serious misfire - causes?

[scannon]

scannon said: "the coils for 12v cars actually ran on 6 volts using a ballast resistor."

 

so what's the difference then between these "12volt" coils I keep frying, and the "6volt" coil on my friends 1965 VW Beetle ?

 

Your coil is essentially the same as the 6v VW coil. The difference is the ignition switch feeds your coil 12 volts in Start mode and 6 volts during the Run mode courtesy of the ballast resistor. It's really a 6v coil. Although the early VWs had 6 volt batteries I would think by '65 they would have been 12 volt systems. Older cars had 6 volt batteries so didn't have the option of a 12 volt start mode.

 

Measure the voltage at the coil with the ignition on and engine not running and see what you get. Then measure it while you go to start but before the engine actually starts.

 

IIRC, once the engine is running you will see something around 20 volts at the coil due to the action of the points and condenser, assuming your distributor has an equivalent to points and condenser.

 

Skip

[Ian7]

Thanks Skip.

VW Beetle went 12volt in 1967 (we had one).

 

I'll give the voltage test a try.

Other feedback I'm getting is that I may have a ballast resistor in the coil by default (depending on brand), but certainly I don't find anything resembling one externally in the car wiring.

Stay tuned...

thx

 

Happy Thanksgiving and/or Columbus Day

[scannon]

Thanks Skip.

VW Beetle went 12volt in 1967 (we had one).

 

I'll give the voltage test a try.

Other feedback I'm getting is that I may have a ballast resistor in the coil by default (depending on brand), but certainly I don't find anything resembling one externally in the car wiring.

Stay tuned...

thx

 

Happy Thanksgiving and/or Columbus Day

 

I would think that if there is an internal ballast resistor then there would have to be three low voltage connections on the coil instead of two so that the coil can be fed 6v or 12v internally to take advantage of the higher voltage for starting. Otherwise, why bother with a ballast resistor, just wind the coil to live with constant 12v and do without the ballast resistor.

 

How about a picture of the coil and the wires connected to it and a closeup of it's label if it has one?

 

Skip

[Ian7]

Camera won't focus that closely, but it's a blue Bosch, part number unreadable (box is in the shop, will check later).

Two terminals on top, plus HT lead obviously.

 

Thinking out loud, you know I'm saying the coil is fried purely because the car is exhibiting the early signs of the same symptoms that a new coil cured the last time. Could be secondary effect of a different problem I suppose.

There are no mystery boxes or connections in any of the car wiring I can find, just battery, starter, alternator, distributor, and coil. The only bit not totally familiar to me is that little bakelite box inside the dizzy where the points would be on an "old fashioned" dizzy.

[scannon]

Is there more than a single wire connected to either of the low voltage connections on the coil?

 

Skip

[Ian7]

Yes, and let me reiterate: Caterham confirmed this chassis was intended for a bike engine application, and since it came pre-wired and loomed, I've pretty much learned to assume things are INCORRECT until proven otherwise. :-)

 

wiring loom near the coil has a pigtail that sprouts off it with 4 identical "white with black stripe" wires coming out;

these are paired into two identical factory spade connectors, simply marked as "coil" on both.

 

connecting them to the coil one way allows engine to run; reversing them on the two coil terminals - engine does nothing,

how about this - I start engine, and while running, pull off one 'pair' of coil wires at a time to see if one is redundant? any side effects foreseen? damage to electrical system? electrocution of idiot owner?

 

here's an added bit, perhaps showing my complete electrical ignorance: as a stopgap measure, I'm running an electric fuel pump off of the live terminal on the coil as a convenient source of electrons, but have been since long before the first coil failure; potential source of problem do we think?

 

cheers

[scannon]

Ian,

 

Many bike engines run two coils and no distributor using a wasted spark setup where each coil fires two spark plugs together, one cylinder being on compression stroke and the other one on exhaust stroke, thus the wasted spark.

 

It looks like the two pairs of wires on your setup is for just such a system. However, I don't think this is what is causing your coil problem. I think you need to measure the voltage at the coil both running and not running but with the key on. Also measure it on each pair of wires when disconnected from each other. While you are measuring, check voltages on both pairs with the key turned to Start. You also need to trace out the wiring to find out what is connected at the other end of those two wires. Do you have or can you get a wiring diagram for the bike engined Caterham?

