Failing fuel pump
 

I have been fighting a situation that causes my 1935 Ford Convertible Sedan to stall (as if running out of gas) and fails to start back up until it has completely cooled off.

In the course of restoration a new tank was installed, new fuel pump was installed, new vented gas cap, new carburetor installed and fuel line has been blown out.

I finally resorted to reworking the fuel line from the pump to the carb and inserted a pressure gauge with some clear fuel line.

I ran the engine at a fast idle for about 9 minutes with no issue. So I increased the engine speed. The fuel pressure started to shake and eventually went to zero. I let the engine cool (but not completely) and it would not start. The pressure gauge still showed 0 psi. I could see gas movement in the clear fuel line, but never got high enough to reach the carb.

This morning I tried to start it again and it started. Fuel pressure was back to 3 psi.

My conclusion is the fuel pump fails when it gets hot. When there was zero fuel pressure my IR temp gauge read 180 on the fuel pump.

Has this happened to others? Is the "new" fuel pump defective? Would you recommend adding an electric fuel pump (if I can find one that delivers 3-6 psi and runs on 6 volts). ?

Re: Failing fuel pump
 

There will be those who deny the existence of vapor lock, but your IR temperature gauge tells the story. Under-hood heat soak raises temperatures to the point that fuel flashes from a liquid to gaseous state in the system, causing fuel pumps to lose their prime: Liquid fuel does not compress, while gas (no pun intended) readily expands and contracts, failing to open and close the pump's valves as designed. While it's true that there are other causes for the symptoms you've experienced, modern fuel evaporates at a much lower temperature than in the days before Ethanol (dirty word), vapor lock is my guess and I'm sticking to it.

Re: Failing fuel pump
 

O.K. have you ever used silicone sealant anywhere the fuel system? It's a NO NO, as it turns to snot from the gas and can easily cause you a fuel delivery problem. Had a similar problem years ago and the prior owner used silicone on the sending unit gasket and on the drain plug. The stuff turned to jelly and would periodically plug to fuel line. If you have dual exhaust how close is it to the fuel line?

Re: Failing fuel pump
 

No I have not used any silicone sealant anywhere. My fuel line is well above the exhaust pipes.

Re: Failing fuel pump
 

the key here is that things work when at ambient temperature and fail as temps rise. any guess as to the nature of the problem i would think need to address that issue.

anyway, it should be easy enough to test whether or not the fueling is the issue as the carb's float bowl can be tested for the presence or absence of gasoline when the engine refuses to fire. and can be easily filled by hand if necessary. a more convenient method would be to simply spray some very combustible material (ether, brake cleaner, carb cleaner, etc.) into the intake while cranking the engine. if she won't fire at all, it's most likely not a fueling issue.

Re: Failing fuel pump
 

Hi. To rule out the fuel pump you can install a temporary fuel line direct to carb with gasoline coming out of a portable tank. Gravity will provide enough pressure. If engine runs fine then you may have a problem with fuel pump (leak or weak diaphragm). This can happen on a "new" (but crap) pump...

Re: Failing fuel pump
 

Yes I had a small piece of gasket material wedge the fuel pump intake valve open. Pump would not pull gas up to the glass bowl. Took the pump apart removed the gasket material that came from the fuel filter and all is good.

Re: Failing fuel pump
 

I have about 20 flatheads out in the garage and the aluminum fuel pump risers on almost all of them have warped bases, a lot of warpage. That has to eliminate some of the fuel pump rods travel. I buy ones at swap meets that are still nice and straight, most are warped bad. Something you can check for.

Re: Failing fuel pump
 

Thanks for the suggestions guys.

Re: Failing fuel pump
 

I might also recommend that you inspect the flexible rubber fuel hose that connects the steel line coming from the tank to the fuel pump. I know for a fact that due to the effects of ethanol gas and/or old age they can develop a strange condition that will allow fuel to flow for a short time and then as temperatures rise they begin to suck air and fuel delivery rates drop drastically. It happened to me and a friend of mine also had the problem. His truck would start and run fine...for a while - until underhood temps rose to a certain level and then the truck would die like it was starving for gas, which indeed it was but turns out it wasn't the pump OR vapor lock.

