[Timber]

I'm having a problem with my old 1990 S-10 Chevrolet, it has a 4.3 engine. I bought this truck new, and after 242,000 miles, I've been noticing a strange viberation.

It's most noticable at about 2000 to 2500 rpms, but it seems to be there even somewhat at idling. It viberates, or shakes, or pulsates, or whatever you'd like to call it, for just about 1.5 seconds, then it smooths out for a couple of seconds, then it repeats this process again, and again???

I changed the spark plugs, and found one that looked as if hadn't been firing good, I also went ahead, and replaced the spark plug wires, distributor cap, rotor button, and PCV valve, just for good measure.

Everything I done so far has helped the viberation, but has not eliminated it. I'm considering changing the coil, though it's almost $50.00,

but I'm not sure that'll cure the problem. I'm also starting to question the throttle-body fuel injection???

Some of you may wonder, why I started with the ignition system first, well to be honest, the plugs had not been changed in about 3 or 4 years, and the wires, distributor cap, and rotor button, were original-almost 14 years old!!!

The coil is also the original one, I know, I know your thinking, I must not take very good care of my vehichles.
Actually, I just never had any trouble, until now, you know the old saying, "If it ain't broke, don't fix it." The only problem with that is after 242,000 miles, almost anything could be broke.

I sure could use some advice here, please try to refrain from being cruel,

as tempting as it may be.

Thanks,

 

[uglyjeepoffroad]

Clean the injectors.
That would be my guess.

 

[2711]

wise man say, test coil before replaceing.

one would think that if it was the coil, it would be weak all the time- dont we all wish? I`d personally put a new coil on it anyway. It could be one of a thousand things, and your on the right track- but remember, it is getting old, and has the mileage to prove it-

one might even consider a compression test to rule out a multitude of problems that comes with age and high mileage.
Suppose the timeing isnt keeping up with the engine, that`d give you a stumble on a regular basis at idle...oh, the possibilitys.

 

[RRich]

A virgin 4.3? They run and run and run and --.

Vibration - could be lots of things.
Start with a can of Techron in a 1/2 tank of gas, could be an injector's getting plugged. Takes about 10-20 miles to clean it - that stuff really works!

And a compression test.

The vibration - do you hear it more than feel it, or vice-versa.
Do you only feel it in drive? How 'bout reverse? Neutral?
I hope not, but where I'm going with that is flex plate - they did have a problem with them.

If it was at idle only I'd suspect old cracked vacuum hoses - especially that one in the front of the throttle body.
But you say 2000-2500 - and comes and goes. Not as bad at idle.

Runs fine - or starts a little hard now with age?
May not be related, but those had plastic gears for the timing chain - replaced? If not, do the test for it - before it jumps.

A bad coil won't hurt just one cylinder, your complaint would be more like hard to accelerate, backfiring etc.

Cold, Hot, always? More info needed.

 

[Timber]

Thanks guys, for the quick replies. First of all let me apologize for the bad spelling, it's Christmas, and I've got nine people, counting myself, ("I think")living in my house for a month, fortunately I do have a large house, but it's getting harder, and harder to hold on to what little sanity I do have.

Back to the problem with my truck, I did notice it at first when I was in drive at about 45 mph. I suspected something in the drivetrain. I took it to a transmission shop, and the guy there drove it try several little test, and said, the only thing he could guess is maybe a cracked flex plate, or out of balanced torque converter. He said, I don't think it in the transmission, and after we listened to it awhile, he said it seems like something out of balance, of course he couldn't be sure, unless he took it apart. He suggested I take it to someone who knew more about motors than he did first, and maybe they could figure it out.

I haven't try to check the timing gears yet, but I've thought I should sometime, good suggestion.

I going to have to get back to you, (RRich) I'm out of time for now.

 

[3229]

A little doubtfull but have you checked the cat. sometimes if you have ignition issues (250000 mi. on the same plugs will do that). Anyway if it is a little slugish it could be the problem but I would check it as a last resort, just before the trans.

 

[RRich]

Ooops - I think I gave the wrong impression - the plastic timing gears. I seriously doubt that has anything to do with the vibration. I was thinking about a 4.3 with those many miles and thought about those gears. If they are the original plastic gears you've probably set a record, they usually go at about 130,000 miles. So --.

But the vibration issue - quite likely a flex plate, but exhaust all other possibles first - it's not fun to remove the tranny to find it's OK.

Another thought - look at the vibration balancer in front - if it's got the typical timing cover leak the oil may have destroyed the rubber between the inner and outer rings. It may look OK at first, but the sign is the rubber starts squirting out from between them. It's a much easier fix than the flex plate. And - make sure it's not caked with mud and grease too.

