I've been having a problem with hard starts, and a pressure test showed it to be the regulator. The pump seemed a little weak, but at 70 psi, it was at the low end of acceptable. After sitting overnight, it would start up great, but once warmed up, if it sat for more than 10-15 minutes, it would take cycling the key approximately a billion times to get it to start. Also, it would begin to stall under heavy throttle.

Replaced the regulator with a new one from O'Reilly, and it fired up great... once. Drove for about 23-30 minutes, let it sit for about 15, hard to start again. Finally got it to start by cycling the key on-off several times, just like I had to do before I changed the regulator.

On the way home, it started stalling, and died just before my house. Checked pressure again, and this time the pump showed bad, only ~65 psi at key on, and would quickly drop after it shut off.

I had a spare AC Delco pump that I bench tested and made 80 psi, and held over 70 for ten minutes. Get it in the truck, and still no start. At the service port, I've got 66 psi at key on, drops to 55 as soon as the pump shuts off, and will slowly drop to 40 before ten minutes.

The spider is about 2 years old, the fuel filter is about the same, and the fuel injector connector is about a year old. The fuel pump ground is excellent, and I've got 12 volts to the fuel pump connector.

Sorry for the long post, but I'm at a loss here. It cranks and cranks, but doesn't even try to start, not even a hiccup.

The plugs are firing, I laid one on the exhaust manifold and had my wife crank.

 

Guess I stumped all of blazer forum, too! Here's an update.

Did a little researching, and came across this:
Part 1 -How to Test the 'Spider' Fuel Injector Assembly (4.3L, 5.0L, 5.7L)

I've been to this website before, lots of good info for troubleshooting sensors with just a DMM.

Sounded like my injector itself might be bad, but turns out it's not. Each line sprayed fuel during cranking.

I ended up cutting out the crappy, loose butt splices I used when I put the new fuel injector connector in, and soldered and heat shrunk it properly. Don't know if that did it or not, but I put it all back together, and it fired up fine. Even starts great after it sits for a bit, when before it would take cycling the key several million times to get it to fire off.

I've got my fingers crossed that problems don't return!!

 

This tells you the pump is building sufficient pressure and that the check valve in the pump can hold the pressure. There are no problems in the tank.


The fact that the pump is supplying good pressure, and not leaking down below 70psi, this tells you two things: #1 Regulated pressure is too high for your CMFI system. It should be 55psi to 61psi. Below 55psi the engine will run lean, and above 61psi it will run rich. And #2 The pump is not leaking down below 70psi, so any leakdown lower than 50psi means something is leaking in the plenum. A loose electrical connection at the injector will not cause a leakdown issue. If the ground wire to the injector is intermittently shorting to ground while the ignition is in the run position, it will cause the injector to open, which would be indicated by excessive leakdown, probably to zero psi. Your drop to 40psi could be a poppet nozzle not sealing shut, a leak from the lines in the plenum, or a regulator leak, either internal or external.

Some regulators are adjustable by turning the adjustment screw on the rear of the regulator, next to the vent tube. If yours is not adjustable, you need a new one.

 

Well, like I feared, it's beginning to get hard to start again. After a few days of perfect behavior, it is very difficult to start after being fully warmed up, and sitting to >10 minutes.

Captain Hook: the regulator is new, although I guess it could be bad out of the box.

I just don't understand how after I basically did nothing, the truck started fine under any conditions for a couple days, and then began to require multiple cycling of the key to start.

And if the problem is related to my poor leak down results, why does the truck start great first thing in the morning, when I would think the fuel pressure would be the lowest? If you (fully warmed up) switch it off, and immediately turn it back on, it's ok, also. It has to sit for several minutes, and then it's hard to start.

If it was a carb, I would think it's vapor locking, but I figured a pump pushing 80 psi wouldn't allow it?

I agree it's not the pump, and I doubt the regulator (but I'm not ruling it out, new or not), could something have failed in the spider itself? It's only two years old, but it was the cheapest re-maned one rock auto sells. I know they generally don't fail, but I'm running out of options!