As a test, my buddy showed me a video where he removed the rubber fuel hose, blocked one end, submerged the hose in a bowl of water and introduced compressed air with his blow gun to the other end. I couldn't believe the air bubbles coming from tiny cracks in the rubber up and down the hose. He replaced the hose and that solved his problem.

Re: Failing fuel pump
 

I use a 6v inline fuel pump/filter set up that is readily available in Ebay.. there is also a seller offering the same set up with a 1-5PSI regulator.. I use all NiCopper lines that are easily bendable and give them a wide radius as needed, Pump and filter are between rubber hoses making replacement pretty easy. I mount the pump on the frame rail just about under the drivers seat.

Re: Failing fuel pump
 

I appreciate hearing all of your experiences. I am considering all of them in my situation. Thanks for all the suggestions / comments.

Re: Failing fuel pump
 

You said you have installed a new fuel pump, Mechanical type ? The 1934-36 new reproduction China made mechanical pumps are no good. They have a new design linkage which has a lot of free play movement before it even moves the pump diaphragm at all. The pump push rod only moves about 1/10th of an inch and so tends not to move the pump much if at all. I have had three of these pumps and all just junk. The best option is to rebuild/restore an original correct AC type pump. Very important to make sure the complete fuel line from carb to tank sender is airtight. Use a vacuum gauge to test that. Regards, Kevin.

Re: Failing fuel pump
 

Back when I use to play with this stuff, I had a bunch of spare electric pumps. When I wasn't sure what was clogged or not working, I would bypass all of the car's stuff and I ran an electric pump from a gallon of gas sitting on the passenger floor straight to the carb and went for a ride. That eliminated the entire fuel system but just the carb. I took somebody along to make damn sure the can of gas didn't fall over. I've had floats that rubbed on the sidewalls of carbs and shut the fuel off. I've had fuel pumps pump at just enough pressure to run down the hill but then vapor lock while driving at 5000' up in the mountains. the pumps on 350 Chevy Suburban's that had worn to where they put out just one pound of pressure less than they were supposed to would run at 1000' level but vapor lock at 5000'. That took me awhile to figure out.

I've had that accessory fuel regulators fail more than once, the ones you twist to set the pressure. I will never use one again to lower the fuel pressure. I had a '66 Austin Mini Cooper S that would shut the fuel off going down the road. I got out, opened the hood and reset the regulator and it ran for another week but then it did it again. I bought two more adjustable regulators that they did the same thing; it might take a week of driving but then it would just run out of fuel going down the road. I finally got rid of all that aftermarket crap and put a stock pump on it and that cured it.

I had a low mileage original paint '57 T-Bird that my grandfather bought new. It sat in his garage for years before he died. I could not get it to pump fuel. It would run and stay running if I first filled the carb up. If let the fuel evaporate from the carb I could not get it to prime cranking the engine. It had a cloth covered fuel line from the engine to the firewall. My grandfather had bought all the extra stuff he thought he would ever need for that T-Bird including that Ford cloth cover fuel line with the brass fittings on each end. He kept all the new spare parts in peanut butter jars. I took that new fuel line out of the jar with the Ford tag on it, and it felt brand new, nice and flexible. Just for fun I covered it in soapy water and blew through it, and bubbles came out from one end to the other. I could not tell it was cracked with the cloth covering over it. Over 30 plus years of working on this stuff I thought I knew it all but then something breaks in an all knew way just to screw with me.

Re: Failing fuel pump
 

Been thru this too and my fix was as follows:

As 'kevinshea' said and I agree with him, 'use a 6v inline fuel pump/filter set up'... between the tank and the mechanical fuel pump. Mine is on a toggle switch so I easily power it up on demand.

Also there are insulating spacers available (they profile the same shape as the gasket between the carb and manifold) that prevent the carb from heating up so much since it is sitting right on top of the Intake manifold. I had vapor lock at least a few times before i used this spacer that is about 3/4 inch thick. The spacer is placed between the bottom of the carb and the top of the manifold mounting location.

With these two upgrades, I have never again had an issue.

Once in a while on a hot day when pulling a big hill, I have had my 85 hp stutter (lack of fuel) but a quick toggle on with the electric fuel pump untill I crest the hill and all is fine once again.

Hope this helps you!

Re: Failing fuel pump
 

So, Scubachief, You had the electric fuel pump in line with the mechanical fuel pump? So when you had the electric fuel pump off, the mechanical pump was strong enough to suck gas through the electrical pump when it was not running? I would think the introduction of the electrical pump would inhibit the flow of gas (at least a little bit).

