Idle Vibration Issue m1008

[CULPEPER]

Hello all. I have a 86 m1008. I have a high humming resonance sound when at idle. The vibration can be felt mostly on the air cleaner and seems to be less in the front of the motor. When it is at idle the noise that resonates in the cab and in the box of the truck is super anoying. I have taken off the bell housing to inspect flywheel for cracks...turn up void. The harmonic balancer appears to be intact without separation. There is clearly an out of balance situation, but I cannot tell what it is...based upon a visual diagnosis with a flashlight of the flywheel and harmonic balancer while it is running. There is just too much vibration. Engine mounts are intact also. I would appreciate any direction someone could point me and others that may have this issue. Problem does seem to subside with additional throttle...at least the noise stablizes but still noticable. What should I be looking for?

 

[davo727]

Dont they all do that?

Sorry, Anyway maybe start it and one at a time loosen the fuel line nut at each injector for a second or two and make sure you get an rpm drop as that cylinder stops firing. If you loosen one and the engine tone doesnt change then you found a dead cylinder.

 

[CULPEPER]

Thanks for the reply. This is my first cucv and I am going to try and post a youtube video of the truck running. Also, I am going to try loosening the fuel lines individually to find out about a possible dead cylinder. Incidentally, the truck doesn't show any blow-by and seems to run out fine on the road. Just at idle speeds it is super resonant and vibrational. Thanks again!

 

[Rustmaster]

"it is super resonant and vibrational"
That is kind of how mine was when i got it. I ended up with a non-typical harmonic balancer issue. Mine ate the super small "key" that is in the key-way and then it seemed you could feel every cylinder...Lump,lump,lump ect. Mine felt tight until it fell off the dam crank on the way home from buying it. A total trip of 11 miles. I hope it isn't your case.

 

[CULPEPER]

[media]http://www.youtube.com/watch?v=CkTjyTMpKAs[/media]
Check out the youtube video of the vibration viewed from the bed of the truck. I did a second video but it didn't upload. It was of a screwdriver lightly held by the rear with the tip bouncing popping up from the aircleaner while truck was running. I am going to go out and check around more since there is some daylight left to work with. Thanks again.


Update: I was out there circling this thing like a rabid dog getting ready to strike when I decided to do an oil change and further inspection of the vehicle. I did find out that the power steering pump had lost a bolt and was somewhat cocked and was sheering it's way through the mount. I disconnected all the belts and fired it up...still the vibration is there...no surprise. So the vibration is loosening attachments...yeek! I felt the engine mounts again and they are still solid and doing their job. You can feel the vibration in the driveshaft(drivetrain) but not on the frame.

I havn't checked each individual cylinder yet to find a dead one, b/c I would think the motor would run like crap and there is no blow-by. Something is purely out of balance. I think it's the torque harmonic balancer or something? Hopefully this helps you all out there that know what they are talking about.

 

[SmokeyDod]

I know you probably have done this, but use a pr. of pliars and tighten the two wing nuts holding the air filter on. Sometime its hard to get them tight enough with just your fingers. Try it-you might get lucky before you start doing more serious things. Hope it works. Smokey

 

[CULPEPER]

Okay...it's not the harmonic balancer...but it did need to be changed after I took it off it had some dry-rot and a couple chunks missing on the blockside. Nonetheless, didn't help. I did notice that the drivers side engine mount is actually touching the frame mount...on the rear side of the mount. It is not suspended by the rubber. I am getting new mounts tomorrow but I wont' be able to tackle that until the weekend. Wish me luck...and I'll still take advice it you have some!!!!!! Actually still need to figure out how I am going to change them.

 

[doghead]

I would think that the mounts touching metal to metal would do what you show in the video. I bet you found the problem.

 

[army98]

Do you have a roung paper or cork gasket under your air cleaner? Mine doesn't and it vibrates bad, I can feel it all around the truck, If my hearing was not bad I would probaly hear it too lol.

 

[motormayhem]

Sounds like you hit the resonance frequency of some sheet metal.

 

[2mtrucks]

My air cleaner bolts were not tight enough also and made much noise than I would ever have attributed to a loose air cleaner.

 

[CULPEPER]

I replaced one motor mount. Still debating on the next...passenger side...looks like a tight fit. But it looks good no metal on metal there. Incidentally I found out that they use small block engine mounts on these. Don't ask for the 6.2 or you'll find out later that you needed the small block mounts. Still vibration...posted a couple new threads on other issues I have found.

Not the mounts, not the balancer. Thanks again!

 

[AllenEM]

Check to see if your exhaust is up against something

 

[IBEZKUM]

My truck makes that noise, when I first start it and its in high idle, goes away when the idle kicks down,
Its the skid plate on the fuel tank. I also had the air cleaner issue, it only had one wing nut. Hope this helps

 

[CULPEPER]

That's the thing. I doesn't do it in the initial startup and high idle. When it kicks down...then the vibration starts. I have tighted the wingnuts and the skidplate for the tank does rattle once in a while. I am very appreciative for all your help.

 

[WillWagner]

What is the RPM when it vibrates? The idle might be too low. If it doesn't vibrate any where else in the range from off idle to rated RPM, there most likely isn't an engine issue. Raise the idle 25 or so RPM and give that a try.

 

[Wolf.Dose]

Did you check whether the starter is propperly tight. Depending on rpm this sometime gives some vibrations which will be in a resonance with a non propperly tight air filter housing which will create unknown noise. If the tread of the studs is used, means the nuts can not span the air filter cover propperly, use some washers to ad some treat gain.
Wolf from Germany