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Old 03-28-2010, 08:55 PM   #1
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Fuel PSI range to carb on GM 454

I understand SOME Winnie models using the P30/GM 454 setup also included an electric helper fuel pump to supplement the regular engine mounted mechanical unit.

I'm not yet sure if my '87 Winnie Super Chief has the extra electric pump, but I do have a Carter 7 PSI electric handy that I could add - but would prefer to only have it in use if the PSI at the Carb drops below 3-4 PSI or so, rather than steadily run. I have a suitable Hobbs Switch to use for controlling the setpoint for cut-in of the added electric pump, but dunno what the "normal" PSI is at the carb from a properly running OEM mechanical fuel pump is?

I'm thinking the OEM mechanical is probably around 5 PSI or so - but may be wrong, and have no idea what "normal" PSI might swing from different engine RPM and loads? I'm really looking for the added electric to operate primarily as a helper, not a full-time unit - but need an insight into typical OEM mechanical pump PSI ranges in varying driving conditions. YES, I'm also aware of recommended fuel cutoff in case of accident - and my Carter electric setup also includes a fuel bypass feature for proper fuel flow when that pump is shut down...

Any suggestions as to a good cut-in PSI setting for an added electric helper fuel pump?
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Old 03-29-2010, 04:25 AM   #2
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John - the normal fuel system pressure for a carb engine on average is 5-7 psi - I have seen slightly higher pressure (1-3 psi) on heavy duty applications but 5-7 is the norm- also one of the reasons they added an electric pump was to combat vapour lock and I beleive there was a bulletin out and a service/repair kit that included a low pressure electric pump (fuel injection pumps on newer vehicles usually runs at 30 psi or higher on average) to install as a fix for vapour lock on earlier P30 chassis with the big block Chev engine- at some point G.M. installed an extra pump on the production line as standard equipment and I have seen reference to these factory installations and RV's without the extra pumps on other forums - I would try a cut-in pressure of 3-4 and see how it works first - to high a pressure will force the needle of its seat and flood the carb so try a lower setting first- do you have any problems with vapour lock?
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Old 03-29-2010, 04:44 AM   #3
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5-7 will work as stated i ran 7-8 on a 8500 rpm car never had issues look on the fram rail on passenger side mine is behind the gen.
dave
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Old 03-29-2010, 11:24 AM   #4
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Originally Posted by whem2fish View Post
5-7 will work as stated i ran 7-8 on a 8500 rpm car never had issues look on the fram rail on passenger side mine is behind the gen.
dave
Sounds like about 5 PSI setting would work well then if I need to add the electric, the Carter I have is a 7 PSI unit, so shouldn't overpower the carb needle seat.

Are you saying you have the added electric booster pump, and it's located on the frame in the generator area? I have a fuel filter in that location, but no pump - I *thought* I had read that the manufacturer-added booster pumps were usually located inside the fuel tank? I wonder if a few others might chime in as to where theirs is physically located, if they have one?

NO issues with vapor lock I'm aware of, but we haven't had this '88 Winnie Super Chief long enough to be aware of all it's possible quirks - and we DO have lots or steep grades and high summer temps to deal with - I just prefer to be on the safe side, and besides, I already have a couple of these 7 PSI Carters laying around unused...
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Old 03-29-2010, 12:01 PM   #5
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Gary,

'87 Ford E350 chassis with 460 V8 here.... pump is inside the fuel tank, filter is driver's side on the rail, half way between tank and engine. I think inside the tank was pretty common, in the '80's anyway.

Bob
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Old 03-29-2010, 01:42 PM   #6
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im the 2nd owner 1985 fleetwood southwind i ask the owner about this fhe said it came that way it is a holly red pump (i think 11-13psi) with a regulator to bring it down then next to it is a small canister fuel filter
dave
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Old 03-29-2010, 09:51 PM   #7
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I need to check for an existing installed in-tank pump - but the way the 80 gallon tank is mounted makes any visual inspection pretty much impossible - and as I understand it, the power to the pump is controlled by contacts in the oil pressure sender - so the tank pump only operates AFTER oil pressure is present above a certain PSI - makes listening for the pump noise sorta hard with the engine running, maybe.

I'm not able to easily see wiring to the tank, so hard to determine if any of the wires I might see are fuel level sender, or in-tank pump. For sure, no EXTERNAL booster pump has yet been evident. Only clue MIGHT be any extra wires off the oil pressure sender - haven't yet seen exactly where that is installed on '88 Winnie 454 - any help?
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Old 03-30-2010, 12:40 AM   #8
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Fuel Pump

