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Fuel Pressure Fluctuating

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Old 01-09-2013 | 06:50 AM
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Fuel Pressure Fluctuating

A month ago I upgraded my fuel system. 1/2" draw straw, 3/8" line, 10" tall CAT filters, high pressure piston pump, and a FASS regulator. Everything worked great, my fuel pressure was about 8psi at idle and 15psi at WOT. The truck sat for a week while I did the hydroboost conversion. When I fired it up I had about 13 psi at idle. When I drove it around it went past 15 psi and my gauge only goes to 15. I have no idea how much I'm pushing but I'm afraid of blowing my front seal. I backed the screw out on the regulator but it hardly made a difference. Now it doesn't start very easily and I have to pump the throttle to keep it going. And when I do that I get a lot of white smoke. After driving it a little it runs fine and idles fine. I don't understand what changed. Any ideas?Thanks.
Old 01-09-2013 | 08:13 AM
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Did you mess with the wires on the cold start advance and fss?
Old 01-09-2013 | 01:02 PM
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No I thought of that but I checked them a they're fine. It acts like there's air in the line. But there's no reason for that since I didn't touch any part of the system. And I just started it this morning and I realized that my grid heaters aren't turning on. I plug it in every night but the heaters usually cycle a little. I think that's my issue and why I was seeing white smoke. I'm still curious why my fuel pressure fluctuates. I guess it's time to look at wiring diagrams.
Old 01-09-2013 | 03:01 PM
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Colder out, thicker fuel on start up causing higher pressures? Maybe it will go back to normal after some run time?

What side of the filter is the fuel pressure taken from?
Old 01-09-2013 | 03:19 PM
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Maybe, but its not any colder than it has been. And it doesn't change after some run time. In fact today it went up 3 psi. It was 12 psi at idle and now it's 15. Fuel pressure is taken after the stock filter at the regulator. It runs fine. I'm just afraid of a spike in pressure and blowing the front seal. Maybe the regulator is bad. It was brand new when installed it a month ago.
Old 01-09-2013 | 05:47 PM
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Do you have any timing in the pump? Does the truck seem idled up?
Old 01-09-2013 | 07:08 PM
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Check around everywhere you were working, since this was not an issue before, maybe the intake temp sensor/wiring since it is routed by the brake booster. I always check anything that I might have disturbed without knowing like leaning over the inner fender and snagging something.
Old 01-11-2013 | 01:27 AM
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Idle is the same and timing is about 1/16". I double checked all the wiring and everything is still hooked up. I was able to make the heaters cycle when I disconnected the air intake sensor. So I know they work. I'm assuming I just haven't heard them cycle because its usually plugged it. It's been starting fine now. I got my fuel pressure running about 9-12 psi at idle and 14-15 at WOT. I just didn't expect it to fluctuate that much. I'm assuming its the nature of the piston pump since its mechanical.
Old 01-11-2013 | 06:14 AM
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Now im stumped. When I went to work yesterday my pressure was 9-12psi with a max of 15. When I left for home this morning it was a minimum of 15 and went higher. How much I don't know since my gauge only goes to 15. I'm going to call FASS in the morning. I don't understand why the regulator would fluctuate like that. It kinda worries me. What pressure does the 2nd gen piston pump put out?
Old 01-11-2013 | 10:47 AM
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are you running a mechanical gauge? if so are you using a snubber? could be a gauge issue. last winter i got a bit concerned with my fuel pressure too when i saw pressures spiking a bit. i initially blamed cold weather thickening fuel and that may have been what hastened the gauge failure. i was not running a snubber or a pressure regulator with my lppp at the time.
Old 01-11-2013 | 12:26 PM
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I run a snubber valve works great. A 2nd gen lp not regulated can make up to 50 psi roughly. Though my p-pump can pull it down from 27-15 at wot sooooo.
Old 01-11-2013 | 01:03 PM
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Yes the the gauge is mechanical and it was new when I put it on. I didn't have a snubber at first. I only ran it that way up the road and back to test drive it. I made my own snubber. I made an 1/8" NPT adapter with a .04" hole through it. When I put that on the gauge quit bouncing. You don't suppose I wrecked the gauge already? Also when I first fired it up I got all excited and forgot to hook up the return line at the regulator. The gauge pegged and I shut it down after 30 seconds.
Old 01-11-2013 | 02:05 PM
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both your regulator and gauge are suspect now that we have the full story. you should check with fass if that is who made your regulator. i would be most concerned about the reg. have you talked to them yet? be honest with them about having run without plumbing the return briefly. hopefully if something blew out it is serviceable.
Old 01-11-2013 | 03:01 PM
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I backed the screw on the regulator out pretty much all the way and it still reads 12-15. Yes I called FASS and he doesn't think the regulator is bad. I told him what I did and he said its not likely that it affected the regulator. He thinks either the snubber or the gauge is suspect. I don't see how the snubber would affect pressure. It's just restricting flow to make the gauge read steady right? I'm going to get another gauge and try it.
Old 01-11-2013 | 04:05 PM
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as long as the fluid passing through your snubber is only going to the gauge it cannot affect anything else. try another gauge and let us know what your findings are.



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