EFI fuel pumps 'vapor locking', then dying?

[needabronco]

I recently finished my efi swap, and everything was running great. I put around a 100 miles or so on it around town to make sure there were no issues. Last week I headed up to Colorado to camp and experienced what I can only describe as 'vapor lock' issues, each time it happened I was above 10,000' and was in 4 Low, idling in first gear. What was happening seemed like fuel was boiling in the fuel line and fuel rail and overheating the fuel pumps. It happened a total of 3 times the last which was the worst was at 13,000'. My engine is in excellant condition and never runs hotter than 190*, even in 110 degree heat. Now my engine will run for about 5 minutes then it dies, after the accumulator runs out of fuel. Both pumps turn on but feel week, how can I check my pumps idividually to determine what the problem is? I think the low pressure pump is week and doesn't keep up with the high pressure pump(?).

My fuel system consists of a low pressure pump that feeds an accumulator then to the high pressure pump. My fuel lines are routed at least 12-18"s from the exhaust and the lines are routed up to just under the master cylinder, from there, there is about 8"s of high pressure line to the fuel rail. Both pumps were new from BCB, and are mounted on the frame rail between the tanks.

Anyone experience this and have a good permanent fix?

Thanks
Casey

 

[Socal Tom]

I suspect that do to the high altitude, and the heat trapped under the rig when it doesn't move, as well as the distance between the tank and the LP pump the fuel between the LP pump and the tank boiled creating the vapor lock condition between the tank and the pump.

To keep an eye on my fuel pumps I put a glass filter between the LP pump and the accumulator, and another one on the return line to the tank. That way you can see if fuel is flowing.


There are a couple of possible solutions. Here are my recommendations in order of what it most likely to work in the long term.
Solution 1)
In tank pump
Solution 2)1 pump system
This will work if you have an after market tank. If you have a stock tank then you probably need the 2 pump system.
Get rid of the accumulator and the LP pump. Mount the HP pump within 12 -24 inches of the tank ( meaning use less than 2 ft of hose, and use a small filter to keep the pump clean)

Solution 2) Move the LP pump as close to the tank as possible, and mount it as low as possible. Any fuel filter between the tank and pump should be a small filter ( larger filters hold fuel longer and give it more time to get hot. Add a small valve to the return line between the accumulator to the tank, adjust the valve so you hold 3 to 5 psi worth of pressure. This takes load off of the LP pump, and ensures that fuel between the LP pump and the HP pump are under pressure so they don't boil.


Also, reduce the length of your fuel line as much as possible so that fuel doesn't hang around underneath the rig.
Tom

 

[COBlu77]

I never could get the LP/Accumulator/ HP pump system to work at high altitude. I've probably posted this 10 times, but I tried everything and could never get the 2 pump system to work reliably at high altitude. I went to one good Walbro HP pump mounted to the crossmember right in front of the tank. No LP pump, no accumulator, no fuel starvation, no problems. Eventually I was able to trade someone with a BC tank designed for an in-tank pump for my older version. I now run an in-tank pump and think that is the ultimate solution.

As best I could tell, at altitude the LP pump has to work at a 100% and they are not designed to do so. Also, putting the HP pump any distance from the tank makes it a puller not a pusher, which is not how they're designed. At higher altitudes it takes more work from the pumps to pressurize the fuel to 30-40 psi. Eventually the LP pump overheats and shuts off. It also creates a vapor lock at the point of the LP pump or the accumulator.

Everyone I know in CO that has done an EFI conversion, has either gone to an in-tank pump or has had some issue like you're having. Socal Tom has it dead on.

 

[needabronco]

You guys are both dead on with what is happening, and now it seems the lp pump is only working for a few minutes then shuts down, and eventually the accumulator emptys out and the hp pump runs dry. I guess this was an expensive lesson.... Is there a way to test the pumps out to see if they are any good anymore?

Glad to hear it's a common high altitude issue, not something I missed or messed up with my conversion.

If I could afford a 23 gallon tank with the in tank pump, I'd just do that. But for now I need to figure out how to do this with 2 tanks.

I'm not happy about spending another $150 on pumps to try something else out, thats 1/3 of a new tank and pump!

On a good note I managed 16.22 MPG's on the road between Delores and Ridgeway Colorado, and 13.5 wheelin....

 

[COBlu77]

Congrats on the MPG's.

I kept trying to use 2 tanks, also. That only made the situation worse, because the Pollack valves I kept buying weren't up to the higher pressures that EFI requires. Eventually the valve would be pulling from both tanks and would usually pull from the front one, because it was easier to pull from. I'd think I was running on the rear tank and I'd run out of gas, because the front was empty. I thought at first I was getting really great mileage from the conversion. Like I said, it drove me crazy for about 6 mo's, several pumps, Pollack tank switches and a few tows home.

Until you can swing a tank with an in-tank pump, I would run one HP pump, just in front of the rear tank and run strictly from the rear. You could then use a LP pump, on a relay switched through your fuel gauge switch and just pump from the front to fill the rear. You could tee into the filler vent on the rear tank. I plan on eventually doing this with my spare tank, but it hasn't been a priority, because 23 gal is plenty and the last thing I need is more weight. There are other ways, but I think that they'd become a plumbing nitemare.

 

[FASTERDAMITT]

One fuel pump level with the bottom of the fuel tank works fine for me. I am in Palm Springs where the temp is sometimes 120 degrees. What I was explained by mass flo is the pump does not like drawing the fuel up out of the tank in heated situations. When I bought my system I mounted the pump up on the frame. I had all kinds of problems. An in tank pump or level with the botom will most likely solve your issue.
As for the twin fuel tanks, I use my second tank only as storage. When I need fuel I have a transfer pump that sends fuel to the main tank.