Re: Failing fuel pump
 

I had another observation today.

I've been gone a couple of weeks and so the Ford sat for a while. It took a lot of cranking to get it started. Since the current setup I am using to debug this problem was done with clear fuel line and a T connection to a low fuel pressure gauge.

From sitting there was no gas visible in the line. After multiple cranking, I could see gas and bubbles being pushed up the line to the carb. It finally reached the carb and then with a couple more cranks, it started. However, as the car is running a see many bubbles with the gas going up to the carb.

Could this be a sign I have an air leak in the line? I do have a 2 inch rubber hose on the tank side of the fuel pump. Could this be a sign of a bad hose (suggested earlier in this thread). I would not expect to see any bubbles once the engine is running. If I could attach a video I would but I think I can only attach pictures.

Plus, when the car is off, the fuel pressure gauge only holds pressure for a minute or so. If it is a closed system, maybe that tells me there is an air leak.

Re: Failing fuel pump
 

Rich, your travelling air bubbles most certainly prove an air leak. The rapid loss of pressure after shut-down is an unrelated issue, and not necessarily a problem anyway. The most common source of air leaks are at connections, of which you have a pretty fair handful. Starting at the rubber hose clamps, replace any that are NOT worm drive clamps. For the life of me, I don’t know why spring (garbage) clamps are still furnished with fuel filters and such. As with radiator hoses, always tighten over a couple of days, to allow the rubber to compress and form a good seal. The next most common are at the mechanical pump gaskets. Pump castings warp, gaskets dry out, threads strip out, ferrules, tubing, and fittings need freshening up. All these on the suction side from tank to pump are suspect in producing air leaks, invisible, as they leak air in, not fuel out.

Re: Failing fuel pump
 

Thanks, I'll check all screws on the fuel pump (which is "new" but maybe from China) and replace the only 2 inch of rubber hose / clamps (mentioned by earlier posts) to see if that is a source of the air bubbles.

Re: Failing fuel pump
 

Yes is was a mechanical fuel pump from Speedway. I don't know but you are probably right, it came from China. Yes I did notice there is not a lot of throw with the push rod.

Re: Failing fuel pump
 

I've been looking for those insulating spacers but have not found one yet. I have a Holly 94 style carb. Can you point me to a vendor that has them?

Re: Failing fuel pump
 

Dashman's is the only one I am aware of that makes the phenolic spacers.


https://www.ebay.com/str/dashmanshotrodandspeedparts


If you are crafty you can make one out of plywood using a gasket as a template, its basically the same thing. But their prices are so low I have bought several from them rather than make one.

Re: Failing fuel pump
 

Fantastic, Thanks!!

Re: Failing fuel pump
 

the hole in a cog will expand in size when heated is what i keep in mind when dealing with objects stuck on a metal rod. it's important to know too, that the rod will also expand when heated. so's best to try to direct the heat to the cog rather than the rod. it's how the ring gear was put on my flywheel about half a century ago.

here's a brief explanation as to why...

A hole in a cog (or any metal object) expands when heated because the metal atoms vibrate more intensely, forcing them to move farther apart from each other. This, known as thermal expansion, causes the entire object—including the boundaries of the hole—to expand uniformly outwards, increasing its size.

Re: Failing fuel pump
 

Today I removed the 2 inch rubber fuel line on the tank side of the fuel pump and clamped off one end and applied a vacuum to the other end (with a vacuum gauge/pump). Amazing it could not hold the vacuum applied at all. I took a new fuel line with a thicker wall and did the same test. It held a vacuum. Looks like that old rubber hose could be a source of the air leak.

I put in the new fuel line and started the Ford up..... I still see bubbles in the fuel line from the fuel pump to the carb. I also tried to tighten the fuel pump diaphragm bolts (maybe 1/8 turn). Still see air bubbles in the fuel line.

I am leaning towards an electric fuel pump.

