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In tank pump pressure spec?

85_Ranger4x4

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Does anyone know what the low pressure pump in the tank is supposed to put out before it gets to the frame mounted high pressure pump?
 


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alwaysFlOoReD

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Iirc...
5 to 10 psi.
 

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Doesn't have pressure, technically, just flow, I would guess 40gal/hour minimum, probably rated at 50-60gal/hr
Which would be the same for high pressure pump

Pressure comes from the fuel the system can't use, like oil pressure
The intank pump was "low pressure" so yes probably rated at 10psi for use on carb systems, so pump keeps spinning at full speed but because of the design its not "pumping" any fuel above that pressure

But high pressure pumps can do 80+psi so fuel pressure regulator was added to release fuel back to the tank once the desired back pressure was reached, like 30-40psi, or 60psi on later models

If you want to test fuel pump get a container and hot wire pump and see how much fuel it can pump out in one minute, then do the math
And you can put a pressure tester on it to see its "stall speed" pressure, thats the point when the design(gaps) reaches it limit, so its spinning but not pumping fuel until pressure is a bit lower
 

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On the old carb pumps, there was a fuel flow spec, like RonD indicates. Spec was something like one pint in ten seconds. (Thats an example, not a true spec.)
 

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I put a new one in my truck a last year, I am only getting like 3psi max which seems low.

Runs great for the most part, letting it breath and it isn't as whoopie as I think it could be. And the carb manual recommends 7psi.
 
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As long as the float bowls stay full, it shouldn't matter?
 

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I read one time it was like 8 psi. But yes flow is most important.
 

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Yes, the flow is what matters vs the pressure
Flow vs Demand = pressure(well back pressure)
3psi at idle means 3psi of unneeded fuel at the carb, but at WOT that could drop to 0psi so flow was not enough to keep float bowl full when max. fuel flow is needed, pump is under rated for horsepower/fuel demand
If the 3psi could be maintained at any fuel demand then there would be no problem

Above 5psi is usually spec for most engines and carbs to have enough reserve flow for that engine/carb setup

Fuel injection is different in that the fuel needs to SPRAY out of the injector tip to get best air/fuel mix, vs being SUCKED out of a Jet
So you need higher pressure to get that spraying pattern vs dripping out, lol
You need a pump that can maintain a flow that can hold pressure above say 30psi for any fuel demand

The pressure in EFI needs to be stable so computer can correctly calculate open time for each injector
Less fuel flows out at 10psi vs 30psi, computers are usually OK with +/- 8psi difference at the injectors
So higher pressure pumps are usually capable of much higher pressure than computer requires, i.e. 80+psi, that way there is always enough reserve flow to maintain the 30psi, or 60psi, back pressure at the injectors

But higher pressure pumps have a big problem, they have almost no suction to pull fuel in to the pump
Which is why the low pressure "lift pump" was required in the tank when Rangers were first converted to EFI
The high pressure frame rail pump can't suck in fuel from the tank

Lower pressure pumps have good suction, i.e. mechanical fuel pumps on the engine could SUCK fuel up and out of the fuel tank from 4ft or more away from the pump

In tank high pressure pumps don't need the suction because the gasoline weight pushes fuel into the pump
 
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85_Ranger4x4

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That is what I am wondering about.

And its a spectra pump so I dunno if I got a bad one or if they are all like this.

I have heard other guys run the low pressure pump with a V8 fine though.

I have played with the rods and jets to no avail, trying to throw more fuel at it doesn't help.

So I get to wondering if the more fuel isn't there to start with.
 

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Seems most carbs I've dealt with over the years required 5 to 7 psi of pressure. On our off road builds we would use a pressure regulator and dial that pressure down to around 3 psi in most cases. The key was to lower pressure to help prevent flooding out the engine when the float gets to bouncing... while not starving the engine while on WOT runs.

I assume you tested fuel pressure before your pressure regulator? Speaking of that regulator... I had quit using that style regulator for the most part on our stuff and switched to the diaphragm style regulators. I had some issues with your style maintaining consistent pressure and providing adequate flow.

Float level and drop play heavy into all of this too. Seems last time I asked you never checked it because you were happy with the drivability. If you haven't check... might be time to do it.

For flow volume... I usually did the un-scientific pop bottle test. Your pump should about fill a pop bottle in about 10 seconds. Try doing it in front of the pressure regulator and again after the regulator. Wouldn't surprise me if that regulator was causing some volume issues.
 

85_Ranger4x4

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Seems most carbs I've dealt with over the years required 5 to 7 psi of pressure. On our off road builds we would use a pressure regulator and dial that pressure down to around 3 psi in most cases. The key was to lower pressure to help prevent flooding out the engine when the float gets to bouncing... while not starving the engine while on WOT runs.

I assume you tested fuel pressure before your pressure regulator? Speaking of that regulator... I had quit using that style regulator for the most part on our stuff and switched to the diaphragm style regulators. I had some issues with your style maintaining consistent pressure and providing adequate flow.

Float level and drop play heavy into all of this too. Seems last time I asked you never checked it because you were happy with the drivability. If you haven't check... might be time to do it.

For flow volume... I usually did the un-scientific pop bottle test. Your pump should about fill a pop bottle in about 10 seconds. Try doing it in front of the pressure regulator and again after the regulator. Wouldn't surprise me if that regulator was causing some volume issues.
I flat out deleted the regulator when I swapped the fuel pump last summer and it made no difference. I thought 3psi for a new pump was kinda low but it seemed to run the same. When I first did the V8 swap I had a cheap Mr Gasket pump on the frame, it had been losing pressure (it was probably down to like 4-5 when I did the 5 speed swap) so I swapped in the '86 in take pump last summer to see if I could get some psi back and to replace my flaky fuel sender.

