Fuel pressure reading for 5.3?

[C10CONFUSED82]

I am having issues with my C10 starting and staying running. I went to auto zone and rented one of there fuel pressure guages, really nice one. My reading at key on engine off is 51psi. With the engine on and idle its 48 psi. With the regulator disconnected from the vacuum line it jumps to 55-58psi. Is this okay? I have a external fuel pump feeding the fuel supply. Checked fuel filters and replaced one of them. The one after the fuel pump. There is two filters one before and after the fuel pump is this okay also? Thanks all to who reply back.
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[MHarvey]

I'd leave the regulator unhooked, as everything I've read says the LS motors need a steady 58 psi to run correctly. I'm in the middle of building an 86 C10 myself, with a 6.0 and 6L90 trans. I swapped over to a 1987 model TBI fuel tank with internal baffle, then used the 87 in-tank pickup with a 255 lph Walbro pump. I am hoping to fire it in the next couple of weeks (still have to send the ECM to get re flashed). I'm running Holley billet fuel rails and regulator, and the instructions with them even say to leave the vacuum port open on the regulator and set the pressure to 58. Hope this points you in the right direction.

[C10CONFUSED82]

Originally Posted by MHarvey

I'd leave the regulator unhooked, as everything I've read says the LS motors need a steady 58 psi to run correctly. I'm in the middle of building an 86 C10 myself, with a 6.0 and 6L90 trans. I swapped over to a 1987 model TBI fuel tank with internal baffle, then used the 87 in-tank pickup with a 255 lph Walbro pump. I am hoping to fire it in the next couple of weeks (still have to send the ECM to get re flashed). I'm running Holley billet fuel rails and regulator, and the instructions with them even say to leave the vacuum port open on the regulator and set the pressure to 58. Hope this points you in the right direction.

Thanks for the reply. Should I cap the vacuum port that the pressure regulator was hooked up to? Also could it be that I just have a week external pump? Not supplying enough pressure.
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[MHarvey]

The instructions with my Holley regulator said to leave the port open, and not to cap it. I'm not sure if this would apply to all regulators or not, but I would assume it would have the same effect . Your pump should be fine as long as it maintains 58 psi at all times, but you should check it with a gauge as you drive to make sure it's not dropping under throttle. Also, on the fuel filter question, one before and after should be ok, as most systems are set up this way. Just make sure that the filters are capable of flowing as much or more than your pump, so that they aren't a restriction.

[C10CONFUSED82]

Originally Posted by MHarvey

The instructions with my Holley regulator said to leave the port open, and not to cap it. I'm not sure if this would apply to all regulators or not, but I would assume it would have the same effect . Your pump should be fine as long as it maintains 58 psi at all times, but you should check it with a gauge as you drive to make sure it's not dropping under throttle. Also, on the fuel filter question, one before and after should be ok, as most systems are set up this way. Just make sure that the filters are capable of flowing as much or more than your pump, so that they aren't a restriction.

Thank you for your reply. Sorry to ask this stupid question. When you say leave the port open are you meaning the vacuum port? So if this is correct, you are saying take the vacuum line off the regulator and leave it disconnected, also do not plug the line you disconnected. Is this correct? My psi is not 58 continuous. Is more like 48 at idle and do not at throttle. This is with it being connected, regulator. But, when I disconnected it. It would stay at 56 at idle.
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[MHarvey]

Yeah, just leave the vacuum port on the regulator open to atmosphere. You'll have to either plug the hose coming off of the intake, or remove the hose altogether and cap the spot where you took it off the intake. If you don't cap where it comes from the intake, it'll create a vacuum leak. You should try to drive it to see how it does on the 56 pounds of pressure you have, it may be alright. I know most of the things I've read says that problems arise when the pressure gets below 53-55 psi consistently, so you may squeak by at 56, if it will hold that pressure steady through the rpm range.
One thing though, if this is the factory fuel pressure regulator, you may end up having to use a higher pressure pump and running the vacuum back to the regulator. I'm not sure on the factory style regulator if you can run it uncapped without ill effects. We may be comparing apples to oranges with my Holley regulator. I'd still try it though to see how it runs, and at least it should help you determine if your problem is fuel pressure related.

[C10CONFUSED82]

MHarvey thanks for the help. The funny thing about all this is that when I first had purchased the truck. The regulator was disconnected from the vacuum line. I thought maybe it had just came on done, so I connected it back. I see know that it must of been done for a reason. Ever since then I have been having issues with the car. Maybe this will bring things back to where they where when I bought it. It ran a lot stronger and felt better. The only different part of the original set up is that I plugged the vacuum port, originally it was not. Thanks again.

[MHarvey]

No problem, hopefully that gets you back where you were when it ran better.