lower fuel pressure after stud job - Ford Powerstroke Diesel Forum
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  #1  
Old 09-30-2013, 05:41 PM
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lower fuel pressure after stud job

I just had a bunch of work done including ARP's, all new injector cups, one injector among a laundry list of other things including 6.4 banjo bolts. My fuel pressure before the work never went under 50 at WOT running the SRL tune. The truck hesitated badly and smoked under WOT because of a bad injector. After the work, I noticed my FP drops to the low 40's at WOT with SRL tune. I went back to the stock tune and it'll stay above 50. No difference at idle before or after the work under either tune, it's always 62-64. The blue spring has been installed for a year or so. Could it be the 6.4 banjo bolts?
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Old 09-30-2013, 06:47 PM
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Nope, not the bolts. I didn't see any change on mine. As well, due to the orifice size, it was probably more of a feel good mod unless you are pushing 800+ hp and changed the fuel lines as well.

Now that your truck is running better, you can expect more fuel to be used in a WOT run, especially if you stay in it longer. Unfortunately what you are seeing is frequent for a larger PW tune, even without larger injectors or nozzles. You could try to roll into the accelerator and you may find the pressure doesn't drop quickly nor as low. It is tough to build pressure once it has been quickly lost.
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Old 09-30-2013, 06:55 PM
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I did not ask for the banjo bolts, he let me know he installed them after the fact. Would a new OEM pump keep up or is the aftermarket upgrade the way to go? I will be running the SRL+ when SCT gets done repairing my SF3.
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Old 09-30-2013, 07:34 PM
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A very good upgrade is a 6.4 low-pressure volume pump in-line before the HFCM. Whether you need a new pump or need the system checked is your call. If you had followed some of my comments on other threads, unless you are racing or beat on it regularly, you seldom need to worry about low fuel pressure or be cognitive on when to let off. You can always go RR.
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Old 10-02-2013, 06:10 AM
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That's the first I've heard of the inline 6.4 pump. It seems that most people get concerned when the PSI gets under 40...
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Old 10-02-2013, 07:28 AM
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I still have the original fuel pump and system. If I have a larger PW tune with my larger injectors, my fuel pressure will get below 40 psi. If I were to run 1/4 mile at WOT from a stop, I would see fuel pressure approaching 30 psi (maybe less). But I don't do that with my truck. With a tune that has a PW of <2.0 ms and I don't just punch it, my pressure never gets below 50 psi (blue spring). Usually my pressure sits mid 70s no matter what I do with the pedal on any tune except a race tune.

The lift pump ensures the HFCM doesn't have to work as hard to deliver the fuel. The RR crowd would say you are measuring pressure at the wrong place and "what about the aft cylinders?", but line drop front to back, including pressure on a sequential firing engine is minimal, unless you have a restriction, or as I said earlier, you have a 1000hp monster that drinks diesel like a hoser drinks beer. There are a few here that have gone this way for their fuel upgrade. The reliability is already known to be good and you don't need to do a bunch of plumbing to install it. This is what I would do before going to an aftermarket RR system.
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Old 10-02-2013, 07:43 AM
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Thanks for the explanation, Frank. I'm wondering if my pump is not up to par and I don't want it to get to point of damaging injectors. My idle PSI is never aobve 64 and I know that is OK, but I wonder if a new unit would be worth it to replace the unit that has over 225K miles on it.
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Old 10-02-2013, 04:29 PM
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I know you just did your stud job... but what about doing a regulated return? That has its own FPR and would probably fix your problem
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Old 10-04-2013, 02:52 AM
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Try taking your tune back to stock and see what WOT does. I'd replace the blue spring first with a new one. My truck with 155s and blue spring won't drop under 59 at WOT on tow tune or 55 WOT on performance
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  #10  
Old 10-04-2013, 03:23 AM
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In stock form, it stays above 52. The blue spring is a little over a year old...
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