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in the pic with the rotor and cap, the cap does not look good. the post for #5? does not look good.
do not use a condensor with the MSD, or bosch. thats were i mounted mine in my 2.7. |
What shape and how old are the spark wires? Even if they look good they could be breaking down from age. I just had a set of wires that looked perfect in my Mustang 5.0L but upon close inspection at night the wires looked like an electrical octopus laying over the engine! In the dark you could see them arcing and carrying spark over the surface of the rubber! Since you improved spark energy it could be that the wires simply can't contain the extra energy now.
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Your saying that seeing the cables light up is not a problem, got it. |
sal, i agree. i said in an earlier post craig bought a new set and his car ran worse. put the old ones back on and it ran better. new ones can be bad too.
west, do you make this crap up as you go along sounds like OP might have fixed it with the cap. if that does no fix it he needs to look into fuel/mixture and air leaks. |
Here's my personal opinion about ignition:
You really only ever need just enough ignition energy to jump the spark gap. Often folks install way to strong ignition system for the needs of the engine. Not a good idea to over provision the ignition system as it causes a bunch of other issues. If you are not doing a turbo setup then a simple basic ignition is all you need. Even the factory changed from CDI after the 3.0L. The 84-89 3.2L uses very basic 12vdc old school coil and it's good for 7000RPMs. Not downing the after market CDI systems, I'm just pointing out that if the stock system can fire the plug and light the mixture you can't really improve things much. Furthermore, these systems that produce 2 sparks back to back are not that beneficial and only mask the real issue, 1 spark needs to do it every time! |
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"coil out put to chassis" I have seen this, but only with the HV wire to the distributor removed. If that happens otherwise there is a open, high resistance between the coil and the spark plug, or a gap to wide to jump. Or even to much pressure in the cylinder...FI. |
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Inductive energy storage, the Kettering system, was always been a better system for plug firing if one could remove the limitations of mechanical power switching. With the Kettering system spark energy is stored in the coil PRIOR prior to firing. Whereas with CDI it takes time, however brief, to transfer energy from the storage capacitor to the coil primary. With CDI the coil inductance resists the transfer of energy into the coil primary. Once the solid state switching devices came along the "dwell" period could be raised as RPM rose, 99% even. |
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Dual plugs are used to help light the flame front from both side of a Hemi cylinder at the very SAME time. When using dual plugs vs single plug in a Hemi cyl it allows you to not need so much ign advance to generate peak torque conditions (max cyl pressure). The down side of the hemi single plug is that the plug is offset far to one side of the cyl and this results in needing a lot more ign advance than with dual plug. The more ign advance results in fighting the piston on the up stroke before TDC. It's the trade off needed to achieve max torque. This is why the very same exact engine build with dual plug vs single plug, the dual plug will generate more torque on the dyno. |
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I have a 1973 2.7 with MFI. I drove it over 100,000 miles with points and stock CDI. I fine tuned the MFI very successfully in this time, but installing a good CDI system has made a HUGE DIFFERENCE in the way the engine runs, idles, revs and just plain has been a revelation. Multi spark works. A hotter spark works. You have to go into this with your eyes wide open. A more powerful CDI is not a plug and play deal. You need good ground, good +12 vdc power, good plug wires and a rotor and cap and wires that are up to the extra power. I have bench tested the Bosch, MSD, and a Daytona-Sensors CD-1. The aftermarket units put out 3 to 4 times the power that the Bosch does. If multi spark is so bad why do companies like BMW MB Porsche and others use it for starting and idling? Research it. One weak spark is not good enough for most old P cars. My opinion with lots of research and practical experience. Here is a link to my original post of my CDI experience http://forums.pelicanparts.com/porsche-911-technical-forum/796003-bosch-3-pin-cdi-replacement-4.html |
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Also for fuel ratios that tend to run on the rich side most of the time the high energy system tend to keep the plug a bit cleaner. Just don't expect miracles to happen by installing a better ignition if the old one works. It's the same with multi electrode plugs (BOSCH 4 or 2) they really don't help if the standard style plug can do the job. For engines with very high cyl pressures like Forced induction Turbo or high compression then I agree you need extra ignition to jump the spark gap (or close the gap down) as cyl pressures increase. But for most normally aspirated engines you don't need these high energy system. BTW - love your car. Is that a high compression 2.7L? |
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The question becomes....how fast is the "swirl" the A/F mixture is in just prior to the spark, and then how fast is the flame front from that spark advancing vs the "swirl" speed. It should be pretty clear that if the second spark ignites an unignited portion of the mixture due to the "swirl" then a more rapid combustion of the overall cylinder "fill" will result. |
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Upon firing the plug, how much, what %, of the previously stored energy is simply returned to the storage capacity? |
Hopefully ignition system energy of the spark and voltage of the spark are not being confused.
