Odd Problem With Fuel Pumps (...That's Plural)

[BloodyKnuckles]

I'm just about spent!

I have been chasing an on going problem with my wife's DeSoto 251. Since I bought the car about 6 or so years ago I can't get proper fuel delivery. I have rebuilt the carb twice, flushed the lines to the tank and vented the tank. I have replaced the fuel pump about 4 times up to this point and everytime I think I have it fixed. I drive it and it will either vapor lock during start up or starve for fuel upon accelleration.

What I have found throughout this time is which makes me think I have fixed it was loose lines. Not overly loose but I thought maybe loose enough to cause an air leak.

So as a last ditch effort I just purchased and installed a new mechanical pump and as a back up for vapor lock a Mr.Gasket electrical pump was installed with a pressure regulator. The mechanical pump will not pull through the electrical pump if the pump is turned off. Which boggles my mind because I know others who run these and the mechanical pump will pull through it when off.

I can drive the car just fine with the electric pump on but I want to only use it as a back up for vapor lock starts.

What am I missing here???

BloodyKnuckles

[Adam H P15 D30]

I think the fuel pump is driven off the cam like most engines. Maybe a flat lobe for the pump??

[Don Coatney]

I suggest you still have a leak in the fule line between the pump and the tank or possibly the line inside the tank. Such a leak will suck air before it sucks fuel. Have you replaced this line the full length? Suggest you do so and keep all splices to a minimum. The electric booster pump should not be required.

[55 Fargo]

I'm just about spent!

I have been chasing an on going problem with my wife's DeSoto 251. Since I bought the car about 6 or so years ago I can't get proper fuel delivery. I have rebuilt the carb twice, flushed the lines to the tank and vented the tank. I have replaced the fuel pump about 4 times up to this point and everytime I think I have it fixed. I drive it and it will either vapor lock during start up or starve for fuel upon accelleration.

What I have found throughout this time is which makes me think I have fixed it was loose lines. Not overly loose but I thought maybe loose enough to cause an air leak.

So as a last ditch effort I just purchased and installed a new mechanical pump and as a back up for vapor lock a Mr.Gasket electrical pump was installed with a pressure regulator. The mechanical pump will not pull through the electrical pump if the pump is turned off. Which boggles my mind because I know others who run these and the mechanical pump will pull through it when off.

I can drive the car just fine with the electric pump on but I want to only use it as a back up for vapor lock starts.

What am I missing here???

BloodyKnuckles

Okay, so you have great fuel delivery with the electric fuel pump, which is installed near the tank, and is pushing fuel, rather than pulling from the front.

Is your gas tank stock, any restrictions of any kind through from tank, through hoses, and steel lines, that would make it difficult for the mechanical fuel pump to suck the fuel to the carb, in a manner needed.

Vapor lock, poor fuel delivery when hot, do you have the heat shield on over the fuel pump, are the lines from fuel pump to carb, touching or too close to the manifolds, engine or any other heat source, this can create problems of fuel delivery when under hood temps soar.

You mention, you cannot pull fuel, through the electric pump, so is this alll the time or intermittant, or just when your engine is good and hot.

What type of mechanical pump do you buy, all the same, from same place?

What reason do you not want to run the electric pump exclusively, did you create a return fuel line for it?

Hope this works out, I am sure it will, good luck....

[Merle Coggins]

It depends on what type of electric pump you have on wheather or not your mechanical pump will draw through it. I have an inline solenoid pump on my truck and the mechanical pump will pull through it just fine. I've seen other electric pumps that need to have a bypass check installed in order to be used in the same application. I believe these are the rotory vane or gear pumps.

