1956 mercury 312 stalling

[Abchoppers]

Hi all, I’ve been bugging the guys at Jalopy Journal for a couple weeks so I’m here to spread the love. 1956 mercury custom 312, got it about a month ago. Bought it from a great guy who only drove it about 2,000 miles in 20 years, so it sat a lot. Initially had a lot of hesitation on take off. Upon recommendations I inspected the fuel tank and it was not rusty, fuel line was clear. I changed the fuel pump, the inline filter after the fuel pump, and ultimately the carb. It has a new Holley 4bbl. That cleared up the hesitation, but a new problem arose.

Randomly the car will act like it’s running out of gas and leaves me stranded. After many attempts to restart, usually involving pouring gas directly into the carb, it will start and then run fine. I have a hard line from tank all the way up to pump, with the exception of a 6” rubber hose going from steel line to fuel pump. After pump is a hard line to an inline filter that has two short rubber hoses to connect, after filter is hard line directly into carb.

Here are some things I’ve noticed when this happens.
1. When removing inline filter the fuel pump definitely pumps gas out of the line while cranking.
2. When removing line from carb, gas does not always pump out. Sometimes a little, sometimes none. Gas filter is brand new and was changed to another new one with no luck while stranded.
3. When stranded the primaries do not shoot gas into the first 2 barrels of the Holley. So must be the filter, but it’s new and I’ve tried more than one
4. Car will only start after 15 minutes of messing with it by pouring gas into carb directly, starts up and dies. Do this multiple times till it reluctantly starts and lots of vigorous foot pumping gets it to clear up, then runs fine

I’m stumped and can use your knowledge
Thanks in advance
Ryan

[cadillac512]

Hi Ryan.



First thing I'd check is the fuel line from tank to pump. You need a way to pull vacuum on that line after removing it from the fuel pump. A couple feet of hose and mouth suction will do, but some folks balk at that. Clear hose will let you know if fuel is coming and you'll see it before tasting it!
If that's ok you need to check vacuum on the suction side of the pump...should see 12+ inches of vac while cranking with your gauge on the suction side and the other side open.
If that's ok hook up the suction side and crank til you get fuel, then hook your pressure gauge to the carb side of the pump and crank it... looking for 2-6 lbs of pressure.

If you can suck fuel with a hose and the pump fails either vac or pressure tests,it's bad.


Oh...make sure the tank vent is working!



Terry

[Abchoppers]

Originally Posted by cadillac512

Hi Ryan.



First thing I'd check is the fuel line from tank to pump. You need a way to pull vacuum on that line after removing it from the fuel pump. A couple feet of hose and mouth suction will do, but some folks balk at that. Clear hose will let you know if fuel is coming and you'll see it before tasting it!
If that's ok you need to check vacuum on the suction side of the pump...should see 12+ inches of vac while cranking with your gauge on the suction side and the other side open.
If that's ok hook up the suction side and crank til you get fuel, then hook your pressure gauge to the carb side of the pump and crank it... looking for 2-6 lbs of pressure.

If you can suck fuel with a hose and the pump fails either vac or pressure tests,it's bad.


Oh...make sure the tank vent is working!



Terry

Thank you for the reply Terry. I just was driving it up and down my driveway to try and duplicate the problem, sure enough it stalled again. As it was stalling I was able to look at the fuel filter and it did not appear to be pumping. After it stalled I pulled the tank line off from the fuel pump and hooked up my brake bleeder. It took a few pumps but gas started to flow out of the line. I hooked it back up and it started right up. I need to get a vacuum gauge and perform your other tests. I guess it’s either a fuel tank full of crap, even though it looked ok to me when I inspected it, or a bad ( new) fuel pump. I’ll do the vacuum test and report back. Oh and I also blew out the vent line and it is clear
Thank you again

[paul2748]

Have you ever taken the gas cap off the car when it died? If so, did you get a whooooosing sound ? If so, that means the vented cap (most 56's used a vented cap) isn't working. The fuel system needs a vent to equalize pressure the air inside the tank.


Or run the car w/o the gas cap on and see if it still dies. If it does, then the vent system is not the problem. If it doesn't die, then maybe your problem is the vent system (vented cap.)


Another possible cause is something in the tank (I know you said it looked clean) There could be something that is being sucked into the outlet tube which cuts off the fuel. When the car dies, suction is gone and it drops back into the tank. Restart the car and it get sucked into the outlet again.

[miker98038]

I don’t know about the Merc’s, but my 55 bird had a “sock” or filter in the tank on the pick up tube. Loose debris would get sucked onto it (a handful of old raffle tickets) and the car would die. No suction, they’d fall off and away I’d go. I doubt you’ve got raffle tickets, but maybe a plugged sock choking it off? Long shot, and like I said I don’t know if Merc’s used them.

I might pull the cap when the tank wasn’t full, and put some compressed air on the line from the pump back. See if anything blows clear. Low pressure, not 100 psi.

[Bob from Northport]

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How about the fuel pump pressure?? 54' runs about 4-5lbs. I'd make sure that the pressure is not lower than that.
Also, there is not a electric fuel pump in line somewhere??

