Vibration at 1500 RPM

[finall]

Mystery tech question. What is it? The person who figures this out is a Genius, and I will bow to them and call them a god on this forum.

What: 07 SUV. 11K Miles.

Problem: Having vibration at 1500 RPM, in drive, under light load (eg. on flat highway.).

Resonance (vibration) sounds like engine growl or exhaust resonance. Makes engine sound rough. Resonance transfers to body and floorpan.

Diagnosis: Happens at any speed, so not speed related.

Therefore RPM related to drive train, as long as RPM is 1500-1600. Higher or lower RPM, no resonance, and engine is smooth. No codes set.

Most of my cruising is done at around 1500 RPM range, so the resonance gets very annoying.

Growl gone if rolling with engine at 1500 RPM and in neutral. So guessing problem is in drivetrain behind engine?

Checked another 07, and sound Hz is in same range. 06 Does not do this.

Are all 07s like that? I know they changed the exhaust on the 07's to 3.5" pipes. It sounds terrible. If within design, still not normal. Makes our 07 a bad driving experience.

Took a 07 H2 Shop Manual and tried to diagnose, but do not understand "orders of vibration", and how to pinpoint source.

Anyone out there with an 07 encounter this?

[HUMMERcustoms.com/TAZ]

Has it done this since new?

If not can you think back during driving anytime from new having anything happen strange? Hit curb hard or crossed something that may have been high enough to drag the bottom on. Anything that just stands out more abnormal occurence.

I would not think it would be anything to do with increase size of exhaust pipe. Freak things happen with any part of a rig.

Hope someone can help you find the answer. It would help if you had someone ride with you and open door to lean out and listen for signs.

Good Luck!!!

TAZ

[Adam in CO]

That's easy. The only reason I win is because I'm first but most have had this problem.

The exhaust is vibrating on the stock UCP. Just bend it out of the way a little and it will stop.

[finall]

Hi AdaminCo:

Great! You are referring to the Under Carriage Protector I assume?

I will look into this and post the outcome.

[finall]

Hi Taz!

Thanks for the help.

I do not know if the vehicle has done this since new. I bought it used, with 11,000 miles on it.

A brand new 07 SE SUT that I took out for a drive around the block also had this resonance at the same RPM, but it was about 50% less than on our 07 SE SUV.

The resonance does not sound like a wheel out of balance, no click-click like a bad CV or U joint. It is also engine RMP related, but not speed related (where I would think damage to the wheels or underside would show up).

[finall]

Ok, I have now crawled under the vehicle.

YES!!!! The crossover exhaust pipe (going from right side to left side collector) is totally pancaked against the UCP (undercarriage protector). GM tried to pancake the exhaust pipe so it would clear, but failed. I had to drop the back of the UCP bolts by 1/2" before the exhaust cleared.

The rub point has filed down the UCP at the contact point and exhaust pipe also. If this was left alone, it would have eventually made a hole in the stock exhaust and UCP!

Lots of loose metal rust filings in the area, so it was easy to spot. I could not even slip 1 piece of paper between the two pieces of metal. Could this be the problem? Either way its off to the dealer to fix the exhaust.

I easily removed the UCP (3 bolts) by loosening the front skid plate (5 bolts), and will go for a 50 mile test drive later today. Let's just hope that this is the problem. Either way, it is off the the dealer for warranty exhaust repair.

AdamInCo: you may be the Hummer God after all......More to follow.