OT: Head scratcher

"Jan Andersson" wrote

Was the engine ever used in an aircraft?

Nope.

Jan

You say it has 2 coils and that if you disable one or two of them it will run... Sounds odd that with both coils disabled it will run.

2 distributors? Does this mean that there are 2 6-wire distributors and both handle all 6 cylinders? Another one not set correctly? Not enough electrical power to run 2 coils at a time (bad battery, bad alternator, bad connections). One will work so that one plug fires but when you put two, the current is not enough to produce spark to both at the same time?

A lot of guesswork ;)

I ran dual magnetos and dual-plugged heads on a Shovelhead Harley once.

Why interlink the distributors? Detach the interlink.

Anywho, many years ago I asked Jake Raby about dual-plugging some aftermarket heads and he scoffed at the idea.

Today he offers exactly that. Check out his setup.

The 2 coils draw twice as much current when the circuit is closed (points? closed). So if a ground is defective, or the +12v feed wire or a ballast resistor or a capacitor is defective, then you won't have full voltage on the one terminal of the coils or 0 voltage on the other terminal and thus reduced spark voltage. Removing the one coil, reduces the demands in current, so the voltage difference between coil's primary terminals increases and produces a stronger spark, enough to run the engine.

Regards, Bill Spiliotopoulos.

? "Jan Andersson" ?????? ??? ?????? news: snipped-for-privacy@mid.individual.net...

I'm with Bill. What engine? Did 911's ever use dual dizzy's?

J.

Just a guess but is it posible the timming is off on one side. Does it matter which coil you unhook for it to run better?

Have you checked spark on both sides?

other then that what about the carbs, is one running much richer then the other.

Just tring to kick start your brain.

Is the firing order the same on both distributors? If not, the cylinders are fighting each other when two fire at the same time.

One OF two disconnected, it will run. And only a certain one.

There is one distributor body that has two distributor units on it.. master is driven by a shaft like in a VW, and the slave is next to it, driven by a toothed belt. Only the master has a Hall effect sensor. Both have mechanical advance. Each has 6 spark plug leads. One feeds 6 plugs on the top of the combustion chamber, and the other feeds 6 plugs at the bottom of the combustion chamber. Mechanically they are synchronized to each other, both rotors point at #1 cylinder at the same time.

Battery is fully charged.

I'm wondering if the disabled coil is shorting internally and causing the whole system to go crazy.

Ahha! I will go and check the ground wires for both coils. I didn't do that yet. (duh).

No ballast, no capacitor. No points either.

Jan

Bill Spiliot> The 2 coils draw twice as much current when the circuit is closed (points?

You got it :D

This is a 91 911 Carrera 4. I have a perfectly running Carrera 2 to take parts from, for a few more days.

I have swapped distributors, coil control units, and ECU. New head temp sensor, and crank position reference sensor.

Will check coil wiring better, and try swapping out the coil.

Jan

Yes it matters. One coil runs the lower side plugs, the other coil runs top side plugs in the same cylinders. Both are timed the same mechanically at the distributor (firing order), but I assume a computer could control the secondary plugs to fire slightly at a different time, to get a cleaner and more complete burn. So it's not a left/right side distributors. If I disable the coil that runs the lower 6 plugs, the engine runs fine. If I just pull of the plug wires to the lower 6, it makes no difference. It seems like the coil wiring is what is causing the problem.

I will need to re-check where I get sparks when it runs poorly. Got 12 leads to check... :)

Fuel injection. Good fuel pressure.

Jan

Hey Jan I just had to change out a distributor with a compu-fire (I think the electrical tape made it hard to tell) because it was shorted, but if you changed the distributors and coils I would look at the wires powering the coils for a short.

I thought about that too, but teh firing order is identical and correct. It is not backfiring or popping through the exhaust, it just feels like it's firing 3, missing 3, firing 3, missing 3... and won't tolerate any throttle at all.

I have isolated the problem to be something related to the coil or it's wiring, or whatever non-visible components are within that part of the wiring harness. It runs so good with the lower plugs (coil driving them) disabled, that I conclude all the other basics to be ok.

Jan

Erik Dillenkofer wrote:

That's next on my list.

Jan

hmmm 6 aircooled cylinders, 12 spark plugs, two interlinked distributors, two coils huh?

OK just tease us will you. ;-) Is this like a 1989 Porsche 3.6l engine or something?

"faulty resistors commonly found in the stock plug connectors. Electromagnetic interference (or EMI) caused by poor quality wire sets can cause engine computers to receive incorrect information, leading to drivability problems." Did you check the knock sensors?

Maybe it is firing prematurely and burning off the fuel way BTDC compression stroke? Probably a safety device built in so you don't destroy an engine with over 11:1 compression. ;-)

Just guessing here!

91 actually :)

"faulty resistors commonly found in the stock plug connectors. > Electromagnetic interference (or EMI) caused by poor quality wire sets can > cause engine computers to receive incorrect information, leading to > drivability problems." Yes I have read that elsewhere.

Damn near impossible to get to.... but I doubt that they could be the cause, since the engine runs perfectly with just one coil. And the knock retard is only max 6 degrees, the engine would still run and respond to throttle.

I don't think it's possible, problem persists even with plug wires disconnected for the lower 6.

Keep them coming, it's better than nothing!

Jan

Have you tried jumping the power from the uper coil to the lower one. Sorry its been many years since selling my 911 and I don't remember what the enging wiring was like.

I can call the owner of Porsche repair shop tomorrow and see what he thinks.

HASSAD dual distributor