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EFV-8 Club Forum / General Ford Discussion / is this vapor lock?

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Posted By Discussion Topic: is this vapor lock? -- page: 1 2     TomO 09-03-2011 @ 6:38 AM reply profile send p.m. Senior Posts: 7264 Joined: Oct 2009 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 Stroker 09-03-2011 @ 6:28 AM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 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 Stroker 09-03-2011 @ 6:28 AM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 double post deleted This message was edited by Stroker on 9-3-11 @ 7:04 AM ford38v8 09-02-2011 @ 8:53 PM reply profile send p.m. Senior Posts: 2780 Joined: Oct 2009 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 supereal 09-02-2011 @ 11:57 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 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. Stroker 09-02-2011 @ 9:21 AM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 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. TomO 09-02-2011 @ 8:31 AM reply profile send p.m. Senior Posts: 7264 Joined: Oct 2009 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 ford38v8 09-01-2011 @ 4:11 PM reply profile send p.m. Senior Posts: 2780 Joined: Oct 2009 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 Stroker 09-01-2011 @ 3:30 PM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 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. ford38v8 09-01-2011 @ 3:16 PM reply profile send p.m. Senior Posts: 2780 Joined: Oct 2009 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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