Engine Vibration at High RPM

[STiffler]

I just bought #1616 yesterday. It is absolutely beautiful, with 39K original miles. Besides a couple of minor problems (radio on switch is faulty, left rear speaker not working, oil pressure switch spastic/sticks), I absolutely love it.

I've owned several Grand Nationals, and the last one was laying down about 450 whp at 20 psi & 96 octane. Actually, I just sold the GN the other day, and decided I needed something else cool to quell the heartache. One of the reasons I mention it, is because I'm familiar with the smoothness of the 3.8 liter GN V6. They don't idle especially smooth, but rev fairly smoothly, without the out-of-balance feel that I've felt with other cars in the past (like my buddy's '83 Mustang GT.

With my new Sy...it feels very smooth at idle, and lower rpm, but when I get on it (close to or at WOT), it feels out of balance (a slight shaking of the whole vehicle) in the higher rpm range (>4K rpms).

I'm curious to know if this is an inherent characteristic of the Sy/Ty motor.

 

[TYTILIDIE]

Re: Engine Vibration at High RPM

No its not. Ill say that the trucks are wellknown for suspension or drivetrain vibes, not really so much with motor. Except at idle ofcourse these thins can sometimes be shaky.

 

[STiffler]

Re: Engine Vibration at High RPM

No its not. Ill say that the trucks are wellknown for suspension or drivetrain vibes, not really so much with motor. Except at idle ofcourse these thins can sometimes be shaky.

Ah...that was my other thought...thinking that maybe the cause was somewhere in the drivetrain...T-case, or front diff?

 

[Don W.]

Re: Engine Vibration at High RPM

:2cents: Well if you haven't given it a basic tune, including checking for vac leaks, I'd suspect a slight (random?) miss as well. Although with your GN experience you can prolly tell the difference.

Maybe an engine accessory is going south on ya?

 

[STiffler]

Re: Engine Vibration at High RPM

Sigh...I'd love to give it a basic tune...or at least start with changing the spark plugs. Man, I thought the GN's weren't the easiest, but looking on the passenger side, it took me over a minute just to find them with my eyes! HITF (how in the f**k) do you get to them?!!! Looks like taking of the CAC would make a lot easier, but that sounds like a moderate hassle as well.

This truck looks to have been very well cared for, but I think the seller did mention that it could use a tune. But what does that entail? The GN's have a coilless ignition (very nice), but I see the ol' distributor on the Sy. Besides a fuel filter, plugs, and timing check, what else would a basic tune include?

TIA,
Terry

 

[Don W.]

Re: Engine Vibration at High RPM

I personally find it easier to just take the wheel wells out. Leave CAC alone. Once you do that plugs are rather easy. Basic tune? Opinions vary, but at a minimum I'd suggest plugs, wires, cap and rotor, set timing.

 

[TYTILIDIE]

Re: Engine Vibration at High RPM

If you dont want to remove your wheel wells, you can just go in from the side and do it.

 

[kwick6]

Re: Engine Vibration at High RPM

Vibration could be from your front propshaft. If your still on the stock propshaft, I suggest replacing it with the Gilbert shaft just so you never have to worry about it again. You can do some searches on here for Gilbert to see why its such an essential mod to have.

Gilbert Propshaft

For a basic tune-up, do plugs, wires, cap/rotor. If your into one stop shopping, you can get them on my site.

Tune-up kit

Make sure that whatever mods have been done to the truck aren't doing any damage, ie. the wrong chip, timing isn't at zero, etc.
A laptop with datamaster(scantool) will give you a good idea on the state of the tune.

To access the spark plugs you'll want a variety of 3/8" extensions, but the most important thing is a 3/8"drive spark plug socket w/built-in swivel(just an example, most local autoparts stores stock them)