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Old 01-30-2010, 05:00 PM
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5.7 vortec starts and dies

I have a 98 GMC K1500 4x4 with the 5.7 Vortec. It always been a little hard starting with long cranking times. Now it just starts and dies a second or so after starting. The oil pressure gets up to 40 or so at around 1000 rpm and then dies. I replaced the fuel filter and still the same,looked at the crankshaft position sensor and it seemed fine. Checked fuel pressure on the rail and it hit almost 70 when I just had the key on. Starting the motor it dropped to the upper 60's and dropped down to nothing after the motor died. Even when I just turned the key on and then off the fuel pressure dropped to zero . Is this a bad fuel pressure regulator or a leak down there in the manifold ? I just don't want to start chasing the problem with new parts that weren't bad.Thanks Ken

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Old 01-30-2010, 08:23 PM
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could be the pump or fuel pressure regulator. pull the vacuum line off of the fuel pressure regulator if it has fuel in it its bad.try to tap your fuel pressure gauge in at the filter to see if the pump holds pressure at that point.it will drop some but should not drop real fast after the key is turned off. should hold for at least 30 seconds.if i am thinking correctly these trucks have what they call a spider assembly under the upper intake? if so you can pull the upper intake and see if they are leaking but that of course would mean new gaskets. i wouldn't do that until the fpr and pump check out ok.
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Old 01-30-2010, 08:34 PM
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Your pump is not flowing enough fuel, or you are losing power to the pump. There is a prime terminal in the underhood fuse box right next to the fuel pump relay(it is just a single hole). Put a test light in it and see if it is keeping power.
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Old 01-31-2010, 06:58 AM
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If pressure is dropping off that fast, it's possible that you have a hole in the hose between the pump and the pickup assembly, which will squirt the fuel right back into the tank.
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Old 01-31-2010, 07:19 AM
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hole

I will check and see if I lose pressure that fast at the fuel filter that should tell me if it's the pressure regulator or if it's in the gas tank on the hose for the fuel pump and I guess if thats the case it's time for a new fuel pump . Thanks Ken
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Old 01-31-2010, 11:46 AM
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Quote:
Originally Posted by paidtofit
I have a 98 GMC K1500 4x4 with the 5.7 Vortec. It always been a little hard starting with long cranking times. Now it just starts and dies a second or so after starting. The oil pressure gets up to 40 or so at around 1000 rpm and then dies. I replaced the fuel filter and still the same,looked at the crankshaft position sensor and it seemed fine. Checked fuel pressure on the rail and it hit almost 70 when I just had the key on. Starting the motor it dropped to the upper 60's and dropped down to nothing after the motor died. Even when I just turned the key on and then off the fuel pressure dropped to zero . Is this a bad fuel pressure regulator or a leak down there in the manifold ? I just don't want to start chasing the problem with new parts that weren't bad.Thanks Ken
Sounds like the fuel pump relay. There are two modes start and run. The key trips a relay for cranking where the pump is turned on for 10-15 seconds and then shuts off, once off it cannot be immediatly brought up again. Another circuit is looking for idle tach speed or greater, when the computer sees that and oil pressure it determines the engine has started and kicks in the fuel pump run relay which keeps the pump going after the pump start squence relay times out.

Bogie
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Old 01-31-2010, 01:50 PM
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Quote:
Originally Posted by miller_time
if i am thinking correctly these trucks have what they call a spider assembly under the upper intake? if so you can pull the upper intake and see if they are leaking but that of course would mean new gaskets. i wouldn't do that until the fpr and pump check out ok.
you are correct about the spider assembly (central sequential fuel injection). i'm actually working on my '97 gmc p/u right now and have all that crap pulled off. i doubt if one of the lines is leaking that would make the engine shut down, as it should just affect that particular cylinder. my guess would be the fuel pump or fuel filter. the pump has been replaced twice now - i only have 182,000 miles on odo. and the fuel pump replaced at least once by me.
there is also a fuel pump relay in the 'fuse-relay center' box above the horn under the hood. maybe a bad fuse?
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Old 01-31-2010, 04:18 PM
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You can try jumping the relay socket to force the pump to run and see if the vehicle will contine to run. If it does you have eliminated the pump, filter and the rest of the fuel system. This will lead to checking the pulses from the distributor module and the oil pressure cutoff switch
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Old 02-02-2010, 07:11 PM
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Quote:
Originally Posted by T-bucket23
You can try jumping the relay socket to force the pump to run and see if the vehicle will contine to run. If it does you have eliminated the pump, filter and the rest of the fuel system. This will lead to checking the pulses from the distributor module and the oil pressure cutoff switch
I jumped the fuel relay and my pump ran fine but my truck still died after second or so like it was doing.
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Old 02-02-2010, 07:34 PM
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Quote:
Originally Posted by oldbogie
Sounds like the fuel pump relay. There are two modes start and run. The key trips a relay for cranking where the pump is turned on for 10-15 seconds and then shuts off, once off it cannot be immediatly brought up again. Another circuit is looking for idle tach speed or greater, when the computer sees that and oil pressure it determines the engine has started and kicks in the fuel pump run relay which keeps the pump going after the pump start squence relay times out.