[Abchoppers]

I did not think of the gas cap trick while it was stalled and not starting. I did though blow out the gas tank vent line and I could hear that it is clear. It’s a line the goes from too if fuel tank and exits right next to the gas cap with a rubber grommet. Next time it gives me a problem I’ll try the gas cap trick for sure

[Abchoppers]

I just opened up the sending unit on the tank again to look inside. I can see what looks like a round hockey puck type filter on the end of the pick up line, but there’s no way to really get to it. I pulled the line from the tank to pump also and blew air through it to the tank. I could hear the air blowing into the fuel as I did it. I reconnected the fuel line and started the car. Looking at the fuel filter I could see it actually pumping fuel from the pump whereas normally I don’t see that. After a few minutes I stopped seeing that but the car still ran and still had fuel in the filter. I took a pic of the tank but need to learn how to post it, it does have stuff floating in it but still looks pretty clean to me

[Abchoppers]

No electric pump, I’m picking up vacuum gauge after work today and will report back with the findings

[Ole Don]

Go back and read post five. I had a 55 sedan, I removed the tank and cleaned it. The clean tank gave all sorts of crud. I made a new sock out of three layers of fine screen, folded together, and wired on the pick up tube flare.

[dmsfrr]

Originally Posted by Abchoppers

.... I changed the fuel pump...
Randomly the car will act like it’s running out of gas and leaves me stranded ...

Originally Posted by Bob from Northport

How about the fuel pump pressure?? ...

The new / replacement mechanical fuel pump you put on, where was it made?
99.9% of them come from china and they're defective in the box. If they work at all then quit after only a few miles you got one of the good ones. (haha)

Hopefully you still have the old fuel pump you took off, send it somewhere good to have it rebuilt.
Example...
https://vintageautopumps.parkerspack...m/contact.html

[Abchoppers]

The pump was a Carter that I had read was the best out of the new pumps. Like a dumbass I threw out the old fuel pump ��. I guess I’ll know when I put a gauge on it, but I’ve read the same thing you said about bad pumps. I might go electric if this one is bad

[Abchoppers]

I’m thinking if I pull the tank I’d probably go with a new one, I’ve seen them for under $300. I didn’t know you could separate the tank though and clean it out, good to know

[Abchoppers]

I just tested the fuel pump. I’m getting 4 psi on the push/outlet side of the pump, but the suction side is not really registering anything. It just jumps the needle and maybe hits 1-2 but doesn’t hold. I put it on the brass nipple coming out of pump with clamps and a fuel line to the gauge. Maybe I’m doing that part wrong? It doesn’t seem like it could have no suction and still run great.
I took a video of the clear filter while running, I can visibly see the fuel pump sending gas into the filter, just trying to figure out how to post the video

[cadillac512]

The pump could very well have the inlet check valve not sealing. Higher pump speed or liquid in the valve may make it pump just enough to run part of the time, but your test sure indicates a problem. If the pressure side of the pump is open while you check the suction side for vacuum and you get the result you describe, the pump is a dud or has crud holding the valve open.


Terry

[Abchoppers]

Originally Posted by cadillac512

The pump could very well have the inlet check valve not sealing. Higher pump speed or liquid in the valve may make it pump just enough to run part of the time, but your test sure indicates a problem. If the pressure side of the pump is open while you check the suction side for vacuum and you get the result you describe, the pump is a dud or has crud holding the valve open.


Terry

I tested again with the same results, gauge just flickers around 2-3 inches of vac. What are your thoughts on adding an electric fuel pump and keeping the Carter mechanical for my vacuum wiper needs? I’m thinking of using a Carter 4070 electric and running it through the mechanical. I’m also planning on trying to get Carter to send out a new mechanical but I figure an electric is good to also run as a back up

Thank you all for the help, much appreciated
Ryan

[cadillac512]

I think that's a reasonable plan, as long as you make sure the tank is clean so the new electric doesn't have trouble. A suction screen before the electric is a good plan...not paper but screen type. I like to hang the electric pump on reinforced rubber straps to keep noise down.


By the way...I like my electric wiper conversion on my '41 Merc!


Terry (glad to help)

[Abchoppers]

Originally Posted by cadillac512

I think that's a reasonable plan, as long as you make sure the tank is clean so the new electric doesn't have trouble. A suction screen before the electric is a good plan...not paper but screen type. I like to hang the electric pump on reinforced rubber straps to keep noise down.


By the way...I like my electric wiper conversion on my '41 Merc!


Terry (glad to help)

All great info, thank you. I’m thinking this was my problem after doing the pressure test, but I’ll definitely put a pre screen on just to be sure. I ordered the Carter and a wiring kit with a relay and fuse. I’ve read about the rubber straps or grommets to keep noise down and it’s a great idea, I’ll be picking those up too.

I would love electric wipers, it’s on my list. Right now my credit card is on fire from car parts haha
Thanks again for your time and patience
Ryan

[Abchoppers]

Quick update - new Carter 4070 pump installed, all is well now. The mechanical pump was definitely losing prime. Runs much better now. I mounted pump on rubber bushings but still have a decent amount of buzzing through the frame rails. I’m going to play with different rubber bushings and washers tomorrow, but hard work is done and it all worked out.
Thanks all for the suggestions and help
Ryan

[cadillac512]

Good deal. Nice when the plan works! I had to "hang" mine on fiber reinforced rubber straps to totally isolate the vibration and sound.



Terry