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Old 08-15-2012, 05:00 PM   #1
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Fuel Pressure Specifications for 454 SPFI

I am looking to find out what the fuel pressure specifications are for a Sequential Port Fuel Injected 454. For my vehicle I took the following Data and trying to judge whether this is within specifications.

At Key On - Surges to 58 psi and then drops back to 52 psi
At Idle - 49 psi
Upon Light Acceleration - 53 - 55 psi
At WOT - 58 psi
Upon Engine Shutdown - Surges to 58 then drops back to 52
Very Little Pressure decay after shutdown - 51 psi at 10 minutes 49 psi an hour later

Does this look "normal" for this engine with SPFI? I had engine troubles on a trip. I replaced the fuel filter on the road which seems to have solved the issue based on no issues on my return trip but am trying to be proactive to determine whether I have a weak fuel pump or not. Any help would be greatly appreciated.
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Old 08-15-2012, 07:39 PM   #2
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Engine NOT running 55 - 62 psi at 0 rpm
Note: Check pressure with the key ON and the engine NOT running

Also note: Some fuel pressure testers are +- a few psi

I think you're in the right area though, plus I'm sure you'll have some head loss (pressure) since the fuel lines are longer than the normal chassis.
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Old 08-15-2012, 08:15 PM   #3
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I agree, that's ballpark for port-injected EFI.
You had fuel issues - throw any codes that would give more info?
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Old 08-15-2012, 08:45 PM   #4
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Yes, I had issues about 90 minutes into a drive. Ambient temps were very warm. Reading 102F in the induction air temp (read from OBDII Port). Engine sputtered and coughed/backfired. Started losing power. More & more throttle but less and less power. Even had engine stall. I started noticing a pattern that I mostly started to lose power on and after a hill climb, after passing or after doing higher accel on an on-ramp. This trouble resembled we had driving in the mountains of Penn 6 years ago. That problem was ignition related. Saw arcing on the coil tower. Replaced plugs, cap, rotor and ignition coil. Completely solved that issue. With that history in mind, I tried a similar remedy this time by replacing, coil cap and rotor on the road. Upon initial drive-away, it seemed to eliminate the problem. 10 miles down the road it started doing the same thing. I babied it down the road to our final destination and noticed that if I didn't get into the throttle, it mostly seemed normal or at least I didn't lose all power and stall.

The next morning I took the toad to the local NAPA store, picked up a replacement fuel filter. I crawled underneath and replaced the fuel filter at the campground. Two days later drove home without any incident for the 180 mile drive. I will say though that it was at least 20F cooler that day. So not for sure that temperature had anything to do with my issue. For now, it seems normal but I wanted to do my due dilligence (at home) to avoid an on-road issue again. Thought it prudent to try to rule out a fuel pump issue.

The coach only has a little over 15,000 miles on it and that was the first time I changed out the fuel filter.

Thank you very much for the reply. Any other thoughts?
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Old 08-15-2012, 08:50 PM   #5
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Response to gauto5150. No DTC codes. Fuel pressure upon key on (engine off) goes immediately to 58 psi then backs down to 52 psi. Looks like Pressure regulator is responding to changing engine vacuum as evidenced in the pressure change upon light accels and WOTs. I am just not sure if the pump is supposed to develop any more pressure than 58 psi. Took a short drive and pressure NEVER gets about 58 psi no matter what.
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Old 08-15-2012, 09:21 PM   #6
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lkaras, If it has a closed loop fuel system, then fuel pressure is determined by the regulator, not by the pump. Most EFI fuel pumps can put out 90+ psi, but they start to draw a lot of current. I'm told that some RVs do not have closed loop fuel systems - maybe part of why some tend to vapor lock.

You have OBD real time. If it happens again, I'd be looking for fuel trims that go way up (engine trying to get more fuel) and 02 sensors that indicate lean. There may be an indication of injector pulse width - or injector duty cycle which would be high under fuel starvation. And of course, you can look at fuel pressure.
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Old 08-16-2012, 10:54 AM   #7
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Thank You cb1000rider. Unfortunately I only have access to a few OBDII parameters through my Garmin Eco Route HD Device. Unfortunately these other parameters you suggest are not available.
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Old 08-16-2012, 11:55 AM   #8
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have an android phone? For about $30 you can have access to almost all OBD parameters... Or you can buy an Android tablet.

This requires a bluetooth dongle, see my prior posts.
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Old 08-16-2012, 12:31 PM   #9
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Thank You very much. I'll check it out!
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Old 08-17-2012, 11:24 PM   #10
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I did one last test tonight. I removed the fuel filter and put a fuel pressure gauge to dead-head the pressure from the pump. The pump pressurized the fuel line to 85 psi. Does that seem a little low to anyone?
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Old 08-18-2012, 07:52 AM   #11
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There is a filter on the pickup side of the fuel pump that you might want to look into. The screen picks up dirt from the tank and if it can't pass through it will restrict the fuel. When you turn the engine off the material will fall off and the next time you start it it will run fine for a while till it stops up again. Just somthing else to look into. I have seen this many times. (Retired auto truck & anything mechanic)
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Old 08-18-2012, 10:05 AM   #12
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Not for your engine but my experience was with marine engines that although they are MPI with electric fuel pumps they are mechanical regulators. Trash causes over fueling and some had screens that were too fine and would plug causing under fueling. Might be worth checking the regulator out as well.
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Old 08-20-2012, 07:55 AM   #13
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All good input. Thank you!

I have recently heard that the normal pump pressure for Key On - Engine Off is 55 - 62 psi. Per my earlier post, I get 58 but only for a few a second then it backs down to 52. I know it's only a few psi but might this be an indication of a pressure regulator going bad?

What is the normal failure mode of a pressure regulator on this engine? Does the spring weaken and you get reduced pressure or do they usually just fail outright?
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Old 08-20-2012, 07:58 AM   #14
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Quote:
Originally Posted by rssnape View Post
Not for your engine but my experience was with marine engines that although they are MPI with electric fuel pumps they are mechanical regulators. Trash causes over fueling and some had screens that were too fine and would plug causing under fueling. Might be worth checking the regulator out as well.

Thank you for the input. Just so I fully undertsand your feedback, are you saying there is a screen at the pressure reuglator too? OR Are you referring to the "screen" at the pump in the tank?
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