My 2002 chevy tahoe sometimes wont start and when it does it runs rough and black smokecomes out of exhaust

May need plugs,wires,filters, coils, I need more info. Is it worse when warm?

could be fuel pump or even crank or cam , timing sensor. Did it start running strange before this?

You have so sort of wiring issue, check the battery supply to the fuse box under the hood, it may be corroded.

The list of possible causes is long.
You'll have to figure out if it is fuel or ignition related to proceed.
I would check fuel pressure and spark first.
If you can't duplicate the symptom it may be tough to diagnose.

not enough info, what engine, fuel injected? if so what type, multi port, or throttle body? oil pressure is not the problem, it could have a Hi-Perf. oil pump. fix the leaks, they will make a horrible odor. and coolant leaks will make it run hot.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/david_4c166ba81493f541

Somewhere around 40-50psi depending on whether or not your vacuum is high or low. High vacuum - lower by roughly 9psi. Low vacuum - switches to higher pressure by the same increment.

Sounds like the intake gaskets are sucking air when cold. When it warms up then they expand and take up the space and no longer **** air. You can test the theory by spraying a little water on the intake while it's running if it starts missing even more then that is most likly the problem. It's not a hard job to do, but if you do not have wobble sockets then it will be a little more diffacult.

But if they want 600 bucks to do plugs and wires then you need to find another shop to work on your tahoe! That's alot of money for something that only takes a few minutes to do, and the parts shouldn't be much more than 150-200 on the high side!

replace fuel pump relay. check all fuses to ignition and pcm .make sure they are not loose. check coil wires make sure they not loose.look at battery if you have the ac delco seal battery make sure green eye still there .if its black have battery check out.

Go to Advance or Auto Zone and have them run an obd scan on it and it will pin point why your light is on and could solve your problem. This is often done for free.

Check your exhaust. If the vacum is not complete, the truck may idle like ****. Same for your catalytic converters and O2 sensors. do a system check at a garage.