Vapor lock problem on a 1956

[ron56]

I've run into a problem that has me scratching my head. I've rebuilt my car from the front to the rear and it has run fine for around 1,000 miles over two years. I have electronic ignition, Holley 1841 carb, 312 with auto. The other day I got about 10 miles from home driving on surface streets and all of a sudden the car started running rough. I got turned around and headed home with the car only able to run around 30 mph. At no time did it backfire just wouldn't run but if I gave it a accel pump shot the motor would pick up and then die back down. So I'm thinking that I have a fuel pump problem. I got a electric pump from CASCO so I mounted it in the body brace bracket by the front door. It would pump fuel through the stock pump (which was new at the rebuild). It this point I'm thinking I'm good. A few days later with the outside temp a few degrees warmer I started out and this time when about 15 miles on surface streets the engine started to act up the same. I switched on the electric pump and no change. The motor would still pickup with a accel pump shot but then drop back to around 30 mph. Again made it home ok. I checked the fuel filter and it was free flowing, I pulled the bowl off the Holley along with the jet plate and blew out all the passages but there seem to be nothing wrong. Checked the needle and seat, I couldn't see anything wrong. The bowl was as clean as it could be. The float level was fine. Again the new electric pump filled the bowl so it's working. The car again ran fine but I haven taken it very far. If the problem is vapor lock I wonder why the electric pump didn't help. Does anyone have any suggestions? One more thing when the car was running poorly I could rev the engine very high without any issues so I'm pretty sure the problem isn't ignition related especially when a pump shot will pick the engine up.

This page contains affiliate links for which I may be compensated. As an eBay Partner, and Amazon Associate I may be compensated if you make a purchase at no cost to you.

 

[CtCarGuy]

I have a simular problem whereas the car will only run on the electric. I replaced the tank, the 2 filters in front of the electric pump, the fuel line to the pump, put in a pre-tested new pump, changed the filter in the bowl and the inlet filter. I mention all of this because I have a new theory. I think the first filter (a inexpensive in-line) may be causing enough restriction to not allow the mechanical pump to pull fuel. That change is scheduled for tomorrow Also there have been a lot of bad fuel pumps being sold. I got my pre-tested one from Prestige. I know at least the vacuum portion is working. Got caught in a sudden rain storm the the old vacuum wipers worked fine.

 

[Ward 57]

Have had kind of the same problem. Plenty of fuel, replaced the condenser I think it's the coil. Got one original coming but the package seems to have been lost. Classic symptoms of a failing coil.

 

[Critterpainer]

After the changes you have made, I would suspect a weak condenser or coil. They are quick to change out and will allow you to rule that out as a possibility. Usually vapor lock stalls the engine until it cools a bit. A quick way to prevent vapor lock (sorry but this is a true redneck repair) is a gallon of Diesel to a tank of gas. It will not cause the engine to smoke and will help to rule out vapor lock as the issue.

 

[Ward 57]

After the changes you have made, I would suspect a weak condenser or coil. They are quick to change out and will allow you to rule that out as a possibility. Usually vapor lock stalls the engine until it cools a bit. A quick way to prevent vapor lock (sorry but this is a true redneck repair) is a gallon of Diesel to a tank of gas. It will not cause the engine to smoke and will help to rule out vapor lock as the issue.

I just replaced my coil but now it's raining but it does start and idle better. Will post again once I can take it for a test drive.

 

[ron56]