Gary - if you have an electric pump you will have a fuse for it in your chassis fuse panel (factory installed) or an in-line fuse if it has been added - in-tank fuel pumps are usually installed on fuel injected engines and will pressurize the system for the first ten to fifteen seconds after the key is on (before cranking the engine) and that is the humming noise you hear on an FI vehicle and an in-tank pump is cooled by the fuel itself so it has to be part of the pickup tube assembly which means that the wiring connector to the sending unit will have more wires than a standard setup (more than two - sending unit signal and ground wire) - electric fuel pump wiring usually has three or more wires - check any plastic wire conduit coming from the tank for these wires if you cannot get to the top of the tank- and also the oil pressure sending unit can be used in the fuel pump circuit or it can be used to cut off the ignition circuit instead ( or both in some applications ) but usually its in the fuel pump circuit on FI vehicles.
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Old 03-31-2010, 03:32 PM   #9
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Originally Posted by RV Mech Tech View Post
Gary - if you have an electric pump you will have a fuse for it in your chassis fuse panel (factory installed) or an in-line fuse if it has been added - in-tank fuel pumps are usually installed on fuel injected engines and will pressurize the system for the first ten to fifteen seconds after the key is on (before cranking the engine) and that is the humming noise you hear on an FI vehicle and an in-tank pump is cooled by the fuel itself so it has to be part of the pickup tube assembly which means that the wiring connector to the sending unit will have more wires than a standard setup (more than two - sending unit signal and ground wire) - electric fuel pump wiring usually has three or more wires - check any plastic wire conduit coming from the tank for these wires if you cannot get to the top of the tank- and also the oil pressure sending unit can be used in the fuel pump circuit or it can be used to cut off the ignition circuit instead ( or both in some applications ) but usually its in the fuel pump circuit on FI vehicles.
Thanks for the info - pretty much matches other input I've read - but also makes me wonder if the in-tank pumps I read about were typically only factory installed on FI engines - mine is carbureted...

I've never seen any specific info that includes the fuel system setup on my '88 Winnie Super Chief - and none of the MH documentation that came with my MH make any mention or include diagrams including anything other than the basic engine mounted mechanical pump.

When the snow stops falling here in eastern Oregon, gotta get in some "quality time" under the MH checking things out further...
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Old 04-04-2010, 01:42 PM   #10
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OK - looked at something I saw on another trip down under the 454 in the '88 Winnie - and took this pic of what looks like the take-off point for the engine oil pressure sending unit - PLUS, what looks like a possible control module for an added electric fuel pump? Dunno what else it could be for, but it's located at the passenger-side front of the engine at the block edge just above the oil pan. I *thought* others has indicated that the 454 oil pressure sensor point was on the topside of the engine, near the distributor?



Any comments welcome - and if weather improves, might get under the MH again today - try to at least listen back at the fuel tank for any sounds like a electric fuel pump when the ignition is switched on - IF it will come on without actually starting the engine...
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Old 04-04-2010, 02:59 PM   #11
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I've been very hesitant to enter this thread but I have personal knowledge of what they have and don't have...
First Rochestor carbs and most others like fuel pressure at the carb at 4-6 PSI, Hollys will take a dab more if you like them on your rig....
My 87 Winny (Chiefton) had NO provisions for the engine manual pump so they stuck the electric in the fuel tank....
Now my 83 had a stock A.C. delco on the engine and it would lean out with a heavy pull up the hills and IF the pedal was on the metal it would flatout die, SO I installed the carter street/strip electric pump and all was well on the hill climbs.
Problem was the mechanical pump could NOT draw e'nuf fuel through it on moderate hills and it took some time to figure that one out cuz the Carter boyz stated it would......Don't believe them folk's.
Out of frustration the manual pump (AC Delco) was changed out with the "Edelbrock 1722 manual pump" and the Carter street/strip pump was removed and replaced with a high volume low pressure electric (just for starting) and everthing is fine on any heavy pulls.
The distance from the tank to the manual engine pump is close to 30 feet (3/8 fuel line) and with any type of vacumm in the fuel tank just makes the manual fuel pump work even harder but the Edelbrock with a 110 free flow GPH and 6 PSI will carry it through easily.
If your running just "Electric" IMHO please carry a spare cuz they can & will drop dead at the most improper time....Just my thoughts

Jim
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Old 04-04-2010, 03:08 PM   #12
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Your picture just came into view......I would short the 2 wires together and listen for whatever starts up...!!!
Might be your missing fuel pump and that switch went south.

Jim
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Old 04-04-2010, 06:43 PM   #13
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WELL, happy to report that decent weather today permitted me to get under the Winnie fuel tank while my wife switched on the ignition...

YIPPEE! There was that neat sound of the pump inside doing it's thing - ran for a few seconds each time the ignition was switched on - and I assume it will then run steadily once engine oil pressure comes up - so, that makes one less chore for me to work on or worry over!

At some point, I'd like to at least temporarily install a fuel PSI gauge in the line to the carb to check and verify actual operating PSI - but will get to that later...

Thanks to all for the helpful input!
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Old 04-04-2010, 10:31 PM   #14
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Fuel pressure

Gary - the large canister with one wire is the sending unit for your oil pressure gauge and the other two wire one is the oil pressure/fuel pump switch - small block Chevs have these at the top behind the intake manifold and big blocks are located on the side like yours - glad to hear you already have an electric pump!
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