How low the battery volts have to drop before it want start the engine on a 2004 GMC envoy 4.2L?

SOURCE: 2004 GMC Envoy has trouble idling

Try the fuel filter. Sounds like the engine might be running rough due to weak fuel pressure. Its cheaper to replace, especially if it's still original from 04. Try running some injector cleaner through a couple of tanks of high octane gas.

SOURCE: battery removal on a 2004 GMC Envoy

The battery is on the right side behind the fuse box. You need a metric set to undo the 3 screws. Theres one that attaches to the body, one to the bar that goes along the top, and theres one on the left side below the vacuum hose and air induction. After you've taken out those three, you should lift the whole thing out(battery and shroud) together. It's hard to take the shroud off before you lift the battery out. After that, you have to pry the shoud off the battery. The two terminals in the back make it hard. Then just go to any auto parts store and they'll give you a new one. 

Jim Goldsmith

• 2005 Answers
• Posted on Jul 22, 2010

SOURCE: 2004 gmc envoy leaking power steering fluid and

replace the leaking power steering hose

SOURCE: Headlamps won't come on 2004 GMC Envoy...High

Check Relay #46 in underhood fuse panel.

SOURCE: Oil pressure drops to zero at idle on 2002 GMC

You could have three possable problems that I can think of. 1) Your oil viscosity is too low and you need to change it to a higher level. A 5w/30 or 10w/30 oil may thin out too much when it warms up to normal temp and shows low on your gauge. 2) The preasure relief valve is partially open due to a small piece of debris caught under the seat. Unscrew the oil filter and look at the small disk that is near the threded part on the filter base. Theres a spring behind it to keep it closed so all the oil goes into the engine and not bypass back into the oil pan. Push up on it slightly with a small tip screw driver and see that it fully seats in the hole, put a new filter on, and try it. 3) If these two things don't improve the condition, get a socket for taking the oil preasure sender off and get a oil preasure gauge to test the actual oil preasure the engine is producing. You may have a weak pump in the engine. If the preasure is within good specs, I'd change the sender unit with a new one.
Let me know what happened-
Craig