EFI fuel pumps 'vapor locking', then dying?

[needabronco]

Chuck I'm not sure what happened?

I bought all of the parts from you in January of 07' and finally got around to installing them this summer. The whole efi conversion only has maybe 200 miles on it. The Pollak valve was stuck when I hooked it up, but after I switched it a couple of times it seems to work. The fuel pumps also worked great, but now the LP pump runs but sounds and feels week? It also dies after a minute or two.

Below about 10K' the pumps worked great, above that they started having problems. I can understand the barometric pressure thing and see how the pumps would have to work harder to keep the same relative fuel pressure and supply.

I'm trying to justify an efi tank with pump to my wife.... Hopefully that'll fix it for good.

 

[chuck]

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.

I sort of understand what you are saying about pos. suction pressure, I think. If I understand this right another way of saying the same thing is at sea level it is possible to suck water up about 30 feet before it separates from it's own weight and as you gain altitude the 30 feet becomes less. Diff. fluids would have a diff max number and a given pump will have a fraction of that?
At any rate whither I understand what you are saying or not could you give us a real number using the following? You have a tank 14" high 1/2 full and a 5.9 PSI pump mounted to the crossmember 4" from the top of the tank, the hose would be less than 1 foot long. What would the diff in PSI be between sea level and 10k feet?
I agree that the intank pump is the best way to go but many people have no trouble with the 2 pumps and Acc and some people have no trouble with just a HP pump and a stock pump. I would like to understand why but don't think the altitude is the problem as it would be the same for everyone. The problem must be with the individual set-up

 

[chuck]

Many years ago I bought a 64 chevy pickup with a 350 that had 2 gas tanks and 4 AC fuel pumps and a vaper lock problem. It had 1 pump just out side each tank just before the selector valve, one just after the selector valve and one near the carb. After a lot of messing around I found that the hose on the suck side of both tanks had small cracks near the end. They did not leak gas at all but when you pushed it hard or got up around Big Bear it would vaper lock. To make a very long story short I ended up with 2 pumps, one for each tank and new lines. I think something like this is going on here. I know that most of you are thinking, no that is not my problem but unless you go out and look now you don't know for sure. PS, the 64 I bought from my father-in-law who told me aboutthe vaper lock problem and how he had just replaced all the fuel pumps and hoses the month before I bought it. I learnedthe hard way, you can't assume you got to look.
QUOTE=needabronco;1148542]Chuck I'm not sure what happened?

I bought all of the parts from you in January of 07' and finally got around to installing them this summer. The whole efi conversion only has maybe 200 miles on it. The Pollak valve was stuck when I hooked it up, but after I switched it a couple of times it seems to work. The fuel pumps also worked great, but now the LP pump runs but sounds and feels week? It also dies after a minute or two.

Below about 10K' the pumps worked great, above that they started having problems. I can understand the barometric pressure thing and see how the pumps would have to work harder to keep the same relative fuel pressure and supply.

I'm trying to justify an efi tank with pump to my wife.... Hopefully that'll fix it for good.[/QUOTE]

 

[Socal Tom]

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.

I had an RV with the factor ford setup. It died on my a couple of times climbing the hill back from a trip to the desert. It would be fine going out, but coming back it quit several times, however I think it probably did work with fewer problems than we see in the EBs. I noted a couple of differences between the ford setup and what I had.
1) The ford setup used an intake LP pump, so it had better cooling and max head pressure
2) I couldn't confirm, but it appeared that the ford accumulator had a float valve, so it only bled air back to the tank, not a continously circulating fuel, so this would reduce the load on the LP pump and keep some head pressure on the accumulator and the HP pump.

In my mind the issue is that the LP pumps we use are designed for intermittent use. The work load of the pump is measured by the volume of fuel it moves, not the pressure. With 5.9 lbs of pressure it will pump 30-40 gallons per hour like you said, but with an open system like with the accumulator, they pump wide open all the time, and I think eventually that helps overheat the pump.

