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Fuel pressure/injectors/tune issue?

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Old 06-23-2013, 01:05 AM   #1
mcm95403
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Default Fuel pressure/injectors/tune issue?

Short history first: A few weeks ago I installed my Holley AFPR and set the pressure to 46 psi w/o vacuum. I've been really bust with work so I didn't pay much attention at first to how it ran.

I thought it was running better but I've noticed the last couple of weeks that my mileage on the freeway has been significantly lower - 23-21, easily dipping into the upper teens at times - where usually it's hovering around 27, sometimes 24-23. I've also noticed that it's not running well (as in rough, not as responsive) but then takes off hard kind of like a switch is flipped when you hit it to half throttle or more.

I thought that perhaps I have a leaky injector, maybe chewed up a plug, or something like that. Tonight driving home I was thinking aobut it and tried bumping up the fuel pressure by about 10 pounds. All the symptoms immediately went away. It's now back to motorcycle-like throttle response, mileage went right back to 27 at cruise on flat sections of freeway, no more rough idle, no problems.

I have the Bosch III injectors which are supposed to be 24 lb/hr at 43.5 psi and a PCM4less tune. So I'm wondering if the tune is just that far off, are the injectors undersized for the new engine, or is running almost 60 pounds of fuel pressure "normal" for my setup?

Sorry, but I don't have any data logging available.
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Old 06-23-2013, 01:47 AM   #2
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I'm running Bosch III injectors at 48psi and injector constant set at 27. Data logs show that is working good
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Old 06-30-2013, 01:34 AM   #3
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I spoke to FIC and PCM4less this week. It appears that I need bigger injectors.

While I'm in there I may just go ahead and locate a Super Ram.
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Old 06-30-2013, 08:17 AM   #4
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If you got sold the Bosch yellow 280-155-700 they're too small. Without stated what you have and what you flowrate is programmed for it's pretty hard to advise.
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Old 06-30-2013, 08:26 AM   #5
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Datalog will tell you what it needs.
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