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Laytean
Samba Member
Joined: July 15, 2017
Posts: 1
Location: Eugene
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 Posted: Sat Jul 15, 2017 1:14 pm Post subject: Coil readings good or bad? |
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72' Bus with a 1.8L running Carbs not fuel injection.
I'm having an issue with a weak yellow spark. Coil ohms perfect as to specs stated in other threads, but I have 11.88Volts going into coil on + - while off. Once running the volts going into my coil read 6.55-6.82 volts going to + - leads on the coil. I'm assuming there is either a resistor wire, or an ignition problem?
I fouled out my brand new plugs in 6 days.
Any advice would be much appreciate as my Bus is my Daily. |
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Abscate
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Joined: October 05, 2014
Posts: 22668
Location: NYC/Upstate/ROW
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| Posted: Sat Jul 15, 2017 2:52 pm Post subject: Re: Coil readings good or bad? |
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That 11.8 Volts is the first problem. It should be battery voltage , which should be 12.5 for a full charge
Ignition switch, wiring are possible culprits. Don't put in a hot start relay, fix what is wrong.
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 12722
Location: on a bike ride somewhere
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| Posted: Sat Jul 15, 2017 3:58 pm Post subject: Re: Coil readings good or bad? |
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| Laytean wrote: |
| I'm having an issue with a weak yellow spark. |
This is largely a myth. The "best" spark would be ultraviolet in color, and invisible to the human eye. Blue is colder than that. Yellow or orange sparks indicate excess ionization of sodium molecules in the air of the plug gap. Some sparks change color mid-gap as the molecules in the atmosphere are not perfectly mixed.
--
Let's look into why you have a sudden voltage drop once the bus is running. The current path is the same in the switch with the key on, engine running or not. The big difference here is that with the engine on, you should be seeing closer to 14 volts, since the alternator will be charging the battery, and the entire "hot" (#15 and #30) wiring of the bus should reflect that. A one-volt drop is not uncommon by the time the current reaches the coil, since these cars have a bit longer wiring than most.
Can you get voltage readings at the starter positive post, the battery positive post, and fuse box (any spade) with and without the engine running?
Robbie
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TomWesty
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Joined: November 23, 2007
Posts: 3482
Location: Wyoming,USA
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| Posted: Sat Jul 15, 2017 4:55 pm Post subject: Re: Coil readings good or bad? |
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Before you do anything, clean all connections from the battery. Both the connections on the battery posts. Make sure you disconnect the ground side of the battery (negative) and crawl under the bus and clean the connections to the starter. Now, unbolt the ground cable where it bolts to the body. Be ready for this to be so corroded that it snaps the bolt off. If the bolt doesn't break you are lucky. Take some sandpaper and sand where that ground cable connects to the body until you see shiny metal. Also shine up the ground cable side that contacts the body and re attach everything. Now fire it up and see if you have higher voltage at the coil.
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busdaddy
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Joined: February 12, 2004
Posts: 51148
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Sat Jul 15, 2017 7:05 pm Post subject: Re: Coil readings good or bad? |
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| Laytean wrote: |
| ........ I have 11.88Volts going into coil on + - while off. Once running the volts going into my coil read 6.55-6.82 volts going to + - leads on the coil. ........ |
What color is the wire(s) that's attached to the + terminal you are reading that on?, also mention if you have some sort of points replacement module in the distributor.
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telford dorr
Samba Member
Joined: March 11, 2009
Posts: 3555
Location: San Diego (Encinitas)
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| Posted: Sat Jul 15, 2017 11:42 pm Post subject: Re: Coil readings good or bad? |
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^^^ All of the above^^^
- the coil voltage at terminal #15 [black wire(s)] better be around 14 volts with the engine running (but with the quality of voltage regulators these days, I'll take anything over 13.5).
- the voltage on terminal #1 (green wire) will vary with engine speed, although connecting a meter here may kill the engine. You need a really high input resistance to measure, like 10 megohms or better, and the voltage spikes could get to upwards of 350 volts [it bites!]
- I prefer to bench-test coils using a good solid 12 volt source and the proper condenser. A good push button substitutes for points (press, hold for a second, release). Judge by the resulting spark at the coil secondary terminal to ground (or, more conveniently, to the coil #15 terminal). You'll need to cobb up an adjustable spark gap of some sort. Note: the coil case has no internal connections. It's truly a three terminal device.
- the resistance measurements of the coil windings don't mean a whole lot, unless they're radically off the mark. Secondary spark performance is much more telling.
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