Here is the altitude scenario as I see it. Fuel boils at about 250 degrees at sea level ( depends a lot on the fuel), at higher altitudes the boiling temp drops as the pressure drops. The pressure between the LP pump and the tank is even lower as the pump is sucking the fuel. The more fuel it needs to suck, the lower that pressure can get, and therefore the boiling point gets lower. At somepoint the heat under the rig, and from the pump create air bubbles in the line between the tank and the LP pump. The LP pumps sucks air, and eventually is damaged by running dry.

Guys with later model rigs that have the evap controls and the pressurized gas cap probably resist this better than guys like me with vented tanks, since the pressure in the tank helps keep the boiling point higher

Tom

 

[Socal Tom]

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.

I did the back pressure thing. I added a needle valve and a gauge between the accumulator and the tank. I adjusted the needle valve to keep 3 to 5 pSI on the accumulator tank and the LP pump lasted much longer. Previously they would die after about 8 hours on the trail ( never a problem on the street), after the fix the pump lasted over a year with multiple trail runs in the middle. Eventually that pump failed too.

I never got a tank selector switch to work, what worked best was using an LP pump for each tank, and a 3 way valve on the return line. The pumps would only get power when that tank was selected. They have a check valve built in ( at least mine did) so fuel only flowed one direction. I think the twin pump setup in combination with the needle valve on the return line would probably work pretty well. It should also be noted that if you use a filter between the tank and the LP pump, the filter is the same a a couple of feet of fuel line.
Tom

 

[Socal Tom]

At any rate whither I understand what you are saying or not could you give us a real number using the following? You have a tank 14" high 1/2 full and a 5.9 PSI pump mounted to the crossmember 4" from the top of the tank, the hose would be less than 1 foot long. What would the diff in PSI be between sea level and 10k feet?

At sea level air pressure is 14.7psi, and 10K feet its 10.2
if you assume that the pump pulls vacuum = to -5.9PSI, then at sea level the pressure of the fuel in the line is 14.7psi less the 5.9 = 8.8 then add the weight of the fuel which would be small since it works out to 3 inches of fuel in a column 3/8 of an inch wide. I estimated the fuel to weigh 2 ounces so that means the pump has to pull it up so that drops about 1 PSI from the the system, so at sea level you end up with about 9 lbs of pressure at the pump.
At 10K feet, everything is the same except the air pressure, so deduct the 4.5 PSI and you end up with 3.3 PSI on the pump. If I understand my math right the boiling point of water at this point is about 170 degrees or 42 degrees less than at sea level. If you just take the 42 degrees off of the 250 degree fuel boiling point estimate, then you end up at about 208. I'm pretty sure that you can end up boiling the fuel in the line. If you add a filter between the pump and the tank you allow the fuel to sit longer and gain more heat as well.
Tom

 

[RnrdTheFox]

They have a check valve built in ( at least mine did) so fuel only flowed one direction.Tom

Do you know which HP pumps from the factory have the check valves???

I've had similar problems as described in this thread and am running the two pump/accum setup.

I've been thinking about going to the bone yard and pulling two HP pumps to put on the frame rail by each tank then running those lines into a tee and then to the fuel rail. I'll use my Pollak valve for the return line and for switching between the two pumps and fuel guage senders.

I think the problems I've had are temp related but I'm not sure about the LP pump. Each time it's happened I put my hand on the LP pump and it was only warm to the touch. I can also hear the bubbling in the fuel tank because of vapors being pushed back into the tank at times. I've never had problems on the street even in 102* heat or hrs of driving.

I also think that the big reason the frame rail or intank HP pump setup seems to work, is because the majority of the fuel system is under pressure to the fuel rail and that increases the boiling point.

I wish I could figure out how to put a HP in my 23 gal tank and stock aux tank.

 

[Socal Tom]

Do you know which HP pumps from the factory have the check valves???

