I changed the coil positive terminal to ground, and connected the coil negative terminal to the ignition module.

Gas mileage went up 5 mpg to 17mpg, the exhaust tone became resonant, clear and crisp, and no more gas smell was coming from the tailpipes.
The Haynes maual said if the negative terminal of the coil is connected to ground, expect a 60% LOSS of spark plug energy. (1970 280S and 1971 250)

I know this is counter-intuitive, but the results were amazing. Anyone else been there, done that?

Hi

When I installed my Crane 3000 system and installed a new Bosch electronic ignition coil I kept the ballast for the coil. One day I bypassed that and got what you described. I never tried reversing the connections before but it would be interesting to try. Why did you do this to begin with? And anyone know what is happening here?

Oreo

MunchenTaxi -

I am baffled. Do you have the blue Bosch coil? And does it test OK?

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Yes, I have the Bosch blue coil (a new one)
I was getting 12 to 12.5 mpg, the exhaust had a muffled sound, constant gas smell at tailpipe. So I tune the Zeniths 8 times and no change. I reset timing, no change.

So, after mucho frustration, I go to Page 96, Section 10, Haynes manual for 1968-1972 230, 250 and 280 and RE-READ THE INSTRUCTIONS.
The Haynes maual said if the negative terminal of the coil is connected to ground, expect a 60% LOSS of spark plug energy.

It works like a charm.

I'm going to give it a try myself and will report back on my results.

Oreo

On a similar tangent, realized my my Pertronix coil and Ignitor were still running through the stock ballast resistor. Did a little online research and found that this resistor should be bypassed.

With my coil power up 25%, idle stumble has been eliminated, and car is pulling stronger. I can't believe I didn't do this sooner.

As with Oreo, will try your polarity switch and report back.

Hi MunichTaxi

Can you tell us again what kind of ignition system are you using? Points or Bosch electronic? I re-read my Crane manual and it says that "Improper coil connection may damage ignition module"......brrrrr I'm getting cold feet!

To verify Bosch coil -ve = terminal 1, +ve = terminal 15
By ground do you mean the wire going to the distributor?

Thanks
Oreo

Hi All

I was very intrigued with this hypothesis and I went thru all my technical manuals for all kinds of car makes. All indicated that coil negative is ground (distributor). In the venerable Stockel automotive book it said that negative is ground. This makes the spark plug electrode in the seconday circuit negative too. Theory is that the center electrode is hotter than the side electrode and so electrons flows better from a hot surface to a cooler surface. It said if the polarity is reversed up to 30 per cent more power is needed to create the spark. However, polarity is still very much opposite to MunichTaxi's Haynes manual. I'm confused - unless MunichTaxi's coil is different somehow???

Oreo

On any normal car of recent vintage, the coil grounds through the points (or electronic substitute) and the plus terminal is connected to the ignition switch. It's been well known for decades that if you reverse these two, the system gets all messed up. Let's not worry about old Fords or MGs for the present.

What I did was connect the positve terminal of the coil to the chassis (ground).
Then I connected the negative terminal of the coil to the ballast resistor.

The voltage reading at the negative terminal of the coil is 2.9 volts ( which is in specification, of 2.8 to 3.2 volts.)

Go to Page 96, Section 10, Haynes manual for 1968-1972 230, 250 and 280 and RE-READ THE INSTRUCTIONS.
The Haynes maual said if the negative terminal of the coil is connected to ground, expect a 60% LOSS of spark plug energy.

The magazine Skinned Knuckles has a thorough discussion of coil polarity in tits august 2004 issue.

__________________
Douglas
1959 M-B 220S cabriolet

http://images.google.com/imgres?imgurl=http://www.mbzponton.org/valueadded/maintenance/ignition/coil_resistor1.jpg&imgrefurl=http://www.mbzponton.org/valueadded/maintenance/ignition/coil.htm&h=270&w=360&sz=24&tbnid=JLC8lNR-L2gJ:&tbnh=87&tbnw=116&start=2&prev=/images%3Fq%3Dignition%2Bcoil%26hl%3Den%26lr%3D%26ie%3DUTF-8

if you want to upgrade do it the right way

I am already aware of the Sokoloff article on the ponton page. The skinned Knuckles article was more about the specifics of coil polarity.

__________________
Douglas
1959 M-B 220S cabriolet

Ahhh, my favorite month.