TheSamba.com :: View topic - Proof that the Bosch Blue Ignition Coil is WEAK!

Sat Mar 07, 2009 9:44 pm

The Bosch ignition coil is weak and incapable of firing wet fouled spark plugs in a flooded engine. With a weak ignition coil, you need to hold the throttle completely open while you crank the engine until the spark plugs dry off enough, before the Bosch ignition coil is capable of firing the spark plugs. If your battery connections are in good condition and your battery has enough energy to crank the engine long enough and you don't burn out the starter in the process, you might able to get the engine started.

I have tested the Bosch Blue ignition coil and points on an engine with a 34PICT-3 with a leaky float valve that caused flooding, and the Bosch Blue ignition coil would NOT start the flooded engine. I tested the same engine with an inductive switching high energy ignition system and a variable permeability air gapped core ignition coil and it WOULD start the flooded engine EVERY time. I didn't need to wait for the spark plugs to be dried off. The variable permeability ignition coil was able to fire the wet fouled spark plugs!

If the failure to start the flooded engine was a carburetor/fuel mixture problem, a stronger ignition system would NOT have been able to start the engine. But in fact a stronger ignition system DID start the flooded engine every time, proving that the Bosch ignition system is weak and not up to the challenge of working in REAL WORLD engine conditions.

The inability of an ignition system to fire the spark plugs in a flooded engine and the failure to start the engine is a symptom of a WEAK ignition system. The carburetor caused flooding is just an additional problem that was revealed by the weak Bosch ignition system!

The resistive loading of a new spark plug gap in a properly running stock engine is around 1.0 MΩ (1,000,000 ohms). As the spark plug begins to foul, and also in more extreme engines, the resistive loading of the spark plug gap may be as low as 500 KΩ (500,000 ohms).

A weak ignition system, such as a Bosch Blue ignition coil and points, may be able to fire new spark plugs with small spark plug gaps as long as the fuel mixture is ideal. However, when the spark plugs get older, and especially when spark plug fouling conditions exist, that will decrease the resistance across the spark plug gaps, the fouling load resistance across the spark plug gaps bleeds off the current before the voltage can develop high enough to jump the spark plug gaps and you have misfires and you cannot start the engine. NO Spark, NO fuel mixture Ignition, NO Start!

The following table shows the distance in inches that a spark can jump with various loads across the spark gap. This shows the ability of various ignition coils to fire spark plug gaps, with different spark plug gap load resistances, to simulate new spark plug gaps, as well as spark plug gaps that are fouled. The distance of the spark gap is directly proportional to the voltage. The larger the gap, the higher the voltage across the spark plug gap. All tests were performed at atmospheric pressure on the same day.

Also note that under the compression inside the cylinders, the distance that a spark can jump is many times smaller. The testing in free air is still a valid measurement of the voltage that the ignition coil can develop under actual resistive loading. The gap that the spark can jump inside the combustion chamber is dependent on many variables including compression ratio, volumetric efficiency and throttle position and it is NOT consistent.

The following testing was performed at a very low repetition rate, which shows the maximum spark that each ignition coil is capable ot delivering. Dwell time is not a factor in this testing as it would be at higher RPM.

A 1.00 MΩ load is equivalent to a new spark plug inside a stock engine in good condition.

A 500 KΩ load is equivalent to a spark plug inside an extreme engine or a spark plug that is beginning to foul.

160 KΩ, 120 KΩ, and 80 KΩ loads are equivalent to severely fouled spark plugs.

Code: 1.00MΩ 500KΩ 160KΩ 120KΩ 80KΩ

Stock VW Bosch Coil 0.42" 0.19"
Compu-Fire
Inductive Switcher

Bosch Blue Coil 0.42" 0.20"
Compu-Fire
Inductive Switcher

Jacobs Ultra Coil 0.63" 0.53" 0.13"
Mileage Master
Adaptive Spark Inductive Switcher

Jacobs Ultra Coil 1.05" 0.82" 0.70" 0.42"
Pro Street
Adaptive Spark Capacitive Discharge

Note that when the Bosch ignition coils were loaded to 500 KΩ, their output voltage was less than 1/2 of what it was with a 1.0 MΩ load. The output voltage with a 500KΩ load was so low that you are not likely to be firing the spark plug.