I was speaking of the LP pumps with the check valve. I was using the autozone pump ( it used to be lifetime, but apparently now its one year).
Tom

 

[Viperwolf1]

Do you know which HP pumps from the factory have the check valves???

I've had similar problems as described in this thread and am running the two pump/accum setup.

I've been thinking about going to the bone yard and pulling two HP pumps to put on the frame rail by each tank then running those lines into a tee and then to the fuel rail. I'll use my Pollak valve for the return line and for switching between the two pumps and fuel guage senders.

I think the problems I've had are temp related but I'm not sure about the LP pump. Each time it's happened I put my hand on the LP pump and it was only warm to the touch. I can also hear the bubbling in the fuel tank because of vapors being pushed back into the tank at times. I've never had problems on the street even in 102* heat or hrs of driving.

I also think that the big reason the frame rail or intank HP pump setup seems to work, is because the majority of the fuel system is under pressure to the fuel rail and that increases the boiling point.

I wish I could figure out how to put a HP in my 23 gal tank and stock aux tank.

The pollack valve, at least the one I have, is only rated for 5 or 6 psi. If you figure out the parts to put a hp pump in the tanks then spread the word. I'd feel better if I could just put some lp pumps in the tanks.

 

[scsm76]

I have a dual pump system with accumulator and have had vapor locking, but only on the trail and at high elevations (9,000' plus) . I have a single 23 gal. rear tank. The vapor locking has become quite annoying, this last trip it happened 4-5 times in a 2 hour trip. To make it work again I have to run the low pressure pump only to get fuel flowing through the accumulator tank again. It is definitely a heat issue made worse by high elevations. I think the accumulator mounted under the hood is the main heating source for the fuel aided by the fuel flowing through the fuel rails and a little from the fuel lines. All my fuel lines are located on the driver side frame rail and only come within 10 inches of the exhaust header as it comes up to the accumulator located right behind the driver side headlight. My fuel lines are all hard lines with the exception of 12" leaving the tank to the LP pump and about 10" from the accumulator to the HP pump and the 16" to the fuel rail. The return line is plumbed pretty much the same except it goes through a cooler before going back into the tank. I have single exhaust running out the passenger side. Every time it shut downs I check through everything in the system, both pumps are running the fuel accumulator will be empty and you can here bubbling in the tank. The fuel in the tank is very warm (I haven't measured the temperature but too hot to touch). I have new fuel lines in good condition and even pressure tested all my lines to check for leaks. The cooler helped some but it still happens occasionally. The only other thing I can think to do to make it work better is to relocate the accumulator somewhere cooler, but I can't find a good location out of harms way.
I have finally given up on the two pump system and will be installing a in tank HP pump as soon as it arrives, fortinitly I have teh BC tank setup to take the mustang in tank pump.

 

[RnrdTheFox]

The pollack valve, at least the one I have, is only rated for 5 or 6 psi. If you figure out the parts to put a hp pump in the tanks then spread the word. I'd feel better if I could just put some lp pumps in the tanks.

I was talking about only using the Pollak on the return line and for switching the sending units and HPs. BTW, the new pollaks are rated at ~60 PSI valve pressure. The old one is solinoid based not motorized and rated at a lower psi. The old one also started hanging between tanks which as it's own issues. Link to the schematic http://www.frybrid.com/forum/showthread.php?t=213

 

[chuck]