A update on my vapor/??? problem. I've done some more testing and here's what I'm finding:
I had a bit of a chat with Chris Ames (the water pump spacer guy) about vapor lock problems and he told me a couple of things that helped him. One was insulating the line from the fuel tank to the frame rail and the other was to wrap the left side exhaust pipe. So I took his advice and insulated the line from the tank to the frame rail with some DEI stuff. I also a installed fuel pressure gauge. On a mid 90 deg day I drove for 1hr and 40 minutes stop and go mixed with 50 mph portions. First thing I noticed was the fuel pressure started out at 6 psi at idle and then as I drove it would drop to about 4 psi at idle. After it got good and warm the fuel would drop to 2 3/4 to 3 psi under hard accel. After about 1 hour of driving I drove home and pulled the car right up to the garage door and left the car in gear and after about 20 minutes the the temp gauge was to the far right. The car still ran fine. So at this point I think I no longer can blame anything in the ignition system. I did make two changes after the two trips when I had my problems. I added the fuel line insulation and I did remove the carb bowl and the jet plate on the carb and blew out all the passages. I'm sure nothing was wrong because the fuel circuit, jets to the venturi are large passages, and if the much smaller air bleeds were plugged that would only make the car run rich.
With no other changes I drove the car for 45 minutes and then back with the same results. Fuel pressure didn't drop below 2 3/4. If I run the electric pump the pressure will stay at around 4 1/2.
Then I added the exhaust wrap on the left pipe from the start of the hump over the rear end to almost the end of the tail pipe. I then repeated this same trip and this time the fuel didn't drop below 3 psi. The air temp was still in the mid 90's. I'm thinking that Chris's suggestions did the trick but I still don't understand why when I first had the problem and then added the electric pump, why turning the pump on made no difference on how the car ran.
I'm wondering if the drop in idle fuel pressure from when I first start the engine from 6 psi down to around 4 said anything about the fuel pump. It will go down to 4 psi within a few blocks, too short of a run to heat the fuel I would think. I tried to buy a new pump from our t-bird suppliers but they don't seem to have any in stock. Wanting to put the problem to bed I ordered a new pump from a O'Reilly auto parts store. The brand name was Precision Fuel Pumps which looks to be a store brand. When I opened the box the first thing I noticed was it was a pump with Philips screws which I heard are the problem pumps. I moved the pump lever back and forth and figured it was defective right out of the box. I went ahead and mounted it anyway and the car would run on the electric pump but not on the mechanical pump. Not wanting to order another of the same fuel pump I had them order a Delphi pump ( to the tune of about $50. extra) hoping that this will be a pump from a different manufacture. I should get the new pump next week.
Does anyone have any idea what the fuel pressure would be during a hard accel? The only spec I see is 4-5 psi at 500 rpms.

 

[Ward 57]

I really don't think it's a vapor lock problem. These cars are not known for that. Had a beetle that did and the symptoms were different. You should have more pressure no matter what. Have you looked at the source of the fuel and not the pump? It could be the pick-up in the tank or a crimped fuel line. If you still have the original pump, have it rebuilt. I have heard nothing good about aftermarket pumps.

 

[doug7740]

A update on my vapor/??? problem. I've done some more testing and here's what I'm finding:
I had a bit of a chat with Chris Ames (the water pump spacer guy) about vapor lock problems and he told me a couple of things that helped him. One was insulating the line from the fuel tank to the frame rail and the other was to wrap the left side exhaust pipe. So I took his advice and insulated the line from the tank to the frame rail with some DEI stuff. I also a installed fuel pressure gauge. On a mid 90 deg day I drove for 1hr and 40 minutes stop and go mixed with 50 mph portions. First thing I noticed was the fuel pressure started out at 6 psi at idle and then as I drove it would drop to about 4 psi at idle. After it got good and warm the fuel would drop to 2 3/4 to 3 psi under hard accel. After about 1 hour of driving I drove home and pulled the car right up to the garage door and left the car in gear and after about 20 minutes the the temp gauge was to the far right. The car still ran fine. So at this point I think I no longer can blame anything in the ignition system. I did make two changes after the two trips when I had my problems. I added the fuel line insulation and I did remove the carb bowl and the jet plate on the carb and blew out all the passages. I'm sure nothing was wrong because the fuel circuit, jets to the venturi are large passages, and if the much smaller air bleeds were plugged that would only make the car run rich.
With no other changes I drove the car for 45 minutes and then back with the same results. Fuel pressure didn't drop below 2 3/4. If I run the electric pump the pressure will stay at around 4 1/2.
Then I added the exhaust wrap on the left pipe from the start of the hump over the rear end to almost the end of the tail pipe. I then repeated this same trip and this time the fuel didn't drop below 3 psi. The air temp was still in the mid 90's. I'm thinking that Chris's suggestions did the trick but I still don't understand why when I first had the problem and then added the electric pump, why turning the pump on made no difference on how the car ran.
I'm wondering if the drop in idle fuel pressure from when I first start the engine from 6 psi down to around 4 said anything about the fuel pump. It will go down to 4 psi within a few blocks, too short of a run to heat the fuel I would think. I tried to buy a new pump from our t-bird suppliers but they don't seem to have any in stock. Wanting to put the problem to bed I ordered a new pump from a O'Reilly auto parts store. The brand name was Precision Fuel Pumps which looks to be a store brand. When I opened the box the first thing I noticed was it was a pump with Philips screws which I heard are the problem pumps. I moved the pump lever back and forth and figured it was defective right out of the box. I went ahead and mounted it anyway and the car would run on the electric pump but not on the mechanical pump. Not wanting to order another of the same fuel pump I had them order a Delphi pump ( to the tune of about $50. extra) hoping that this will be a pump from a different manufacture. I should get the new pump next week.
Does anyone have any idea what the fuel pressure would be during a hard accel? The only spec I see is 4-5 psi at 500 rpms.