 

If you determine that a ballast resistor is needed you may be able to use the extra pair for the start mode and the existing pair for run mode with a ballast resistor in line. It might be a good idea to spring for a ballast resistor and install it in the hot wire going to the coil and run the car to see if the coil still heats up and also check the performance of the engine to make sure it is not affected by the lower voltage.

 

For the fuel pump, I would find another source for it as when running, point, condenser and coil systems typically show 20 - 40 volts and this would certainly not be conducive to long pump life. This may not be the case with your pointless distributor but we need to know what that voltage is when running. Whether or not the voltage is jumped up by the condenser I would still suggest you find a new source for the pump.

 

Skip

[Ian7]

" Do you have or can you get a wiring diagram for the bike engined Caterham? "

yes, they sent me the entire wiring system shown on an 8x11 sheet, clearly a copy-of-a-copy-of-a-copy-etc. Can't make out any of it.

 

" For the fuel pump, I would find another source for it as when running, point, condenser and coil systems typically show 20 - 40 volts and this would certainly not be conducive to long pump life. "

that would certainly explain my 'bad luck' with two short-life fuel pumps. pardon my ever-deepening ignorance, but how does the low tension coil spade connection that the fuel pump is connected to see up to 40 volts without back-frying other components in the system?

"Whether or not the voltage is jumped up by the condenser I would still suggest you find a new source for the pump."

no condensor (of the sort I'm familiar with) is evident in the system, unless it's potted into the mystery box that makes up the 'points' in the dizzy...

 

thx as always...

[scannon]

" Do you have or can you get a wiring diagram for the bike engined Caterham? "

yes, they sent me the entire wiring system shown on an 8x11 sheet, clearly a copy-of-a-copy-of-a-copy-etc. Can't make out any of it.

 

Is that because it is illegible or because you are not familiar with wiring diagrams? If it is reasonably legible send me a copy and I'll see if I can figure it out.

 

" For the fuel pump, I would find another source for it as when running, point, condenser and coil systems typically show 20 - 40 volts and this would certainly not be conducive to long pump life. "

that would certainly explain my 'bad luck' with two short-life fuel pumps. pardon my ever-deepening ignorance, but how does the low tension coil spade connection that the fuel pump is connected to see up to 40 volts without back-frying other components in the system?

 

The action of the points charging and discharging the condenser cause the voltage in that circuit to be higher than line voltage. Try charging a condenser then touching the lead and case and see what happens. Compare that to touching a hot 12v lead.

 

Typically, the ignition circuit is not shared with anything else.

 

"Whether or not the voltage is jumped up by the condenser I would still suggest you find a new source for the pump."

no condensor (of the sort I'm familiar with) is evident in the system, unless it's potted into the mystery box that makes up the 'points' in the dizzy...

 

There may be a condenser in that mystery box. Measuring the voltage with the engine running will tell us that.

 

thx as always...

You're welcome. I hope we can get this figured out.

 

Skip

[Ian7]

wiring diagram is a literal blur, not a figurative one :lol:

 

stay tuned

[scannon]

Ian,

 

I was wrong about the ballast resistor. I emailed Aldon asking them about ballast resisters and here is their reply:

 

There shouldn't be a ballast resistor/wire in the system and we don't advice it.

We suggest you check the resistance of the coil,it should be 3 ohms.

Also make sure the coil is situated in a cool spot and not overheated by the engine or exhaust.

Does the distributor have any part number or markings on it to confirm if it is suitable.

If you have any queries with this please contact Rob in our Sales Department on 01384 572553.

 

I guess the next step is to measure the coil resistance.

 

Sorry about the bad info, I was relying on experience from the 60s and 70s when ballast resistors, points and condensers were on almost all cars.

 

Skip

[scannon]

Ian

 

I had a conversation with Ben from RMSC/Caterham USA today about your problems. He suggested that you get rid of the electric fuel pump and go with the mechanical type for the cross flow engine for two reasons.

 

1. He has replaced many electric fuel pumps on cross flow cars because people turn the key on and don't start the engine. The heat generated without flow once pressure is built up kills the pump motors. A dash switch for the pump would help with this problem.

