Joeroket

Interesting reading. Thanks for posting those. I guess the heat warp on the fuel rails will be my first thing now.

Spark, fuel, and air are all present at time of no start. Injectors have pulse during this time. I will take a can of carb clean with me next drive.

Battery and Alt are brand new, old Alt had .4V of ripple current and old battery did test bad, but the problem started a while back and has been a pain in the arse since August. I do have some heat wrap laying around that I can throw on the rail and see if that helps.

Thanks for that. I will take a look and check all the ground locations. I have tried the wiggle test on the main portion of the harness that feeds the knock, crank, and cam sensors. I even pulled that section of the harness out for a visual inspection and found nothing of note.

It doesn't appear to be vapor locking. There is 60 Lbs of pressure and when I crack the Schrader valve when it is a no start condition it has a nice flow of fuel.

I can try that. The shop did do a back pressure test and he said it was ok. The local shop was able to troubleshoot while the hot no start condition existed.

I have an 07 yukon xl1500 denali that runs good until about 10 minutes or so of driving after it is warmed up. It runs as long as I keep the throttle cracked a little but at idle it will die and wont start for around 20 min. Has been to a local shop that was stumped and the dealer who said they couldnt reproduce it and told me my battery and negative cable was bad and that was probably causing the issue. The local shop did tell me that he watched all sensor voltages slightly increase for no apparent reason and that has him thinking its an electrical issue. The dealer told me they were seeing voltages randomly dip, thus their diagnosis that the neg cable and battery were the culprit I have changed the fuel pump, crank sensor, the three cam position sensor components, throttle body, alt, battery (it was actually bad) connector for the crank and cam sensors, and both battery cables. I have also cleaned the ground points and connectors for the both battery cables. When testing the grounds I have never seen more than .1 ohms from any point to any other point. The positive side shows full continuity from the starter post to the fuse block. When it warms to running temp it runs rough. Tonight it died so I waited it out and started it up after about 20 minutes. While it was in the driveway I popped the hood and grabbed my meter, it was running pretty rough, to verify voltages and ground. Everything seemed fine but I noticed that after the hood was open for about 5 minutes it started idling better. I shut the hood and gradually the idle started to get rough so I opened the hood again and the idling smoothed out. Closed it once again and the roughness returns. It certainly seems like a heat issue in the engine bay. Also I have never been able to reproduce the dying issue in my driveway no matter what I do. It only does it when on the road. The only thing I can think of now is that the harness has an issue somewhere and something is increasing in resistance under the high temps of a closed hood. Any ideas?