Well I finally resolved my drive line vibration that I had at 70MPH. It was the driveshaft after all.

Now I appear to have an engine vibration.

It is a small but noticeable vibration mainly between 4500 RPM and 5500 RPM. It is most noticeable when driving it and accelerating hard from 4500-5500 the RPMs in 2nd and 3rd gear. It feels like the vibe comes in a 4500 and falls off at 5500 RPM. I dont feel any vibe at leading up to 6.5K RPM redline. Also the engine is running very well with no other ill effects. No knock counts either.

I can also feel this vibe with the car parked, clutch in and free revving it to the mentioned RPMs. Much less noticeable with the car still than while driving it.

I currently have 10K on the motor and this absolutely was not present from the time it was brand new up until recently. I just noticed this in the last week or two.

The only engine work I have recently done is replace the water pump drive seal in the timing cover, re-lash the valves which are set at 1/2 TPZL, replace the driveshaft, transmission mount. I am confident this vibe is NOT driveline related. It responds to RPM.

I replaced the transmission mount. No change.
I checked the headers and exhaust pipes. Not banging anything.
I check the motor mounts. Look fine.
I check the plug wires. They appear to be on solid.

Any ideas?

 

It can be hard to tell if a Motor mount is broke just by the naked eye. Might want to recheck them

 

Change the plugs

 

Plugs have less than 10K on them. Delcos too by the way.

I am trying to understand how plugs might cause this?
BTW, what plugs do you guys like?

 

I run autolite 104s. I would still check them. Its easy and cheap.

 

almost every engine vibration (that wasn't a misfire) i have had was from the pressure plate or flywheel. almost always.

 

I dont think its a misfire, it just runs too damn strong. But I will replace the plugs anyway.

I am planning on installing a new Monster clutch with new flywheel, once they start selling them for the LT1 next year.

Just to make me feel better, what are the chances that this might be something rotating assembly related? God I hope not. It was well balanced before the motor was built 10K miles ago.

I also have a ASP underdrive pulley and I know for a fact that the outer ring has occasionally rotated in relation to the inner section of the hub. I once had marks that lined up and now they dont. The hub does not show any signs of damage and appears to have no run out.

 

if there was an imbalance internally i would expect more to be going on, like low oil pressure or knocking. if that is not the case best bet is external. why not scan the obd to make sure you don't have a miss? the engine can still feel strong even with a light, high speed miss.

 

You may want to disconnect the serpentine belt and see if that helps. This way you can isolate the problem to the accessories or engine/flywheel.

 

I appreciate the help you are providing.

I am OBD1 so its a no go on miss detection. No codes are looged of any kind. The BLMs are 128 +/- 10 points in any given cell. Most of the time, they are very close to 128.

It seems that I have a bit more 1500-2000 RPM low load bucking or cam surge than usual. And the idle is just a tad more bouncy than normal.

 

Will do.

 

no problem dude. just remember, if it is a rotating assembly imbalance, your bearings are going to take the brunt of it. same goes with even small misfires. if you feel it, your bearings really feel it. then your wallet feels it. i am dealing with that right now. i am not looking forward to pulling this engine at all.

 

I say change your plugs too. However, I wont back up the autolite 104s. I ran them and they crapped out way too soon. Same with the Delcos. I went back to using the old tried-and-true NGK TR6, after that my plug troubles disappeared.

 

Got some TR6's. I will try to get them in tomorrow.

 

Hey:

Did you change to a poly tranny mt? And what type of motor mounts do you have? The only 3 Times I have had A off beat vibe in a car was when I changed the tranny mt to poly and had not done the motor mts yet and had a tunnel mt torque arm, I could feel a buzz about 5,000 rpms, it annoyed me till I changed the motor mts later, and now I'm used to it. The other time was the front balancer got loose it got worse over a week, it wasn't bad then it got more noticeable as time went, caught that in time. and last is when a stall converter started ballooning, but that was all RPMs after 3,500. I thought I would share with you as it might help point you in a direction to find the problem. How is your clutch, any problems with it? Are you absolutely positive its not in the driveline?

Dub

When In Doubt Do Without

 

I had missfire at the same rpm.and was vibrating.check the transmition mount.I replaced my with 2002 model mount.

 

I am currently using a new aftermarket rubber transmission mount. Even the previous mount was rubber.

Positive its not drive line cause it happens, while driving at the exact same RPM range. It seems to closely follow the torque curve.

Regarding the balancer. Like I mentioned before, I know for a fact the the out ring of the ASP under-drive balancer has spun some in relation to the inner part of the balancer. I know this cause I marked the balancer at #TDC to help me set the crank position to adjust valves and replace springs. One day I put my mark on the balencer at 12 O'Clock and nearly dropped the valves into #1 cylinder cause the position was not up. This told me that the balancer has spun some.

I called ASP this morning and they are confident that the balancer has worn and now the balance is slightly off causing the problem. I am going to pull it and send it to them and they are going to rebuild it for $25.00.

I will also put my stock balancer back on tonight, after I buy a new fan belt, and try that out. If the vibration is gone, then clearly its the ASP balancer. This ASP balancer was bought used so it may have had a great deal of use before I ever got it. Hope thats the heart of the problem.

 

How did you cure the misfire?

 

Could it be a tire, On my xterra it is doing something similar. I just replaced the brakes and now when im on the pedal the steering wheel has a vibration.

 

i think i have a slight misfire also! But i get alot of vibration, due to poly trans mount and also my balancer shakes i guess i need to replace it.

How do you fix a slight misfire? it cant be plugs cause mine are brand new! i use BOSCH quad firing thingy..