 

2. Weber carbs apparently like only around 2 - 2.5 psi fuel pressure while the Caterham pumps provide significantly more. It forces fuel past the needle valves causing rough running and idle. If you stay with the electric pump you need to get a pressure regulator that will keep the pressure in the range. He also said to change the power to the electric pump from the coil to the ignition switch.

 

Skip

 

 

[Ian7]

Thanks Skip,

Sounds like you had a more productive exchange with Aldon than I did. Both the people I spoke to on the phone over there felt the best thing for me to do was return the dizzy for evaluation. Hmmm.

 

I would definitely prefer a mechanical fuel pump. Since its late and I don't want to type much, and leaving out the story of an entire day of total comedy with myself and my engine builder trying to figure out why the damn engine wouldn't run. Short answer is : camshaft he put in doesn't have a fuel pump drive lobe on it. !!!!!!

 

I took the engine to him in late March for a freshening; he found the cam lobes wiped out, and after 22 weeks of waiting ( @#$%^%$#&^%$ ) for the engine, I sure wasn't taking the motor back out again. Hence the electric pump.

 

Voltage checks tomorrow, stand by...

 

Thanks as always.

[Ian7]

Here's what I found:

 

static resistence across coil engine off = 3.6 ohms

 

key at run position, have 12.1 volts at neg terminal of coil; a few mV at pos terminal

 

when cranking, see about 9.5V at coil neg terminal (seems about right)

 

when running at idle and slightly above, still only 11.8V at coil negative;

engine dies if you put the voltmeter across the coil pos when running (no surprise?)

 

didn't see that 20-40 volts at the coil neg terminal that I have the fuel pump running off of; would the voltage at the coil neg post rise with rpm maybe?

 

thx

[OrangeS1]

It sounds like the coil polarity is reversed. The coil terminal marked (+) should receive direct battery voltage from the ignition switch (no ballast resistor) and the (-) terminal should go to the Aldon switching module in the distributor. The voltage on the (-) terminal should change as the engine turns over and the module switches the coil on and off. Since it's a complex waveform ( a switched square-wave with a big inductive "kick" the voltage indicated on a meter will very much depend on the type of voltmeter that is used. A analog meter (one with a moving pointer will average the reading , but a digital meter will be totally confused with the waveform and will give an essentially meaningless reading. It's possible that the Aldon unit is not switching the coil circuit off for a long enough interval (similar to having too much "dwell" on an old fashioned mechanical breaker point based system). It might be worthwhile to connect an ammeter (analog only - 10 amp range) in series with the coil (+) terminal and measure the CURRENT when the engine is not cranking and then cranking and/or running.

[Ian7]

Thanks.

 

As an aside, I think I posted this elsewhere: one of the most humorous aspects of this problem was my phone call to Aldon earlier in the summer.

They confirmed that I did have the correct-as-specified-by-Caterham distributor, but in the opinion of Aldon, its inappropriate for the application !!!

 

Certainly the built-in advance curve is too short; maybe the 'dwell equivalent' is also less than ideal

cheers

[OrangeS1]

Since Aldon does not specify the operation of their "Ignitor" ignition system other than claiming it will work from with a power supply of 6V. to 16V. DC, one can't be absolutely sure of what it's actually doing. However, similar systems that replace breaker points with a magnetic trigger usually are set so that the magnetic trigger interrupts the coil current for a fixed amount of time for every ignition event. That means that the current is interrupted for a fixed period of 8 to 10 milliseconds per spark event. At low speeds, the coil will draw almost as much current as if it were simply connected directly to a battery and the average current will gradually decrease as RPM increases. This means that the "effective dwell time" is increased at low engine speeds, unlike a mechanical point system. This does allow for more average current through the coil and more "coil saturation", but also increases the power being dissipated in the coil and the heat load. For this kind of a system, having the coil in a cool location is critical.

 

Measuring the "engine stopped" current and then the "engine running" current and communicating those numbers back to Aldon, should give them the info to know if the trigger pulse length is correct for your device. Changing the primary polarity will not reduce the heat load, but will give a correctly polarized spark which will work better with worn plugs.