CASCO is showing two different rebuilt pumps that they sell. These pumps are rebuilt from cores that are made in USA, Canada, or Mexico. They use hex head screws or fillister head screws (slotted).

(See attached)

They do not rebuild cores made in China. Typically these use phillips head screws and the bottom sediment bowl has a red washer and a phillips head screw.

https://www.classictbird.com/Fuel-Pump-Rebuilt-1-Per-car/productinfo/9350R/

https://www.classictbird.com/Fuel-Pump-AC-Rebuilt-1-Per-car/productinfo/9350RAC/

No one is selling a new fuel pump at this time. Currently I am testing a new fuel pump for CASCO and after 500 miles of driving it looks promising, but it is not yet available.

doug7740
1955 Thunderbird Blue

 

[ron56]

As a point of reference one can buy the Delphi/AC pump from Jegs or Summit for about $50. less than the cost of a rebuilt from CASCO. I took my Airtex 4406 pump apart and really couldn't see anything wrong with it. After driving my car over the weekend I'm now more convinced that my problem is a vapor issue. With a temp of around 100 degrees I made a trip down the freeway, this is using only the electric fuel pump and the dead Precision pump. After about 15 minutes of freeway speed I could watch the fuel pressure drop the longer I drove. Interesting it dropped to 1 psi and still pulled up a pretty good hill at 70 mph with seemingly no issues. As I pulled off the freeway and got on surface streets on my way home the pressure still was very low. Just a few blocks from the house it was below 1/2 psi and the pressure went to zero as I drove into my driveway. I let the car idle and it quit. I left the pump running and got my IR gun and the pump body was 130 deg. along with the outside of the frame rail where it is mounted. The bottom of the stainless steel fuel tank was at 100 (same as ambient). I shut the pump off and went back out after about 10 minutes and turned the pump on and the pressure was bouncing at around 1/2 psi. This morning I turned the pump on and the pressure went back up to 4 1/2. I have a couple of thoughts: The line from the tank to the electric pump seems clear because if I disconnect it fuel will flow out by gravity at a good clip. I replaced the flex line from the steel line to the pump when I replaced the Airtex with non working Precision pump. I'm wondering if the station where I buy the ethanol free gas still has winter low vapor grade fuel in it's tanks. I've never seen anyone buy the clear fuel when I'm there with the t-bird or my other cars. It just seems strange to me that all of a sudden with the warm weather this year I'm having a problem, when for the last two years no sign of a issue. I also question if I shot myself in the foot by drilling a vent hole in my gas cap. I can see that the cap will vent under vacuum (it has what looks like a check valve built into the cap) but when I blew with my mouth I couldn't blow hard enough to see if the cap would vent under pressure. That might mean that the tank would maybe build pressure in hot days which should help my problem.

 

[Ward 57]

