4.3 Vortec Fuel Pressure Questions

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4.3 Vortec Fuel Pressure Questions

Postby 97_lt1_sleeper » Fri Nov 12, 2010 7:11 am

I'm working on the g/f's truck (97 4x4 S10, 4.3 Vortec vin X), and I think it's got fuel pressure issues. When you key on, it does build pressure, up to about 60 psi according to my test gage, but it immediately all bleeds back off to near zero when the fuel pump prime ends. It takes it a couple seconds to start, but once it starts, it reads about 54 psi at idle, and will jolt up to around 60 and back down if you snap the throttle really quick.

I'm thinking that the internal check valve in the pump may not be closing to maintain pressure, and that the pump itself is only mildly weak. I just put a new Napa fuel filter on it before testing.

Does anybody know what pressure it should be? I thought ~62psi was the target but can't confirm. Is the pressure supposed to bleed back so low after the pump primes? Am I stuck with replacing the whole fuel pump hanger assembly if any of the above are the actual issues?

Thanks in advance for any help anyone can give. I've not worked with the actual Vortec fuel systems before.
'99 S10 Std. Cab Stepside, ZQ8, LS2, T56, Posi 8.8, LS1 front brakes, C5 Z06 Wheels
'97 S10 Std. Cab Stepside, LT1, 4L60E, 2500rpm Stall, Narrowed Disc Brake Posi 8.8
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Re: 4.3 Vortec Fuel Pressure Questions

Postby Rickracer » Fri Nov 12, 2010 7:33 am

Should be 63 psi minimum, and should hold within 5~7 psi for at least 20 minutes. The "hold spec" is from memory, so it may not be deadly accurate, but the first part is. 8)
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'93 S10 SB,RC, Comp XR276 Hydraulic Roller, Vortec head 363, 400 + hp, built 700R4, JW 2800 stall lockup converter, 3.73 posi, disc brake, narrowed 8.8 Exploder rear, LS Camaro front discs, Cal-Trac clone traction bars, Best N/A passes to date: 8.0 in the 1/8th, 12.75@106 mph in the 1/4, gonna spray it soon... :mrgreen:
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Re: 4.3 Vortec Fuel Pressure Questions

Postby 88LT1Blazer » Fri Nov 12, 2010 7:34 am

Your pressures are normal. The problem is the regulator. The pressure should remain once the prime is done. This is why the starting is longer than normal. It has to build the pressure to be useful. Change the regulator. It is bleeding down when it should not be.
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Re: 4.3 Vortec Fuel Pressure Questions

Postby 97_lt1_sleeper » Mon Nov 15, 2010 8:17 am

I got to thinking about it and decided that I could troubleshoot the pressure loss by just putting a fuel pressure check gage at the outlet of the fuel filter, taking the regulator out of the question entirely. When the pump primed, it would get up to 70ish psi but would drain back to near zero psi in about 10 seconds. It bled down more quickly when the whole system was hooked up with the gage at the check port, so the regulator is probably not working too well either.

So my question now is whether there is any type of check valve I can put inline of the pump outlet to make up for the fact that the pump itself won't hold the pressure? Or does the stock pump not even have a check valve in the outlet like the Walbro's do? I figure that with that and a new fuel pressure regulator, it might hold pressure like Rick says it should. I'm just not looking forward to spending $400 on a new pump / hanger / sending unit assembly just so it will start a little easier.
'99 S10 Std. Cab Stepside, ZQ8, LS2, T56, Posi 8.8, LS1 front brakes, C5 Z06 Wheels
'97 S10 Std. Cab Stepside, LT1, 4L60E, 2500rpm Stall, Narrowed Disc Brake Posi 8.8
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Re: 4.3 Vortec Fuel Pressure Questions

Postby 88LT1Blazer » Mon Nov 15, 2010 8:38 am

Here is the regulator. At Autozone. This is just for reference. I would try this before replacing the pump.
Fuel Pressure Regulator
Gp-Sorensen/Fuel Pressure Regulator
Part Number:
800-315

Price:
$47.99
88 S10 Blazer, LT1/4L60E Conversion, Center console with shifter, Typhoon cluster upgrade, 3.42 gears with G80

Fan Wiring At It's Best!!!
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viewtopic.php?f=22&t=24204
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Re: 4.3 Vortec Fuel Pressure Questions

Postby Rickracer » Mon Nov 15, 2010 8:41 am

I just checked Alldata for that specific M/Y, pressure spec is 60~66 psi, and should hold within 54~60 psi after the pump shuts off. You can change the pump inside the module/hanger, it's a PITA, but it can be done. If you do replace the whole thing, make sure you use a Carter, Delphi, or AC Delco, everything else I've seen is junk. :? 8)
And as Kent suggests, I'd probably do the regulator first, just to be sure, :thumbup:
Rickracer
ASE Certified Master Automotive Technician (well over 3 decades of experience, :thumbup: )
'93 S10 SB,RC, Comp XR276 Hydraulic Roller, Vortec head 363, 400 + hp, built 700R4, JW 2800 stall lockup converter, 3.73 posi, disc brake, narrowed 8.8 Exploder rear, LS Camaro front discs, Cal-Trac clone traction bars, Best N/A passes to date: 8.0 in the 1/8th, 12.75@106 mph in the 1/4, gonna spray it soon... :mrgreen:
76 Chevy Vega Drag Car, TWIN TURBO 355, P/G trans w/ brake and JW 4000 stall vert, 4 link back half, narrowed 9", 3.50 gears, 29.5x10.5W ET Drags. Best time9.669 @ 139.79, Latest video: https://www.youtube.com/watch?v=S59riYn ... ata_player
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