Tom

 

[flousberg]

I had the exact same issues in MOAB. It totally sucks to be on the trail climbing an obstacle and have it die on you.

Solution: in tank pump.

FASTERDAMITT, it is not temperature as much as altitude. Mine did it too me at 13,000' and 75°F on the Flat tops by GS.

 

[Sabas]

SoCal Tom hit it on the head. I have run 1 fuel pump, just outside the tank.
I also routed my fuel lines away from the frame rails. The frame rails get really warm on long days.

Sabas

 

[needabronco]

I think I'm going to park it for a couple of months and save up for a BCB efi tank with the pump($$). It seems to be the best route for curing my high altitude woes and get rid of the POS Pollak valve that I also suspect to be a problem. I just wish I did this to begin with I'd have save a couple hundred bucks and the plumbing olympics I have under the rig.

 

[trailpsycho]

Didnt you say that your HP pump is still good, just plumb it alone and give it a try. No need to park a perfectly good Bronco...

 

[COBlu77]

Didnt you say that your HP pump is still good, just plumb it alone and give it a try. No need to park a perfectly good Bronco...

Ditto! That's all I did to keep running, until I could afford to do it right.

 

[needabronco]

Problem is the HP pump has quit on me several times and now I don't trust it! It would probably work fine or make a great trail spare, but I'm just not sure about it... It sucks being towed in by a friend, but my family and I do run lots of solo trips, and I want the best in reliabilty...

 

[Socal Tom]

You can test the HP pump by hooking it up and letting idle for a long while. Its usually the LP pump that is the issue. They aren't rated for continuous use like the HP pump is.
Tom

 

[U-Bronco]

Hi Guys,

Been having similar issues... I am running the dual pump + accumulator but considering going to the single HP pump mounted on the crossmember... What fuel filter should I go with in between the tank and suction of the HP pump?

Thanks
-U

 

[FASTERDAMITT]

Again, don't mount the pump anywhere near above fuel level. It must be at the level closest to the bottom of the tank. Mine was mounted on the side of the tank on the very bottom until I eliminated problems.

 

[roundhouse]

Im running a HP pump on the frame.
No lift pump.

I had the same problem.

Mine was the fuel heating up and boiling in the tank.


I installed a power steering cooler in the return line near the tank.
That cured it.
You might need 2 coolers in the return line at high altitudes.

 

[Viperwolf1]

I've been experiencing the same problems on these last couple of hot days. I have both tanks plumbed through the pollack valve to a lp pump on the frame. Has anyone tried to mount a lp pump vertically with the suction side down between the tank and axle tube? That would put the mid section of the pump just below the mid-level of my 23 gal tank and put the suction fitting about level with the tank bottom. That looks like the only solution I can see with my current equip configuration.

 

[chuck]

The 2 pump/acc system was used by ford for a number of years and they did not/do not have the problems talked about here. I am not saying anyone is wrong, just trying to figure out what the real problem is. For example, I have to wonder why altitude would effect the fuel a low pressure pump will pump. No matter what the alt. it's still the same pump pumping the same fuel. My thoughts on this is that maybe the tank is not venting right at high altitudes? Or maybe on the suck side of the LP pump there is a leak that allows air into the system but not gas out? A loose clamp? A weak seal in the selector valve allowing air in? It would seem to me that something like this has to be happening because the LP pump will pump a lot more fuel than any small block can use. If you think of the low pressure system like this, the fuel flows from the tank to pump to acc. and the excess returns to the tank you can see that if everything is in good order it has to work. The LP pump pumps 20-30 GPH at 5.9 PSI. If you figured the low side of 20 GPH and figured that 1/2 of that was air from the tank that returns to the tank you would still be getting 10 GPH of fuel into the acc. for the HP pump. If you get 10 MPG at 60 MPH that means you will comsume 6 GPH, at 10 MPH you would consume 1 GPH, anyway you want to look at that you can not use more fuel that the LP pump will provide to the Acc. tank. The whole idea of the Acc tank is to remove the air that will come from the non-EFI tank with the fuel.
The HP pump is all about the pressure. The HP pump moves 30-40 GPH at 70-90 PSI. The fuel regulator will bypass the excess fuel back to the Acc tank or fuel tank depending on where the neg. pressure is limiting the fuel rail pressure to around 40 PSI. If the HP pump were to draw more fuel than the LP pump could provide because the LP pump was pumping too much air the excess fuel from the HP will return to the Acc tank and back to the HP pump.
I am fine with you guys pointing out where my thinking is off.

 

[rcmbronc]

Here is my opinion. A pump has what is called net positive suction head required (NPSHR). This is the amount of positive suction pressure available. At sea level you have approximately 30 feet of this availabel due to atmospheric conditions and this decreases as you gain altitude. One of the problems with the LP/HP/ACC setup is that the LP pump typically pumps to very low discharge pressure which makes it run out to max flow on its curve, which also makes the pump require more positive suction head. My opinion that the wide open flow and increase in altitude end up making the pump cavitate on the suction side which heats up the pump and makes it shut down. Mine has a slight tendency to do this even at low altitude. I am going to try creating some backpressure on the LP pump either with restricting the line coming into the ACC or leaving. THis should make the LP pump work with less flow and decrease the HPSH that is required. I have not had time yet to do this, but it is my theory.

This all said the intank pump would be the best.

 

[Viperwolf1]

I have the factory vent configuration on both tanks and it's in good working order. My fuel return line is plumbed into the drain on the main tank and the filler vent line on the aux. I don't believe air is being sucked in from the tank or anywhere else. I'm confident that I do not have any air leaks. The last time this occured I had both tanks nearly full and I don't think sloshing fuel would allow much air to get to the bottom of the tanks.