EFI fuel starvation

[tj]

I've worked out all the bugs in my EFi conversion (1991 Mustang EFI on a 1970 302) except for one.

I occasionally end up with fuel starvation while driving, regardless of the fuel level.

Stationary everything works fine and my plug in fuel pressure gauge reads right on factory spec for both idle and high RPM. But if I've been cruising for a while and push the pedal down the vehicle stumbles for about a minute or so before the fuel catches up. If I go around a corner or start up a hill, same think but it could be me giving it more throttle.

Here is my fuel delivery system: vented fuel tank-> 3/8ths rubber fuel line to Fram high volume HP-1 fuel filter -> 3/8ths rubber fuel line to a high volume low pressure fuel pump -> 3/8ths rubber line to B.C. Broncos fuel accumulator -> 3/8ths fuel line to Ford high pressure fuel pump -> Ford plastic 3/8ths plastic fuel line to Mustang steel line & duel distributor -> stock Mustang fuel pressure regulator -> 7/16ths line from pressure regulator to fuel accumulator and back to the tank. The pumps and filters are adjacent to one another at the same with each other and about even with the bottom third of the fuel tank.

All fuel lines are new, fuel tank is new, fuel filters are new, accumulator & low pressure pump are new. High pressure pump and regulator are used.

The Fram filter is rated for a higher volume than the low pressure pump. The low pressure pump is rated for about twice the volume as the Ford high pressure pump so I suspect the low pressure pump has set up a fuel flow into the accumulator and back to the fuel tank via the return line.

Pressures are spot on when measured with the vehicle stationary and flow is OK under light throttle cruise but the volume is not there a second after opening the throttle.

Has anyone ran into this problem before? I couldn't find anything in the archives. I think it is a flow restriction and wonder if it could be caused by the low pressure pump pumping fuel into the accumulator.

Any ideas? Instant cures?

 

[justinoshea]

I had a fuel delivery problem during cruise & WOT that ended up being a voltage issue; new 130 amp alternator fixed it.

Check the flow rate of your entire system. catch some fuel in a can or bucket from the return right before it goes into the tank. turn on the pump and run it for 30 seconds. (verify rail pressure). calculate the flow from the amount in the can and the time it took to fill. if it is below the pump rating, you have a problem.

 

[Broncobowsher]

It sounds like the accumulator isn't doing it's job. Double check that the high pressure pump is drawing fuel off the bottom of the accumulator. If it is pulling it off the top it will suck the first bubble it sees.

Another thing to check, rig a test light to the high pressure pump and go for a drive. When the fuel pressure drops off does the light stay on? If yes then it really is a plumbing issue. If the light turns off as the fuel pressure drops off you have an eletrical issue dropping off the power under accel.

Further checks, adaquate flow, unhook the return line from the EFI regulator and put into a gas can (plug the accumulator to prevent leaks there), you should have a good flow out the return line back into the accumulator. The high pressure pump may be bad and not have enough volume to exceed idle loads.
Same check for the return line back to the tank, this time for the low pressure pump flow.

 

[jurob]

what is set your fp at? factory reg should be in the 39-43 range with vac off. what does it go down to when the problem occurs? you are able to observe fp while driving?

why 2 pumps when 1 good pump is more than enough? you should have installed a efi inine 10 micron before the pump and a efi inline 100 micron after the pump. one filter good for one pump and another good for another doesn't soound like a good idea.

which 2 pumps do you have? i don't know high pressure and low pressure. i know for the intanks walbro made a 255 hi and lo pressure. no need for high pressure is you are n/a because 255lph of fuel is alot. i presonally run 255 walbro in lines y'd into each other and that should be good to 750+ hp.


pull your vacuum hose to your regulator with veh running. see fuel? could be bad reg.

assuming your pumps are both rated to at least 88lph i would remove one and see how it does. also bypass filters to see if thats a restriction.

 

[Duke Nukem]

I've been running a low pressure/high pressure fuel pump combination with the BCB accumulator in between for a few years now with no problems. It is not your setup that is causing this issue. As was mentioned earlier, verify first whether it is a flow versus electrical issue.

 

[jurob]

Duke,
curious, why a hi and low pressure pumps inline of each other?

 

[Broncobowsher]

Duke,
curious, why a hi and low pressure pumps inline of each other?

It's acturally more of the accumulator in the middle that we are after. If you get to running severe angles there are times when the fuel pickup in the tank can suck air. This is worse with less gas in the tank. On a carb this is no big deal as the fuel bowls will typically keep the engine running long enough to get out of the situation, plus what ever is left in the fuel lines.
But EFI can't take momentary losses in fuel pressure. Loose fuel going into the pump and it looses pressure, loosing pressure elimanates any fuel getting to the engine and the engine stalls in a couple of revolutions.
The low pressure pump is to pum fuel from the main tank into a mini fuel tank (the accumulator) where the high pressure pump always has a source of fuel.

The single pump theory works fine on street truck that never go offroad and/or keep there tanks full. I have known people who could tell how much gas was in the tank by how hard they could hit the gas from a stop before the engine starved for fuel because the pickup gulped air. Modern OEM use a chamber that surrounds the pump, with a little venturi action from the return line it sucks fuel off the floor of the gas tank and overflows over the top back into the tank. This is what lets modern vehicles run at all kinds of stupid angles on fumes. The accumulator is the same thing except outside the gas tank and uses a pump to fill it instead of fancy venturi pump action.