One problem I have with my setup is that the electric pump won't push fuel through the mechanical pump. I wanted to use it to prefill the float bowl after extended periods of non-use, but it doesn't work. I got the lower pressure rated pump to be sure I wouldn't override my float needle, but I guess I need the higher pressure one so that it will pump through the mechanical pump's check valves. It did help me with a "vapor lock" situation once though... It was a hot day and everything was running good until I stopped for a potty break. Upon restarting it stumbled and would bearly run. I flipped the switch for the pump and it cleared out. When I got going down the highway again I turned off the electric pump and it continues to run fine. I don't have a heat shield above my pump and I think the manifold heat cooked the pump when the air flow stopped.

Merle

[BloodyKnuckles]

I suggest you still have a leak in the fule line between the pump and the tank or possibly the line inside the tank. Such a leak will suck air before it sucks fuel. Have you replaced this line the full length? Suggest you do so and keep all splices to a minimum. The electric booster pump should not be required.

I have not replaced the entire line yet. None of the fittings are wet or dirty to say that they may be loose or leaking. That's why I haven't changed them yet. Also, when I installed the electric pump I cut the hard line and the inside looked perfect, no signs of corrosion. I agree with you on the electric pump. That's why I'm about done. Thanks Don.

Okay, so you have great fuel delivery with the electric fuel pump, which is installed near the tank, and is pushing fuel, rather than pulling from the front. Correct.

Is your gas tank stock, any restrictions of any kind through from tank, through hoses, and steel lines, that would make it difficult for the mechanical fuel pump to suck the fuel to the carb, in a manner needed. Stock tank, no restrictions that I may be aware of. Possibly the pick up screen.

Vapor lock, poor fuel delivery when hot, do you have the heat shield on over the fuel pump No, are the lines from fuel pump to carb, touching or too close to the manifolds , engine or any other heat source, this can create problems of fuel delivery when under hood temps soar.No. They have been rerouted away

You mention, you cannot pull fuel, through the electric pump, so is this alll the time or intermittant, or just when your engine is good and hot.All the time

What type of mechanical pump do you buy, all the same, from same place? Airtex 3 times and 1 rebuilt one from George Ashe

What reason do you not want to run the electric pump exclusively I want to run the mechanical, did you create a return fuel line for it? No I haven't

Hope this works out, I am sure it will, good luck....

Thank you.

It depends on what type of electric pump you have on wheather or not your mechanical pump will draw through it. I have an inline solenoid pump on my truck and the mechanical pump will pull through it just fine. I've seen other electric pumps that need to have a bypass check installed in order to be used in the same application. I believe these are the rotory vane or gear pumps. The one I purchased can be used as a booster to a mechanical pump or stand alone

One problem I have with my setup is that the electric pump won't push fuel through the mechanical pump. I wanted to use it to prefill the float bowl after extended periods of non-use, but it doesn't work. I got the lower pressure rated pump to be sure I wouldn't override my float needle, but I guess I need the higher pressure one so that it will pump through the mechanical pump's check valves. It did help me with a "vapor lock" situation once though... It was a hot day and everything was running good until I stopped for a potty break. Upon restarting it stumbled and would bearly run. I flipped the switch for the pump and it cleared out. When I got going down the highway again I turned off the electric pump and it continues to run fine. I don't have a heat shield above my pump and I think the manifold heat cooked the pump when the air flow stopped.

Merle

The same reason you installed yours is why I decided on mine. I have a vapor lock issue if shut off when hot and restarted.

So, It is excessively hot in North Carolina right now. I took the DeSoto for a long drive through the country. After about 25 minutes of steady 45-55 mph it started to fall flat but I kept it running. Then I stopped at a stop sign and pulled out. While accellerating through 1st it would not properly run. It acted as if it was running out of gas.

I let it sit for about 45 minutes while I sweated my butt off walking through an architectural salvage yard:rolleyes:.

Then on my way home,after about 25 minutes it did the same thing. I removed the gas cap completely with the same results as before.

I pulled into the driveway and set it on fire.

Just kidding. Very frustrated right now.

I am going to remove the sending unit and inspect the pick up tube now and will report my findings soon.

