my car is and 87 berlinetta 2.8 mfi. i've been trying to figure out why my car vibrates more then it should (specially at idle). today i was looking at the harmonic balancer and i think it might have been damaged when i put the engine in. (you can see it wobbling slightly when the car is running) would this make the car shake a little? it's nothing too major but at idle thesteering wheel vibrates and the corners of the dash board vibrate up and down. anyone have any ideas? thanks for any help
(it's not the engine mounts, tanny mounts, bellhousing bolts) the exhaust is loose and the cat is gutted and a couple vacuum lines need hooked up.

Hi did you fix the vibrating already. mine is doing the same but I haven't found the cause. My harmonic balancer wobbles the same. Did you change it? Thanks

a loose harmonic balancer isn't helping any
and busted up vacuum lines are also contrbuting.

maybe flywheel??? I know they have weights on them and if u use the wrong flywheel it will vibrate.

Maybe u have a part of the engine hitting against the frame?

My bird pulls 14,5 inch HG. in idle vacuum. I think thats still low. When I bought it it had more lines disconnected than connected. I replaced all the vacuum hoses. It s just a guess but if the outer ring of the harmonic balancer moves then I m adjusting the wrong timing. Could that contribute to the low vacuum to. The compression is fine with all cylinders. It s kinda hard getting parts in Europe so I m guessing around a lot. Thanks guys.

A wobbly balancer will cause the engine to vibrate. Our engines are internally balanced...weights on the crank. The balancers are neutrally balanced. BUT, if it's damaged and wobbling, it WILL throw your crank out of balanced, WHICH IS VERY BAD. Fix it ASAP. A wobble will make the entire crank wobble, which will grind up and trash your crank bearings and can even break a crankshaft in half.

Vacuum leaks, no matter how minor, will also cause engine shake and rough idling. I had a TINY vacuum leak from my intake manifold and the car would idle really lopey sometimes....soon as I plugged it, it stopped sounding like it had a cam.

So, replace the balancer with one of the right size that is neutrally balanced, and plug all of your vacuum leaks. Even if it means bypassing sensors that arent connected right, just plug the leaks to see if it helps. ANY vacuum leak will cause problems...

Thanks again. i will order the balancer immediately. Thanks.

Replaced the balancer and it didn t change much. Do you mean by "it sounds like it has a cam" that it has that deep sound like an old musclecar. Cause mine sounds like that even though it has a new replacement muffler on it and there is nothing wild installed in the engine. Thanks for a reply.

No, by cam-sounding, I mean it was 'lopey'. Not a smooth, steady running...sounds like it's misfiring a little or something... You'd have to hear it to know what I mean.... And the exhaust note that has that musclecar sound...welcome to the third gen V6 F-body. This particular motor produces a very muscle-car sound for being only a V6...I always liked that about it.

Does the balancer/crank pulley wobble since you replaced the balancer? Maybe the crank pulley itself is bent if there's still a wobble. If that's the case, and you plan on mildly modifying the car at all, I'd buy a set of underdrive pulleys. That'd take care of your wobbly crankshaft pulley right there.. It comes with an alternator pulley too but most people agree not to use it....turns the alternator too slow I guess.

I like the sound too. The wobble has disappeared with the new balancer only the car shakes still a lot. Especially around 1500 rpm and in idle. It doesn t make an unusual sound though. And I replaced really quite a lot of parts: distributor and cap, wires, EGR-Valve spark plugs oxygen sensor fuel filter PCV-valve air filter harmonic balancer and most of the air hoses. The compression is high due to carbon buildup and the vacuum is low around 15 inch HG.The accessories all turn freely only the serpentine belt is probably stretched. Two strange things show up when I hook up the Autoxray though: PS high and ATM in high gear, TCC not locked. It's just a guess but could the faulty 4th gear switch trick the ECM into believing to change the fuel curve as if on the highway? But then the fuel in the car is probably bad as well since it sits for two years. The injectors all work at least by sound (stethoscope) and fuel pressure is within limits. There are no spark wires crossed and the timing is adjusted to specs either. The next thing I will look at is the flexplate I don t think so but maybe some has changed it and installed the wrong one. Or maybe the engine mounts are broken but they don t appear to be so. I forgot to check the timing chain test last weekend when I replaced the distributor. Oh I forgot, the mechanic that sold the car worked at a GM dealership in Linz he couldn t fix it either so I kind of take it personally to get the car running smooth again. Thanks.

