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Harry Ferguson Tractors Discussion Forum
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weak coil spark, no plug spark?? help!!

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kev139

08-26-2005 18:29:54




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Hi guys, need help again. My TEA died last weekend while changing an implement. No spark was found.
I have changed the points, coil, condensor, plugs and added a resistor because the coil required one.
I have bypassed the key switch for all tests. It is a converted 12 volt system with 3 wire alternator.
When I hold the high tension coil lead 1/4" from ground I get a thin orange spark, when i connect it to the distributor, no plug spark.
With points open I meter 12volts at all points.
With points closed, I meter 12 volts up to the resistor, 4-5 volts after the resitor up to the coil positive, and .4 - .5 voltsat the coil negative to the distributor.
Coil measures 1.5 ohms and the resistor measures 1.5 ohms.
I have found no shorts in the distributor yet I still have weak spark at the coil and no spark at the plugs.

Help??!!!!

Thanks

Kev

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Fred Hambrecht Sr

08-27-2005 13:15:38




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 Re: weak coil spark, no plug spark?? help!! in reply to kev139, 08-26-2005 18:29:54  
The coil does its deed when the points open. The amount of current flowing thru the coil is determined by the voltage applied.

With the engine running you have about 13.8 Volts, half of that is 6.9V Across 1.5 ohms, the current flow is 4.6 amps. Now with the tractor not running the 5 volts you measure will cause a current flow of 3.3 amps or a reduction of almost 30 percent. While cranking, it is even worse.

How can you solve the problem, easy! Bypass the resistor during the start cycle. I am not familiar with the starter on your tractor, but if you have from left to right 12 Volts resistor coil, at the junction of the resistor and coil run a wire from the voltage supplying the start relay to the coil resistor junction.

You will now have an increased voltage during the cranking cycle and a hotter spark. When you quit cranking, the alternator provides more voltage, the relay supply is disconnected and everything works great.

Hope that helps, it worked great on a 9N and a JD MT.

Good luck Fred

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Jerry/MT

08-26-2005 22:18:30




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 Re: weak coil spark, no plug spark?? help!! in reply to kev139, 08-26-2005 18:29:54  
You've provided a lot of info to help someone diagnose your problem. All your voltages look right with the points open and closed. What is the condition of the rotor and the distributor cap? Arc the terminals clean?Is the rotor cap contact touching the carbon button in the top of the cap? Any cracks in the cap or signs of arcing within the cap? Do you have metalic wire plug and coil wires? Are you sure that the points are set properly? What about the wear in your distributor? Push on the distributor shaft radially with the points closed. What type of motion do you get at the points when you do this? With a lot of bushing and/or shaft wear, the dwell is significantly reduced and a weak spark results. Report back on what you find

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kev139

08-27-2005 07:49:10




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 Re: weak coil spark, no plug spark?? help!! in reply to Jerry/MT, 08-26-2005 22:18:30  
Hi Jerry, my cap looks to be in good shape, not yet a year old as well as the wires. I have cleaned out the cap to eliminate tracking but never hurts to try that again.
I do have wear in the distributor, when I turn the shaft clockwise and counterclockwise there is more than .002" movement, which is what I have seen you state before as a measurement.
Could this be my issue?, quite honestly I used the tractor for an entire winter previous with no issues with that movement, maybe its gotten more excessive than I remember.
Which bushing is this and where is located on my distributor?

I'm feeling pretty defeated these last couple of days.

Thanks for the help and any further input.

Kev

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Jerry/MT

08-27-2005 10:24:52




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 Re: weak coil spark, no plug spark?? help!! in reply to kev139, 08-27-2005 07:49:10  
Don't get discouraged. I look at these types of problems as a challenge;man versus machine! The key issue is to make sure that with the points closed when you push RADIALLY on the shaft, the points don't open or even move. Radially means pushing on the SIDE OF THE SHAFT. I believe you were rotating the shaft against the advance springs. There is a bushing in the distributor body that supports the shaft. Mine was so worn that when I pushed on the shaft radially with the points closed, the points opened around 0.030"!I got a sickly orange spark and the engine ran like a three legged dog! And it just "happened" one day while I was pushing snow. In reality it had been happening over a period of 50 years. It just got bad enough one day to to cause a big problem. I thought it was carburetion until I checked the spark. It cost me $100 to get the distributor rebuilt (new shaft and bushing) as opposed to nearly $200 for a rebuilt unit. I took the $100 I saved and got a Pertonix electronic ignition and it starts in a quarter turn and idles smoothly. I'm not pushing electronic ignitions because they don't solve problems, they just require less maintenance and mines a working tractor.
By the way, did you make sure that the rotor spring was touching the button in the cap? Bend it upward to make sure that it is. Easy does it however 'cuz you don't want to break it.
Let me know what you find out.

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kev139

08-27-2005 10:53:40




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 Re: weak coil spark, no plug spark?? help!! in reply to Jerry/MT, 08-27-2005 10:24:52  
I now understand radially, having said that, my distributor shows almost no movement at all, seems very solid. I'll try the spring trick, I may even replace the cap and rotor to rule out more variables.

Thanks

I'll keep ya posted.

Kev



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Jerry/MT

08-28-2005 14:18:58




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 Re: weak coil spark, no plug spark?? help!! in reply to kev139, 08-27-2005 10:53:40  
Something is puzzling me about your numbers. You ve got 12 v on one side of the reisistor and 4-5V, lets say 4.5 v on the other side and it ohms out at 1.5 ohms. That implies your current is 5 amps ((12-4.5)/1.5). Your coil ohms out at 1.5 and the voltage drop is about 4 V (4.5 - .5)from the coil to the distributor so you current is 2.7 amps. Somethings not right. The current should be constant. Make sure that your resistor is really 1.5 ohms and is not shorted some where. Neglecting the wire resistance (strictly not true but it's pretty small compared to the resistor or the coil), your circuit is dropping 11.5 V across 3 ohms, so the current should be around 3.8 amps. That would imply the voltage drop across the resistor and the coil should be 5.7 volts (Delta E= I X R =3.8 x 1.5 =5.7) Could you recheck your mesurements? And measure the level of voltage at the battery side of the resitor, don't assume it's 12 V if you perchance did that.

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kev139

08-29-2005 18:58:34




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 Re: weak coil spark, no plug spark?? help!! in reply to Jerry/MT, 08-28-2005 14:18:58  
Ok guys, here is what I"ve tried so far.
I have removed the ballast resistor and the associated coil. I installed the NAPA IC14SB coil, results still the same.
I recorded my findings, battery was a little weak from cranking.
Points open, 11.5 volts at all points up to the distributor.
Points closed, 11.5 volts up to coil positive, .1 volts measured at coil negative and distributor.
Coils measures at 4.3 ohms.
With points open no continuity to ground at all points except distributor housing.
Still get weak coil spark.

To long without a tractor..... ..

Thanks guys!

Kev

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Jerry/MT

08-30-2005 19:41:31




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 Re: weak coil spark, no plug spark?? help!! in reply to kev139, 08-29-2005 18:58:34  
What's your point gap, Kev? Should be like 0.022 ". That's the only thing left.



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