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96 5.7 Vortec Hard Start


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#1 JeffDCalgary

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Posted 13 December 2010 - 07:02 PM

I read a number of these regarding hard starting, but mine seems different enough that I do not want to start taking it apart without some more insights.

Here is the story: 96 GMC 5.7 Vortec. 250KM. Just replaced intake manifold gaskets. No idiot lights on. No more coolant leaks (use the flepro kit!)

After sitting 12 hours fuel pressure is at zero. After three cycles, fuel pressure is at 50. Will not fire. Using bleeder to bleed out air can get pressure up to 55-58. Willnot fire.

Dump 2 oz gas in throttle body truck starts fine and runs on about 50-55 pounds. Throttle up engine and fuel pressure goes to 60. Shut off engine and fuel pressure goes to 60. After two hours pressure drops to 45-50. One cycle and back to 60 and starts fine.



Everthing I read says: fuel pump (probably), regulator (could be), injectors (hope not).

Thanks in advance for your help.


#2 alz

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Posted 14 December 2010 - 11:52 AM

Sorry, I can't help, but how was the IM job? I need to do this on my 5.7.
99 GMC Suburban 4x4

#3 ChevyTech77

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Posted 14 December 2010 - 01:04 PM

60-66 psi. 1 psi less than 60 and it will start hard, if at all, and run like garbage.

Edited by ChevyTech77, 14 December 2010 - 01:05 PM.

Chevy tough.
Anytime baby!

Every screw up is an opportunity not to make another one.

#4 Rod R

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Posted 14 December 2010 - 03:56 PM

Hi Jeff.. welcome to the GM Trucks forum for Classic Trucks.

... sounds like you are telling me the story about MY truck and fuel pump from 2 years ago ...

.. based on what you are saying ... EVERYTHING points to a fuel pump that is on it's way to failure...

when you do get around to changing the fuel pump here is a few things to consider:
- always get your fuel pump ACDelco at a dealer or a Delphi from a good parts house and don't try to save money on a cheaper brand like Airtex..
- also replace the external wiring connector harness (they corrode in our winter rust seasons)
- also replace the in-tank filter sock
- if you can't remember when the in-line fuel filter was changed then get a new one and put it on

ChevyTech is right ... there is a very low tolerance to dropping pressure on these fuel pumps for the 96-99 Vortec setups ... if the pressure drops much below 58-60 psi then the poppets valves on the tip of each injector will not open and close properly

I read a number of these regarding hard starting, but mine seems different enough that I do not want to start taking it apart without some more insights.

Here is the story: 96 GMC 5.7 Vortec. 250KM. Just replaced intake manifold gaskets. No idiot lights on. No more coolant leaks (use the flepro kit!)

After sitting 12 hours fuel pressure is at zero. After three cycles, fuel pressure is at 50. Will not fire. Using bleeder to bleed out air can get pressure up to 55-58. Willnot fire.

Dump 2 oz gas in throttle body truck starts fine and runs on about 50-55 pounds. Throttle up engine and fuel pressure goes to 60. Shut off engine and fuel pressure goes to 60. After two hours pressure drops to 45-50. One cycle and back to 60 and starts fine.



Everthing I read says: fuel pump (probably), regulator (could be), injectors (hope not).

Thanks in advance for your help.


Edited by Rod R, 14 December 2010 - 04:01 PM.

Rod Ramage, Saskatoon, Saskatchewan CANADA
1997 Chevrolet Cheyenne C2500 xcsb w/ 5.7L Vortec & 4L60E; 3.73 gears w/ G80 (231,000 km)

#5 JeffDCalgary

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Posted 14 December 2010 - 06:17 PM

I read a number of these regarding hard starting, but mine seems different enough that I do not want to start taking it apart without some more insights.

Here is the story: 96 GMC 5.7 Vortec. 250KM. Just replaced intake manifold gaskets. No idiot lights on. No more coolant leaks (use the flepro kit!)

After sitting 12 hours fuel pressure is at zero. After three cycles, fuel pressure is at 50. Will not fire. Using bleeder to bleed out air can get pressure up to 55-58. Willnot fire.

Dump 2 oz gas in throttle body truck starts fine and runs on about 50-55 pounds. Throttle up engine and fuel pressure goes to 60. Shut off engine and fuel pressure goes to 60. After two hours pressure drops to 45-50. One cycle and back to 60 and starts fine.



Everthing I read says: fuel pump (probably), regulator (could be), injectors (hope not).

Thanks in advance for your help.

Thank everyone; Will try fuel pump first. In terms of the intake manifold it was pretty time consuming. Be sure to use the FelPro Gasket set. It costs less than the GM set and is much sturdier. I found a good set of instructions on the web : http://www.market-pl...take/intake.htm
and I also ahve the shop manual.

#6 Heineken022

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Posted 17 December 2010 - 11:20 AM

I had the same problem with a 96 K1500. Took it to 3 places and none of them could figure out what it was. Had to leave it overnight at each place because it only happened when the truck hadn't been started in a while. Decided to go for the fuel pump. There is a damper or pulsator that connects the fuel pump to the fuel line. This is where some of the problems arise with the pumps. It is only there to connect the two and is what it is to keep the humming down. I think you can replace it with a rubber hose but I bought another one to keep everything as stock. The problem with them is they sometimes crack inside and the pump ends up spitting fuel into the tank instead of the line.

I ended up replacing the fuel level floats as well while everything was apart. I replaced pumps in the past only to have the fuel gauge go out after being disturbed.

I also found the easiest way to get to the fuel pump was to loosen the 4 bolts that hold the bed on and raise it just enough to get the pump out. Beat the hell out of dropping the tank.




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