General Stalling Troubleshooting Not Related To Your Imperial's Carburetor


Imperial Home Page -> Repair -> Fuel System -> Stalling

Question from Rob (1955):


My name is Rob, and I am looking for a gas cap for a 1955 Imperial. I have had a stalling problem since I bought the car, and have narrowed it down to the gas cap. One of the previous owners got this weird gas cap, and drilled 4 small holes in it, And I guess he thought that was vented. I have been looking all over San Diego for a cap, and no one has one, I tried Napa, and  they didn't even have a part # for 55-56. I hope someone has one they would like to sell, and I hope it clears up my problem.




From Dick:

These are very hard to find, and have been since the cars were new. My 1957 catalog states that "Gas Caps for the 55 Imperial are not available".

Please tell us what has led you to the conclusion that your problems are the fault of the gas gap. There are only two possibilities for gas cap function (I'm not discussing fit or cosmetics here, just function). Either it MUST be vented, or it doesn't matter because the tank is vented by some other device. Either way, the car should run fine with a vented cap, even if it doesn't require one. If your present cap is not vented, you can drive the car with the cap loose for a short distance, to determine if finding a vented one will make any difference.

My suspicion is that there is some other problem (collapsed pickup sock?) that is causing your problem, but tell us your symptoms and someone here will no doubt have some ideas about the cause.

From Terry:

I have a NOS gas cap on my '55 with holes in it.  It vents fine and should not effect your car's operation. I'd guess you have a partially plugged fuel line.

From Jim:

Chrysler at one time advertised a "Life Time" filter in their fuel tanks. It may have been nothing more than a brass screen. If you're Imperial has been stored with "dead" gas in the tank, that filter could be partially plugged.

In my lone experience with this problem, I applied air pressure from the outlet line at the fuel pump & heard air escaping at the tank. Applying air at the tank filler resulted in the tank ballooning and no fuel passing through the line.

My shade tree solution was to ram a stiff wire through the tank outlet & destroy the Life Time filter. I then drove off in my $900.00, 1953 Custom Imperial Town Limousine, happy as if I had good sense.

From John:

Have you checked the fuel pump pressure on the original pump? The carburetor floats might be out of adjustment and drain enough going uphill and fast turns. The electric pump would fill them especially if the jets are worn. I am just guessing but when you wrote about the pause and then you had power the thought came to me. That would give the time for the carburetor reservoir to fill up. You could have kept the alternator if you had added the bypass resistor before the coil. 12 volts to start and 6 volts to run. You must have had an aftermarket radio too. This was done at the ignition switch: start circuit was 12v and the run circuit was 6v. I am presuming that there was no pinging going uphill.

Follow-up from Rob:

Someone told me that the cap vents, but should not be able to suck in air, that is why the cap has that valve like thing on it. I have had the gas tank drained and cleaned out, and fuel lines cleaned out too. The carburetor has been rebuilt and the fuel pump is rebuilt and putting out with the correct pressure, so I was hoping that this funky gas cap was the problem.  with a vented cap there is a pressure that is created (you can hear a "whoosh" sound when the cap is opened). This pressure is not possible with my cap because of the holes that were drilled in it. The car hesitates sometimes when I go up steep hills with turns in them, (usually to the left) it doesn't matter if the the tank is full or almost empty, and it doesn't happen every time. The car also has an extra aftermarket fuel pump on it that is electric (this is not something I put on the car, it was put on by one of the previous owners), if the car hesitates and I ease up on the gas or "flip the switch" on the electric pump the car will run better. My car has been like a puzzle to me since I got it. I have been returning it to original as I have been going along. Bad mechanics and one of the previous owners have left me with a lot to do. The Engine was rebuilt by one of these mechanics and he put in the plug tubes and sparkplug gaskets. When I bought it from the previous owner it was burning oil like no tomorrow. I took out the plug gaskets and it hasn't burned a drop since. It had aftermarket air on it that was done at the dealer that was a 12 volt system (it had 6 volt generator, and a 12 volt alternator). I had to replace the thermostat, so I removed the air at the same time (the bracket used one of the bolts on the thermostat housing) I also removed the 12 volt alternator. In doing this I found that the generator was dead, and not hooked up, (wires were taped so they wouldn't short out and stuck in the voltage regulator) I had the Gen. rebuilt and hooked up properly and all my electrical nightmares fixed themselves, ( points burning all the time, dead batteries, etc.). All this after the engine was rebuilt, the transmission twice, and a new wiring harness, in the last year. This weird fuel thing is the last of my problems( I hope). I have started doing most of the small work myself, following the shop manual, all with good results. In doing this I have found that original works best (I have followed that for years with my other cars) so I am hoping that the gas cap is the culprit here, as the gas tank and fuel lines were done by someone I trust.

Reply from Dick:

Cars of this era don't have a vapor return line to the tank, so that the only pressure in the tank is from the vacuum created by pumping the gas out of it. If there is no vent on the tank, the tank will sooner or later collapse, or the car will stall, when the vacuum gets so strong that the fuel pump cannot overpower it. If you hear a "whoosh" when you open the gas gap, there is something wrong - if you have a vented cap, the vent is not working right. The caps with valves in them are supposed to let air enter the tank, but not let air or fluid escape.

Your problem sounds to me like "vapor lock", probably caused by the installation of the electric pump without renewing all the rubber hose connections in the fuel line. This causes the pump to ingest air, if there is any pinhole leak anywhere in the system. A pinhole leak may be way too small to cause a gas leak, but will still allow air to enter the line.