I don't know of any external way to check the flex plate - unfortunately. They crack around the crank bolts.
One possible way - if it has an inspection cover where you can see the flex plate - run it up on a hoist - remove inspection cover, have someone rev the engine till it vibrates. You MIGHT be able to see it vibrate a little fore and aft. If you have a strobe light or timing light attached to a coil wire it'll really help you see it. Coil wire will give a better light - fires twice per revolution as opposed to once every two revs. It will show the variations in position, where using a plug wire may not.

 

[thomjpster]

Timber, is is a throttle body, or the CPI tuned port?

I'm not sure (I've never taken mine apart) but the tuned port cpi engines have a ballance shaft in 'em?

If it's a cpi, also keep an eye on the oil. The injector spider will develope a leak and flood one side of the engine. (knocking on wood) I havend had any problems with mine yet.

Don't forget that all the bushings are 10 years old now, mabe somethings just shifted, and vibrating sometines.
Good luck, Thom

 

[Timber]

Sorry for taking so long to reply. I bought some Techron fuel injector cleaner today, but haven't had a chance to drive it very much yet.

I also stop by a reputable, auto repair garage today, and they hooked it up to their computer, they found nothing wrong. The shop owner listened to it, felt of it, and said he believed it was internal, or it could be the harmonic balancer, and maybe even the flex plate, but he said, from his experience, a crack flex plate makes a noise while idling, and sometimes the noise quits, when you put it in drive. Which of course mine's not doing???

His final conclusion was, with that much mileage it be very hard to pinpoint, what was causing it. He also told me it wasn't a bad vibration, and since it wasn't making any bad noises, it probably wouldn't hurt, to keep driving it, until it got worse.

So, I guess I'll just give the fuel injectoin cleaner, a little time to work, and go from there. I do greatly appreciate everyone's replies, and will keep checking out everyone's suggestions. Hopefully, with everyone's help, and a litte luck, I'll figure it out, before something breaks!

Over the years, that I've owned this truck, I've changed oil, and oil filter every 3000 miles. I've also tried to maintain everything else as good as I could, and after all the mileage that I've put on it, I must say it been good to me.

 

[1536]

My parents had a Grand Cherokee with what sounds like the same problem. They took it in the the shop and they found a broken motor mount. That solved the rough idel, and it is a simple thing to check.

 

[RRich]

He's right - partially. A cracked flex plate can go away at speed, - or get worse at speed, or have specific speeds it vibrates at - or come and go. Sometimes in gear, sometimes only out of gear. Ya never know. Remember it's just a crack around the crankshaft bolts, it can wobble to any harmonic vibration it wants to. Sometimes the timing light trick shows it up.

Just thought of something - happened to me on my Suburban. Different engine 454, different trans, but similar symptoms.
"Sometimes" I'd hear a noise, sometimes not. "Sometimes I'd feel a vibration, sometimes not, sometimes with noise, sometimes not. Sometimes accelerating, sometimes not. Totally unpredictable. Sometimes not for days, but --.

I thought it was the flex plate - it was, sort of. I pulled the inspection plate - found all 4 bolts - actually nuts on studs - that hold the torque converter onto the flex plate were loose - one nut was missing. Tranny had been rebuilt by previos owner - or a shop - everything was loose. Not just the torque converter, but tranny mounts, even tranny to engine bolts. Everything was finger tight!
A torque wrench cured the troubles.

Crawl under and look - hopefully it's that simple.

Another similar - my Chev PU - has a vibration too - "sometimes" too. But the exhaust is routed a little too close to the crossmember - rattles, sometimes feels like the world is going to end. Easy fix, just haven't done it yet.

Inside the engine - it's pretty hard for something to go bad and vibrate like that - you'd have other symptoms along with it.

But - maybe letting it get worse will be a "have to."

Let us know.

 

[SteveInColorado]

I vote for the harmonic balancer. If you get a good clean mirror and a flashlight, you can do a good inspection on it. I've actually seen a couple Fords that were still intact, but the outer ring turned on the rubber. Threw them out of balance, but not a lot of visible evidence. You'd never be able to tell without looking REAL close.

After that, I'd agree with the flexplate or torque converter thing. Timing, maybe, but nothing else engine related should be able to cause it. A broken motor mount normally shows up in my experience with a load change.

Steve.

 

[Guest]

Well, after reading all the excellant replys, I'll try my two cent attempt at helping. Have you checked the idler pully, i've seen those go bad. Also if it has air, check to see if your compressor may be bad. Also if the computer check didn't show it, check the o2 sensor. That's all I can think of right now. good luck. Let us know if you find the cure.

P.S. Look at the alternator. If the problem kicks in and out, it could be the bearings on your alternater.