If I shift below like 3500rpm (like I normally do) driveabilitly is great.

Ok, story time.

Way back when I V8 swapped the truck the it had a C5 3 speed automatic. Ran great, no vibe at all.

Then I 5 speed swapped it and noticed this weird vibration at around 3500 under hard acceleration. Power kind of flatlines too.

So I redid the rear suspension (which needed done) to no effect.

Driveline angle was close, like 3* off so it wasn't perfect. The distance between the outputshaft and the mounting base of the M5OD compared to the C5 is a little taller. Swapped the transmission crossmember with one for an explorer last summer and got it down to 1*. No effect.

Well that is weird, maybe I need traction bars? Gopro did show a little spring wrap but it doesn't really look like a whole lot. I actually bugged James Duff asking if they could piece together a kit that would fit a first gen with a 31 spline 8.8 but they never replied.

Well last month I was driving in really wacky weather, tornado sirens when I left town and the whole bit. I was trying to maintain 55mph in fifth and as I kept feeding it more onions I felt the secondaries in the pedal, just to take it easy on the truck I grabbed fourth. Guessing I was bucking a 50mph headwind (so the truck would be plowing air like it was going over 100)

And there was my vibration, constantly cruising in fourth. :dntknw:

So unless the truck was "pushing" hard enough to be wrapping the explorer leaf springs at 55mph cruising... well I get to thinking maybe it isn't driveline/suspension related? Most of the time I had the 3spd I lived in town, never really drove it far or fast. Did the automatic just mask the possible fuel issue by not letting it wind out? I didn't pay good enough attention at the time but I don't think it shifted that high and I never ran in any tornado weather in it to load the truck like I did last month.

Float height right on at 7/16". Tried playing with the tune and throw a little more fuel at it last summer which didn't gain anything, the next notch up on the chart (both over and up) was too rich. I have tried to push thru the vibration and get into the secondaries a couple weeks ago and while I could feel the secondaries in the pedal nothing really happens...

Its been too cold to do much since the great tornado race to do much, aside from a spell a couple weeks ago when my wife killed a tire on her car and I did the secondary test while I was dd'ing it I haven't really done much at all with the truck.
 
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don4331

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Do you have a fuel pressure gauge in the truck - that would be the easiest way to tell if you are having fuel delivery issues under load. The other one is do you get detonation because the truck is running lean. Actually, that's a test you can do* - run the engine to the point where you are having issue, then immediately turn off the engine, let it coast to stop and pull a couple plugs. *Assumes you don't have a permanently mounted fuel pressure guage.
In our drag cars, you always watched 3 gauges - Tach, oil and fuel pressure - drop in fuel pressure and the engine was running lean and the detonation would instantly wipe out the engine.

Assuming your 302 makes say 240 hp (WOT at power peak) and you are running a little rich (0.6 lb fuel/hp/hr), your pump needs to make at least 25 gallons/hr.

The aside - Running into 50mph headwind at 50mph will be enough to flex the springs. The quick test would be put it in 4x4 and see if there is any difference (probably not something you want to stop to turn the hubs in for when running from tornados, but something to test on your daily drive) Note: If there is really different wear between front and rear tires you would get inconsistent results at best.

@RonD The low pressure engine fuel pump pulled from the rear tank in long box supercab f150 4x4 the neighbour had- that's way more than 14' of suction. :p. It was known for occasional vapour lock on hot summer days and you would have to switch to the front tank and hope it had some gas still in it (Yes, Saskatchewan gets over 40C/100F in August).
 

85_Ranger4x4

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Do you have a fuel pressure gauge in the truck - that would be the easiest way to tell if you are having fuel delivery issues under load. The other one is do you get detonation because the truck is running lean. Actually, that's a test you can do* - run the engine to the point where you are having issue, then immediately turn off the engine, let it coast to stop and pull a couple plugs. *Assumes you don't have a permanently mounted fuel pressure guage.
In our drag cars, you always watched 3 gauges - Tach, oil and fuel pressure - drop in fuel pressure and the engine was running lean and the detonation would instantly wipe out the engine.

Assuming your 302 makes say 240 hp (WOT at power peak) and you are running a little rich (0.6 lb fuel/hp/hr), your pump needs to make at least 25 gallons/hr.

The aside - Running into 50mph headwind at 50mph will be enough to flex the springs. The quick test would be put it in 4x4 and see if there is any difference (probably not something you want to stop to turn the hubs in for when running from tornados, but something to test on your daily drive) Note: If there is really different wear between front and rear tires you would get inconsistent results at best.

@RonD The low pressure engine fuel pump pulled from the rear tank in long box supercab f150 4x4 the neighbour had- that's way more than 14' of suction. :p. It was known for occasional vapour lock on hot summer days and you would have to switch to the front tank and hope it had some gas still in it (Yes, Saskatchewan gets over 40C/100F in August).
The gauge is under the hood.

Totally spit balling but I would guess it is around 200hp.
 

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Are you able to watch the gauge using your GoPro?
 

85_Ranger4x4

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Are you able to watch the gauge using your GoPro?
I thought about that last night.

I am going to try Gump's pop bottle test too.
 

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