Bogie
I jumpered the fuel pump relay so it would just run , tried starting my truck and it acted the same. Just ran for a second or so and died. 1000 rpms and around 40 psi oil pressure. Still searching for an answer . Thanks
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Old 02-03-2010, 01:52 AM
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Your security light isnt flashing is it? If so its the VATS system shutting the injectors(poppets) off after 3-4 seconds of running.

I have pulled the air intake off of the throttlebody of a Vortec 350 truck thathad a dead fuel pump. I walked beside the truck as the truck was started and backed up into the garage, pouring gas into the t-body when the ngine was about to die.

Fuel pressure should be 58-66psi when running, if you snap teh throttle open quickly the fuel pressure should spike up to 62-66 psi.
there is no vacuum hose that runs to the FPR, the FPR/fuel metering block/poppets are found inside the intake manifold this is always exposed to engine vacuum.

Clamping the return line underneath the truck where the metal lines are actually rubber for a short bit, should cause the fuel pressure to spike to 100psi or so. there are special little mini vise clamps that are designed to safely pinch rubber hoses. or you can use visegrips(be veruy careful to not harm the rubber). the return line is not under much pressure when the return line isnt clamped. The return line is the smaller of the 2 lines that carry fuel. there is a vent in there as well.

If your rail pressure is going down to ZERO very quickly after the truck is stopped or quits. You either have a:
1) leaking fuel pressure regulator
2)leaking poppets
3)worn pump allowing fuel to run back into the tank.
4)leaking hose that goes from the fuel pump to the fuel senser insid eteh fuel tank

Vortec poppets cleaning procedure and CSFI to GM multec 2 MPFI Gm conversion installation kit.
http://members.shaw.ca/betterthanyou...g%20Poppet.htm

If you clamp the return line, then cycle the fuel pump, then before the pump stops running, clamp off teh supply line. Now if the rail pressure still dips down to ZERO quickly yoiu know know that its either a bad FPR or leaky poppets.


peace
Hog
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Old 02-03-2010, 04:10 AM
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I tried to check the pressure just after the fuel filter but I couldn't get a good seal (couldn't get the right fitting ) but I could hear my fuel pump work harder from dead heading it and my fuel pressure went down slower than when I had it on the rail so it might be the poppets or my pressure regulator I will check out how to clean the poppets but I think it is the regulator leaking since I could hear some noise in that area when I jumpered the fuel relay Thanks Ken
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Old 02-03-2010, 05:53 AM
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Quote:
Originally Posted by Hogg

Vortec poppets cleaning procedure and CSFI to GM multec 2 MPFI Gm conversion installation kit.
http://members.shaw.ca/betterthanyou...g%20Poppet.htm

Hog

lol, i just found it funny that one of the fixes would be to get away from csfi completely and go w/ mfi
i should probably try cleaning those little 'poppets' on mine before buying a new $300 spider assembly....and i bet it turns out that it was just my egr to begin with.
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Old 02-03-2010, 02:41 PM
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ok, so i've been thinking about this some more. are the battery cables hooked up securely to the battery? once the truck gets up and running maybe one of the cables comes loose and the battery is next to dead anyway maybe? just a thought...
i wouldn't think it has to do with the distributor because if one cylinder wasn't getting a spark it would just come up as a random misfire...right?
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Old 02-03-2010, 04:34 PM
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Yes the batteries are charged . I wish it were that simple. This did start somewhat quickly . It didn't seem progressive. My alternator originally failed me so I parked it until I replaced it . The day I replaced it it was hard starting and dying after a second or so , then it started and ran fine when I put it in the garage after replacing the alternator it started doing what it is right now so I couldn't even drive it out of the garage after replacing the alternator and here I sit.
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