I am happy to report my wife's acquisition of her 2nd 96 LS Blazer in white to go with her nearly identical red one. The new one was bought new by a friend and it spent the last 16 years in a garage. It has 1/2 the mileage of the red one. The rubber on the door seals feels like new. The owner took impeccable care of this truck. It looks like it just came off the assembly line, except one small problem. Having replaced the spider and later the lower intake manifold gaskets and the fuel pump on the red Blazer I am at least familiar with some of what to expect when the red Blazer gets sick. I am a believer in the 60psi fuel pressure needed for proper spider injection to work. I would like to see what some of you might think about a new trick that the new Blazer is playing. The owner explained that for the last 4 months the truck would have a no start problem. That is is it would act like it was not getting gas. He had a charger connected to the battery. The battery was a new one and it was fully charged. He turned the key and the truck fired right up and ran perfectly as I have ever heard a Vortec run. Smooth as silk. I drove it home up and down hills accelerating no hesitation with AC on I amazed how tight the suspension was and how quiet the inside was. Nice truck. Parked it in the drive and started it several times no problem. So I put the pressure gauge on the Schraeder valve and read 51psi. OK I have been burned by pressure gauges reading funny before so I put on the red Blazer and 60psi and holding it all day. This morning I removed the filter and gas was clean no H2O so I put the pressure gauge on the line from the tank and still 51psi. I am pretty sure that reading pressure at this location is unaffected by other parts of the fuel system such as the return, bypass etc that I remember being part of the pump system. When the pump failed on the red Blazer it was obvious because it did not pump. The 51psi holds for a while, not as good as the red one. I guess I am really surprised that the truck runs like there is not a problem on 51psi pressure. I am not looking forward to removing the tank. But that is probably the solution. I was wondering if anyone had experienced their Blazer having low pressure but at least after starting, the truck actually not showing symptoms of the low psi. How low can it go? And back to the Battery charger that the owner had hooked up. He told me that when the truck would not start he put the charger on it and it would start. He had not checked the pressure so how he arrived at this I don't know. Possibly the 14VDC goosing the pump to run a bit faster? I have not verified this since I do not currently have a hot charger. May try jumping it from the red Blazer.

 

What you need to keep in mind: Fuel pressure and leakdown should ideally be checked when the engine is cold. If the engine is warm, or hot, heat radiates off the engine and causes a rise in pressure when the engine is shut down. When the fuel pressure between the fuel pump and the fuel pressure regulator reaches regulated pressure, the regulator will send the excess fuel/pressure back to the tank. The regulator is mechanical, so this will happen if the engine is running or not.

Fuel pressure and leakdown must be checked when the fuel pump is running and the engine is off. GM does not publish any "engine running" specs for this engine. When the ignition is initially turned to the RUN position, the fuel pump should run for ~2 seconds and shut off. While the pump is running, pressure must be 60psi to 66psi. Pressure must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails one or both parts of the test, there is a problem with the fuel delivery system. Further diagnosis is necessary to determine what the problem is.

If fuel pressure is below 60psi, there will be driveability issues. If fuel pressure is between ~55psi & 60psi it may or may not start without having to manually add fuel. It will however, run. From ~55psi down to ~43psi, good luck When pressure drops below ~43psi, the poppet valves at the intake ports will not open and squirt fuel. The engine will not start or run.

Your reading of 51psi is too low. If ambient temp is ~70F or higher, and the engine is tuned near perfectly, it might start on its own, but don't hold your breath Once the engine is idling, fuel demand is lower, until you try to accelerate. The next step in diagnosis is to modify the fuel pressure tester so it connects directly to the pressure line from the pump. This is most easilly done at the fuel filter connection. All fuel pressure and flow must end at the fuel pressure tester. While the pump is running, pressure must be 73psi to 108psi and it must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails one or both parts of this test, the tank needs to come down for further diagnosis. If it passes both parts, and there are no external fuel leaks, the problem is inside the plenum.

EDIT: If the battery is even slightly low on charge, the pump is failing, or there is a poor electrical connection for the pump, connecting a battery charger might be all it needs to build enough pressure to start the engine.

