Regarding that fuel pressure regulator on the driver side of the fuel rail, I replaced mine out of preventative maintenance and save the old one as a spare in the toolbox. AC Delco if I remember right was around $75 for that little piece. It's got the one vacuum line, if the diaphragm in the regulator ruptures and you have a vacuum leak you can just plug the vacuum line and it will run fine with 5 PSI more fuel pressure. You'll notice with that line plugged you have 60 PSI at idle. You hook up the vacuum line and it drops to about 55 PSI as it sends some fuel back to the tank. I suppose that was designed to help with vapor lock or something.... And yet they did away with it. Probably just as smart as deleting the fuel filter, LOL. Cut down on production costs per vehicle by a couple dollars. Just like not utilizing the second bolt for the oil pick up tube to the oil pump! It all adds up for the GM corporate Penny Pinchers.

 

I was reading your symptoms.... A Tech 2 would be incredibly useful. I always start with verifying battery condition, cables.... Not visually, but measure resistance, and clean the connection to the battery. And then I verify all grounds.

Your symptoms sound like a problem I dealt with several years ago. Something was basically causing too much commotion on the com cables between the body control module and all the other modules. Turned out to be where the harness goes into the driver's door. Inside the rubber boot, insulation wore off a couple wires and shorted off and on, intermittently. The 12 volt + is always looking for a path to ground. And that meant going through various modules creating all sorts of bizarre random symptoms. Doors locking and unlocking, etc. (submerged wires under that door sill have the same effect frequently)
It's always worth inspecting those wires going to the doors, as well as the rear hatch.

One symptom of having a short is frequently the alarm randomly being set off..... or the interior dome lights turning on on their own.

Good luck. Electrical issues lead to early baldness from pulling your hair out.

 

@Idkorcare80
echo the advice already given

The AS relay clicking, poor cranking, door locking issues can symptomatic of the battery voltage dropping under load, so it's worth getting it health checked, not just voltage or charge.

Do you still have the DTC codes?

Anything aftermarket (Radio, Alarm, Remote Start) or water ingress affecting the Serial Comms bus could be an issue.

 

.... So rather than go through your entire harness inch by inch, your best bet is to focus on places where the harness moves. Like the door openings. And anywhere that it could be submerged in collected rainwater like under the door sills. Your engine and transmission move as well, so carefully check the areas of the harness that get motion. (Often what breaks the ground strap on the back of the driver side cylinder head) Look for anywhere that it rubs, such as down around the power steering lines, as well as the harness next to the starter that also goes up to the camshaft position sensor and the oil level sensor in the oil pan. Same thing for the harness that goes from the driver side of the transmission. That includes the harness that goes back to the transfer case, that goes front to back over the top of the transfer case. Some places any abrasion will be obvious, other places like inside the large grommet in the door opening you will need to lay eyes on the wires.

Another sign of an intermittent short, is that it fluctuates with the weather. It's almost as if humidity can affect it.

Here's where you start pulling your hair out..... Don't be surprised if after all this inspecting you don't find anything, but the problem disappears. All that means is you disturb the wiring and separated the short, which may reappear. That's where you break out the razor blade and open up those sections of the harness that move to look at the actual wires :-)

 

The fuel pump pressure regulator plays a big role in this type of fuel system(arguably the best type).

There is a pressure differential on each side of your injectors. Intake manifold pressure vs fuel rail pressure. As you open the throttle blade, pressure in the manifold increases, so fuel pressure must increase the same amount to overcome the extra pressure to ensure the correct amount of fuel is dispensed according to what the ecu commands.

atmospheric pressure at sea level is roughly 14psi. When the throttle is closed intake pressure reduces due to engine created vacuum. Let’s just say for this example intake pressure is 8psi with the throttle closed. If fuel pressure is 60psi and intake pressure is 8psi that makes a difference of 52psi. When you open the throttle all the way pressure will increase almost to atmospheric 14psi. If your fuel pressure were to stay at 60psi there would only be a difference of 46psi pushing fuel through the injectors, and the engine would receive less fuel than it needs.

In many cars this is just compensated for in the computer or regulated with a fuel pump driver module that changes the output of the pump. However, this way ensures even pressure to all the injectors and makes tuning much easier.

sorry for being a nerd

 

Can Also Lead To Erectile Dysfunction .....​​​​​​​

 

Did you calculate that the 2003 H2 has the diaphragm type pressure regulator on the fuel rail? I think the following year they went to a returnless system, pressure is maintained differently. Interestingly my 2003 has a map sensor on top of the manifold, as well as the fuel pressure regulator controlled by vacuum. So is the ECM reading the manifold absolute pressure to send a signal to the injectors? But then the actual vacuum in the manifold is controlling how much fuel pressure the injectors get? Now that's a mechanical system so the ECU has no idea what it's doing. LOL, can't quite geasp the logic of that :-)

 

Just letting all know I appreciate the help. Gonna see what i can get into this weekend. Let the truck sit a couple days not on a maintainer to see if the battery dropped enough but seemed to run fine every time I checked it and the voltage was fine

 

Already bald so good there and agree on the Tech 2, was gonna get one when my only problem was the air suspension but now it seems like I have a better excuse. I only drive the truck 1000-1500 miles a year. I briefly toyed with the SP205 splice pack, but didnt really notice a difference pulling random non critical pins other than what i pulled no longer working. Im like 98% sure i dont have leaks.

This air suspension/relay clicking short almost acts like one of the height sensors is causing the issue because its clicks worse when you get in or out, or stand on the running board but the sensors themselves dont seem that sensitive.

 

I cleared the exact codes but the only ones i saw referenced MAF and misfires. It does have an aftermarket radio the previous owner had installed and it did cross my mind that it could be worth disconnecting it for a little while. I guess ill just have to drive it a little more to track this down. I need to run the gas down anyway so I can replace the fuel pump, its been unusually loud the last couple times the tank got low so I think its on its way out but do not feel like it was causing my issue. I dont get the tach reading like it did when it was running bad. It was normal at first but cruising at 60 it was 0 or barely bouncing but if I accelerated it would come up but drop soon as you were coasting or maintaining speed