Engine Vibration

Hello,

It sounds like you have a balance shaft drive gear that is stripped and not running the shafts here is a diagram of what I am talking about below. Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.

I cannot find a picture of your harmonic balancer to know which style you have. Most have an outer ring that is glued to the center hub. Many years ago those lasted the life of the vehicle, but now, for some reason, it is somewhat common for that jelly to let go and the ring can spin on the hub. The place where that usually causes a problem is when there is a timing mark on that ring. That puts it in the wrong place.

Some engines are "externally balanced", meaning there are two counterweights they could not cast as part of the crankshaft. Instead, you will find a small weight welded to the torque converter or flex plate, and weight added to the hub of the harmonic balancer. The only way the heavy spot on the harmonic balancer could shift is if the keyway was broken apart or the key sheared off to allow the hub to rotate on the snout of the crankshaft. That is not common, but eventually the balancer would slip so badly that the serpentine belt would stop driving the generator and power steering pump. You would also feel the slop when you tried to wiggle the balancer.

Some harmonic balancers, mostly on import engines, have the pulley for the serpentine belt cast as part of the outer ring. On those, if that ring slips, eventually it will burn the bonding material away and fall off.

The clue to a mechanical imbalance problem is the vibration will change a lot with changes in engine speed. At idle you might not notice any problem, but at a certain higher speed, (the harmonic), the vibration will get real bad. At a still higher speed it may be less noticeable. Think of the pendulum on a grandfather's clock. There is only one speed at which it takes very little energy to keep it swinging. You have to exert a lot more force to make it swing faster or slower than its normal speed. A crankshaft bends in the middle due to the forces put on it by the connecting rods. There is a happy speed that is its natural speed, just like the clock pendulum, at which very little energy is needed to keep that occurring. However, the actual energy being input by the connecting rods stays constant, so in effect, way more energy than what is needed is being put into it. (As a point of interest, big block Chevy engines that are run real fast, as in around 7,500 rpm, often break into three pieces on the race track due to that bending along with the use of special lightweight harmonic balancers and flywheels). If your engine's happy speed where the vibrations occur is 700 rpm, every multiple of that is a harmonic, meaning the vibration will be worst at 1,400, 2,100, 2,800, etc. Rpm. The harmonic balancer is weighted and designed to dampen those vibrations, and they do a real good job. Even if they did not, you won't break a crankshaft because the forces being put into it are nowhere near what is encountered in a race engine.

You need a professional's opinion. If this only occurs at idle or low speeds, a stuck-open EGR valve will cause rough running. Many engines do not use EGR valves so you need someone who can look at it and feel the vibration.

In the early 1970's Chrysler had some muscle car engines that used externally-balanced crankshafts. They were famous for excellent parts interchangeability between years and models, and this included the ability to install the wrong harmonic balancer and / or flywheel for the crankshaft being used. That resulted in an irritating vibration that some people just lived with. For your problem, it would be obvious if the problem developed right after a part was replaced. Since that is not the case, a broken part would cause other symptoms besides just a vibration, so you have to look for things that does not apply to. For example, torque converters lock up at highway speed for better fuel mileage. If that lock-up clutch was slipping, you'd have a noticeable chatter for one or two seconds when that occurred; typically around 35 - 40 mph. Tapping on the brake pedal will make that chatter occur again.

A cracked hub on a harmonic balancer will cause a knocking noise that will quiet a little if the engine is run without the serpentine belt.

As I recall, your balance shaft is run by a pair of gears so that is not likely to get out-of-time on its own. You mentioned that was checked, but it takes more than just looking at the shaft. The timing marks must be checked. If it were possible for something to jump time, the equivalent of one tooth off on a balance shaft is enough to cause a noticeable vibration.

You can also try disabling one cylinder at a time to verify it is not a misfire causing this. If you find one where there's no change in how the engine is running when you unplug an injector, ignition coil, or spark plug wire, look closer at compression and camshaft lobes for that cylinder.