Re: Failing fuel pump
 

If you decide to install an electric fuel pump, just to start it and then turn it off and run on the mechanical pump you must make sure the electric pump is an "open" type, that is one that you can blow through when the pump is turned off. Most pumps are the opposite they are closed when there is no power to them, they are made both ways. You want the fuel to be able to go through the pump when it's turned off and running on the mechanical pump. Then you want a low-pressure pump, there are just a couple Airtex pumps that are open when off and have a low pressure for the old Ford carbs, so you don't overflow your carb. If you install a regular electric pump, it will flood over and then your will need to install regulator which I have had nothing but problems with. The Airtex catalog has a section where they list the electric pumps by pressure and if they are open or closed when off. I was automotive mechanic for 30-years. Every year they would send out new parts catalogs, and I would take the old one's home. Try and find the Airtex catalog online and find the reference pages that lists the electric fuel pumps in order, then find an "open" when off pump, 6V or 12V, and 1 1/2 lbs. of pressure. Then mount it as close to the tank as possible with large fiter before the electric pump.

Re: Failing fuel pump
 

Hello 'rbassemir',

RE: "So, Scubachief, You had the electric fuel pump in line with the mechanical fuel pump? So when you had the electric fuel pump off, the mechanical pump was strong enough to suck gas through the electrical pump when it was not running?"

I installed a Flow Thru type 6 volt electric fuel pump... and with it in your hand, preinstalled, you can easily blow air thru it.. and fuel easily flows thru without restriction too. The original rebuilt mechanical fuel pump has no issues at all pulling in the fuel.

I might add that I replaced the fuel tank and the fuel lines as part of the very first upgrades when I began my restore.

Hope this helps.

Take care!

Re: Failing fuel pump
 

I relearned... that it helps to pump the accelerator pedal three or four times prior to cranking. I recalled in the old days I had to do this with my 1965 Buick Skylark and read that in a post on this site a few years back and on then recalled having to do that in the old pre-fuel injection days. Give that a try as well.

Re: Failing fuel pump
 

it's because most carbureted cars BITD had an accelerator pump built into the carb. like the ones on these cars, that pumped extra raw gasoline right down the barrel of the carb when the gas pedal was pumped. not all carbs used such a thing though.

bad news is that also permitted the flooding of the engine with little effort if applied with too much enthusiasm. :(

Re: Failing fuel pump
 

I bought an electric fuel pump and working on the installation. In your setup, do you leave the mechanical pump inline or did you remove it / or by pass it with the electric pump.

Scubaking also used an electric fuel pump but I don't know his set up left the mechanical pump in line with the electric fuel pump. He said he toggles the electric fuel pump on / off manually as needed if the engine sputters. So I am guessing he leaves the mechanical pump in line.

Re: Failing fuel pump
 

Thanks Scubacheif, I missed your earlier replay.

Re: Failing fuel pump
 

great input Flathead Fever ... I will have to check to see if the one I bought is open.

Re: Failing fuel pump
 

Good evening,

I do still have the mechanical fuel pump installed... and it is inside the engine compartment so that it is mostly pulling fuel vs. pushing fuel. I have the flow thru type 6 volt electric pump installed so it is situated between the tank and the mechanical fuel pump. It is also a low pressure type pump and I seem to recall it is no stronger than 5 psi.

It makes sense to have the electric fuel pump installed in the fuel line closer to the fuel tank since it pushes better than it pulls the fuel... but mine is within 18 inches of the mechanical pump and has worked just fine pulling fuel.

I control the electric pump from a toggle switch mounted under the dash within easy reach of my right hand should i need it while on the road.

I was waiting at a road construction hold-up the summer before last... before I had mounted the phenolic spacer [ https://nystromperformance.com/produ...p-adapter-copy ]. Engine stuttered and shut down. Vapor lock. I powered up the electric pump which apparently re primed the carburetor and with just a bit of cranking I was able to get the old gal running and decided to turn around and go another way. Point is that the electric pump saved my trip that time for sure.

Now with the electric pump installed and with the phenolic spacer isolating my Holley 94 carburetor from manifold heat, i have not had a single other issue. Now I do use pure gasoline with is less prone to vapor lock over ethanol blends I am advised.

This setup removes a lot of stress such as the stress of having a great breakfast with my wife... and then getting back into the old gal for the ride home only to have it not fire up. That happened a few times before I made all of the upgrades mentioned above.

Another great upgrade was ditching the standard lead acid 6 volt battery for a optima red top battery.

Hope this helps in your decision making... and all on this forum weigh in if you see anything else I should do to improve my old gal. :)