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


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[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

 

[drakon543]

Block the front tires so it doesn't roll then put the truck in neutral. Then check for any play in the univerals. While its still in neutral check for any play at the input shaft of the rear diff. Then jack up the rear and check for any play at the input shaft again. If there is no play you might have something going on in your xfer case. Also with 2 dead cylinders its no wonder its sluggish. Im honestly going to say unless your looking for a project truck with your son its time to call it a loss and cut this truck loose and get some of your money back.

 

[Tonyrodz]

I really hate when people are so dishonest when selling a vehicle ! It seems like the good people always get screwed! ! I'm sure the seller knew all these issues, how could he not ?

 

[Lonegunman]

Thanks again guys. He only paid $1200 for it so worse case scenario we'll find something else for him to get to work.

I feel bad because I test drove it, like I said I'm no mechanic but I'm not clueless, the only issues with the truck at the time was a slight miss at idle, truck had plenty of power, no knocking or other sounds that shouldn't be there, 4wd worked etc etc

Yeah the guy had to know about the trans mount not being bolted down

His reason for selling it was he couldn't figure out what was causing the miss at idle and he was tired of putting time and money into it

 

[drakon543]

He probably knew everything that was wrong with it and dumped a bunch of magic fix all fluids into it just so it would seem like it was in better shape just to sell it. There are ways to hide almost all problems until you sell something and its just not your problem anymore.

 

[DallasTahoe]

Well in all honesty the miss at idle can be from the blown head gasket, I know that for a fact so he may not have known about it, but the other stuff yea he might be suspect. Pull the gauge cluster out and check the bulb for the check engine light and replace it and then see if it comes on once you start it up that will be the real test of honesty


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[Lonegunman]

Okay, did as you suggested , the only movement at input shaft was about an 1/8" rotational no side to side or in and out movement, was about the same whether rear tires were raised or on the ground.

I also checked the transfer case side, video below. I know I need u joints, exhaust system, a head gasket to start and trans and motor mounts to start.

I also found out the noise that I thought was external towards the rear was in reality internal to the motor. As you'll hear in the videos it's hell to hear anything with the temp exhaust we threw together but on video one you can hear the noise at 8 seconds and 53 seconds, it's a "pop" after fire maybe?

In video two you can hear it at 15 and 33 seconds. The vehicle was in park and my son had it up to about 1500 rpm but it also did it at idle

Video three shows the movement at the transfer case side of the driveshaft and how the driveshaft and transfer case can be moved by hand probably do to the nasty trans mount, plus it shows the nasty u joints.

 

[DallasTahoe]

Definitely stop running it, you will cause more harm than good. The pop I'm thinking is a backfire due to the blown head gasket. The play you showed in the driveshaft is normal except the lack of an actual mount. I think it's salvageable. Start with head gasket and tranny mount second. It will be a good opportunity to pull the covers and see the condition of the valve train


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[Tonyrodz]

My 01 Express van with the 5.0 vortex motor ran very similar to the first video , turned out to be a bad distributor. Just for the he'll of it, have you checked that? Was popping and misfiring like crazy.

 

[Lonegunman]

Okay, did as you suggested , the only movement at input shaft was about an 1/8" rotational no side to side or in and out movement, was about the same whether rear tires were raised or on the ground.

I also checked the transfer case side, video below. I know I need u joints, exhaust system, a head gasket to start and trans and motor mounts to start.

I also found out the noise that I thought was external towards the rear was in reality internal to the motor. As you'll hear in the videos it's hell to hear anything with the temp exhaust we threw together but on video one you can hear the noise at 8 seconds and 53 seconds, it's a "pop" after fire maybe?

In video two you can hear it at 15 and 33 seconds. The vehicle was in park and my son had it up to about 1500 rpm but it also did it at idle

Video three shows the movement at the transfer case side of the driveshaft and how the driveshaft and transfer case can be moved by hand probably do to the nasty trans mount, plus it shows the nasty u joints.

 

[Lonegunman]

Thanks again guys, I'll keep this post up to date. Going to check the dizzy today. Already removed pass side valve cover, didn't see anything out of place, no broke Springs or bent rods