EFI fuel starvation issue.

[jim3326]

Good info with the fuel in tank angles, thanks. I was thinking maybe you had the accumulator on the wrong side of the HP pump from the way you listed it.
I have the same system (except the vented cap, mine has the expansion tank vented to the air cleaner) 23g. tank, filter, LP pump, acc, HP pump, pressure tapped between hardline and flex at frame 40psi, return to acc tee to tank. I haven't gone crawling yet but soon.

Jim W.

 

[garberz]

.....So solution one is modify my trail habits and never have less than 1/2 tank and be aware of my angular limitations and how long I can exceed them with my accumulator

Or

Cut open my tank and install a different pickup system.

Crap!

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If your going to cut open your tank, you might as well go with an in tank EFI pump.

 

[chuzie]

Good point on the pump. I reinstalled the tank for now. Time to do some research.

Btw- my idle run time on the accumulator is 7 min not 5 as previously stated.

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[garberz]

Have you seen these?

http://www.autoperformanceengineering.com/html/pickups.html

Dan Wheeler did a fuel cell thread and used these. Looks interesting.

http://classicbroncos.com/forums/showthread.php?t=174515&highlight=Walbro

 

[englewoodcowboy]

Don't know how hard it is to get inside of your tank but if you can drain it and install a baffled sump around the pick up say 4" high and have a 1/4" hole in a couple places around the bottom it may work to catch and hold fuel while you are in a camber situation briefly. You could even get a little mor involved by placing the holse in a manner that in those off camber situations that the fuel cannot drain from the baffled sump on particular angles such as nose up or down etc.

 

[chuzie]

I have enough in my accumulator for those brief off camber situations. Usually they are not too brief either because of traffic, a long climb, or working a complex obstacle.

Something to note...

I had a LOT of trouble priming my system today after I ran the accumulator dry with an empty tank.

I grounded the fuel test circuit and let it run for a good 10 minutes with 10 gallons in the tank and no fuel was moving.

I ended up disconnecting the LP line going into the accumulator and applied a small bit of suction and the fuel started flowing. THEN it was not flowing out of the accumulator. I disconnected the LP output line from the accumulator (supply to the HP pump) long enough to purge the air and all was well.

Why does my LP pump not have the guts to recover from a completely drained system and prime?

 

[chuzie]

garberz, I looked at those pickups. I like that they prevent the system from sucking air but I need something to keep fuel in the lines all the time not just keep the air out.

 

[chuzie]

Okay looked at the pickups again and read some stuff on pirate and looks like they are the ticket.

Gotta find a way to do this without cutting into my tank cuz that is just a pain in the butt. Thinking three pickups total. One in each rear corner and one in front center.

This should be interesting. More to come....

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[garberz]

Basically a check valve that lets in gas, but not air. Running two or more, it should never suck air. Please update on what you decide to do. I'd like to cut the top of the tank and use a Mustang in-tank pump and three Walbro's. NWM's 23 gal tank. That's coming up soon for me.

Mark

 

[MarkH@Wildhorse]

It sounds like you have the NWMP tank, not our current Sherman EFI tank.
I thought I had a pic, but I can't find it.
I used those walbro pickups (5 of them) and placed them in the corners of my NWMP tank to get rid of my pick up issues.
I might have a pic at home of it all.
I also run an accumulator and my truck will run way after I run out of oil pressure...

 

[chuzie]

Yep, that looks just like mine. Guess the guy I bought it from was either misinformed or just straight up lied about it. I don't care who made the tank; would have bought it either way.

Can I assume cutting it open the way you have in your picture is the best approach or do you think there is a better way?

 

[BUCKNBRONK]

I have that older efi tank in my rig, never had it run dry on any angle. is it possable ur pickup tube has a hole or a crack in it 1/2 way up chuzie?

 

[chuzie]

I didn't test the pickup for damage but I suppose it could be a possiblity. Nonetheless, the angle tests I did clearly show the pickup is easily uncovered.

Going with 4 of the Walbro pickups. Two MP-12 and two MP-14. Two in the front two corners and trying to determine where I want to place the two rear pickups. The angled rear piece is going to force me to drop the tank and perform another test to see where the best to place to place them will be.

 

[chuzie]

Installed a new carter p4070 and the return flow is significantly greater than the previous pumps. Hope this helps. More to come......

 

[chuck]

The ACC tank must have a return hose to the tank. That hose is how the ACC gets rid of the air that the low pressure pump picks up from the tank. Without the return to the tank the air will stay inside the ACC until there is only air. The HP pump will never suck gas through the ACC. Only the LP should be able to put gas into the ACC so if your HP sucked gas into the ACC you need to find out why. The low pressure pump will flow 55 liters per hr. you can't use that much fuel. So the LP should be fine.

