V6 Blazer won't hold fuel pressure

I am new to this forum and sure can use some help. I have a 2000 s-10 Blazer ZR1 with the vortex V6. It would not start so I bought a new fuel pump on line and changed it. It ran OK but would not start after it set a while. I put a fuel pressure gauge on the check valve and as soon as the pump turns on it goes to around 48 to 52 pounds. The second the pump shuts off the pressure drops to 0. It leaks down right away. I also noticed when the engine is cranking sometimes the fuel gauge drops to empty. It does not do it all the time. What is the check valve for the fuel pressure? The other night I started it by( believe it or not) by holding my hand over the throttle body like a choke in the old days. Once it started I put the plastic air block hose back on and it ran for over a 1/2 hour well I picked up the shop. The throttle responce was good and no misses or shakes. I shut it off and it would not refire. What should I look for? Thanks guys.:smile:

Fuel pressure is too low, and leakdown is excessive. Key on engine off, fuel pump running, fuel pressure must be 60psi to 66psi. Must remain above 55psi for 3 to 5 minutes after the pump shuts off. The excessive leakdown needs to be addressed first. It could be the check valve in the fuel pump, a leaking fuel line anywhere from the pump to the injector, or the fuel pressure regulator. The fuel pump needs to be isolated from the system after it pressurizes the system to determine where the leak is.

As old master says find that leak down.
Was it a complete fuel pump module or just a pump replacement?
Aftermarket pump or ac delco /delphi pump?
Also do a complete fuel pump pressure test.
Guide lines below.
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

Hey,thanks for your input. The pump is an aftermarket one bought on e-bay. I will have to get a new pressure gauge today.I used the one I use on my Trans Am with TPI and it only goes to 60 psi. I will go down to advanced auto or somewhere and get a larger one. I was surprized at the high pressure needed to fire the injectors. How do I remove the plastic cover over the fuel regulator? I played around with it a little last night but it was getting late and I did not want to break it. Also,can you buy just the pump from delco? The local parts stores say you have to buy the whole assembly. Thanks again and I will post pressures ASAP.

Hey,thanks for your input. The pump is an aftermarket one bought on e-bay. I will have to get a new pressure gauge today.I used the one I use on my Trans Am with TPI and it only goes to 60 psi. I will go down to advanced auto or somewhere and get a larger one. I was surprized at the high pressure needed to fire the injectors. How do I remove the plastic cover over the fuel regulator? I played around with it a little last night but it was getting late and I did not want to break it. Also,can you buy just the pump from delco? The local parts stores say you have to buy the whole assembly. Thanks again and I will post pressures ASAP.
Aftermarket is bad news.:rofl::nono:
Run the fuel pressure test as outlined.
To see if it is fuel pump or regulator is bad.
Did you install the complete module or just the fuel pump?

Ac/delphi pumps are the complete module/assembly.
But the only way to go if you do not want to be replacing it every 30 days.

I changed just the pump. I will run a test today.I bought a new test kit last night. I will post results asap.

I changed just the pump. I will run a test today.I bought a new test kit last night. I will post results asap.

It is best to replace the complete module.
And always get the ac /delphi pump module.

Post back the complete fuel pressure test.

OK, I just tested the system and I get only 50psi at the test valve. I took off the return line and there is no difference with the return plugged off. However I did try it with the return completly open and no fuel at all is coming out the return line. I cycled it four or five times and nothing at all.
I also noticed when I turn the key on the pump cycles about 2 to 3 seconds goes up to 50psi then turns off and the pressure drops to 0 as I said. However I noticed the pump cycles when I turn the key off also. Is that normal ? I put a new gas tank in a few years ago and don't remember that doing that or I just did not notice it. Thanks again for more input.

I also looked around good and there are no leaks that I can see anywhere.

