I got it back together it still makes the noise. Any Ideas?
Thanks in advance for any advice
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Freshman User
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I appreciate the advice but it really seems more mechanical than that. Any time I've heard detonation it has been a random rattle. This is a very consistenr noise that perfectly matches engine speed at steady load above 50 MPH. any big changes in throttle ( on or off ) and it goes away. It is too high to be bottom end and too deep to be lifter noise. Ambient temp makes no difference either, summer or winter and it still does it. I am at a loss. Again, I appreciate any input and can not say detonation is not it for sure. It just seems too consistent for that. Thanks again.
Fleet Mechanic
Joined: Apr 2007
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From: patricia ab canada
on my ranger one cylinder went lean and it rattled so bad i thought a rod had gone bad.you said it will rattle at various rpms but when you floor it it goes away.when you floor it your accelerator pump dumps raw fuel into the intake,thus richening up the a/f ratio causing it to stop rattling.
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It also goes away when I ease up a bit on throttle too. I found a new symptom today though. If I floor it the noise starts at about 3000 rpm and gets louder with increased rpm. It is very consistent with engine speed too. after doing this it has developed a momentary hesitation on moderate to hard acceleration. It's like the ignition cuts out for a split second then everything is fine. I can hear the hesitation through the carb too. It is not backfiring, just a slight poof noise once in a while on acceleration. I'll be checking plugs this weekend in case I have a lean hole though.
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Cargo Master
Joined: May 2007
Posts: 2,071
Likes: 36
From: British Columbia
Piston slap?
Try to recreate the noise with the vehicle stopped, hood open and working the throttle by hand.
Try to recreate the noise with the vehicle stopped, hood open and working the throttle by hand.
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Hotshot
Joined: May 2004
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From: The hills of No. Calif.
As Beanscoot said, will it make the noise at idle or under a no-load condition, such as when you free rev the engine? Try running it up to 3 grand or so while sitting and hold it there and see if it does it, if so, then vary engine speed as you described above to see if it will still lessen or go away under acceleration/deceleration.
If you can simulate the condition while sitting, try pulling a plug wire one at a time and see if you can isolate it to one particular cylinder. If you kill a cylinder and the noise goes away, then you can tell it's caused by that cylinder. I'm sort of thinking wrist pin knock here...
If you can simulate the condition while sitting, try pulling a plug wire one at a time and see if you can isolate it to one particular cylinder. If you kill a cylinder and the noise goes away, then you can tell it's caused by that cylinder. I'm sort of thinking wrist pin knock here...
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