TCC not locked is normal. It won't lock until ~40-45 mph usually. Mine locked dead at 40. As far as "PS high and ATM in high gear".....my only interpretations of that are something with the power steering, and...the car thinks the transmission is in 3rd or 4th gear?? I really don't know..sounds odd to me.

You're replaced a pretty good amount of pieces there. Try changing that fuel out--old, bad fuel can cause all sorts of problems. That might just be your ghost in the machine right there. But low vacuum---I'm not sure what a normal reading is, but if that is low, check all your vacuum lines...those suckers are everywhere. And check for any vacuum fittings, etc. coming out of the manifold that haven't been plugged.

Normally vacuum should be around 16 to 19 in HG I think. Right now I m looking forward to get the car to my place ( it s at my girlfriend's now) which is about a 40 miles drive. (girlfriends and dead cars don t mix all too well). The ride should empty the gas tank enough I hope and hopefully it will run smoother after that. Thanks again.

I have just added a brand new flexplate to my list of replaced parts. Helped a little at best. Still vibrates like hell and I m out of ideas.:hail:

Back to basics...dont know why I didnt think of this last time... Does your motor shake a lot? Maybe you've got a bad motor mount and it's transmitting the vibration through the car.

Doesn't low oil cause the engine to kinda vibrate more than it should? I could be wrong.

Never heard that specifically...I suppose it's possible, but I can't really see how unless it's low to the point that it's not getting proper lubrication...

Visually the mounts seem to be okay. When running the driver s side one moves a little more than the other one but not much. We hooked the car up with an exhaust gas examiner and everything seems good too. Unhooking the MAF sensor doesn t change anything either. The same is with the oxygen sensor.

I have a couple of ideas. first is to double check the spark (distributor) timing. If off enough it can cause all kinds of problems.

To further isolate the problem, unbolt the torque convertor and push it towards the rear of the car (away from the flex plate). Start engine and see if vibration is still there.

If no vibration, then it is either the convertor or the transmission pump.

If still vibrates I'd do a search here to see if the flexplate for your engine should have a balance weight. I believe there was a changeover someplace along the way.

Doing a compression check is also a good idea. May have a dead cylinder from a rounded cam lobe.

RBob.

Thanks for your reply. The thing is that I did all that. The only thing I cannot identify is the builing year of the engine. I took the engine number to my local GM dealership and they didn t know what to do with the numbers. However it is not the original engine in the bird anymore. Since the transmission was built in 1991 (the Bird is a 1989) my guess is that the engine is a 1991 as well. But from the intake plenum it has the 2.8MPFI emblem on it. In a thousand years the car might be an interesting find for archeologists.

In your shoes I you do my best to find out what year engine you have. There are a ton of net resources that can help in that regard. Most engines will even have build & casting dates on them.

RBob.

Two things. First, I assume that your vibration problem is when your car is not moving. But if it happens specifically when you are driving and you hit a certain speed, check the drive shaft. Bad U-joints or an improperly balanced drive shaft can cause serious vibration.

Second, I've noticed that low, dirty oil will cause some vibration. Just my opinion.

The vibration is most pronounced at a stand still when the transmission is in N. When I move it in D but stand on the brakes it almost seems gone. When driving it gets back. I have searched the www but couldn t find anything about my engine number: A 090317 AAk. The engine number is stamped at the front of the engine and not on the passenger side which makes me believe that it is not a 1989 since the factory manual says it should be on the pass. side.:hail:

My V6 shakes at idle as well, but I still have more tests to do before I am at the point you're at.

About your engine: I'm pretty sure all the 90 through 92 cars got the 3.1 (LH0) V6 instead of the 2.8, so it has to be an 89 engine or older.

Youre right..they did come with 3.1's. Sounds like the engine and tranny are non-matching though. Why would you put a 2.8 plenum on a 3.1....unless you didnt have the 3.1 plenum! Theyre basically the same motor...just the 3.1 has more stroke, so it's got more torque, tad more hp, and a lower-shifted powerband. Is the new motor full serpentine? Does it have a vacuum or digital EGR? Maybe you can at least narrow its year down by using stupid little clues like that. Assuming EVERYTHING on the motor is OEM style from the same year.

The EGR is the old style and it is an all serpentine engine. The radiator is from a 1991 though. My guess is that maybe somebody tried to put a 3.1 in and make it appear as a 2.8 so nobody (cops) would recognize it since it is not legal where I live.

