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gadam05 I am looking for some help to solve a problem with my 1930 model A. I've owned the car for 26 yrs.and never had this occur.
The car was running in my driveway while I was doing some yard work. The car stopped suddenly, and I could not get it to start and run more than a few seconds. I have checked the following: gas flow, 0k, carberator, ok but swapped to another to be sure. Ignition: starter engages, car tries to start, turning over rough, but runs for only a few seconds. checked point setting,ok,,timing-right on., rotor and distributor body and cap ok,, spark plugs gaped ok. I have not checked the coil, How can I do that? Is that a possibility? I need some ideas, please. |
Re: gadam05 Check the condenser first by changing it with a known good one. If that don't work, change the coil to a new one.
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Re: gadam05 I like to do the easiest checks first. Just hold the coil wire 1/4" from a head nut and see if you have a good blue spark while cranking the engine with the key on.
Pull the choke for a couple revs. Do you have gas dripping out the carb intake? |
Re: gadam05 Make sure gas cap is venting .
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Re: gadam05 Condenser got my vote
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Re: gadam05 Well, with all the coil & condenser guess, it should be easy enough to pull the coil wire while cranking it over to see what the spark looks like. When you say it is turning over rough, my initial thought was timing gear. If it had jumped a tooth or two, it could create some symptoms as you are suggesting.
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Re: gadam05 Hello,and thanks to my respondents. I appreciate your ideas. Checked my gas cap venting----ok. changed my condenser--- no change. checked my coil spark--spark was good but not blue in color,so I changed the coil. now have a blue spark, but no change to my problem. Because this problem began when the car just stopped while it had been running at idle just sitting in neutral in the driveway, I would Question the thought of the timing gear jumping a tooth.
I do appreciate the ideas---and welcome any other thoughts. Thanks |
Re: gadam05 I don't know about conditions in the States, but here in NZ, since converting to non lead fuel, it's quite often the case that after idling a vintage engine for a length of time, that the plugs foul up.
For almost all running problems, the plugs were the first thing to check with running problems? Keith |
Re: gadam05 One of our club members had something similar happen. It turned out to ne a frazzled coil wire that only made intermittent contact. Try replacing it.
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Re: gadam05 I was wondering if you have 10% ethanol crap gas and it got so hot just setting at idle that the crap gas started to boil and give trouble?
How is the running when the engine is cold? |
Re: gadam05 Did you clean the points when you checked the gap?
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Re: gadam05 Could be the timing gear.
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Re: gadam05 he says will run briefly, so timing gear not on my list right now....
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Re: gadam05 I now have an authentic used old stock Model A coil. It works fine in its mount and also works fine when held in hand and disconnected entirely from the car except for the wires. It does not need to touch the firewall at all. BUT... earlier I had a replacement coil of uncertain vintage in my new restoration. It used a clamp mounting screw and nut to tighten the firewall mounting bracket around the coil. The clamp and firewall mount assure a good full time ground for the outside case of that coil and it did reqire grounding. After about 350 miles of initial running, vibration loosened that screw, the coil slipped down just a bit and the fresh paint on it eliminated the electrical grounding. The car stopped running suddenly and completely till the coil was repositioned and the clamp tightened. Finding that was a real mystery. The symptoms you list could be a variation of this anomaly.
By the way, I have never been clear on the wiring logic for the high voltage coil component of the coil. Wiring diagrams do not show a current source. Can anyone explain this? Rancho |
Re: gadam05 The black wire from the terminal box supplies the voltage to the coil primary. The red wire runs from the coil primary through the switch and grounds at the points to complet the coil primary circuit.
I don't know of any coil where the metal can is connected to the coil primary circuit, and the coil mounting should not need to be grounded. You only need a feed wire and a ground wire to complete the coil primary circuit, and if either one is through the can, the points can't do their job. |
Re: gadam05 last i knew the coil secondary grounded via the can; the other end of the secondary is obv. the high voltage coil wire. An automotive coil is in essentially a DC transformer, with 12 v in and 10-15 K volts out. Of course, DC voltage doesn't fluctuate so this violates the principles of a transformer. BUT add the points to make and break the primary and voila you have fluctuating voltage after all
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Re: gadam05 Quote:
http://mgaguru.com/mgtech/ignition/pics/circ_ic.gif |
Re: gadam05 Notice in Mike's picture the secondary is tied to the primary winding, and not the can. This is the typical coil practice.
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Re: gadam05 I just experienced a similar situation with my 31 SW, and after a long list of tests it was the condensor that was the problem. I replaced the coil, distributor body and cap, did compression test, ,checked oil for sign of water, insulated dash light wire completely, checked timing, made sure intake manifold was torqued properly, changed distributor. Now the A RUNS GOOD. And I am Hot and Tired after a 105 degree day. Good luck ,hopefully this will give you some ideas.
Jim from Kansas 1931 SW FORDOOR |
Re: gadam05 No wonder condensers die so fast & points burn out without them, the secondary voltage goes straight through them! If the secondary was grounded through the can would it make the condenser & points last longer?
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Re: gadam05 The condenser discharges back into the coil giving it an extra "boost". The coil and the condenser form an oscillation or ringing that can be seen on an engine O scope.
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Re: gadam05 I'd love to see that waveform. Charlie Kettering was a genius to come up with this LC circuit, much to the chagrin of the magneto manufacturers
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Re: gadam05 Quote:
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Re: gadam05 2 Attachment(s)
Quote:
The high oscillations on the left show the spark jumping the spark plug. The spark continues until the voltage drops low enough to not be able to jump the plug gap. The next group of oscillations is the coil and condenser bouncing the remaining current back and forth until it dwindles to near zero and the points close to build up the magnetic field for the next cycle. The second picture is when I switched my scope to SUPERIMPOSED, so it shows the 4 spark plug patterns stacked on top of each other. This makes it easy to compare how each plug is firing compared to the others. |
Re: gadam05 Thank you Mike V Florida and Tom W! So the standard arrangement (applicable per my testing to authentic Ford coils) is internal connection of the secondary (High Voltage) winding to the "grounding" side of the Primary winding and so it has a ready current supply. The coil I described, and first had in my car, either did not have that arrangement or was defective in that respect. It needed to have its outside case grounded. Strange. But in the clear diagram from Mike V Florida we can see how it is supposed to be and why the regular unit does not need firewall grounding of the case. I note the old Ford units had a metal case but modern coils seem to be non-metallic.
Hope this leads to a solution for gadam5. Rancho |
Re: gadam05 thanks, Tom !
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