I have a dual pump system with accumulator and have had vapor locking, but only on the trail and at high elevations (9,000' plus) . I have a single 23 gal. rear tank. The vapor locking has become quite annoying, this last trip it happened 4-5 times in a 2 hour trip. To make it work again I have to run the low pressure pump only to get fuel flowing through the accumulator tank again. It is definitely a heat issue made worse by high elevations. I think the accumulator mounted under the hood is the main heating source for the fuel aided by the fuel flowing through the fuel rails and a little from the fuel lines. All my fuel lines are located on the driver side frame rail and only come within 10 inches of the exhaust header as it comes up to the accumulator located right behind the driver side headlight. My fuel lines are all hard lines with the exception of 12" leaving the tank to the LP pump and about 10" from the accumulator to the HP pump and the 16" to the fuel rail. The return line is plumbed pretty much the same except it goes through a cooler before going back into the tank. I have single exhaust running out the passenger side. Every time it shut downs I check through everything in the system, both pumps are running the fuel accumulator will be empty and you can here bubbling in the tank. The fuel in the tank is very warm (I haven't measured the temperature but too hot to touch). I have new fuel lines in good condition and even pressure tested all my lines to check for leaks. The cooler helped some but it still happens occasionally. The only other thing I can think to do to make it work better is to relocate the accumulator somewhere cooler, but I can't find a good location out of harms way.
I have finally given up on the two pump system and will be installing a in tank HP pump as soon as it arrives, fortinitly I have teh BC tank setup to take the mustang in tank pump.

I mount the Acc on the outside of the inner fender just in front of the spring bucket. That might help the fuel temp a little but how is it getting so hot that you can't hold the tank? My guess is that is the problem but why. I believe you typed that the exhaust is not near the lines or tank? That would leave one or both of the fuel pumps, my guess is the LP pump. Sounds like that pump gets hot and boils the fuel. Can you check it? Maybe Tom is on to the problem by slowing down the low pressure fuel the pump might not work as hard so run cooler. Or maybe a diff/better pump.

 

[rcmbronc]

I sort of understand what you are saying about pos. suction pressure, I think. If I understand this right another way of saying the same thing is at sea level it is possible to suck water up about 30 feet before it separates from it's own weight and as you gain altitude the 30 feet becomes less. Diff. fluids would have a diff max number and a given pump will have a fraction of that?
At any rate whither I understand what you are saying or not could you give us a real number using the following? You have a tank 14" high 1/2 full and a 5.9 PSI pump mounted to the crossmember 4" from the top of the tank, the hose would be less than 1 foot long. What would the diff in PSI be between sea level and 10k feet?
I agree that the intank pump is the best way to go but many people have no trouble with the 2 pumps and Acc and some people have no trouble with just a HP pump and a stock pump. I would like to understand why but don't think the altitude is the problem as it would be the same for everyone. The problem must be with the individual set-up

Yes, it does give the value of how high you can lift fluids.
You cant really give numbers for your example. What I can tell you is that atmosperic pressure is 14.7 at sea level and 10.1 at 10k elev. This equates into a loss of 10.6' of NPSHA. 7" of fuel in a tank is only .58 feet of positive suction head from the fluid. Another issue is that as the temp of the fuel increases so does its vapor pressure which wil also reduce the NPSHA. One factor that can easily effect the system is the suction hose. Losses in the suction of the pump also decrease the NPSHA. The problem is that is dont have any specific pump curves and specs for the LP pumps used. I think that the higher flow LP pump used, the more the problem. I still say that the problem is that the LP pump is running at too high of flow with low pressure. If there was some backpressure against the pump it would help. The NPSHR for a pump typically decreases alot when the pump is in a low flow higher pressure location.

Dont get me wrong Chuck, I am definately not digging on you about this. I like your fuel injection acc. and use one along with alot of your other parts. I have the LP/HP/ACC system and can at times if the tank gets lower hear the LP pump cavitating, so I would like to figure this out too.

We need someone to adapt a HP pump on the stock bronco sending unit to put a hp pump in a stock tank - are you listening Chuck?

 

[roundhouse]

I added a cooler, later I got rid of the lift pump cause it died, and just run the HP pump on the frame just in front of the rear tire.

havent had any more problems, but Im at 2500 feet.

I run efi filter at the engine and a plastic clear filter between the tank and pump, and when the filter clogs, (often, now with the ethanol crap in the gas) it will draw hard enough to rip the clear filter element so no suction issues.

im not running the accumulator thingie, yet. Just havent needed it, but its a good idea. If the gas ever goes back to where I can afford to actually drive the thing and go wheelin I mingt need the accumulator.

