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Discussion Starter · #1 ·
Hello I'm from the Jeepster board, and I hope I don't offend anyone here? I definitely didn't want to try, and hijack the "Diagnosis this Noise" thread, but I know there's very many knowledgeable people here, and I've had a long running problem that I can't seem to solve.
I have a 1990 Chevy S-10, with the 4.3L engine, automatic overdrive, and about 270,000 original miles!
Doesn't use much oil, gas mileage is about what it was when new,and you can still squall the tires taking off, and shifting into second gear, so it it still seems to run strong.
Now what's the problem? It vibrates! You can remove the belt, still does it? You can drive it, or check it in park, it vibrates, when the engine reaches somewhere around 2500-3000 rpms. It does the vibration for a second or so, then smoothes out, and then it does it again, and again, etc, etc.
I've changed the harmonic balancer, made no difference. I checked the flex plate the best that I could, it looked fine. The only time I notice a big difference, is somedays when the weather is warm, and damp, the vibration is almost un-noticeable?
Could it just be the MAP sensor, or anti knock sensor, or is it something much worse?
I've had two different garages check the codes, and there was no problem there, I change the throttle position sensor, that didn't help?
Maybe it's time for a new timing chain, after all this mileage, but it's been doing this for almost 3 years, with no real change.
I know, I know, I should've tried something else by now, but I really hate just buying replacement parts, on a wild goose chase, and not solving the problem. Thank you or whoever, that might can help.
 

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Vibrations in the engine while to vehicle is not moving are only a few things. First, watch the harmonic balancer while the engine is idling. Does it wobble? Also watch the flex plate through the inspection port while the engine is running. Same thing...does it wobble?

Having the vibration go away when it is warm tends to make me think that the problem is in the torque converter or transmission. I'd go for the TC first...
 

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Just to try the obvious, How are the moter and transmission mounts. The fact it vibrates at idel and smooths out at higher RPM means it may be a Harmonic vibration. At 2500-3000RPM when it comes and goes does the vibration start and stop suddenly or does it kind of fade in and out?
 

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Things like compression - one or more low, ignition, one not firing right, EGR leaking a tad, vacuum leak, a leaking or dirty injector - all sorts of tune related items.

And then there's the mechanical possibility.
I wasn't aware until a few days ago that some 4.3's have an internal balance shaft - not till I pulled down my 95 astro to do the water pump and pulled the timing cover to check the chain. "What's this? Another gear?" My 89 didn't have one. (Yup, I have 97, 95, and 89 Astro vans - love 'em.)

Not sure when the transition ocurred, but research on the internet found the early versions use needle bearings on the balance shaft, then they switched over to flat bearings (bushings) more like crank or cam bearings. The needle bearing type causes vibration when they go bad. At your mileage that's a possibility. I don't know how involved replacing it is.

Maybe someone else has?
 

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I don't know much about S10s, but on most vehicles, you should be able to unbolt the torque converter and push it away from the flexplate slightly - that way you're only checking the motor, and not including the tranny or torque converter.

Pete
 

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Dont forget all 4.3s will vib to a point.. they did try and stop it but you can only do so much.. the 262 is a 350 cut down. so you will allways have 2 up and 1 down or 1 up and 2 down.. Other then that its a sweet motor.
 

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Discussion Starter · #7 ·
peteyg,
I replaced the harmonic balancer, with a new harmonic balancer, and it made no difference.

I did not try watching the flywheel while it was running, through inspection plate. I should've mentioned this is a 2 wheel drive S-10, and I had to drop the exhaust pipes down just to get the inspection cover off. But I did inspect the flywheel the best that I could, and I didn't see any reason to suspect any problems with the flwheel. I'm still even using the original starter, after 270,000 miles!

When I inspected the teeth on the flywheel, and starter gear, they hardly even looked worn. I did buy this vehicle new, and I'm not one to abuse a vehicle, and I always try to do regular maintenance.

I first suspect the torque converter, and I still wonder about it, but a auto transmission mechanic, said he didn't think it was the transmission.

I'm sorry if I sound like I'm trying to blow holes in your ideas. I do appreciate anyones ideas, but I do wish I could get this solved. So I'm just following up with you, or anyone on their suggestions.

This vehicle has become a even better vehicle, with the gas prices we're seeing today. And I will most likely rebuild the engine someday, or buy another motor for it. Thanks for the suggestions.
 

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Discussion Starter · #8 ·
bandhmo2,
I have done the best I could do trying to inspect the motor mounts, and transmission mount, short of taking them out. Didn't see anything that led me to believe I have a bad one, but for peace of mind, I will try to observe them again, alot closer.

The best way I can describe this vibration is almost like a tire out of balance, you can feel it through the vehicle. Don't laugh, and I'll try to describe it like this: quiver,quiver,quiver,quiver quiver...smooths out...quiver,quiver,quiver,quiver,quiver....smooths out...and so on.

I guess this would be more of a fading in, and out effect, and somedays it's hardly noticeable.

Thanks for the reply, and questions.
 

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Discussion Starter · #9 ·
RRich,
With the power it stills seems to have, I suspect more of a tune related problem, such as vacuum leaks, bad egr, or other sensors. And it seems with different weather, it changes alot, from hardly noticeable, to very noticeable.

I guess I should just start, eliminating problems one by one, but I was hoping someone, might be able to help me get on the right track a little quicker.

What mechanics I've let look at it, say that's it's internal, but after 3 years it doesn't seem any different. I would 've thoght if it were internal it would've gotten alot worse by now.

I didn't know that about the bearings you mentioned?

Thanks for your suggestions.
 

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Discussion Starter · #10 ·
Pete88YJ,
I'd never heard that one about unbolting the torque converter, and pushing it back, then cranking the engine.
It sounds risky, but I guess it would work.
I may have to try that eventually.
Thanks
 

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Discussion Starter · #11 ·
mach2_nh,
Well you know I'm trying to remember if this engine(4.3) didn't always have this vibration, if it did I know it use to be hardly noticeable, maybe it's normal considering the mileage, on it. But somedays it rather worriesome.
And I agree the 4.3 is a sweet engine.
I would say someday they'll be quite collectible.
Thanks
 

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""""Dont forget all 4.3s will vib to a point.. they did try and stop it but you can only do so much.. the 262 is a 350 cut down. so you will allways have 2 up and 1 down or 1 up and 2 down.""""


Yes, as a cut down v8 it does have the inherent balance problem, even though they went to a 60 degree Vee.
My 89 - without a balance shaft, always had that little vibration, not bad at all, but it was there.

They corrected that slight vibration with the balance shaft. It's a slightly off balance weighted shaft that runs the length of the block, just above and parallel to the cam. It's driven by an additional set of gears behind the timing gears. The purpose is to cancel out the inherent vibrations. It works!

My 95 and 97's are smooth as silk! You can truly balance that proverbial nickel on them. 95 has 195,000 miles, the 97 has 110,000 miles.
The 89 had 275,000+ when I sold it a couple of weeks ago - I bought it new!

There might be a procedure to check that shaft - ask a good dealer how.
 

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when you check the motor and trans mounts, use a crowbar to try to flex things around, they should move a bit, but not all that easily, and when you get them to flex a bit any cracks will show up for ya....

also with that kinda mileage it may be time to check and replace vacuum lines

thats all i can come up with right now, good luck
 

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Discussion Starter · #14 ·
jeepnut_nh,
Thanks, I too, do suspect it's time to change out the vacuum lines.
I have noticed a couple looking, rather well aged.
Thanks again
 
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