 

There are two problems going on: The regulator is set too high, and there is excessive leakdown somewhere in the plenum. It's possible the leakdown is in the regulator, (past the valve plate) or there could also be a leak from the pressure/return lines in the plenum, (nut kit), or a leaky poppet valve.

Could be a crack in one of the nut kit lines in the plenum. Odd that it only leaks down to 40psi, but not impossible.

Vapor lock is not possible with this system. When the pump is running, fuel is constantly being circulated through the system.

With a fuel leak in the plenum, on a short hot soak, the engine may start hard and will run rich until the excess fuel is burned. Quick starting in the morning could easily be from excess fuel pooled in the plenum. The pump will pressurize the system as soon as the ignition is turned on, usually in less than 2 seconds.

Start with replacing the regulator, we already know it has one problem

 

I don't think there are any "external" leaks in the plenum. When I put on the regulator, I energized the pump at the prime terminal, and watched for a couple minutes, and didn't observe any leaks at all.

The idea of a leaky poppet valve sounds like it could explain it, especially with it starting so easily first thing in the morning. Is this something you think I could observe? Pull the plenum, pull out each line, run the pump so the system is good and pressurized, and watch for any dribbles?

Assuming this turns out to be the problem, is the fuel pressure on the regulator adjustable? I seem to remember reading on here that it was, but I could be mistaken.

 

Some regulators are adjustable by turning the adjustment screw on the rear of the regulator, next to the vent tube. If yours does not have an adjuster screw, you need a new regulator.

If you pressurize the system and remove each poppet: if there's a leak, you should see it. Not going to be a stream, more like a dribble.

Testing the regulator for an internal leak is done by installing a shut off valve in the return fuel line. With the valve open, pressurize the system. When the pump shuts off, immediately close the valve and watch pressure on the tester. If the pressure remains above 50psi, the regulator is leaking internally. If the pressure continues to drop, it's not the regulator WARNING: If the valve is closed while the pump is running, the diaphragm in the regulator will most likely rupture.

 

I ended up replacing the spider, and the regulator, as well. It died last week, and I couldn't get it to restart at all.

With the new spider, I am having none of the "hot soak" hard starting problems as before. I ran errands around town in it today, and each time it cranked right up like it's supposed to. I don't want to be too hopeful, since it seemed to be ok for a couple days after I was in the plenum the last time, as well.

One thing that worries me, though, is my leakdown test results. Pressure is good at 61 psi with the pump running, but it falls to below forty quickly with the pump off. The spider/regulator is brand new, and the pump was tested out of the vehicle, and held above 70 for 10+ min.

I even ran the pump for a few minutes with the plenum open, to check for leaks in the fuel lines, and didn't see anything, with the pump on of off. Also, I checked the fuel pump fittings with the pump running, and didn't observe any leaks.

I suppose I'll test the pump again, in the vehicle this time. Even though it's starting good, I want the system to be right.

 

Is your tester somehow leaking a little at the service port or out of the relief valve. There are also several o-ring fittings that could be leaking. For the leak down problem. Smell gas at the top of the tank, at the fuel filter, o-rings in the spider and the connections at the back of the intake. You seem to know what your doing, that's what makes me question the tester.

 

If the pump holds 70psi for 10 minutes, fuel pump leakdown is acceptable. If it drops below 40psi at the service port, there's a leak, either internal or external. If the engine is not flooding on a hot soak, it's probably not the injectors. If there are no external leaks, the only thing left is an internal fuel pressure regulator leak. There is only one [safe] way to test for it. Install a shut off valve in the fuel return line. With the valve open, activate the fuel pump to pressurize the system. The instant that the fuel pump shuts off, close the valve. If leakdown remains above 55psi for at least 10 minutes, fuel is leaking past the valve plate in the regulator. Caution: DO NOT activate the fuel pump with the valve closed. If the regulator diaphragm is exposed to ~75psi or more, the diaphragm can/will rupture.