Proof that the Bosch Blue Ignition Coil is WEAK!

[Scott Novak]

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: Select all

                          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

[regis101]

Great write up. Now what we need are name brands.

[Bruce2]

Which Bosch Blue coil did you test?

[Scott Novak]

Great write up. Now what we need are name brands.

I'm most familiar with Jacobs electronics products, and they are what I recommend.

For details read:
High Energy Ignition Systems Jacobs MSD Mallory
http://www.shoptalkforums.com/viewtopic.php?t=122428

Which Bosch Blue coil did you test?

The numbers on the bottom are as follows:

PN 0 221 119 027

522

K12V

The Bosch Blue ignition coil has 2.93 ohms of ballast resistance. It has a 10.5 KOhm secondary resistance. It came off one of many used Beetles that I have had.

Scott Novak

[doc]

Really interesting! Is there any threat of a better coil masking potentially damaging problems, e.g., carb flooding or worn out plugs?

doc

[FJCamper]

Above: The Blue Coil on the 917. No place for a wimp.

Gentlemen,

I don't doubt for a minute Scott's investigative work or his conclusions. I believe since the introduction of the Blue Coil that better coil and ignition systems have evolved.

My expectations from my equipment is victory, and the Blue Coil has never failed me.

We have left many MSD systems taking the flag behind us. And yes, it is with all new gear, highly maintained.

I'm sure on the street it would be different. Scott's systems would get you home.

FJC

[Scott Novak]

Really interesting! Is there any threat of a better coil masking potentially damaging problems, e.g., carb flooding or worn out plugs?

Assuming that the fuel pressure is correctly set, the typical problem that someone will have with a worn float valve is flooding after the engine has stopped. The fuel system heatsoaks, and gasoline expands in the fuel lines and is forced past the float valve and floods the engine. It results in difficult starting when the engine is still warm. The engine must be cranked a long time before it starts. The longer the engine is cranked, the more fuel will wash past the rings. Some of the flooding may also be partially due to the gasoline expanding in the float chamber in the carb.

Many people have this problem and don't realize that the float valve is getting weak. They just figure that's the way it is because some cars are hard starting when they are hot. Once the engine is running the problem does not exist as the normal fuel pressure won't override the float valve.

A variable permeability ignition coil will fire the fuel fouled spark plugs spark plugs and start the engine quickly and less fuel will be washed past the rings.

Carb flooding will still produce black smoke out of the tailpipe at startup to warn you of a problem. Many people just ignore such warning signs.

If the engine sits long enough, the fuel evaporates enough that the engine will start and the driver may not even realize that there is a flooding problem. Even with a carb in good working order, it takes longer to start an engine with a weak ignition coil. With a variable permeability ignition coil, starting is nearly instantaneous and less fuel washes past the rings.

A variable permeability ignition coil is also better at igniting lean fuel mixtures often experienced while the engine is warming up and during quick throttle changes, and it reduces or eliminates the misfires that cause hesitation and as a result, your oil remains cleaner longer. Reducing the gasoline washing past your rings is very likely to increase the life of the rings.

A stronger ignition coil will in fact keep firing worn spark plugs that a Bosch coil cannot. If you leave spark plugs in the engine long enough, they will eventually deteriorate and the chance of mechanical damage increases. But they are also leaving spark plugs in new cars for as much as 100,000 miles. Personally I wouldn't leave spark plugs in an engine that long.

However, anyone that leave spark plugs in an engine long enough for them to physically deteriorate is also not likely to be changing the oil either.

Using a weak ignition system in a car so that it will warn you of engine problems will cause more problems that it prevents.

Scott Novak

[Scott Novak]

Above: The Blue Coil on the 917. No place for a wimp.

Unless the ignition coil is being controlled by an adaptive spark ignition system, it won't see any more average current than an ignition coil used on a street vehicle. With an simple inductive switching ignition system, your race conditions don't put any more strain on the ignition coil that street conditions do. The only racing factors that would have an effect on reliability are vibration and ambient heat.

A Bosch Blue ignition coil with an internal primary resistance of 3.0 ohms will dissipate around 70 watts of heat.

A Jacobs ignition coil with an internal primary resistance of 0.40 ohms and an external ballast resistance of 2.6 ohms will only dissipate around 9.3 watts of heat running much cooler and more reliability.