Note that the Jacobs Inductive switching Mileage Master ignition system, with a variable permeability air gapped core Ultra Coil, was capable of putting out 50% more voltage than the Bosch coils with a 1.0 MΩ spark plug load.

Note that even with a 500 KΩ load, the Jacobs Mileage Master and Ultra Coil was capable of putting out 26% more voltage than the Bosch coils could with a 1.0 MΩ spark plug load.

Note that even with an 80 KΩ load (Simulating a severely fouled spark plug) a Jacobs Pro Street Capacitive Discharge ignition system and variable permeability air gapped core Ultra Coil was able to put out as much voltage as a Bosch Blue coil with a 1.0 MΩ load (Simulating a new spark plug). This is 12.5 times more spark current than the Bosch ignition coils can produce. This demonstrates the superiority of a capacitive discharge ignition system to fire fouled spark plugs. This higher spark current is also delivered into a spark under normal engine conditions.

In fact, if you installed a high energy capacitive discharge ignition system, with an air gapped core ignition coil, on an engine that would not start because of severely fouled spark plugs, the ignition system would likely fire the fouled spark plugs and start the engine and the high current sparks would also clean off the spark plugs as you drove.

An air gapped ignition coil varies it's output with the load applied to it. In other words, it puts out more current when you really need it with spark plug fouling conditions.

Because of the built in ballast resistance inside the Bosch ignition coil, as the coil runs longer, it becomes hotter and the losses in the ignition coil become greater. In actual use, the output of the Bosch ignition coil is even less than shown here.

The bottom line is that the stock Bosch ignition system is weak and is not able to fire the spark plugs with less than ideal fuel mixtures and it can leave you stranded.

A high energy ignition system will start your engine under adverse conditions and get you home.

After the spark jumps the spark plug gap inside the engine, the resistance across the spark drops significantly. A variable permeability ignition coil will also provide more spark current under these NORMAL driving conditions.

The increased spark energy of a variable permeability ignition coil will ignite the fuel mixture more quickly and consistently and reduce the variable ignition lag time. A weak ignition coil increases the amount of time it takes to actually ignite the fuel mixture and increase the ignition lag time. An increase in ignition lag time results in retarded ignition timing under many driving conditions, especially at part throttle conditions. By ignition timing I mean when the fuel mixture is actually ignited, not to be confused with spark timing, which is when the spark jumps the spark plug gap and is what we set with a timing light.

There is NO performance or reliability downside to using a variable permeability air gapped core ignition coil. It's one of the few modifications that you can make that improves reliability and performance at the same time.

It is interesting to note that in one of Kettering's original ignition system drawings he shows what appears to be an air gapped core ignition coil with an external ballast resistor.

Scott Novak

Sat Mar 07, 2009 9:52 pm

All i know is I decided to take my car out today for the first time since November. I cranked the engine until I got oil pressure. Then I pumped the gas a few times and cranked the engine again. It fired right up and after a few seconds running it idled at 800rpm.

The Blue coil works just fine for me.

If you have a leaking float valve on the carb you should fix it or the gas can wash down the cylinders and cause serious problems.

Sat Mar 07, 2009 9:57 pm

Isn't there a sticky for this sort of thing?

You know: when you have a hammer, everything looks like a nail.

Sat Mar 07, 2009 9:58 pm

:shock: wow my brain came out my nose halfway through that but it does make sense

Sat Mar 07, 2009 10:04 pm

58 Plastic Tub wrote: Isn't there a sticky for this sort of thing?

You know: when you have a hammer, everything looks like a nail.
Yes... there is. I forgot about it.

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