Need major advice on sons 1999 Yukon

[Lonegunman]

My son purchased a 1999 Yukon just 2 months ago. Truck has 200,000 miles on it so we were expetting to have to put money in it but didn't expect the amount of issues it has to pop up so soon

I test drove it, had a slight miss at idle but besides that it seemed like a good deal, engine ranor seemed to run strong, no leaks, no knocking good oil pressure etc

The slight miss got worse real quick until it was difficult to keep running and had a huge power loss.

Changed the plugs, they were nasty
It was acting like an injector was hanging up, figured the cats maybe be clogged so he removed them and installed a temp exhaust, didn't help

Had him check compression and two adjoining cylinders had no compression, no water in oil

This is his work Truck, he's a locksmith so no vehicle no job.

A few days later he say he heard a loud banging coming from under vehicle, I checked it, it is not an internal engine noise, it sounds like someone is smacked the bottom of the vehicle near the middle of the vehicle.

So looking around I find the transmission mount has no bolts in it, so I find the bolts, realigned the holes in the mount to the transfer, tighten everything up.

So when I get home from work he said it's still do the same thing. I'm not familiar with the vehicle so I started researching

Noticed the skid plate is missing, I thought I read somewhere a mount is under the the skid plate, holes are there but there is no mount.

I can move the transfer case and trans up and down by hand, that doesn't seem right to me. So I had him film a video of underneath the vehicle and me moving it by hand, I have posted ithe in you tube, I'd greatly appreciate any feedback we get.

 

[Lonegunman]

I posted a long list of issues in the drive train section about a 1999 yukon my son just bought a few months ago.

I'm a ford guy so I'm learning, main issue is the trans mount had no bolts, fixed that but having same issue, LOUD noise mid underside of vehicle, sounds like someone is smacking the underside with a large hammer, under acceleration it gets worse, don't hear it in park excep

t for one.

I can move the whole drive train up just by pushing on bottom of t case.

More in my first post.

Someone definitely screwed around with this vehicle, missing skid plate, no transmount bolts etc

 

[drakon543]

Those 2 holes right at the beginning of your video is where the rear transmission mount is supposed to bolt to the crossmember. The other single bolt you mentioned is your torsion bar adjustment. Id leave that alone until you get everything else fixed.

 

[drakon543]

Thats underneath my 97 tahoe

 

[Lonegunman]

Thank you very much for the reply. Is it same to assume what I'm hearing the trans or the T case contacting the under carriage or the crossmember?

The front mount that was missing the bolts seems trashed so I'll be replacing that also

 

[DallasTahoe]

My son purchased a 1999 Yukon just 2 months ago. Truck has 200,000 miles on it so we were expetting to have to put money in it but didn't expect the amount of issues it has to pop up so soon

I test drove it, had a slight miss at idle but besides that it seemed like a good deal, engine ranor seemed to run strong, no leaks, no knocking good oil pressure etc

The slight miss got worse real quick until it was difficult to keep running and had a huge power loss.

Changed the plugs, they were nasty
It was acting like an injector was hanging up, figured the cats maybe be clogged so he removed them and installed a temp exhaust, didn't help

Had him check compression and two adjoining cylinders had no compression, no water in oil

This is his work Truck, he's a locksmith so no vehicle no job.

A few days later he say he heard a loud banging coming from under vehicle, I checked it, it is not an internal engine noise, it sounds like someone is smacked the bottom of the vehicle near the middle of the vehicle.

So looking around I find the transmission mount has no bolts in it, so I find the bolts, realigned the holes in the mount to the transfer, tighten everything up.

So when I get home from work he said it's still do the same thing. I'm not familiar with the vehicle so I started researching

Noticed the skid plate is missing, I thought I read somewhere a mount is under the the skid plate, holes are there but there is no mount.

I can move the transfer case and trans up and down by hand, that doesn't seem right to me. So I had him film a video of underneath the vehicle and me moving it by hand, I have posted ithe in you tube, I'd greatly appreciate any feedback we get.

Yea new mount and you should be fine, the compression loss is definitely a blown head gasket at the least, I had the same issue with no water in the oil, so pull the head and have I checked these vortec heads are notorious for cracking, especially on the valve seats


Sent from my iPhone using Tapatalk

 

[drakon543]

^x2 on the compression issue
Feel free to post any other questions or concerns. If you need any other visuals and my wife hasnt run off with my truck again ill be sure to post up whatever you need.

 

[Lonegunman]

Thanks for the help. It seems that our trans mounts are located in different areas, either it's a change they made in mounting location or mine is in the wrong spot which wouldn't surprise me judging by some of the other things I'm noticing

 

[Lonegunman]

Different view

 

[Lonegunman]

Jacked up the rear to get tires off the ground, could not duplicate the noise or vibration, I'm assuming because there was no strain on any of the components with the tires off pavement

Lowered it and took it around the block, ran very sluggish, applied more power and started getting a bad vibration throughout the vehicle with it clunking towards the rear of the vehicle, at this point I said screw it and floored it, hesitated at first, vibration clunking increased then it's like a switch was turned, vibration stopped, clunking stopped and the truck took off

I would think that means trans , rear diff or driveshaft issues

I'm no mechanic but I've always fixed/restored my own stuff but this damn truck is driving me crazy because I don't know where to start

I have audio of the clunking and will get video and audio today