Jacobs ignition coils are first potted in epoxy. Then the entire ignition coil is potted in thermally conductive silicone compound inside an extruded aluminum case, with epoxy poured on the ends for physical protection. They have been tested at vibrational G forces of over 82 Gs and survived. I wouldn't want to bet that a Bosch ignition coil could handle even a fraction of that vibration.

My expectations from my equipment is victory, and the Blue Coil has never failed me.

Pure dumb luck and ignition coils that aren't very old. I have had several Bosch Blue coils with internal ballast resistors fail on me. I haven't had a failure of a single Jacobs ignition coil.

We have left many MSD systems taking the flag behind us. And yes, it is with all new gear, highly maintained.

MSD doesn't pot their equipment in thermally conductive silicone potting compound to absorb vibrations and equalize circuit board temperatures, like Jacobs ignition systems use. I'm also not too impressed by the MSD ignition circuits I have seen.

Scott Novak

[bugninva]

[
Assuming that the fuel pressure is correctly set, the typical problem that someone will have with a worn float valve is flooding after the engine has stopped. The fuel system heatsoaks, and gasoline expands in the fuel lines and is forced past the float valve and floods the engine. It results in difficult starting when the engine is still warm. The engine must be cranked a long time before it starts. The longer the engine is cranked, the more fuel will wash past the rings. Some of the flooding may also be partially due to the gasoline expanding in the float chamber in the carb.

Many people have this problem and don't realize that the float valve is getting weak. They just figure that's the way it is because some cars are hard starting when they are hot. Once the engine is running the problem does not exist as the normal fuel pressure won't override the float valve.

to a point, the heatsoak and fuel boiling is "just the way it is" and is normal.... with most carbureted engines, and especially the way the vw's carb and intake is setup... that is why nearly all manufacturers always recommend depressing the throttle to the floor when starting a warm engine, this clears out the excessive fuel(EFI took care of this). VW recommended this method up until they went to fuel injection.

[Bruce2]

Which Bosch Blue coil did you test?

The numbers on the bottom are as follows:

PN 0 221 119 027

522

K12V

The Bosch Blue ignition coil has 2.93 ohms of ballast resistance. It has a 10.5 KOhm secondary resistance. It came off one of many used Beetles that I have had.

Thanks. More importantly, where was that blue coil made?

[Scott Novak]

More importantly, where was that blue coil made?

PN 0 221 119 027

522

K12V

The Bosch Blue ignition coil has a 2.93 ohm primary resistance.

It has a 10.5 KOhm secondary resistance.

It has a measured turns ratio of 1:69.76

It was made in Germany. Probably in the 1970's or early 1980's

It looks like this new:


Scott Novak

[perrib]

This post is not to knock Scott or Jacobs ignition, only to show what I have observed. I never used the Jacobs on a Beetle. A friend who had them on 4 of his V8s swore by them. I drove his 13 second 70 Cadillac before and after there was quite a performance gain with the Jacobs. The only draw back I saw was reliability, all four control units failed and Jacobs warranty was so short it seemed non existant. He liked them so much he did not mind changing them every six months. This was in the early 90s. I was very impressed but did not want the expense of two spare Jacob units in the car. The MSD system I bought lasted several years with no failure and also made a huge difference in how my VW engine ran. I still did not trust it for offroading and stuck with points. I saw earlier posts by you stating even more reliability issues in new models. Like FTC all my Bosch coils (black, blue, red, new, used) have never failed. Though I have seen plently of failed Bosch coils the two used ones (Black, Blue) bolted to my rail have been pound hard for 19 years and never failed. I agree even with Porsche points they don't perform like a MSD or Jacobs. I do know how to make a Bosch coil fire fouled plugs from my days of trying to run duals and a single DCNF off road. It is odd how two totally experiences can be had from the same product. Perhaps the 12 Jacobs units I saw go bad were just a bad batch.
It does happen.

[farmer]

Like Bruce menthioned, its important WHERE the new coils are manufactured. About 5 years ago, (if memory serves) i began to experience this problem with bad "blue Bosch" coils on engines that ran poorly, had severe warm start problems, sporadic misfires at idle and elevated emissions.

I then began to test a bunch of new and very little used "Blue Bosch" coils (11 total) I have forgotten where they were all made, but some of them came from Malaysia and was absolutely horrible. Now, my/our way of testing was a little different. My local auto electronics guy tested the spark and his machine converted it to KV output.

Now Bosch claims that their "Blue " yanks out 20 KV. NONE of the tested ones gave more than 17 KV when cold. We then held a load on them for 15 minutes and checked again. 6 of them dropped to between 11 and 13 KV. the last 3 dropped to 9 KV. Thats barely enough to make a spark in a healthy stock engine !