Thanks to all that responded.

BloodyKnuckles

[Merle Coggins]

When the pump is running does it click or hum? From my experience the "clicker", or solenoid, type pumps will allow fuel to pass through when not running but the rotory types won't. I've seen the rotory types listed as stand alone or booster for mechanical IF you also purchase and install a bypass kit. (usually in the fine print) The bypass kit plumbs in parallel with the pump and allows your mechanical pump to draw fuel through the check valve, but if the electric pump is running it won't pump back through the check to the inlet side.

If you have a clicker type, then I can't explain why it won't draw fuel through it. Maybe the internal check spring is too strong for your mechanical pump to draw through.

Merle

[Niel Hoback]

For what its worth; when I was researching proir to buying an electric pump, I read that many buyers were very unhappy with the Mister Gasket pump. I did not buy one on that basis. The Airtex performs perfectly,,,,,,, so far.

[Don Coatney]

It did help me with a "vapor lock" situation once though... It was a hot day and everything was running good until I stopped for a potty break. Upon restarting it stumbled and would bearly run. I flipped the switch for the pump and it cleared out. When I got going down the highway again I turned off the electric pump and it continues to run fine.

Merle

I have doubts that your problem was "vapor lock". Sounds more like fuel in the carburetor boiling. It is my belief that vapor lock in these Mopar flathead engines is not possible. There are several threads on this subject and a forum search of vapor lock will explain where I am coming from. Your fuel pump is located on an equal plane or below the fuel tank. Vapor lock can possibly occur if the fuel pump is located higher than the fuel tank and there is enough heat to vaporize the fuel before it reaches the fuel pump such as in flathead furds and others. The lower suction pressure in a heated fuel line before the pump will cause the fuel to boil and the pump to not pump. The higher pressured line after the fuel pump and before the needle valve in the carburetor raises the boiling point. However the fuel sitting in the carburetor bowl at atsmopheric pressure may boil after a hot engine is shut down. This is not vapor lock but instead fuel boiling in the carburetor float bowl. An electric fuel pump may resolve this problem but it is not a vapor lock issue in my opinion.

[BloodyKnuckles]

I have doubts that your problem was "vapor lock". Sounds more like fuel in the carburetor boiling. It is my belief that vapor lock in these Mopar flathead engines is not possible. There are several threads on this subject and a forum search of vapor lock will explain where I am coming from. Your fuel pump is located on an equal plane or below the fuel tank. Vapor lock can possibly occur if the fuel pump is located higher than the fuel tank and there is enough heat to vaporize the fuel before it reaches the fuel pump such as in flathead furds and others. The lower suction pressure in a heated fuel line before the pump will cause the fuel to boil and the pump to not pump. The higher pressured line after the fuel pump and before the needle valve in the carburetor raises the boiling point. However the fuel sitting in the carburetor bowl at atsmopheric pressure may boil after a hot engine is shut down. This is not vapor lock but instead fuel boiling in the carburetor float bowl. An electric fuel pump may resolve this problem but it is not a vapor lock issue in my opinion.

Ok. What about an improperly operating heat riser? I disconnected the spring and moved the valve forward thinking that it is the closed position. Is that correct? I am hearing gas boiling and the fuel pump perculated a couple of times in the glass bowl.

Should I try a heat shield on the fuel pump?

Also, I pulled the sending unit. The inside of the tank is Spotless!!!! I was absolutely amazed. I guess that's a good thing to know.

Thanks again guys.

BloodyKnuckles

[Don Coatney]

I dont think the heat riser will matter much but what do I know? I also dont think a heat sheild matters much.

How is your fuel line routed both to the pump and after the pump?