 

Captain Hook your explanation of the the fuel pressure vs starting makes complete sense. I did all pressure checks with the engine cold. With the fuel pressure gauge on the fuel line coming from the gas tank I read the same 51 psi. I haven't put a volt meter directly on the fuel pump to make sure there isn't an electrical issue but I will before I drop the tank. So far the pump I put in the red Blazer has worked fine, even the gas gauge works. I think it was from Auto Zone so that is probably what will go in this one. I wish I had an easy way to get 15 gallons of gas out of the tank. Any ideas?

 

if the pump works at all,just remove your fuel relay,and use a paper clip to bypass it to drain the fuel out from the filter into a bucket. turn key on,then just stick one end into one of the holes,then move the other end to each one until you find power. ive done this 2-3 times. just helps having a 2nd hand to remove it when you swap buckets.

id strongly advise getting a new ac delco pump. you can get em for almost the same price for a aftermarket off amazon.

 

I don't want to hijack this tread, but my 99 Jimmy is having a problem and I just tested my pump with a fuel tester from Autozone. Mine is running rough, shows a misfire in #5 and all the plugs on the drivers side are sooty while the others are normal. The exhaust smells very strong. I replaced the plugs, rotor, cap, and the wires are all similar in resistance (around 6.00 with a tester at 20k) except for #5 and it is at 2.26. My pressure shows 60 lbs, then drops to 56 when you shut it off. I timed it for 5 minutes and it was down to 52 pounds. I will go do it again for 10 and see what it does and report back in a bit. If this post is inappropriate please let me know and I will start another one. This post was just what I was looking for on fuel pressure, so I wanted to take a shot at getting some help here.

 

chris015 I was remembering changing the pump on our red Blazer. It was a dead no psi. The new white Blazer does have a working pump. Thanks for waking me up!

 

When I changed the red Blazers fuel pump I remember examining it and the electric motor and impeller. I was thinking that it would be great if you could get the motor impeller assembly by itself. Since the rest of the housing all looked fine. I think I looked for such a thing but did not find it. I was looking at pumps online and ran across a wholesaler listing what appears to be a replacement kit. Listing a Delphi OEM and other versions. I was wondering if anyone had seen or had ordered one of these kits.
I don't feel hijacked CSbrady your fuel problem sounds similar to mine. You might put your pressure gauge right after the tank/pump before the filter. Captain Hook's description of what it should look like pretty much says it all. Pump up to 60+psi and remain above 55psi for at least 10 minutes. Good luck

 

This is about a month after the last No Start event for the red Blazer. It came a large rain storm last night. The Blazer was not driven in the storm, it sat parked in our sloping drive. Wife got in it to Go, Go and it would not start. This time I had the benefit of her help to crank the engine as I watched the fuel pressure gauge connected to the Schraeder test valve. I had already tried it myself and was shocked that after leting the pump prime I looked at the gauge and it read 52psi. Should have been 60+ and I immediately suspected my gauge so I checked it for leaks. No leaks, so I had her crank it as I watched. Again shocked, the psi was +60 but immediately after turning the key off, there was a noise from the top of the engine that sounded a little like a chattering of relay contacts or a valve oscillating trying to close. The gauge went to 52psi instantly! I have had this thing apart, replaced the spider two years ago, replaced the lower manifold gaskets a year ago and the fuel pump about 4 years ago. I know that there are only a few things that could make this noise but I was hoping that someone could enlighten me as to what was happening. The end result is that when the Blazer is in one of these "events"it will not start or fire. Let me back up a bit to earlier yesterday after it would not start for her. I began the routine as I have done by removing the plugs and drying and cleaning then using a syringe squirted about 1/4 cup of gas into each cylinder and replaced the plugs. In my defense for this it worked last time a month ago and fired right up. Truck as always ran flawlessly for this month, from Waco to Houston and Bryan and back, no problem. Until now. I checked for spark, OK. When I turned the key and tried to start I got litle to no pop from the engine. With spark and that much gas in the cylinders would it be reasonable to guess that it was flooded? I tried popping the Injector electrical connector off of the injector block to stop fuel cranked but it never fired. Now I go back to what I saw on the fuel gauge and the chatter with sudden fuel psi dropping. Is this the fuel regulator? What else is there? I need some advice from some one with more knowledge than myself. Please HELP!

 

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