Yeah if you take dealers numbers cast on a part they rarely match up. I hate that. You would think they cast it on there for a reason. Oh well.

On to the shaking in my car...I remember back in the day my motor was fine, but after the dealership rebuilt the bottom end it shakes at idle. Long story, but the bottom end had a blocked oil bearing and so went the bottom end. They replaced the affected parts, put in a new crank. Since then the engine shakes at idle. We have fixed and replaced nearly everything, including the balancer, new cam, vacuum lines, tuned it up, rebuilt and shimmed distributor, blah, blah, blah... It has helped, but its still there.

Hey Nixon,
I'm starting to think someone did not balance the bottom end before it went back together. I wonder if that could cause vibration? If so I'm thinking about a 3.4 short block for now!

I suppose it's definitely possible that the crankshaft wasn't balanced properly before it was installed...that would definitely give you a vibration/shaking. I imagine it would be very hard on the crank and the crank bearings too...if the rpms were high enough and it was bad enough, I could imagine it stress-cracking or breaking...assuming the bearings didnt go first. How long has it been like that? Does it vibrate progressively worse as the rpms go up? I imagine an improperly balanced crank would be shaking like hell by the time it hit 3000-5000 rpms.

If I remember right though..you have a fairly radical cam in that thing don't you?? My stang's engine runs cherry and it's got an emissions legal cam but it shakes like a MOTHER if the cam starts catching a pattern.

The vibrating came before the cam. The bottom end was rebuilt 2X by the dealer probably 30,000 miles ago or about 3 years ago. The first time the guy was an idiot and the car's bottom end failed about a year later. They never said what really happened, just that the same parts had to be replaced again. The 2nd guy was great and did it right. Though I don't know it either time the bottom end was balanced. They just replaced the broken and damaged components and put them back in with what was still ok. So who knows if the parts were even balanced to one another.

After the rebuild, the car used to really get ugly at about 65-75MPH on the hwy. Had the dash pad vibrating all over. Then we rebuilt the suspension, new rims and tires, put in the subframe connectors, and I soundproofed. Now the dash is still. I get a vib I can feel at about 70. Past 70 its fine. Before 70 its fine.

But at idle sometimes it really gets shaking. People come up and ask whats wrong at shows its so noticible. Now once we got the timing straight it helped loads, but its still there. Though to be honest I'm not sure how much vibration is even normal. I always thought the problem was theh belt. See somehow I got a serpentine 2.8 w/o a smog pump. In place of the smog pump an idler pulley was supposed to be added to help control the belt, but mine did not come with it. So the belt goes from the alternator to the balancer pulley and slaps like the dickens. People think its gonna fly off. As it is the car can't wear the belt that it lists for. We had to try on belts till we got one to work. Its still a bit too big though. But they do not carry the next size down. W e did find an idler pulley at a junkyard & it will be going on shortly. Anyway, the engine does move at idle and at park.

See we are also thinking with the block potentially unbalanced, its got to be robbing power too! That could also help explain why the car never ran right after the dealer rebuild, power wise. So to fix the situation...we might swap the 2.8 short block to a 3.4. Everthing of mine would bolt right on. That would tame the cam down, restore some bottom end, and the fuel injectors would be a better match to that engine. That should solve the unbalanced crank issue as well. I figured the 3.4 heads would have been better, if my 2.8 were not already ported. To be honest I have no clue which heads are better. Trying to get that answer on the feiro board. Those guys have done alot of 3.4 short block swaps.

Now to mention the way you are saying it could lead to the crank having serious problems, possibly breaking...the 3.4 swap might be the best plan.

Then later down the road when I get all the parts gathered the 3.8 turbo motor will go in, but that is so far down the line. I just can't stand to wait anymore for some better power.

Found the problem. The crankshaft was bent. Killed some main bearings along with it. There really is those days that make your day.

Whew man...that thing must've seen so very high rpms or something to bend that crank... Least you've got an excuse to put a better motor back in....sucks to hear though.

My guess is that two owners ago the bird went into the green and something big hit the crank as the previous owner replaced the oilpan.
Thanks again for your help.

I have an '89 RS w/ the V6, and it does the same exact thing as yours did: vibrating at 1000-1500 RPM, but goes away when moving. Mine didn't start until I switched it over from an A/T to a 5-speed.

Sounds like something was wrong with your automatic. Maybe a bad/out of balance converter....