[Guest bewillie]

The heat shield does make a difference. Keep all lines away from exhast. I would remove the in fuel line of your pump and put a vacume gauge on it to see if the cam lobe is wiped. Billy

[steveplym]

Throwing this out there as I have not read in your posts where it was addressed. Do you have a vented gas cap? I bought a new gas cap one time and asked for a vented type, I got a pressure cap instead and didn't know it until the car kept falling on it's face at stop signs. I put the old cap back on and the issue was resolved.

Sounds like an easy fix, just finding out what to fix is the trick.

[BloodyKnuckles]

Throwing this out there as I have not read in your posts where it was addressed. Do you have a vented gas cap? I bought a new gas cap one time and asked for a vented type, I got a pressure cap instead and didn't know it until the car kept falling on it's face at stop signs. I put the old cap back on and the issue was resolved.

Sounds like an easy fix, just finding out what to fix is the trick.

That's a valid point.

I replaced the original cap with a nicer one from the same style car. One day I removed the cap and heard a rush of air. So I decided to drill a 1/8" hole in the filler neck. Not sure if that worked though.

Maybe I need to try the other cap again.

Thanks,

BloodyKnuckles

[Cpt.Fred]

hi bloddyknuckles,

hope you're fine over there other than the fuel problems!

like others wrote here, it's a matter of what type of electrical pump you

installed that decides wether you can suck gas through it or not with your mechanical pump.

when i installed mine, i had the same plans in mind, but chickened out of the project due to leaks and other troubles and i'm now a happy customer using electrical only.

no hard starts, no vapour locks, no nothing (since i'm a messy guy and my tank isn't "spotless" at all, i keep having trouble anyway...).

a heat shield on the pump does make a difference when it's hot outside,

i've been through that with another car.

the filler cap issue is really a nasty little trap...

but isn't there another breather on the tank as well?

a worn lobe would be ugly, but i don't think that's very likely.

a pressure test will be the best thing to do for start.

have you tried to apply pressure on the fuel line between pump and tank

and then searched for leaks/ pressure loss?

anyway, good luck to you!

best,

fred

[Robert Horne]

I'm just about spent!

I have been chasing an on going problem with my wife's DeSoto 251. Since I bought the car about 6 or so years ago I can't get proper fuel delivery. I have rebuilt the carb twice, flushed the lines to the tank and vented the tank. I have replaced the fuel pump about 4 times up to this point and everytime I think I have it fixed. I drive it and it will either vapor lock during start up or starve for fuel upon accelleration.

What I have found throughout this time is which makes me think I have fixed it was loose lines. Not overly loose but I thought maybe loose enough to cause an air leak.

So as a last ditch effort I just purchased and installed a new mechanical pump and as a back up for vapor lock a Mr.Gasket electrical pump was installed with a pressure regulator. The mechanical pump will not pull through the electrical pump if the pump is turned off. Which boggles my mind because I know others who run these and the mechanical pump will pull through it when off.

I can drive the car just fine with the electric pump on but I want to only use it as a back up for vapor lock starts.

What am I missing here???

BloodyKnuckles

Maybe "vapor lock starts" is not the correct term. "Evaporation" of the fuel in the carb was my problem after sitting for much time. I installed a Mr Gasket electric fuel pump. It worked good for about a year. I would turn on the key, pump would hum a few seconds, fuel pressure went to 5lb, pump would shut off, and car started easy. The fuel pump does not shut off now, when pressure reachs 5lb, but does maintain about 5lbs of pressure.

My mechanical fuel pump always worked good, but the glass bowl left a drop or so of fuel on the floor. That drop or so of fuel worried me, that it may drip on a hot exhaust pipe.

