1997 Blazer fuel pump pressure may be too low

monty101
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Joined: Mon May 27, 2013 6:59 pm

1997 Blazer fuel pump pressure may be too low

Unread post by monty101 » Mon May 27, 2013 7:01 pm

I got a 1997 blazer 4.3 ltr motor with 20k miles on a new motor and tranny

What should be the fuel pressure when I turn the key on?

It is now showing 60 lbs for 2 seconds while the pump primes. Then it drops to 55 and when
I turn the key to start it , it will jump to 60 and after it starts it drops to 52.

The problem is When I start it in the morning it revs ok but when I take off it acts
like it is not getting enough gas and hesistates. I pump the pedal and the pressure jumps
to 60 and I eventually make it to the stop sign at the end of the street and then when I take
of it runs fine. I think it is not getting enough fuel pressure. I have read in other threads that it
needs 60-66 lbs. Its getting 60 but it acts like that is not enough.

I have replacd the plugs, spyder injectors, and fuel filter. any help would be much appreciated.

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ProTech
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Re: 1997 Blazer fuel pump pressure may be too low

Unread post by ProTech » Mon May 27, 2013 7:52 pm

55psi is acceptable, but 52 is reaching the 'just about too low' stage. 60 is great with the key on, and it will normally drop a few psi once the pump stops running after the 2 second prime. Since it's not falling off completely, I would say you're regulator and the lines inside the intake are probably not leaking.

You might be having something else breaking down under acceleration like an ignition issue. Since the plugs are new, check the wires, distributor cap and rotor, and also the coil. Those can all cause the same problem under accel.
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monty101
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Joined: Mon May 27, 2013 6:59 pm

Re: 1997 Blazer fuel pump pressure may be too low

Unread post by monty101 » Tue May 28, 2013 2:22 pm

I just put some alchol in the tank. I think maybe maybe there is some water in the tank causing this problem.

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ProTech
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Re: 1997 Blazer fuel pump pressure may be too low

Unread post by ProTech » Tue May 28, 2013 2:53 pm

Fuel contamination can certainly cause a hesitation, but usually won't affect pressure readings. Maybe try and take a fuel sample and see how it looks.
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monty101
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Re: 1997 Blazer fuel pump pressure may be too low

Unread post by monty101 » Tue May 28, 2013 5:15 pm

pulled the rotor and distributor cap. They were toasted pretty bad. Rotor contacts were white
REplaced them and the wires. It seems to start a lot better now and has not miss. I may have this
thing fixed now. Thanks for the advice

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ProTech
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Re: 1997 Blazer fuel pump pressure may be too low

Unread post by ProTech » Tue May 28, 2013 5:37 pm

You're welcome, glad to help out!
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monty101
Posts: 4
Joined: Mon May 27, 2013 6:59 pm

Re: 1997 Blazer fuel pump pressure may be too low

Unread post by monty101 » Wed May 29, 2013 10:12 am

Unfortunately I still got the problem. I put my fuel pressure guage on it and ran the hose up through the hood so I can monitor the pressure when the blazer is driven. After it is primed in the morning at 60 lbs, for 2 seconds the pressure drops to 55 and then when i put it in gear it drops on down to 52 and sometimes it stays there when i try to back out into the street and drive up to the corner even with me pumping the accelerator pedal trying to coax it along. I know this is weird I thought when you give it gas it's supposed to lower the vaccum which should increase the fuel pressure. This does not happen when the pressure is 52 even though the motor is revving while its hesitating along as I drive it up the street. It barely makes it to the corner stop sign but then when you take off the pressure will be at 52 idling but it will immediately jump to 60 and drop to 55-58 after i get up speed. No hesitation. I shut her down and the pressure was 48 and then it rose to 58 and after 10 minutes it dropped to 55 and then 4 minutes later it dropped to 50. It will eventually drop to zero by morning.

What is causing this morning hesitation and low pressure. Is it the pump? Is it air in the line? I've driven it all over since I drained all the bad gas and replaced it. So, I don't think its air in the line. The fuel regulator is new since I just put a new delphi spider on it and a new fuel filter. I called Dephi and they said the pressure regulator is set to check the pressure at 60 and that is what it is doing, So, I don't think its the regulator. I'm thinking I need a new pump. If it was the regulator it would do it all the time. The pump may not be doing this all the time only because it gets heated up after it has run awhile and the heat makes the moving parts expand to take up space created inside it because it is worn out. Everyone says they won't run on less than 55 lbs of pressure. Mine runs ok at that pressure but as I've said early in the morning it won't get that high until I drive it up the block to the first stop sign. Then it runs great......

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ProTech
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Re: 1997 Blazer fuel pump pressure may be too low

Unread post by ProTech » Wed May 29, 2013 11:45 am

It's either the pump or the plastic fuel lines that go to the spider injector. They can crack and leak down pressure, but you probably would have noticed that when you replaced the injector assembly. You're probably going to have to put a pump in it. The pressure should never drop to zero, even overnight, so you've got a pressure leakdown somewhere.
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