Interesting about the Chinese pumps. If you Goggle "where are Precision Fuel Pumps made" it states they are made in the USA. But on the box it states they are made in China and have the Philips screws and the red washer as Doug 7740 stated. As a point of reference one can buy the Delphi/AC pump from Jegs or Summit for about $50. less than the cost of a rebuilt from CASCO. I took my Airtex 4406 pump apart and really couldn't see anything wrong with it. After driving my car over the weekend I'm now more convinced that my problem is a vapor issue. With a temp of around 100 degrees I made a trip down the freeway, this is using only the electric fuel pump and the dead Precision pump. After about 15 minutes of freeway speed I could watch the fuel pressure drop the longer I drove. Interesting it dropped to 1 psi and still pulled up a pretty good hill at 70 mph with seemingly no issues. As I pulled off the freeway and got on surface streets on my way home the pressure still was very low. Just a few blocks from the house it was below 1/2 psi and the pressure went to zero as I drove into my driveway. I let the car idle and it quit. I left the pump running and got my IR gun and the pump body was 130 deg. along with the outside of the frame rail where it is mounted. The bottom of the stainless steel fuel tank was at 100 (same as ambient). I shut the pump off and went back out after about 10 minutes and turned the pump on and the pressure was bouncing at around 1/2 psi. This morning I turned the pump on and the pressure went back up to 4 1/2. I have a couple of thoughts: The line from the tank to the electric pump seems clear because if I disconnect it fuel will flow out by gravity at a good clip. I replaced the flex line from the steel line to the pump when I replaced the Airtex with non working Precision pump. I'm wondering if the station where I buy the ethanol free gas still has winter low vapor grade fuel in it's tanks. I've never seen anyone buy the clear fuel when I'm there with the t-bird or my other cars. It just seems strange to me that all of a sudden with the warm weather this year I'm having a problem, when for the last two years no sign of a issue. I also question if I shot myself in the foot by drilling a vent hole in my gas cap. I can see that the cap will vent under vacuum (it has what looks like a check valve built into the cap) but when I blew with my mouth I couldn't blow hard enough to see if the cap would vent under pressure. That might mean that the tank would maybe build pressure in hot days which should help my problem.

The venting of the gas cap is not a bad thing. You don't want to have a vacuum issue even though the EPA may not approve. I'm intrigued how you plumbed a pressure gage so you can see the real time pressure. Yes you would think the added pressure in the tank would help. The reason you see nobody else using non ethanol fuel is the cost. Premium+ prices and the new vehicles will run on the cheapest fuel as anti knock technology may degrade performance but they don't notice.
I'll scratch my head as to why the heat would have such an effect on fuel pressure even with an electric back-up pump. The only other thing I can think of is if there is another flexible fuel line in the system that swells when hot restricting the flow.

 

[doug7740]

Bellow is a Tech Tip that I wrote about the fuel tank venting on a 1955/ 1956 Thunderbird.
Gas Cap Tech Tip: The gas cap on your T-Bird must be vented to allow air to enter the tank. If air cannot get into the tank vacuum will be created which can stop the flow of fuel to your engine. Last summer, I had to replace my gas cap and I discovered that when I removed the gas cap after running the engine for a while, I could hear the sound of air rushing into the tank. To vent the fuel tank, the 1955 and 1956 gas caps have a rib stamped into the surface which allows air to enter from the outside edge of the cap to the center. The problem with my gas cap was that the inside diameter of the gasket was so small that it prevented the venting process. The problem was easily fixed by removing the gasket from the gas cap and increasing the inside diameter of the gasket by cutting it with a razor blade. Removing just a little bit of the gasket from the inside diameter corrected my venting problem.


doug7740
1955 Thunderbird Blue

 

[knuckle47]

Adding all of these folks to my “Rolodex”

The first two are a simple google search. Cowboy John took and extra few tries but found him

Rebuilt Antique Water Pumps & Master Cylinders in Florida at

Cowboy John's Auto Parts, based in Webster, FL, specializes in antique car parts and have the rebuilt part you need. From water pumps to master cylinders, view our selection and shop today!

cowboyjohnsautoparts.com

 

[CtCarGuy]

I have a simular problem whereas the car will only run on the electric. I replaced the tank, the 2 filters in front of the electric pump, the fuel line to the pump, put in a pre-tested new pump, changed the filter in the bowl and the inlet filter. I mention all of this because I have a new theory. I think the first filter (a inexpensive in-line) may be causing enough restriction to not allow the mechanical pump to pull fuel. That change is scheduled for tomorrow Also there have been a lot of bad fuel pumps being sold. I got my pre-tested one from Prestige. I know at least the vacuum portion is working. Got caught in a sudden rain storm the the old vacuum wipers worked fine.

Update: The reason the mechanical pump would not work was because of the hose. I replaced the hose to the pump when I put in the new pump. It took 3 years to figure out. Someone suggested examining the hose. The fuel line is 5/16" from the tank. The opening in the house was 3/32". I built a new hose using 5/16" fuel hose and now my mechanical works fine. I did check with the suppliers, of the 6 I wrote to, only NPD replied and said all the hoses are 3/32". I am surprised that no one else has had this problem. Hope this helps.