[Merle Coggins]

I have doubts that your problem was "vapor lock". Sounds more like fuel in the carburetor boiling. It is my belief that vapor lock in these Mopar flathead engines is not possible. There are several threads on this subject and a forum search of vapor lock will explain where I am coming from. Your fuel pump is located on an equal plane or below the fuel tank. Vapor lock can possibly occur if the fuel pump is located higher than the fuel tank and there is enough heat to vaporize the fuel before it reaches the fuel pump such as in flathead furds and others. The lower suction pressure in a heated fuel line before the pump will cause the fuel to boil and the pump to not pump. The higher pressured line after the fuel pump and before the needle valve in the carburetor raises the boiling point. However the fuel sitting in the carburetor bowl at atsmopheric pressure may boil after a hot engine is shut down. This is not vapor lock but instead fuel boiling in the carburetor float bowl. An electric fuel pump may resolve this problem but it is not a vapor lock issue in my opinion.

I agree with you on the term "vapor lock", but I don't have any other term to describe what happened. It was in the mid 90's that day when I was traveling back from the WPC meet in Dayton. Nature was calling, so I pulled off the freeway and into a gas station to use their facilities. When I came out of the gas station and jumped back in the truck it fired right up. I backed out of the parking spot and headed back out on to the road. Just as I got out on the road it stumbled and almost died. I managed to coast it back into the gas station parking lot at their second entrance and bearly keept it running while playing with the throttle pedal. I thought I was going to be stranded in the middle of nowhere Indiana. Then I remembered my electric pump, flipped the switch on, and within a couple of seconds my engine was purring again. I pulled back out on the road, got back on the freeway and then switched the pump off again.

My theory is that the manifold heat cooked the gas out of the fuel pump and somehow made it unable to pump. After I used up the gas in the float bowl the carb started running out of gas and couldn't get enough to sustain much more than idle. Once I force some gas through the fuel pump it took off and kept going.

That's my story and I'm sticking to it.

Merle

[bamfordsgarage]

...When I came out of the gas station and jumped back in the truck it fired right up ... Just as I got out on the road it stumbled and almost died. I managed to coast it back into the gas station parking lot at their second entrance and bearly keept it running while playing with the throttle pedal....

Merle

My D25 behaves in a similar fashion when the engine is hot on a warm+ day. After a brief stop with the engine off the car fires right up but sometimes dies about 10-15 seconds later from lack of fuel. This time frame often coincides with pulling back onto the highway, crossing through an intersection, etc.

I found that the natural reaction of disengaging the clutch and trying to re-start the engine is wrong. It takes a lot of cranking to get liquid fuel moving up to the carburetor.

Instead, I just leave it in gear with the gas pedal down and, because the fuel pump continues stroking, flow is always restored within 2-3 seconds and we're on our way again. Mind you, 2-3 seconds seems like a very long time when you are coasting through a busy intersection and the lights have just changed.

[greg g]

will it ru with no gas cap on???

[BloodyKnuckles]

will it ru with no gas cap on???

No different; on or off.

Thanks again guys.

BloodyKnuckles

[BloodyKnuckles]

Well, I built a copper heat sheild out of a thick piece of flat sheet. Installed it and started it up and it idled fine for about 25 minutes. Then I took it down the road and it began to cough and sputter so I had to flick the electric pump on. Drove some more, flicked off the switch, sputter sputter cough cough. On went the electric pump again. So I decided to bypass the electric fuel pump and run only off the mechanical. First of all it is hot here, really hot. After I bypassed the pump I tried to start it, no go. I tried and tried on it's own to start but I had to resort to starting fluid. Once I got it started I drove down the road. Under semi-hard accelleration it began to sputter again but would still run, to a point. I was able to get home by babying it. Even running on the electrical pump it will, after about 25 minutes, begin to cough and sputter also. I don't think it's a fuel pump issue.

So, what I believe is that the fuel lines are getting way too hot and need to be sheilded from under hood temperatures. They get too hot to touch, rubber and steel. Everything under the hood is hot, real hot.

I think the heat shield is doing it's job as I put my hand under it then beside it under the exhaust manifold with a noticable difference.

I am going to try to find some sort of heat sock to slide over the lines tomorrow.

Is it possible that I may have the float set too low? It is set to proper specs but I am willing to check it again if you guys feel I need too. I rebuilt the carb a few months ago thinking that would solve my problems but it didn't.

