emessys

Hi,

I recently picked up a 99 Tahoe LT 4WD to replace my 99 Tahoe lost in Hurricane Sandy.

Unfortunately,although the body and interior are terrific, this vehicle does not match the mechanical condition of my original, which was lovingly maintained for 13 years.

Main problem I am concerned with right now is an engine vibration from 1800 RPM to about 2000 RPM regardless of gear. Occurs even in neutral. Above or below that RPM range, the engine is smooth and powerful. Shifts perfectly.

I saw a post from years ago with the same exact problem, but no resolution given.

My usual mechanic, as well as several other shops have looked at the vehicle and given answers that conflict, including torque converter, bad crank, bad motor mounts (checked good by my mechanic), harmonic balancer (replaced...no change). No one seems certain of the cause.

I was hoping, since the same problem has been posted before, that someone else may actually had the same symptoms and an answer.

As things stand, rather than expensively chase my tail, I may have to wait until something fails big time, and then decide what to do.

Any suggestions are appreciated.

Thanks
Ira

in2pro

Welcome to the forum...
might want to check the plugs wires and cap, could be needing a tune up...
also check to make sure the wires are correctly connected, having the right 2 wires crossed could cause the vibration , it should also cause a lack of power but its somewhere to start...
Might also consider having the drive shaft balanced...

oldgoat82

I've seen a failing catalytic converter cause strange sounds and vibration in that range. Is your power or mileage down...any funky smells? Do your cats heat up like they should?

emessys

New plugs and cap and rotor. Don't know what the previous mileage was prior to my purchase.

Initially I was getting very poor mileage (maybe 10MPG), but now it seems to be up to about where my former Tahoe was~ 15MPG. Not great , but livable.

Doesn't appear to be a misfire. No EC like I would get when my old Tahoe would sometimes misfire under load, and that wasnt RPM dependent.

Happens in neutral also, so no drive shaft rebalancing.

Have a bad feeling the engine may be kaput (bad bearing(s) etc, but until it dies don't want to spend a lot of money. If it dies I will have to decide whether to replace it.

If its the torque converter/flywheel it will cost close to a grand just to determine if that is the problem. If I knew for sure I would go ahead with the repair, but of course no one will guarantee that.

Considering the money being spent to recover the house and contents and other vehicles damaged/destroyed in the hurricane, not anxious to spend the money.

Ira

emessys

RE: 2 right wires crossed.

I assume that would cause a constant misfire/vibration across the entire RPM range, not just in the 1800-2000 RPM band.

I also think that band correlates with the engines max torque RPM. That would lead me to suspect the torque converter, except that it also happens when the engine is not under load (neutral) which leads me back to the engine.

Ira

Ira

emessys

No strange smells.

What kind of strange sounds?

The catalytic converters on my old Tahoe were problematic at around 135K miles.

This vehicle is at around 118K.

But closer inspection after purchase, and knowing the locale where I purchased it, leads me to believe it may have been in freshwater flooding a few years ago(as opposed to 4' of saltwater flooding that toasted my previous Tahoe (as well as a camper van and my 1964 BSA motorcycle (now hopefully being restored)

If the converters were shot, I would expect to see the EC light coming on.

Ira

oldgoat82

Plugged cats often smell like rotten eggs. It sounded almost like a moan when the vehicle was in a heavy deceleration...the back pressure wasn't being relieved correctly or evenly. Coming down it would sound off going through the range and then return to normal. That's why I'm thinking that if you've ruled out engine vibes and you said it happened when stationary, it could be your exhaust system. If you had a mechanical vibe, it would occur at a multiple of engine RPM frequency and would be present all the time. Of course, at the resonant frequency it would be max and taper off above and below that speed. The band you're talking about seems too wide to be that.

emessys

None of those symtoms.

And 200 RPM is too wide a band? Maybe you misunderstood. Not 1800 to 2000 RPM wide.

!800 RPM to 2000 RPM.

To me it seems like a resonance/harmonic.

Ira