We then tested 2 Pertronix 3 ohm coils. They claim up to 40 KV max. output. We did not see those numbers though. But we saw up to 35 KV cold and they worst dropped to 28 KV warm. And at that point we had loaded it so hard that we could touch by hand, so it was HOT, and not just in the advertiing language.

Almost immediately from that day I have not used much else than These 3 ohm Pertronix coils on normal to hot street engines. And I have had 1 failiure.
A side noote could be that we have tried tosee how the weaker blue coil performed on the dyno compared to the Pertronix. That was quite interesting. First engine was a 70 hp std plus (Stock 34 mm Pict3) Power was within 1 hp., but unburned went up by a whopping 30% to 450 ppm. and CO went up by 0,4. And the "typical" sporadic misfire at idle was there immediately- A clear indication on that it simply did´nt fire all the fuel in there.
2nd time was a 145 hp 2110 street engine. This time power dropped by 2,5 hp. torque dropped 6 NM and ppm rose 30% again, and the misfire came back.
That´s enough proof for me to stay away from them.
T

[Scott Novak]

I never used the Jacobs on a Beetle. A friend who had them on 4 of his V8s swore by them. I drove his 13 second 70 Cadillac before and after there was quite a performance gain with the Jacobs. The only draw back I saw was reliability, all four control units failed and Jacobs warranty was so short it seemed non existant. He liked them so much he did not mind changing them every six months.

This kind of failure rate is unacceptable. But four ignition units failing on the same vehicle makes me very suspicious that there was something wrong with the installation, such as installing them in a hot location.

Perhaps the 12 Jacobs units I saw go bad were just a bad batch. It does happen.

Unless every unit came out of the same batch it's not likely. Unless no product testing is performed, it is rare to have bad batches. Usually a bad batch will be discovered during product testing before the product leaves the factory. Some some companies only perform sample testing and they are more likely to ship out defective batches.

I have considerable distrust for the newer Oval shaped Jacobs ignition systems that were developed after Rostra controls bought Jacobs. The inside information that I have is that they cheapened the circuits and are they are closer to what MSD is selling. While I have personally had good luck with the Oval shaped Jacobs ignition systems, I particularly don't trust the Jacobs FC1000 and FC 2000 ignition systems. These are practically MSD clones and I have heard of a number of failures from people.

I do know how to make a Bosch coil fire fouled plugs from my days of trying to run duals and a single DCNF off road.

I'd like to hear how you managed this as my bench testing and actual road testing has indicated that a Bosch ignition coil is very susceptible to fuel fouling.

--------------------------------------------------------------------

Now Bosch claims that their "Blue " yanks out 20 KV. NONE of the tested ones gave more than 17 KV when cold. We then held a load on them for 15 minutes and checked again. 6 of them dropped to between 11 and 13 KV. the last 3 dropped to 9 KV. Thats barely enough to make a spark in a healthy stock engine !

We then tested 2 Pertronix 3 ohm coils. They claim up to 40 KV max. output. We did not see those numbers though. But we saw up to 35 KV cold and they worst dropped to 28 KV warm. And at that point we had loaded it so hard that we could touch by hand, so it was HOT, and not just in the advertiing language.

The output voltage dropping when warm is partly caused by the internal ballast resistance. The inside of the ignition coil is NOT the correct place to have ballast resistance!!!!!

What load impedance did you use on the output of the ignition coils when you tested them?

A side note could be that we have tried to see how the weaker blue coil performed on the dyno compared to the Pertronix. That was quite interesting. First engine was a 70 hp std plus (Stock 34 mm Pict3) Power was within 1 hp., but unburned went up by a whopping 30% to 450 ppm. and CO went up by 0,4. And the "typical" sporadic misfire at idle was there immediately- A clear indication on that it simply did´nt fire all the fuel in there.
2nd time was a 145 hp 2110 street engine. This time power dropped by 2,5 hp. torque dropped 6 NM and ppm rose 30% again, and the misfire came back. That´s enough proof for me to stay away from them.

Do you mean that the Bosch ignition coil performed worse than the Pertronix?

Scott Novak

[farmer]

Scott I´m no electric gearhead. I am not sure how much they were loaded. I do remember that we pulled "sparks" in the artificial plug in the machine, that was over 15 mm long.

Yes, I explained myself bad. It was the "Blue coil" that performed less good. and it was the same coil in both tests.
T