Replace all the fuel hose with new, and be sure that it shows "SAE 30R7" or higher on the hose. Older hose will not stand up to our modern gasolines. If you seen any sign at all of seepage around any of the fittings on the tank, pumps, or any of the fittings on the chassis, be sure to investigate and cure all those places of potential air ingestion. Your car should not need an electric fuel pump; more troubles have been caused by this Band-Aid approach than have been cured. If it were my car, I'd take it off completely.

Question from Philippe (1957):

Today the weather was fine so I made a short trip (40 miles) with my '57.  As I drove the car on a straight road with little traffic, I wanted to see if the car would go fast. So I put a heavy pressure on the gas pedal!! Speed increased fast to 40, 50, 60 mph but at 65 mph a curious thing appears: the engine suddenly slows down until the speed returns to 60 mph. It is the same feeling as if I've released a little the gas pedal... Then (as I don't release the pedal) the speed increases again until 65 mph then slows down, then increases etc... The gas pedal was not on the floor but there was no effect if I pushed it to the floor, no engine rev modification, like an automatic (and nonadjustable!) cruise control!!  I released the pedal until the speed slows to 55 mph, then I smash the pedal to floor: the car accelerates very fast... until I reach 65 mph!!  So, it is impossible to exceed this speed, the engine speed decreases every time (except in a small downhill where the "max. speed" is 70 mph).  

I suspect two things: a vacuum advance problem (or a mechanical advance problem) or a vacuum problem on the secondary barrels of the carburetor.  But I "feel" the opening of the secondary when I smashed the pedal below 65 mph!! Advance was set to 12 btdc some weeks ago (no test at high speed since), because before the setting was too high (20 !!) but the car ran fine with this high advance (and exceed 65 mph ..). Any advice?


From Stuart:

You might have a broken Motor mount. This will cause the engine to twist and the throttle linkage to bind.

From Roy:

There may be a problem with your coil.  I would replace it and see if that helps.

From Dick:

This sounds to me that your fuel pump is not keeping up with the demand of your engine. If you have a fuel filter, change it. If you don't, try a different fuel pump.

Question from Lance (1966):

My car will idle all day in the driveway. When I take it on the road for 5 minutes it seems like the fuel line is preventing fuel from getting into the carburetor and the car will die. It will start up in a minute go for 1/8 a mile then die again.

I changed the carburetor, I changed the filter ( I have seen air bubbles in the filter, could this be an issue).

I do not know about the tank or the gas. I have owned this car for a couple of months. When I first got it I could drive 30 miles with no issues. The last owner said that it sat for 10 years!



From Norm:

I had a similar problem with a 61. It turned out to be the fact that the previous owner had installed an additional external fuel filter right at the tank. The fuel pump could not overcome the resistance that the two filters (actually 3 if you count the in-tank sock) offered. I removed the extra external filter and have not had a problem since. Your description of bubbles suggests that either the fuel line is corroded and/or the rubber fuel hose is porous.

Also, is the tank cap vented, or not?

From Dave:


Have you tried the condenser? My dad put new points, plugs and condenser in a car. The problem you describe came about. He eventually put the old condenser back in and the trouble went away. In any case it seems something is breaking down when hot.


From Dick:


I am pretty sure you have a vapor lock problem.  Please go here to read more about vapor lock in your Imperial's fuel lines.


From Don:


This sounds like you either have the wrong type of gas cap or the vent on the fuel tank is plugged.  Sounds mighty familiar


From Sherwood:


Change the sock (filter) in the tank. It's always overlooked.


From Jay:

From your description, it sounds like you gas tank is rusted, and the debris is clogging your lines when the fuel flow starts to increase. I had the exact same problem when I got our '62 running after it had sat for 4 years.

You may also have a leak in the line somewhere (drawing in air, resulting in bubbles). In my experience, either a fuel pump works or it doesn't. Meaning if the engine runs at all, the fuel pump should not be a contributing factor to your problem.

Get yourself a long piece of fuel line and connect one end to the metal fuel line near the fuel pump that runs back to the tank. Remove the gas cap. Blow some air backward into the tank. You should hear some bubbling in the tank. If it is really hard to blow, or if it starts out hard then all of a sudden it gets easier when you hear the bubbles, you either have a clog in the line, or you just blew the clog backward and freed the line somewhat.

Can you detect any rusty debris or "silt" in your fuel filter? I like to use the disposable Fram fuel filters that I can see through. If yours is the original aluminum "can" type fuel filter, remove it and dump it out into a glass jar or onto a few newspapers and a paper towel. Any sign of reddish dirt means you have rust in your tank. The rust will continue to clog your fuel lines until you clean all the rust out and seal the tank interior. (I should know. Been there, done that!) If you do find rusty debris in the filter, more than likely you have the finer particles getting past the filter and settling in your carburetor.

Seeing bubbles entering the fuel filter is most likely a bad rubber fuel line somewhere or a leaky connection between the steel "hard" line and the soft "rubber" line. Fuel line is inexpensive. If you haven't already, I would recommend replacing all the rubber fuel lines between the fuel tank and the carburetor with new line. Make sure that hose clamps are used everywhere there is a connection between the hard lines and the soft ones, and make sure they are snug.

From Marc:

I had a similar problem with my 66. It would start, then die quickly, then repeat. Would do this a few times and then run fine for minutes, hours or days until this pattern repeated again. I tried a new coil, thought it might be the neutral safety switch, and a few other causes.

Final result: The Ignition ballast resister had a crack in it's coil spring, causing intermittent fault of the ignition. New $15 part cured the problem.

This page last updated March 18, 2003.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club