I had a major house fire two years ago so I do not have internet access at home. I drive into town, usually every other day, to see how you are doing. Do not panic if you do not hear from me right away.

Awesome in-depth and thorough answers CARADIODOC! Keep it up! We really appreciate you.

Renee
Admin

Thanks for your addition. Your dandy photo shows that this is yet a third design. Most of the trouble comes from those that use the outer cast iron ring as the pulley. That is bonded to the hub, and that gel can let go, then the weighted pulley can rotate on the hub. Older balancers used a non-weighted one-piece cast iron balancer with a stamped steel pulley bolted to it. It looks like yours is a one-piece design with an offset weight pressed onto the hub. Just another way of doing the same thing.

When was the last tune up? Is the check engine light on?

Since it has been tuned up and there is no check engine light, it leads me to question if the transmission is causing an issue. When under a load, you feel the vibration. When your foot is off the gas, it's smooth. It almost sounds like the trans isn't disengaging properly and then slipping.

Without the light, it becomes basically a guessing game from my point of view. Have you had anyone look at it yet?

Being that the engine top has been rebuilt, there are a number of variables which need to be double checked for accuracy during assembly. You may not have a trouble code (yet) because the OBD II monitors have not all yet completed their system tests, and some monitors need two complete drive cycles before they turn on the MIL. Furthermore, if a certain monitor fails, subsequent monitors and tests will not be carried out by the PCM during drive cycles.

My first step in your troubles would be to double check the "simple" things such as fuel pressure, do a cylinder compression test to make sure all cylinders are within about 10% of each other. Double check the spark plug cable routing. I've done many engine rebuilds and have learned that rushing through the last "easy" steps in anxious anticipation to hear the engine run results in making simple mistakes like running the spark plug cables to the wrong cylinder(s).

My second step in your diagnostics would be to double check your assembly. If this includes disassembly to verify components, you may have to tear the engine down a bit to confirm assembly accuracy.
Verify the cam synchronizer installation; you don't need a special tool. Visit: https://www.2carpros.com/articles/mitchell1eautorepair-car-repair-manuals and follow the steps. Very easy.

I wouldn't recommend taking off the heads again. Remember that the head bolts are Torque-To-Yield which means they stretch when torqued down. I've re-used TTY bolts one time without trouble. But the second time they are loosened and torqued to final value, they risk breakage. Then you're in real trouble.

You didn't mention the engine's initial operating condition before you installed the remf injectors. The excessive fuel you describe (read: cat.conv's red from heat) may have damaged the O2 sensor(s). Temporarily unplug them and see if the engine runs any different.

Remove the MAF, spray some brake cleaner to the two wire elements in hopes to remove any dust/contaminants. Blow dry with shop air, careful not to direct a full blast towards the delicate wire elements. Let the brake cleaner do it's job. Use the shop air to just make sure they are dry.

Disconnect the fuel line downstream from the filter, jump the fuel pump relay "load" side to run the fuel pump and get a quart-size sample of fuel. Any water in fuel? Note the quantity being pumped, too. Your quart container should fill up within about 30-45 seconds. Any less may indicate a clogged filter. Remove the filter, repeat the step. Note any change in quantity being pumped.

Ensure the EGR is closed during idle.

If you do succeed in getting the engine running well enough to drive, hook up a diagnostic scanner (if you can get your hands on one - - and I don't mean the cheepie type which just display trouble codes), drive the car, and have an assistant monitor the monitor(s) as they change from incomplete to complete. If you succeed in having a monitor complete it's cycle and you are lucky enough to have it display a fault code, immediately research the P-XXXX code and try to pinpoint the cause. If your O2 sensors are operational, keep a close eye on the LongTermFuelTrim and ShortTermFuelTrim (LTFT and STFT) values. High positive values may mean you have a vacuum leak. Out of range negative values are possible signs of excessive fuel pressure, or leaky injector(s).

...would really like to receive follow up on your accomplishments or failures. Hope this helps.