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1989 Astro 4.3L V6 Vibration

vincecallagv's Avatar
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03-04-02, 07:11 AM   #1  
1989 Astro 4.3L V6 Vibration

My Astro engine vibrates just above idle enough to send a strong vibration through the steering wheel and over time loosen various engine bolts

Diagnostics and results to date

Problem continues with the fan belt off so power steering pump, water pump, fan, air pump, and alternator are out of picture

Replaced the harmonic balancer and while idle vibration was reduced the vibration just above idle ( with fan belt off) was still just as strong

Engine seems to vibrate as it passes through a RPM range with the throttle open or even with throttle closed with engine falling through the low RPM range

Problem is same with clutch engaged ( transmission in neutral ) or with clutch disengaged

Engine has almost 200000 mi , very strong and smooth on acceleration, doesn' burn oil, gets good miliage ( I put new head gaskets and valve stem seals in at about 100000 mi. because it was smokeing on start up )

Vibration problem seems to have developed over time

Could it be an imbalanced clutch pressure plate?
EGR seems to be working,( does cause problems if manually over ridden)
Throttle body ports are all clear, Throttle position sensor responds smoothly on digital ohm meter
MAP sensor also responsive and in range with manual vaccume applied
Air cleaner thermostatic damper appears to work ( closed when cold....full open when engine compartment hot)
Bushings were added to throttle body shaft to eliminate worn shaft bearing areas....repair still looks good

Any ideas

Thanks Vincecallagv

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Joe_F's Avatar
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03-04-02, 08:12 AM   #2  
How does it run with the balancer off? Might have a bent crank or a badly made balancer.

Can you temporarily spool it up with the balancer off to see if it improves.

If you disconnect everything and it still does it, internal problems causing the vibration.

If the clutch is original at this point, time to pitch it anyhow.

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