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Chevy Vortec fuel pressure.

 
greg allen
I love my Chevy Chevette!
Posts: 5
Joined: 05/14
Posted: 05/08/14 08:20 PM

I have a 98 GMC k2500 350 vortec. I replaced fuel pump with a new one. Immediately got 60 lbs of pressure, drove it 2 miles and it killed and wont give fuel pressure above 30 lbs. I took the pump out and exchanged it for another. Replaced pressure regulator, relay, fuel filter. I even blew air through the lines to make sure they weren't blocked. I can't get more than 30 lbs of pressure. I am now seeing little bubbles in the gas when I release the pressure off the gauge. I'm not sure if it did that before. The pressure holds, the pump runs, but wont give the required 60 lbs. Any Ideas? Thanks.  

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wayne712222
V-6 Camaros rule!
Posts: 90
Joined: 11/13
Posted: 05/08/14 09:54 PM

could the hose that connects the pump to the hanger tube have blown out???

i am taking that there was  New strainer installed on the bottom of the pump..

check the ground connection on the frame rail in front of the left rear wheel..

whole new pump assemblies come with a new pigtail connector to install .. cut and splice into the truck side of the harness..

do you have a digital volt meter??? with at least a 10 amp setting.. or a harbor freight around???

i don't recall if that model uses the small fuses for the fuel pump circuit.. you can unplug the fuse.. and use some male quick connects probe the fuse socket and give the fuel pump relay you have removed the cover on a squeeze .to check the amp draw of the fuel pump.. usually around 7.1 amps dc..  please hold the relay on and the amp meter across the fuse contacts for at least 30 seconds.. once in a while the amp draw of the pump goes up..

http://www.harborfreight.com/20-amp-automotive-fuse-circuit-tester-67725.html



the positive side of the fuel pump circuit is controlled by the fuel pump relay and the outer two wires on the 3 wire oil pressure switch..  

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greg allen
I love my Chevy Chevette!
Posts: 5
Joined: 05/14
Posted: 05/08/14 10:12 PM

Thanks for the response. I will check a couple of those tomorrow. I do recall seeing 2 different broken grounding cables. I wondered about them. I noticed one while hooking up the gas filler neck. Where should it mount to? The other I saw is on frame on passenger side of engine compartment.  

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wayne712222
V-6 Camaros rule!
Posts: 90
Joined: 11/13
Posted: 05/08/14 10:35 PM

let me give you the quick list..

negative to the bottom of the engine block..

Chevyrightfrontlowerblockground1998 Zpsef9309b7

on trucks there are also wires from this front passenger side engine ground location to the frame rail.. yep.. that's half the circuit for the fuel pump and tail lights..  i know i took that off with either a 14 or 15mm wrench.. i used a double offset box wrench to get the nut off to free the crank sensor support then removed the stud so i could clean both sides of the cable ring terminals..

Frontlowerblockgroundconnectionchevy Zpsf909e0c7

negative to the inner fender..




Vortec G105 Ground Zpsef7519b0

Tbi Ground Zps2317f7aa

Chevyunderhoodrelayboxconnection Zpsf9ad1cdd


Rearblockgroundvortecv698 Zpsbf2172b0


the ground that comes off the top of the tank and the 4 wire connector goes to the top of the frame rail.. just infront of the left front tire..

Chevypickupfuelpumpgroundframe

94GMC C1500fuelpumpground  

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greg allen
I love my Chevy Chevette!
Posts: 5
Joined: 05/14
Posted: 05/09/14 11:25 AM

Thanks a million Wayne! I'm not sure which one it was. I took off and cleaned the one on the back of the head and the one at the fuse box. The one I saw by the tank was a ground strap that is attached to the box and i attached the other end to the frame. I think this one was an after thought, the previous owner had a truck camper and there's quite a bit of extra wiring. He may have added that. At any rate I am now getting 60 lbs of pressure and the truck starts right up. However the pressure immediately drops when I turn the key off. So what do I check for that? I put in a new regulator  so maybe something else?  

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greg allen
I love my Chevy Chevette!
Posts: 5
Joined: 05/14
Posted: 05/09/14 12:53 PM

It drops from 60-40 and then holds. Maybe that's normal. Seems to start and idle real well. Going to take it for a test drive. I owe you some beers!  

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wayne712222
V-6 Camaros rule!
Posts: 90
Joined: 11/13
Posted: 05/09/14 05:50 PM

that's almost normal..  glad to have helped..  if it dropped to zero.. then you would have an issue probably with the fuel pump check valve that's embedded in the pump

now that it starts.. perform a voltage drop test..

Voltagedroptesting

add 2 tests to the 4 parts..

positive battery post to the underhood fuse box.. 0.04 volts max

positive battery post to the alternator output stud.. less than 0.3 volts ..  thats 3/10ths of a volt verses 4/100ths of a volt as it carries a lot more amperage..

i like to see less that the 3/10ths.. so make sure that your connection at the alternator is clean and tight..  

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tuffnuff
Moderator
Posts: 272
Joined: 01/10
Posted: 05/10/14 08:35 AM

Nice going Wayne.,. you are at your best, as usual.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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greg allen
I love my Chevy Chevette!
Posts: 5
Joined: 05/14
Posted: 05/11/14 04:47 PM

Wayne. I bought a low price digital tester. I did the light/battery test. That seemed O.K. The battery is brand new. However the rest of the tests, voltage was jumping up and down. Not steady at all. Truck starts easily and stays running. Idles a little low and runs rough.  

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wayne712222
V-6 Camaros rule!
Posts: 90
Joined: 11/13
Posted: 05/11/14 08:22 PM

you probably have more connections to clean..



vortec motors also EAT ignition coils..   caps and rotors..

Coilhighvoltageleakareas

Dbbc7910 B2b1 4009 9900 9E95cda84a7b Zpsb8436a2a

some of the internal cap conductors are fairly close together..
http://i1207.photobucket.com/albums/bb476/waynep712/ignition%20system/VortecV8distributercap.jpg  

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