| fordmerc | -- 09-01-2011 @ 6:35 AM |
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'39 rebuilt engine runs perfectly - for about 5 miles - then it hesitates and will stall if I slow down around a corner or stop. Car won't start for about 15 min, then it runs well again (I don't know for how long). Ambient temperature around 75 degrees.
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| TomO | -- 09-01-2011 @ 7:45 AM |
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Did you check the spark? Did you check the float level? It sounds like you may be flooding the engine, but check the spark just to make sure that it is good. Tom
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| supereal | -- 09-01-2011 @ 7:49 AM |
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Probably either an old coil or condenser. Those are the classic symptoms. At 75 degrees, "vapor lock" is unlikely.
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| 37RAGTOPMAN | -- 09-01-2011 @ 8:11 AM |
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also check your fuel cap to make sure it is vented,,,!! when it does not start, check you spark, if NONE, start with your ignition switch, and resister,with a volt meter. then on to the coil and condensor, also see if the coil gets hot,,,!! then also a ANOTHER thing to try [ THIS WORKS FOR ME MORE THAN ONCE ] is a ice pack on the coil, let it set for a few minutes,then try to start,if it Starts send the coil and disstributer to SKIP to have rebuilt. so you will not have any more problems,cause the coil is shorting out when it gets HOT,, Hope this helps, 37RAGTOPMAN This message was edited by 37RAGTOPMAN on 9-1-11 @ 9:47 AM
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| doning | -- 09-01-2011 @ 9:03 AM |
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How do you know if the cap is vented? My gas cap is original to my '37 Ford. Is it vented then?
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| nelsb01 | -- 09-01-2011 @ 12:10 PM |
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Original gas caps were vented. You are lucky if yours is the original cap.
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| ford38v8 | -- 09-01-2011 @ 2:06 PM |
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"If you slow to turn or stop": This sounds like your spark is weak, and will continue to run at speed, but will fail if your RPM goes down. As your coil gets hot (5 mile drive), the internal insulation breaks down and it shorts out. Lower RPMs means higher compression, and the spark blows out. If this is the case, you need to send your coil out to be rebuilt. Skip Haney in Florida is one rebuilder, and has an excellent reputation. Do not replace your coil with new or NOS, as the new coils are low quality, and the NOS are just as old as yours is. Alan This message was edited by ford38v8 on 9-1-11 @ 2:09 PM
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| Stroker | -- 09-01-2011 @ 2:45 PM |
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Alan: I won't buy into your premise that at low rpm's the pressure in the cylinders is higher. Actually up to a point, the opposite is true. I agree though, that the coil is likely the culprit. Fuel delivery problems and ignition adequacy quite often mimic each other. Replacing the coil with one of Skip's improved items simply eliminates a problem that sooner or later will rear its' head.
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| ford38v8 | -- 09-01-2011 @ 3:16 PM |
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Dan, I would also think the opposite to be true, but I remember reading that somewhere. Everything you read is true, isn't it? Alan
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| Stroker | -- 09-01-2011 @ 3:30 PM |
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Alan: It would be true under either of the following circumstances: 1. It is a normally-aspirated diesel. 2. FordMerc makes his low-speed turns at full-throttle using only the brakes. This is why it is generally recommended when testing compression to prop the throttle wide open, as the throttle plates reduce the air available during the intake stroke.
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| ford38v8 | -- 09-01-2011 @ 4:11 PM |
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In any case though, high or low compression, a weak spark is a hundred times more likely to stall an engine at idle than at speed. I didn't read that anywhere, so it might be true. Alan
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| TomO | -- 09-02-2011 @ 8:31 AM |
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Alan, I have usually seen the opposite symptoms with a weak coil. The engine will idle fine, but choke and die at speeds above idle. That is why I asked him to check his float level. A high fuel level will flood the engine at idle, but let it run at speeds above idle. Tom
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| Stroker | -- 09-02-2011 @ 9:21 AM |
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The spark has to be robust enough to overcome the resistance caused by the high pressure in the cylinder. The higher the pressure, the greater the resistance, and the demand for a high-amp, high voltage spark. The pressure in the cylinder is governed by the amount of air flowing into it. At low rpm's, coupled with a closed throttle, there is very little air/fuel charge allowed into the cylinders, so the pressure and spark requirements are less. Conversely, a wide open throttle at low rpms (such as when accelerating), allows more air/fuel into the cylinder, which demands a strong spark. As rpms increase, the ability of the intake tract to keep in step with the increased cylinder pumping demand falls behind, and the pressure drops off accordingly. One could deduce from this that the ignition should work better as speeds increase, however the coil saturation time diminishes with increased rpms.
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| supereal | -- 09-02-2011 @ 11:57 AM |
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That is why a weak or open condenser causes loss of spark power. The condenser, aside from protecting the points, assists in allowing the coil to charge quickly. The "dwell", the percentage of the combustion cycle during which the points are closed, remains the same, except the "real" time for the cycle shortens as engine speed increases. Thus, the loss of spark power mimics a fuel problem as speed increases. Same is true of a weak or internally shorted ignition coil, which becomes less efficient as heat boosts resistance, lowering current.
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| ford38v8 | -- 09-02-2011 @ 8:53 PM |
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Dan, Bob, Tom, I can't fight you, so I'll join you. In a feeble effort to salvage something here, I'll quote Dan, and reply to that: "Conversely, a wide open throttle at low rpms (such as when accelerating), allows more air/fuel into the cylinder, which demands a strong spark." At a stop sign during a tour some years ago, I stalled, and found that it was due to having installed the wrong coil for that particular tour. In those days, I and many others I knew of, carried a box of spare coils, as we were sure the right coil was in there somewhere, and we simply had to find it. Fast forward, of course we now know that all those coils were perfectly good as long as they remained in the box. Dan's statement makes sense, and I probably stalled as I stepped on the gas, thereby introducing an overwhelming air/fuel charge which blew out the spark. I think it likely that I misinterpretted what I read about higher compression at lower RPM, and Dan's explanation clears the mud for me. Thanks, Dan! Alan
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| Stroker | -- 09-03-2011 @ 6:28 AM |
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Alan: In those late 50's years when I was trying to make my flathead outrun others, I had the benefit of some excellent mentoring from those who had been there before. Those early principles are firmly embedded, and have served me well. The air/fuel/spark/timing "needs" of engines haven't changed over time, but the way those needs are satisfied today with modern computerized engine management systems is an area that I find a little intimidating. Dan
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| Stroker | -- 09-03-2011 @ 6:28 AM |
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double post deleted This message was edited by Stroker on 9-3-11 @ 7:04 AM
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| TomO | -- 09-03-2011 @ 6:38 AM |
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Alan, I don't want to fight you, I just related my experience over the past 30 years of driving my Mercury. I remember the days when I had a 5 mile coil and a 10 mile coil and used a modern coil with an adapter if I had to drive further than that. I was buying any coil that I could find, putting it on the tester to find the "good" one, only to later find out the it was a 10 mile coil. Skip Haney and Jake Flemming have changed all of that by rebuilding our script coils with reliable components. Tom
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