1948 Engine Runs Erratically-Strange Problem

[48Super]

I need some help from the straight eight Gurus out there. Here is a run down on my problem and what I have done so far:

The Problem;

Last week, I started the car (1948 Super) after it had been idle for several months. The engine ran fine at first and then began to miss, run rough and eventually stall out. I thought it might be due to old fuel and took the car out for a short ride to fill up the tank with fresh gas. The car would alternate between running fine and missing severely. By carefully working the accelerator, I could keep it running enough to limp back home. I drove it about 5-6 miles this way. When I got home I ran it some more and it would run fine for a while and then get rough and die. After it quit running, I removed the fuel level sight plug and gas was present right up to the bottom of the opening.

What I've done so far:

-Rebuilt the carburetor. Upon disassembly, everything looked good inside. I did not find any dirt, plugged openings or obvious cause for the problem. At least now, I know the carburetor has ethanol-resistant parts in it. I reinstalled the carburetor and got the car running and it still does the same thing.

-Thinking that I may have the dreaded "phase separation"and resulting water in the fuel that can happen with ethanol blended fuels, I connected the fuel pump directly to a can of fresh gas and tried running the engine again. Same problem.

-I removed the filter element from the glass bowl and ran the engine to see if I had good fuel flow. The fuel pump was just rebuilt last year and the car was run without any problems. The pump seems to be building good pressure also, when I loosened the connection to the filter, gas comes out under pressure.

-I removed the spark plugs and they looked OK, so I just cleaned them, checked the gaps and put them back in. The ignition wires are practically new and in good shape. I disconnected the wire from the coil to the distributor cap and held it near a ground while cranking the engine, spark looks fine.

Not sure what to try next. The strange thing is that if I keep the engine running enough to get the through rough spell, it will clear up for a while and run fine before having another "fit". It even idled nicely for several minutes at a time before eventually stalling out.

If anyone out there has any suggestions, I would really like to hear them. I've owned this car for over 30 years and I never had an issue like this with it before.

THANKS!

[jackofalltrades70]

Mike,

Nice to hear from you, but sorry it is because you are having a problem with your convertible. From what you are describing, it sounds electrical. Maybe a weak coil or capacitor starting to go bad. Have you tried to move wires a little while the car is running to see if you can simulate vibration? See if it gets worse or better when the wires are "tugged" or "pushed". Hope this helps, but you've probably already tried most of this. Matt

[trp3141592]

Hi Mike,

I vote for a deteriorated coil: they can fail when they get warm. When you replace it make sure to get one for an 8-cylinder, not a 6.

Other possibilities, though less likely:

cracked distributor cap or rotor.

carbon track on inside surface of distributor

bad capacitor--they're cheap and easy.

Deposits on points. Replace the capacitor if you replace the points. And polarize the generator to protect your new points.

Worn bushing in distributor, allowing the distributor shaft to wobble unpredictably.

Is there a hood insulation blanket? If so, has it sagged down and blocked the air intake? That happened to me in my '53 Special. Engine would run with hood up, would not run on the road. That's when I learned to ask, "What changed?"

I still vote for the coil.

--Tom

Edited July 10, 2013 by trp3141592 (see edit history)

[Pete Phillips]

Is the engine popping (sounds like a small backfire) back through the carburetor? If so, that's a stuck valve. Very old gas can make the valve stems sticky, but my vote is for a bad coil or bad points. Pete Phillips, 1948 Super sedanet (and others)

[48Super]

Thanks for the suggestions. It really seems like a fuel delivery problem to me because I can keep the engine running most of the time by playing with the throttle. There is absolutely no backfiring so I don't think a sticky valve is the issue. I'm going to rig up a gravity fuel feed directly to the carburetor as the last attempt to rule out the fuel pump as the cause. I don't know if it is possible for the fuel pump to have a good output sometimes and not at others (sticky check valves?) I will also install a new set of points and a new condenser just for good measure and because it is easy. The distributor in the car was an NOS part so the mechanical condition of it should not be an issue. I will report back when I have more test results.

[old-tank]

Double check the ignition as planned. In addition as a test run a separate ground wire from the battery to the body of the distributor (parts that are painted separately will not ground as well as parts painted after assembly).

What carb does it have? Some carbs with the main jets in the bottom of bowl can have permanent or intermittent plugging of one jet causing it to run (badly) on half a carburetor --- usually not an issue with carbs with metering rods.

Willie

[55 SURVIVOR]

Sounds like A weak coil,check it with A meter,also check the condensor. Mark M

[48Super]

Problem Solved! New points + new condenser = Smooth Running Engine. I bow to the superior knowledge of my fellow BCA members. I never had this type of an issue with a set of points before, the way the engine was acting I really thought it was starving for fuel. Amazing the trouble a few misplaced electrons can make for an unsuspecting engine. Thanks again!

[trp3141592]

Hi,

GREAT to hear!

--Tom