Drivetrain Causing "out of balance" feel?

[STiffler]

I just bought Sy #1616 a couple days go. It has 39K original miles, and it's been well cared for...it runs beauifully. But I've noticed under hard accelleration, there is an out of balance feel. It almost felt as if the motor was poorly balanced, but in another post, someone suggested that the SyTy's have inherent drivetrain vibrations.

The motor feels perfectly smooth under other conditions, so that makes sense.

So if that's true, are there any fixes? What specifically in the drivetrain causes it?

TIA,
Terry

 

[gkrcr882]

Re: Drivetrain Causing "out of balance" feel?

The 90* V6 does have a tendancy to be a bit harsh at higher speeds, especially on the old pre-balance shaft motors. I know that on my S15 if I accelerate hard and make the engine wind out it will vibrate the truck pretty well. If it seems excessive, try checking your motor mounts, they may have deteriorated over time.

 

[STiffler]

Re: Drivetrain Causing "out of balance" feel?

I'm now fairly confident that it's no the motor. Reving it to the higher rpms in park (>4K) still feels smooth.

I did discover another problem though...it seems to misfire/cut out at around 4K rpms. I noticed it while bringing the rpms up in park, and also...it'll cut out at the same point under hard accelleration. I've only got on it a few times...it seemed fine while accellerating in 1st gear, but it totally cut out (almost like the fuel cut off) in 2nd gear. It also seemed reluctant to shift...and like...wouldn't go above aobut 5K rpms...w/o shifting.

Could this be the boost exceeding 14.7 psi? I've noticed it spike a couple times too...(not always associated with the balking shifts).

 

[gkrcr882]

Re: Drivetrain Causing "out of balance" feel?

Do you know the last time the sparkplugs, cap & rotor, and wires were replaced? Another thing to check is the timing, although it would cause problems at all speeds. You might have some knock if the engine cuts out under load- be sure your running premium, and the ignition system is in top condition. Only other thing I can think of is the fpr might be old or shot, and it might not be supplying ample fuel at higher speeds under load, so its causing it to run lean and cause knock. Ideally you should get or borrow a DataMaster to see what the truck is telling you and why it might be happening. Good luck!

 

[STiffler]

Re: Drivetrain Causing "out of balance" feel?

Do you know the last time the sparkplugs, cap & rotor, and wires were replaced? Another thing to check is the timing, although it would cause problems at all speeds. You might have some knock if the engine cuts out under load- be sure your running premium, and the ignition system is in top condition. Only other thing I can think of is the fpr might be old or shot, and it might not be supplying ample fuel at higher speeds under load, so its causing it to run lean and cause knock. Ideally you should get or borrow a DataMaster to see what the truck is telling you and why it might be happening. Good luck!

The plugs, wires, cap and rotor have about 500 miles on them, according to the seller. And I don't doubt it...they look new. The fpr is newer too (adjustable), so it's probably okay. But I have a new Ty buddy in the CO Springs here...we met today, and he's a good guy. Actually, he just offered to do some "DM" runs (I didn't know what that was until you mentioned the Datamaster), but right...that's the thing to do...

Haven't heard any knock, but that's totally unreliable. The Scanmaster that I had in my GN would pick up knock (a little...of no serious concern) when I never heard it. So...I'll be interested to see if the DM is picking up any knock.