'55 runs rough, backfires and stalls out at highway speeds

Pete986

Pete986

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Jul 22, 2019
Thunderbird Year
1955
I've been enjoying my '55 for the past few weeks, been driving it on local trips.
I wanted to get it on the highway, now that I'm convinced all the gremlins have been worked out.

Up to 60MPH, the car runs great, once I get it above 60, it starts bucking, backfiring, and eventually dies out.

My past experience told me its the plugs. I replaced them all, and though the car DOES run better up to 60MPH, the same thing happens.

I didn't look under the distributor cap yet, maybe I should have before I posted.

Any suggestions?
 

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I have a similar problem with my ‘56. I have a supplemental electric fuel pump and discovered that by turning it on when driving at high speeds the bucking and dying went away. I assume my problem was insufficient fuel supply.
Jim Yergin
 
Can you provide more information? How many GPH?
Where does it install in relation to the stock pump?
Maybe a picture?
 
A2914907-0B8A-4528-BD39-C40D982C1467.jpeg Pete,
Sorry but I have no idea as to GPH. It is a low pressure pump installed in line back by the fuel tank with an on/off switch under the dash. I found it on eBay and installed it to prime the carb after the car had been sitting.
Jim
 
Pete986 said:
I've been enjoying my '55 for the past few weeks, been driving it on local trips.
I wanted to get it on the highway, now that I'm convinced all the gremlins have been worked out.

Up to 60MPH, the car runs great, once I get it above 60, it starts bucking, backfiring, and eventually dies out.

My past experience told me its the plugs. I replaced them all, and though the car DOES run better up to 60MPH, the same thing happens.

I didn't look under the distributor cap yet, maybe I should have before I posted.

Any suggestions?
Click to expand...
Sounds like fuel starvation but it's not necessarily the pump. Check the filters first, including the one in the carb if there is one. If the filters are clear it could be a pinched or partially plugged fuel line. If the lines are clear it's probably the fuel pump. A good stock pump will supply enough fuel without the booster so you may have a weak pump.
 
Thanks! Now I'm considering what you said AND what Jim Yergin said.

I think you're both right, about the fuel starvation.
Filter and lines are good.
It seems to me a stock pump should be able to get over 60MPH.

Maybe I'll look into a better pump and buy the electric pump in the future.
Now that I'm thinking of it, the PO had mentioned problems with the pump.

You guys have given me some stuff to think about here.

Thanks for your input
 
Pete986 said:
I've been enjoying my '55 for the past few weeks, been driving it on local trips.
I wanted to get it on the highway, now that I'm convinced all the gremlins have been worked out.

Up to 60MPH, the car runs great, once I get it above 60, it starts bucking, backfiring, and eventually dies out.

My past experience told me its the plugs. I replaced them all, and though the car DOES run better up to 60MPH, the same thing happens.

I didn't look under the distributor cap yet, maybe I should have before I posted.

Any suggestions?
Click to expand...
Aside from the plugs, have you checked the plug wires as well as the points in the distributor. Under the hood is a hostile environment due to the heat. The plug wires are often neglected due to the awkward placing of the wires. You may have fuel problems or you may have ignition breakdown at high r.p.m.
good luck, J.
 
Jack,
I did a quick inspection of the wires, they look pretty good; they look pretty NEW, actually.
I'm gonna check under the cap tomorrow.

Thanks for your input!
I've only had the car for 5 weeks and I still have a LOT to learn.
I've owned a few 65-66 Mustangs over the past 30+ years.
Thunderbirds don't have much in common besides the brand, number of wheels and shift pattern.
 
Pete986 said:
Jack,
I did a quick inspection of the wires, they look pretty good; they look pretty NEW, actually.
I'm gonna check under the cap tomorrow.

Thanks for your input!
I've only had the car for 5 weeks and I still have a LOT to learn.
I've owned a few 65-66 Mustangs over the past 30+ years.
Thunderbirds don't have much in common besides the brand, number of wheels and shift pattern.
Click to expand...
Looks are not everything. did you put a meter on the wires and check the resistance?
 
I have the exact one on my 56, The response is fantastic, No bucking or coughing. I can drive anywhere and keep up with the expressway traffic.
pic108.jpg
 
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I have a 1970 tbird project, but a brother of mine has a '56 and added an electric fuel pump. In his case, the pump had too much pressure, which is probably why you asked the GPH question earlier. At any rate (pardon the expression), I can't claim to be an expert but I believe the smart thing to do when adding an electric fuel pump is to also add a pressure regulator so overpressure can be dialed back. I suppose a correct gph unit might make it unnecessary (while the carb gaskets, etc hold). Anyway, my brother added a regulator and the car is running great now. Best of luck!
 
Where are you getting the power from? I was thinking from the ON post on the ignition switch?
 
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I'm sorry that the link was of no use to you, I was only trying to help.

You can purchase an electric fuel pump from any of the Thunderbird parts suppliers and there are instructions included with the pump on how to properly install and wire it.

If you are only looking for information on where to get power to the pump, I would wire it to the “I” terminal of the ignition switch, and then through another on/off switch. That way it will only be on while the engine is running, and you can turn it off if you want to. I wired one through the oil pressure switch with a relay, that way if the engine dies in case of accident once oil pressure is lost the pump will shut off.

doug7740
1955 Thunderbird Blue
 
doug7740 said:
I'm sorry that the link was of no use to you, I was only trying to help.

You can purchase an electric fuel pump from any of the Thunderbird parts suppliers and there are instructions included with the pump on how to properly install and wire it.

If you are only looking for information on where to get power to the pump, I would wire it to the “I” terminal of the ignition switch, and then through another on/off switch. That way it will only be on while the engine is running, and you can turn it off if you want to. I wired one through the oil pressure switch with a relay, that way if the engine dies in case of accident once oil pressure is lost the pump will shut off.

doug7740
1955 Thunderbird Blue
Click to expand...

Thanks!
I'm going to get one of those.
I appreciate your time and ideas!
 
I was considering mounting a switch for the electric pump on the transmission.
So it would come on when I put the car in third gear.
I don't have back up lights, so I don't think it would be too crowded down there.
Does this seem like a good or bad idea?
Should I just mount the switch inside the car like a normal person?
 
I had posted a few weeks ago about this issue.

I installed an electric fuel pump, checked ignition parts, (cap, rotor, wires)
Both fuel filters are good.

The car runs great up to 60MPH, after that, it bucks, backfires and eventually stalls out if I don't let off the gas.

I'm open to any suggestions.
Thanks!
 
Likely to be a carburetor issue, not supplying enough fuel at higher rpm - does the car do the same thing in second gear at equivalent rpm? Is the air filter clean? Similar result if dirty and blocked - insufficient air volume at higher rpm causing the fuel mixture to run rich as opposed to lean if the carburetor jets are dirty
 
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