Many of the aftermarket gastanks (newer ones) will have baffles inside to help control fuel slosh. That is the pump going dry during acceleration or turns. Baffled tanks have not been used by factories for probably 10 years or so now (varies by make) as they found they still had issues, the in tank fuel chamber is much more cost effective for mass production.

If you look at older Ford EFI trucks there is a soup can sized can inside the frame rail on the drivers side with 4 fuel lines attached to it. This is an accumulator. Uses 2 pumps. Very effective way of transitioning from carbs to EFI, maintained the same basic fuel tank without extra baffles or engineering (remember this is the late 80's). Once everything was EFI and there was no longer a need for carb application gas tanks they changed. That is when they figured it was more cost effective to eliminate the second (actually the first) fuel pump and just stick the high pressure in the tank. But to keep the slosh and stall condition at bay, the fuel chamber.

A few years ago I owned a Ford car that was a transitation period. That little Escort had a single fuel pump in the tank, but the tank lacked any chamber/accumulator. When the tank ran low, the engine would die in the middle of a left turn. Straighten up, wait a second and the power came back. The opposite would happen on a right turn, the engine would loose oil pressure and the little red warning light would come on if it was a quart low. I could check how much gas and oil I had by how the car responded pulling into the neighborhood. That sucked and it was only a car that had no power and was expected to be driven on flat ground.

Accumulators are a great idea for those that actually plan to go offroad, its just trying to figure what is going on with this one that actually makes it a challange. Something is not right, but what it is I can't pick out easily. Going to a single pump could be useful for diagnosis, but expect problems if you actually work the truck.

 

[Goin Off Bronco]

in line check valve to keep pump primed

 

[ransil]

If you think its the accumulator bypass it and test.
I run my trail truck with out an accumulator and it runs fine.

 

[Broncobowsher]

in line check valve to keep pump primed

What???%)
Fuel pumps have a built in check valve. There should not be a need to add an extra. You need a new fuel pump if you are looking at adding a check valve.
The problem isn't with fuel draining out of the fuel system when parked, it is when driving. A check valve won't do anything except take money out of you pocket and create a future problem spot.

 

[Goin Off Bronco]

You might want to look at this link and search thru the site also. lots of great knowledge. This check valve helps to keep pressure sucked up to the pump(kinda like a finger on end of a straw) this is most desired when your pump is mounted up higher then the pick up point(like I read in this post) also when running a couple of pumps. seems a great part to have. I have it. One pump, one check valve, 1/2" lines,2 filters, regulator and a 3/8 return. NO fuel delivery probs at all. No accumulator(but i did weld a pick up tube in the bottom of the tank that worms around and picks up against the back wall also). Constant 40 psi.


http://www.aeromotiveinc.com/products.php?cat=8&catsub=0&prod=39

or better yet call their tech line. seems things like these often over looked.

 

[Broncobowsher]

Yes, I am very familer with Aeromotive stuff. I grew up down the street from them by chance.
The check valve with duel pumps is when using 2 pumps in parallel like I did on an AMX race car. Small durable pump for street use, kick on the monster pump when putting out the 700HP and then kicking on the bottle.

The accumulator is for a system using the 2 pumps in series (with the accumulator in the middle actually making it a double loop joined at the accululator)

So I will still stand on the no check valve needed. The check valve us good for keeping a pump primed (not a problem as the engine does start and run) or preventing fuel from running backwards through a pump that isn't running (race pumps run in parrallel). I have done several fuel system, worked out the bugs (not patched them but actually found the engineering fault and corrected it).

The system as originally posted is sound, there is just something not right. Finding the problem is just being a little challenging. Once it get up and running the engine will have fuel until the tank is dry.

 

[scsm76]

Are you running the large spin on filter type accumulator, if so check that the pick up tube hasn't come loose.

 

[tj]

Accumulators are a great idea for those that actually plan to go offroad, its just trying to figure what is going on with this one that actually makes it a challange. Something is not right, but what it is I can't pick out easily.

Fuel tank = no baffles which is why I want the accumulator in the circuit.

First fuel filter = Fram HPG1, rated at 90 GPH, has new filter

Low pressure pump = Carter 100 GPH, 8 PSI

Accumulator = B.C. Broncos connected per their diagram for a single tank

High pressure pump = Stock Ford Pickup pulled from a wrecking yard, about 45 GPH

I have a power indicator light permanently wired to the wire going to the fuel pumps so I can keep an eye on that. I do not loose power when the problem occurs.

I can not read fuel pressure when driving. I have a sock '91 Mustang fuel pressure regulator. At idle the gauge reads 40 PSI, with the throttle at 3000 RPM the gauge reads 30 PSI. According to my manual that is spot on for those conditions. I really don't have easy space to install a fuel pressure gauge on my instrument panel and it would require the purchase of a gauge, tube and aftermarket regulator with a gauge port.

The problem doesn't occur when I have been driving at different throttle settings. It seems most noticeable when the engine has been cruising at a single throttle setting for a while and I open it up. What happens is a lot of typical running out of fuel hesitations until the fuel catches up.

It feels a lot like if you have too large four barrel carb that has a weak accelerator pump and you punch the throttle to the floor.

I'm suspecting that my high volume low pressure pump running into what is basically an open circuit may be slightly overwhelming my 90 GPH first filter and maybe setting up adverse currents within the accumulator.

 

[Broncobowsher]

I am starting to suspect less fuel issue and more EFI glitch after reading that.