OK, I just tested the system and I get only 50psi at the test valve. I took off the return line and there is no difference with the return plugged off. However I did try it with the return completly open and no fuel at all is coming out the return line. I cycled it four or five times and nothing at all.
I also noticed when I turn the key on the pump cycles about 2 to 3 seconds goes up to 50psi then turns off and the pressure drops to 0 as I said. However I noticed the pump cycles when I turn the key off also. Is that normal ? I put a new gas tank in a few years ago and don't remember that doing that or I just did not notice it. Thanks again for more input.

I also looked around good and there are no leaks that I can see anywhere.

As in post 3 you need 95-105 direct fuel pumppressure.
Running ressure should be 60/66 lbs of pressure .
engine off cranking you need 65 lbs of fuel pressure.
If your fuel fump will not produce the pressure replace it.

OK, I just tested the system and I get only 50psi at the test valve. I took off the return line and there is no difference with the return plugged off. However I did try it with the return completly open and no fuel at all is coming out the return line. I cycled it four or five times and nothing at all.
I also noticed when I turn the key on the pump cycles about 2 to 3 seconds goes up to 50psi then turns off and the pressure drops to 0 as I said. However I noticed the pump cycles when I turn the key off also. Is that normal ? I put a new gas tank in a few years ago and don't remember that doing that or I just did not notice it. Thanks again for more input.

I also looked around good and there are no leaks that I can see anywhere.

Normal for the pump to activate for 2 to 3 seconds when the ignition is turned off.

Leakdown is still excessive. Plugging off the return line told you nothing. The pump is still not building pressure and it still leaks down.

If a fuel pressure line leaks, the pump can not build adequate pressure and whatever pressure it does build, will leak down when the pump shuts off. You either got a bad pump, or a line is leaking. The only way to determine if the leak is in the plenum or in the tank, is to isolate the pump AFTER it pressurizes the system. The option of course, is pull the plenum off and visually check for a leak, or pull the pump out again.

When you replaced the pump, did you replace the fuel line from the pump to the module housing? (flexible hose about 8" long) If that line is leaking it can give the results you are getting.

I did not replace the line on the pump. I have decided to pull the pump back out of the tank and replace the whole assembly with a delphi unit. Why do they have a different one for a four door and 2 door? I have a 2 door and ordered one for that. They do not come cheap but it is not worth fooling around with and sitting along the road somewhere. Is it common for lines to leak under the intake? thanks again

I wouldn't call it common for those lines to leak in the plenum, it is just something to keep in mind.

As for the 2 door pump, the tank is in the rear where the spare tire is in the 4 door model. The sender is slightly different. Using a GM/Delphi assembly is the only way to go with these trucks as they demand near perfect fuel pressure and volume to run correctly. Cheap pumps just can't cut it and they fail after short amounts of time.

I did not replace the line on the pump. I have decided to pull the pump back out of the tank and replace the whole assembly with a delphi unit. Why do they have a different one for a four door and 2 door? I have a 2 door and ordered one for that. They do not come cheap but it is not worth fooling around with and sitting along the road somewhere. Is it common for lines to leak under the intake? thanks again

2000 does not have fuel lines under the intake.

Good call MT! CSFI system... missed that...sorry.

You guys know your stuff.Thanks for the help. I will let you know what happens. Thanks for the input.This Blazer is nothing like my 350 TPI in my firebird.

Good call MT! CSFI system... missed that...sorry.

No Problem Old Master.
No nut kit and fuel lines to leak but the fuel pressure reg could leak or bleed off pressure in there.

I wanted to give an update on my problem.I bought a complete unit with sending unit and everything. It is a factory unit and all my problems seem to be gone. Fuel pressure is about 65psi and it will hold pressure over night. It is clear to me the after market pumps are no good for Blazers. What a pain in the butt having to drop the tank twice just to save a few bucks. One thing the new pump did require that I change the plug which was no big deal. Thanks again for your help.

Don't beat yourself up too bad, it happens to the best of us. It takes years of hands-on experience to know what parts you can cut corners on, and what parts you can't. I think MT, Maxwedge and I, are the "Senior" members here at AF, we've all been around the block a few times. Glad you got her running.

Changed pump assembly and all is well.65 psi and holds pressure for hours. No more cheap pumps. Thanks for your help.