 

[Edwin Cassini]

I have a simular problem whereas the car will only run on the electric. I replaced the tank, the 2 filters in front of the electric pump, the fuel line to the pump, put in a pre-tested new pump, changed the filter in the bowl and the inlet filter. I mention all of this because I have a new theory. I think the first filter (a inexpensive in-line) may be causing enough restriction to not allow the mechanical pump to pull fuel. That change is scheduled for tomorrow Also there have been a lot of bad fuel pumps being sold. I got my pre-tested one from Prestige. I know at least the vacuum portion is working. Got caught in a sudden rain storm the the old vacuum wipers worked fine.

Sounds to me like you have a Vapor lock, in your Gas Tank. Are you running a Vented or unvented gas Cap.!! On this old cars always run a Vented gas cap. If you do not have one drill 3 or 4 3/32 holes through the top of Cap right on thru till you see day light !! You would be surprised to see Gas tanks crushed inword due to No venting or clogged venting. Plus Car will run faster on the Track, a Hot Rod Trick !!!

 

[Frankie the Fink]

Most likely not vapor lock, much more likely percolation/heat soak and affects MANY older cars. Here's what is happening, after a good run and you park the car in the heat, after a few minutes the underhood temperatures spike and fuel starts dribbing out of the carb "squirters" and raw fuel sits on the intake manifold runners; after about 45 minutes it'll evaporate but until that happens you will be starting a flodded car and those procedures apply. You have to hold the accelerator pedal on the floor which opens the throttle plates and the raw gas is sucked into the engine and then the car should start but will prob run rough for a minute or two. You can test this by buyiing a Harbor Frieght cheap I/R temp tun and "shoot" the carb bowls after a hot drive, any temps north of 135* or so indicates "heat soak"; in addition you may hear the fuel boiling in the carb and see the nozzles dribbling fuel down the carb bores - sure signs of the problem

 

[dunnedom]

Just spit balling. Older fuel lines deteriorate with ethanol fuel. just ordered SAE J30R9 fuel line. one of the things i had to replace on our newly acquired bird which i did with the wrong fuel line! lol. It seems ethanol also boils at lower temps than the old fuel these cars were designed for. Happy Trails!

 

[ZOUBI57]

Hi, sorry if translation is terrifying, but I use me and Google. On my 1956 Thunderbird, I currently have a vapor lock problem. I notice that the fuel supply has been cobbled together with a copper pipe with a external diameter of about 8 mm and passes over the cylinder head cover to go to the back of the original carburetor. The copper line runs from the fuel pump and then through a glass jar in which the filter is located. Do you think that by putting back the original pipes which are made of metal (iron or aluminum perhaps) and of much smaller diameter, it could solve the vapor-lock problem?

 

[Tom Alpers]

Hi, sorry if translation is terrifying, but I use me and Google. On my 1956 Thunderbird, I currently have a vapor lock problem. I notice that the fuel supply has been cobbled together with a copper pipe with a external diameter of about 8 mm and passes over the cylinder head cover to go to the back of the original carburetor. The copper line runs from the fuel pump and then through a glass jar in which the filter is located. Do you think that by putting back the original pipes which are made of metal (iron or aluminum perhaps) and of much smaller diameter, it could solve the vapor-lock problem?

I don't think changing to a different metal line will make any difference. Can you give more details on the vapor lock issue you have. When does it occur? at high speed, low speed, all the time, how hot is the car when it happens, how long does the car have to sit before you can restart it, what is the temperature where you are driving, did you recently replace any parts such as fuel pump. Does the gas tank have a vented cap. Has it always vapor locked or is this something that just started.

 

[OlleHi]

We had around 30 degrees Celsius (86F) in sweden (Hot for being here!) last week when I was out driving. After 30 min the car started to run quite bad, like out of gas. And misfiring.
When I checked the fuel filter it was empty. I suspected vapor lock or maybe the fuel pump. After a while I started it up again, I could se that some bubbles came with the fuel, and it ran for 5 minutes, so it took a while to get home again!
The car was restored 2018-2022, but not the engine. I replaced the fuel pump 10 years ago.
Today when it was around 25 degrees Celsius (77F) I drove and same thing happened again a couple of times. But I only drove maybe 10 minutes before the first stop.
Can it be something with the fuel pump? I opened the gas cap to see if it made any sound, like the tank wasn't vented. You know the pffft sound?
But if something is wrong with the fuelpump, the car wouldn't start again, would it? Is there anything I can check in the fuelpump?

Thanks!
Olle, Sweden

 

[59tbirddavid]

Your motor is starving for fuel, fuel filter is first place to look.