Vibration Under load 98 sohc xlt

[backroads]

Here's the story. Wifes 98 Xlt with 184k started having various issues(see other posts) got her a 06 v8 Limited, I get the 98. So after putting lots of work and money into it, latest being new ball joints , tie rod ends, brake pads, new rear driveline ujoints, rotating tires.

There's still a vibration under load, makes the exhaust shields rattle, but not horrible. Next thing I'm goning to try today is remove the front drive shaft ant test drive it.

In park revving the motor doesn't cause any vibration, just under way, if I accellerate slowly it does't do it.I'll post results later today, but in the meantime any ideas would be most helpful.
Hoping it's not tranny related, it has been rebuilt 2 times, the last time seemed to be good but it's been 50K since then.

Thanks for any input.

Backroads

 

[llamaking122]

Have you checked the U joints?

 

[backroads]

Replaced rear driveline u joints, and removed frond drive shaft with no change. The only thing left is the tranny, or t-case, but the tranny shop says that is not the cause. I'm thinking it's the tranny, under load something is vibrating.

Anyone?

 

[RomeovilleIL]

Check the transmission mounts and front differential mounts. The bolts may be tight but the brackets broken loose from the frame. Have to lift the truck by the frame and look to see if there is any movement.

 

[backroads]

Checked all the mounts, and the tranny shop checked them also, so that's not it.

Could it be an injector thats going bad?Could an injector put out the raght amount of fuel for light throttle operation, and then when you step on it a bad injector not be able to put out any more fuel kinda acting like a half dead cylinder causing the vibration at open throttle?

Thanks

Backroads

 

[swshawaii]

Have you scanned for trouble codes?

 

[backroads]

There's no check engine light, I thought if there is no check engine light there's no codes right?

 

[backroads]

Just did a compression test and all 6 are right at175 lbs.
Replaced all plugs and wires.
Replaced both rear u joints
Removed front drive snaft
Replaced upper and lower intake gaskets
Can't see any vacuum leaks, or bad wiring
Still the same problem is there, vibration when accellerating. Any ideas?This will be about my last night of trying to fix this, then it's going to the dealer.
I'm thinkint tranny problem, injector problem, or vac leak ,or???

Thanks
BR

 

[Kevlar7R]

We need to figure out if it's driveline or engine. Not sure how to explain it, but you can feel the difference sometimes. For instance, does the vibration happen at a particular speed, or a particular rpm?

If you put the truck in a different gear, like say 1st or 2nd, does it still vibrate at the same speed?

 

[Runnin'OnEmpty]

A vibration that's load related and not speed
related, might be a misfire. Since you've already
replaced plugs and wires, I'd take a look at the
coil pack. You can check the resistance with an
ohmmeter; each coil pair should be nearly equal.

IIRC, the values should be around 12-16K ohms,
measured between the primary and secondary
terminals.

 

[Runnin'OnEmpty]

One other thing to try, just for laughs.

Disconnect the RFI condenser that's
connected to the coil pack, for testing
purposes.

I once had one of these shorting out under
load and it drove me crazy trying to find
the problem...

 

[backroads]

I'll check the coil pack tonight.
BR

 

[backroads]

I checked the coilo pac. The secondary resistance is supposed to be 6.5-11.5 K, I have 12.5k on all the secondary pairs.
That could be it! Its 1k ohm too high, would this cause it to miss on acceleration? I think it could. Anyone? And thanks to all who have tried to help out.

BR

 

[Runnin'OnEmpty]

I checked the coilo pac. The secondary resistance is supposed to be 6.5-11.5 K, I have 12.5k on all the secondary pairs.
That could be it! Its 1k ohm too high, would this cause it to miss on acceleration? I think it could. Anyone? And thanks to all who have tried to help out.

BR

I think your coil pack is OK. Those values are close
enough to specs to not cause a misfire.

Since you have the multimeter out, you might try
testing the TPS. A flat spot on the TPS might cause
a momentary lean condition and feel like a misfire...?

Do a search to find the procedure. You're basically
looking for a smooth transition from about 1v to 5v
while the throttle is being opened.

 

[backroads]

Checked the coil pack, and it's ok. Tomorrow I'll test the tps.

 

[backroads]

Update
The vibration is still there but it doesn't do it just under load or when accelerating. It does it in park or neutral too.In park or neutral if I slowly increase the throttle the vibration starts at 2300 rpm and goes away at 2700 rpm.
So what could it be? I guess I'll start diagnosing by taking the serpentine belt off first.
How do I check the balancer?
I guess it could be a loose flexplate, or something inside the motor or tranny.
Any suggestions on what it could be.

Thanks

BR

 

[Kevlar7R]

Based on the mileage of your engine, and the fact that is engine speed dependant only, not throttle, load, or vehicle speed, I'm going to guess harmonic balancer.

The harmonic balancer is 2 pieces, an inner core and an outer pulley, held together by rubber. The relationship between these 2 pieces is tuned to dampen the harmonic vibrations inherent in the reciprocating engine parts. With age, that rubber can shrink, changing the harmonic characteristics of the balancer.

I had this problem on a dodge v6 pickup. Replaced the balancer, all better. Im actually surprised it's not a more common problem.