 

[Ron Gildersleev]

accumulator

Casey, I had the same issue until I removed the accumulator. Have the lp pump at the back bumper & hp pump on front fender. I was right behind you every time you stopped. Down here on the flat it will run w/o the lp pump but not at Montrose elev.. Ron

 

[scsm76]

I mount the Acc on the outside of the inner fender just in front of the spring bucket. That might help the fuel temp a little but how is it getting so hot that you can't hold the tank? My guess is that is the problem but why. I believe you typed that the exhaust is not near the lines or tank? That would leave one or both of the fuel pumps, my guess is the LP pump. Sounds like that pump gets hot and boils the fuel. Can you check it? Maybe Tom is on to the problem by slowing down the low pressure fuel the pump might not work as hard so run cooler. Or maybe a diff/better pump.

I have shock hoops that use up the space in front of the coil bucket. I think the heat is from under hood temperatures combined with circulating fuel through the fuel rails over the engine. It takes about an hour or more of wheeling to make it happen so I don't get to create the problem that often. I run stock steel hood and no vents in the hood or fenders, but am able to keep the engine running cool. What's strange is when it happens I can disconnect power to the HP pump and the LP pump will fill the Acc. tank right up and then it will run again after hooking the HP pump back up, but if I run both pumps it will never fill until it cools down. I have never had either pump shut off they always run so I don't think they are overheating, cavitating maybe, but not shutting down. The pumps never get to hot to touch. The pumps I am running I purchased from you so what would you recommend as a better pump to try?
My bronco has a bent rear housing so I need to finish putting all the 4-link mounts on the new one before I can test it again, I hope to get to that this week.

 

[chuck]

Dont get me wrong Chuck, I am definately not digging on you about this. I like your fuel injection acc. and use one along with alot of your other parts. I have the LP/HP/ACC system and can at times if the tank gets lower hear the LP pump cavitating, so I would like to figure this out too.

We need someone to adapt a HP pump on the stock bronco sending unit to put a hp pump in a stock tank - are you listening Chuck?

I did not take it as a dig. I believe your information and am more knowable for it, isn't that what this site is really all about? I thank you for your info., whither that fixes the problem it is still good info. I am thinking your info may explain the hot pump and the hot pump may explain the vapor lock.

 

[Socal Tom]

I'm currently running chucks tank with a single hp pump on the frame. I'm confident it will work fine for me.

If I had to guess at the best way to fix this problem without the intank pump setup I would do the following things
1) Use a good pump like the carter rather than the autozone pump.
2) put the accumulator someplace cool. I had mine in the engine bay too.
3) Throttle back the return line to the tank. It really does help.
4) Use 2 low pressure pumps as I described above it you run dual tanks
5) The pick up tube on the rear tank should be lengthend/bent so that it reaches the spot where the tank starts to angle up. This spot would be the low spot when you start up hill, so it may help with the stock tank. ( I figured this out when looking at Chuck's cutaway tank. His EFI tank does this already.){ this might be a new product opportunity for someone;-)}

The powersteering cooler idea on the return line isn't a bad idea either. I've heard fuel boiling in my brother's tank at big bear.
Tom

 

[needabronco]

I bit the bullet today and ordered a BC EFI tank with an internal pump. I couldn't quite justify buying new pumps when I could just fix it right (hopefully for good) for a few bills more. Not sure what my wife's going to say about the credit card 1/2 melted down...

Since the problems started I've moved to Arizona, so I'll have to wait awhile before I can test it out at high altitude again. I look forward to simplifying my fuel system...

 

[Viperwolf1]

I put a valve in the return line between the accumulator and tank to limit the amount of hot fuel returning to the tank. So far I have not seen the problem recurr. I only had the problem after several hours of running and I think the fuel in the tank was getting warm enough to easily vaporize when being pulled by the low pressure pump.