The ignition system spark voltage determines maximum total gaps (plug & cap/rotor) and cylinder pressures under which a spark can be produced. An ignition system producing a minimum of 250/300 primary volts is more than adequate. The ignition system energy is the energy available in the spark to fully ignite the fuel charge which is typically 30 milli-joules. Most OEM ignition systems produce 2-3 times this value. |
Please try this
1 check spark plug lead order 2 check sparkplug lead order again 3 Then check that your order is correct to the rotation of the rotor 4 if not reverse the order, A posche will still run if you have it reversed 3 check plug leads in dizzy are ALL the way in 4 check that the coil lead all way in It could be as simple as that Ive done that, then rechecked and rechecked again only to realise the numbers in my head were wrong. |
did you change the coil from the Bosch CDI one to the Bosch Blue coil? or the MSD Blaster coil?
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Tonight's ride
The ride home from work was up eventful. I had an even idle at stop lights and a smooth and quick run through the gears on the freeway. I run opposite the commute so getting above 70 mph was not a problem. The temp stayed normal which was not the case a couple of nights ago and the night before the backfire nightmare.
The new coil is an MSD blaster, recommended in Wayne's article #24. I copied the plug configuration from the cap I replaced. Since the car is a 77 but with just under 34,000 miles I don't think much has changed from the original. For now I am going to sit tight on the ignition, but this conversation has me thinking about new plug wires and possibly going pointless. I am learning a ton and thanks to all for the replies. |
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(sal, he knows, i think he is just stirring the pot....) |
the points work great. but if you feel the need, get it running right before you make any mods.
so you think it was the cap? |
@Orange911s
It was already mentioned several times by others in this thread and I thought it's worth pointing out again. If I had this car to work on the first thing I'd do is check fuel mixtures with my WideBand O2. You really need to be sure it's not running lean. No sense concentrating on ignition issues without verifying fuel first. If it's lean it can easily exhibit mis-fire behaviors. Do you know if fuel mixture is correct? |
could be a plugged cat too. the ceramic can beat itself into a ball and depending on how it rolls up to the outlet, it can either plug it or pass gas through it's honeycomb.
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- Inductive builds up energy over time in the actual coil windings and then releases this energy stored when the field collapses because voltage is removed from the primary winding. This results in a long release of energy but the voltage typically is not as high as CDI. The good thing about Inductive is that the spark lasts considerably longer than CDI but not as strong (less voltage). This style ignition does very well in cylinders that don't have extreme pressures. - CDI uses the coil as step transformer and NOT a holding device, coils can be used either way (CDI voltage stepping or Inductive energy holding) but they are different. In CDI the control module typically has large storage capacitors that charge to 200-500volts and then when commanded the capacitors release this voltage across the coil's primary winding. If the coil has a 100:1 wire ratio then the 500vdc gets stepped up to 500X100=50,000vdc at the output. This results in a very strong spark event compared to Inductive but it does not last as long. The spark is brighter hotter but not as prolonged in length. CDI works very well in Forced induction where cyl pressures are much higher and it difficult to jump the gap without sufficient voltage. Here the chances for not jumping the gap are more likely and is why CDI often fires multiple spark events back to back. In summary: Inductive ignition has 20,000-35,000 volts with spark durations in the 1000-2000micro seconds. CDI has 50,000+ volts with spark durations in the 400-600micro seconds. This site has a great detailed writeup about the 2 system and worth reading. Inductive Ignition | GILL |
"When using dual plugs vs single plug in a Hemi cyl it allows you to not need so much ign advance to generate peak torque conditions (max cyl pressure)."