 

[chuzie]

I have your ACC so it does go back to the tank but I have had folks talk about the downside to a 3 port ACC vs a 4 port (purging air) but no one has been able to provide me specific info on how to fix it.

At this point, I am not convinced the HP was sucking gas into the ACC. I think I was having issues with air in the ACC instead which was causing erratic behavior of the LP.

 

[Viperwolf1]

I think it was an undersized low pressure pump.

 

[chuck]

I have your ACC so it does go back to the tank but I have had folks talk about the downside to a 3 port ACC vs a 4 port (purging air) but no one has been able to provide me specific info on how to fix it.

At this point, I am not convinced the HP was sucking gas into the ACC. I think I was having issues with air in the ACC instead which was causing erratic behavior of the LP.

The HP sucks gas from the bottom of the ACC. All air that is put into the ACC by the LP pump will rise to the top and out to the tank. So the only way for the HP pump to get air is to suck all the gas out of the ACC or you have a neg. pressure leak between the fuel pickup and the HP pump. You can not see a neg. pressure leak most of the time because air is being sucked into the fuel system. So check that the pick up tube is tight in the threaded fitting inside the ACC and the fitting is tight in the housing and the housing to line fitting is tight and the hose that feeds the HP pump is good and tight.
I guess the LP could be too small but I haven't seen one too small. If the LP is not keeping up with the HP there is most likely a restriction between fuel pick up and the ACC. My racer at one point had a fuel starvation problem . A very long story shortened is the hose pick up inside the cell was wrapped up into a knot. Fuel would flow enough most of the time but sometimes not. We would find air in the filter before the pump. Fuel cells are filled with foam so no way to get air there as long as fuel was in the tank. Also look for kinks in the lines.
PS how would a 2 or 3 port ACC purge air?

 

[chuzie]

I am going to follow up on your suggestion and check my connections to ensure no neg leaks are present. The concern I have is when I ran my ACC dry, I couldn't get fuel to enter it after the fact until I cracked open the HP supply line to purge air. For whatever reason the system will not recover on its own from such a situation.

This is what broncobowsher posted in response to my inquiry as to why a 4 port ACC is better than a 3 port here http://classicbroncos.com/forums/showthread.php?p=2331643

"As the LP pumps air into the accumulator it blocks the flow of fuel returning from the fuel rail at the T and forces it back into the tank. Now the accumulator runs dry. Basicly you have a single loop system that has a pressure break between the 2 pumps.

By seperating the return off the fuel rail into the accumulator and the accumulator return to the main tank into seperate fitting on the accumulator you now allow fuel to continue to loop on the HP side and the LP side sucking bubbles has a chance to blow them right back into the tank.

Back to the downfalls of a T on the accumulator. Lets say you have a good LP pump that can pump faster then the HP can. The LP fills the accumulator. The difference in flow goes into the T. Mixes with the return off the rail and back into the tank. If you suck air and the pump can move it, you are just pumping air into the accumulator and blocking the return.
Lets go the other way around, HP pump moves more fuel then the LP pump can (this will also be the case when the LP pump sucks air as the LP pump movong air won't be that good at it). The HP pump is pulling fuel out of the accumulator faster then it is filled. No problem, the excess goes back in through the T-fitting. The flow through the single point off the accumulator is into the accumulator. Yes most of the HP feed is returning to the tank at the same rate the LP pump is removing it (minus fuel burned which doesn't add up to squat most of the time). So you are always putting fuel into the accumulator, never giving the accumulator a place to vent the air out at. How can it get out? You are feeding it with the LP pump, and with the excess flow from the engine. The only outlet is the supply to the HP pump.

3-port accumulators are doomed to fail. That T-fitting just isn't right for the flow to work in independent loops. 4-port accumulators that feed and vet everything off the top (except the feed to the HP pump) are the only way to get an accumulator to work. I think that is why there are so many accumulator horror stories. Systems plumbed poorly because it is easier to screw a T-fitting in them to actually make if flow correctly. I have run 4-port accumulators without issues. 4-port accumulators are how the factory did it in the early years of EFI, just look at the factory part in post #6.

So that is my beef with running a T fitting on the accumulator. Might as well not even run an accumulator at that point."


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[DirtDonk]

To get back to something you said on the first page I think Chuzie, what is your main pressure up at the injectors?
Didn't you say 20 psi? If this is an MPFI Ford setup, shouldn't it be more in the 35 to 40 range instead?

Or is that only when it's starving for fuel? With air in the system then, that could yield the lower pressures I assume.

Just wondering.

Paul