Check for what codes your computer is currently showing. Also check fuel pressure with a pressure gauge. My bet is it’s fuel pump crapping out.
CK5
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The Green Machine - parked
- Thread starter noJeepshere
- Start date
Hot fuel yes, vapor lock at 50-60 psi is less likely. If it was mine I'd be looking at the fuel pressure when it's acting up. Heat will effect the pump and can cause it to get weak and produce less to no pressure. Let it sit and cool and it comes back.
Hook up a gauge and watch what it does. If it starts dropping pressure as heat comes on I would be looking at a pump.
This issue really mirrors what the symptoms of vapor lock, which trips up some. The fact is weak fuel pumps fail in the heat. We went through a stretch in July where we were replacing pumps left and right when it was hot. Fuel pressure gauge showed below spec values on every one we checked in the heat of the day.
Borrow a gauge if you don't have one and run it in the heat of the day. If it's running ok, but below 55psi going down the road, I'd put a pump in it.
Hook up a gauge and watch what it does. If it starts dropping pressure as heat comes on I would be looking at a pump.
This issue really mirrors what the symptoms of vapor lock, which trips up some. The fact is weak fuel pumps fail in the heat. We went through a stretch in July where we were replacing pumps left and right when it was hot. Fuel pressure gauge showed below spec values on every one we checked in the heat of the day.
Borrow a gauge if you don't have one and run it in the heat of the day. If it's running ok, but below 55psi going down the road, I'd put a pump in it.
I hope not, it's the new design that Delphi came up with that's supposed to be indestructible. And there were no codes popping up other than the ones for the cats being bad.
Possible codes that could come up in the case of low pressure is lean fuel trims, o2 sensors trending lean or lean misfire code. However if the issue calms down in cooler temps the codes may not set because the fuel pressure is low but barely in spec.
Another I have found is it seems the rear axle seems to have shifted toward the rear...
The slip joint usually rides at the first grease line an inch away from where it's at currently. Think it's possible the centering pins sheared?
The slip joint usually rides at the first grease line an inch away from where it's at currently. Think it's possible the centering pins sheared?
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Hard to see with the poor lighting in the older photo, but it does seem like the axle has moved.
Also, I think the transmission mount has gone bad, there were some grinding vibes going on under heavy throttle both on the trail and while pulling the trailer. The engine mounts were replaced about a year ago so I doubt they're bad.
Also also, I'm not sure what's going on here, the spring mount is bent away from the frame in the upper corner. I have no idea how that could happen. The one at the spring itself I can see a rock doing that. Also, the last rubber bushing is toast, and since the springs have quite the "s" going on now, I think it's time for a wholesale revamp of the suspension. And the shocks, being 3 years old and abused on the trail, are pretty wore out now and no longer do their job.
Loose bolt would cause the mount to move off the frame
Loose U-bolts would cause the axle to move, and pins to sheer.
Loose U-bolts would cause the axle to move, and pins to sheer.
All of these issues could be fixed, if you link it 
Conclusion after a little digging: nothing immediately shows up as out of the ordinary. The u bolts were more loose than I'd like them to be, but not enough to allow play, and nothing was broken, including the centering pins. I still moved the pin to the 1" hole rather than the 1.5" hole because I didn't like seeing that blue protective plastic on the splines being exposed.
The spring mounts were nice and tight. You can see in the pic where something scraped along the frame and bent the mount.
Kinda hard to see, but are you running a lift block and a zero-rate stacked?
That's what it looks like.
I am. I was assured by ord that that would be fine as the zero rate is bolted to the leaf pack.
When I had a 2" block and an angle shim stacked I had both bolted to the spring
Here is a definite potential problem:
The rear yoke tried to self-clearance during my trip to Moab a few weeks back...
Obviously not a good thing. The 20 year old stock springs are not up to the task anymore of rock crawling, so the Yukon now needs all new springs at all four corners. And I'm going to make some traction bars so I don't have to worry about spring wrap with the new ones.
The rear yoke tried to self-clearance during my trip to Moab a few weeks back...
Obviously not a good thing. The 20 year old stock springs are not up to the task anymore of rock crawling, so the Yukon now needs all new springs at all four corners. And I'm going to make some traction bars so I don't have to worry about spring wrap with the new ones.
Front shaft I assume? The yoke on the axle?
I updated the post. Axle yoke on the rear drive shaft.
The zero rate and the 1” block are giving the leverage to allow this to happen. This is how I destroyed my rear driveline my first trip to Moab. Pinion angle is another factor. You are on the right track with new springs and some sort of traction bar.
I have my own problems in this area. And the springs and a traction bar are also in my very near future. My Tahoe goes back under the knife this fall.
I need to replace the front springs because they're garbage, and since the rear are doing this, ord is going to be happy with me when I place my order for 4 new springs, costing around $1600, but that should be very worth the cost.