Also, I have a friend who drives nothing but carburated cars here and swears by Sta-Bil additives. He says he has had not troubles this year at all. What do you guys think?

I planned on making a 1000 mile round trip starting this Wednesday up to Pittsburgh and wanted to take the DeSoto.

Thanks for keeping up with me on this. It has been frustrating but I am determined to get this right.

BloodyKnuckles

[greg g]

I just did 1000 miles in my 46 in temps in the high 80's low 90's, wiht no fuel related issues. So going with the 90% of fuel problems are electrically related, and 90% of electrical problems are fuel related, when was the last time you checked the points, rotor and spark plugs??? Before I left I checked my points and they were closed down to about .14. Filling, regapping, and doing a general tune up solved a starting issue, and what I realized was a bit of sluggish running.

Do like Capt Fred did and take the air horn off the carb and see whats happenig with fuel level and intermediate power valve, when the engine is running.

Also have you checked the fulcrum pin in the fuel pump to see if it properly in place?

What air cleaner are you running, is it flowing properly?

Since electric pumps push, and it runs beter on the electric, and mechanical pumps suck, and it runs worse, that would lead me to believe you are losing suction between the pump and tank.

Did you check the brass screen in the fuel pump? Is there some debris in the hollow bolt that holds the lower chamber of the pump to the body?

Did you do a flow check of the mechanical pump??

[BloodyKnuckles]

I just did 1000 miles in my 46 in temps in the high 80's low 90's, wiht no fuel related issues. We are in the high 90's to low 100's So going with the 90% of fuel problems are electrically related, and 90% of electrical problems are fuel related, when was the last time you checked the points, rotor and spark plugs??? They are all new recently replaced.Before I left I checked my points and they were closed down to about .14. Filling, regapping, and doing a general tune up solved a starting issue, and what I realized was a bit of sluggish running.

Do like Capt Fred did and take the air horn off the carb and see whats happenig with fuel level and intermediate power valve, when the engine is running. OK

Also have you checked the fulcrum pin in the fuel pump to see if it properly in place? New pump. Do I still need to check?

What air cleaner are you running, is it flowing properly? No different with it on or off.

Since electric pumps push, and it runs beter on the electric, and mechanical pumps suck, and it runs worse, that would lead me to believe you are losing suction between the pump and tank. Possible, but I have replaced all the rubber lines and inspected all the hard lines and all seems good.

Did you check the brass screen in the fuel pump? Is there some debris in the hollow bolt that holds the lower chamber of the pump to the body? It is new and looks good.

Did you do a flow check of the mechanical pump??Not yet. I'm skeptical on the pumps being the problem at this point.

Greg, I really appreciate your input. I have gone through this car so many times and I'm still fighting this problem.

Thanks.

BloodyKnuckles

[BloodyKnuckles]

Pics of engine and shield. The fuel lines are ran a bit crude but I wanted them away from the engine as much as they could be.

I forgot!! I also put a phenolic spacer under the carb. Didn't work. Oh well.

BloodyKnuckles

[greg g]

yep check that pin it seems to be a common problem with the new ones. I did what you did with your fuel line. I ran it to the inner fender, back to the firewall, then forward to a T to feed the duals, but basically the same route.

Since you are handy with the tin snips, my 56 had a sheet metal plate between the carb and the manifold. It faced forward and shileded the float bowl from manifold heat. That will help with perculation while the car sits after running, and during high under hood temps. But what your are describing does not sound like perculation.

Do the flow test, to assure that the pump is providing proper quantity. Pull the line from the carb and direct it into a container, have your better half crank the starter (withthe coil wire pulled) and while it cranks, count the strokes from the pump out put. At 12 strokes you should have 8 ounces of gas or more in your container. If not the pump is not flowing as it should. looks like you have a new line beween the frame and the pump??