It's just all about avoiding detonation while achieving maximum torque! What the resulting timing turns out to be is of little value as long as the engine avoids detonation and achieves maximum torque. As an example, the Porsche 996 with its center spark plug runs advance timing greater than the air-cooled 911s. And the direct-injected 997 runs even greater timing advances than the 996. Furthermore, both the 996 and the 997 have higher CRs than the air-cooled 911s. |
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The CDI system was used by Porsche for the fast spark rise time for fouled plugs which wasn't available in the '60s with inductive discharge systems. Now fast spark rise times can be achieved with today's advanced semiconductors resulting in all OEMs using inductive discharge systems. |
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In the perfect world we would never want to start fuel burn before TDC but because fuel takes time to burn you have no choice but to fire the plug before TDC if you want to achieve max pressures at about 10-15 degrees past TDC. But the evil here is that firing the plug 30degrees before TDC actually fights the piston on the up stroke of the compression cycle and results in loss of torque. With a twin plug it helps light the flame fronts from 2 points in the cyl and the 2 flame fronts can more quickly (in less amount of time) burn all the fuel and this allows you to reduce ign adv. So if in the same engine you now only need 20 degrees adv this results in less fighting with the piston on the up stroke. One can not ignore detonation and some cyl designs are more prone than others. Bottom line is you CAN NOT allow detonation to take place and many times you MUST sacrifice power to avoid detonation. The points you make about the newer cars using more advance simply mean those engines are better designed to not detonate but more ign advance is not better. The holy grail would be to have ign at 0deg TDC and still achieve max torque but that's not possible because fuel takes time to burn. Further complicating this is that fuel tends to burn at a steady rate (amount of time) but as RPMs increase you run out of time and you require more and more ign advance as RPMs go up and this in turn fights with piston on up stroke and torque tends to drop off. |
Battery is being overcharged and MSD is more sensitive to voltages above 15 volts than Bosch?
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Porsche made the switch shortly after those became available. Still not certain that the relatively TINY COP can store anywhere near the energy to sustain a spark for long enough period vs those earlier coil modules wherein the "opposite plug" was also fired. |
I think it was the cap. I have not gotten to the timing yet.
I don't think it is a fuel issue. This all started with a day a couple of weeks ago where I got crank, but no start trying to get home from work. The car was running great before that. I am not as experienced as many of you guys, but I am comfortable swapping parts. I checked with the forum after that incident and the overwhelming push was to look at the CD box and coil. From there, Wayne's MSD upgrade article made sense. I started with the coil swap to the MSD and that did not solve the problem. I then swapped the OEM perma-tune box for the MSD and it was running fine, with a few misses. This escalated into the backfire situation that started this thread a few days ago. I will put some miles on over the next few days and see how it goes, but so far so good. |
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I read the GILL report. They make inductive igntions. They make NO CDI ignitions. So what do you think they are going to say?
Some of what they said is misleading at best and possibly wrong. For example, a direct quote: "Typically a capacitive discharge system will deliver a maximum of 10 millijoules of energy compared to an inductive ignition system delivering more like 50 millijoules of energy and potentially in excess of 100 millijoules. This large difference in supplied energies will mean an inductive system can provide spark duration of 2000 microseconds or more in a single spark, compared to 600 microseconds for a capacitive system." The Daytona-Sensors CD-1 that I have in my 2.7l MFI 1973 puts out 135 mJ [millijoules] of spark energy, NOT 10! Most MSD models put out in the 75 to 85 mJ range. So once I read that and realized that GILL makes and sells ONLY inductive ignition systems, I can't put any credibility to what they wrote in this report. I know inductive systems to a great job but stick to the facts GILL! I do know that a properly installed high quality CDI system in the form of the Daytona-Sensors CD-1 has made a great difference in my 911. It comes with a matching coil so that your are sure the system will perform to its maximum. I have to comment that some posters on this thread rebuild Bosch CDIs as a business and they have been critical in the past of anything but the original Bosch CDI being used in cars that are so equipped. Reading through posts here there is a lot of history of problems with aftermarket CDI whether caused by faulty installation, other components not being upgraded or just plain failure of components. I am convinced that if you choose a good aftermarket CDI, install it properly, and make sure your cap, rotor, and wires are up to the task, you are going to get increased performance out of your early carb of MFI 911. |
Dick,
No question about it, CDI system works as does a good electronic inductive system. Either would be a good choice to replace the older points. BTW - I ran a pro MSD setup in my 84 3.2L and it worked just fine but it did not make any difference compared to the stock ignition so I took it out and went back to the simple stock setup. Used MSD 6200 controller with MSD 8250 coil this is the pro version from MSD same used in NASCAR. Nice unit did the job well but had no effect on performance or running over the stock setup. Quote:
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Distributorless COP INDUCTIVE ignitions... |
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I think what we conclude here is that the older points CDI could be improved. And we have 2 choices: electronic triggered CDI or inductive and either would be an improvement.
But the CDI is somewhat more complex and prone to failure over time, it simply has more components like the big capacitors that don't stay in spec over time. While the inductive systems have darlington transistors that are extremely reliable. Here's what Motec has to say: MoTeC > About Ignition Systems > Overview They don't sell any ignition products but do sell top self ECUs. |
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