Vibration, Motor Mount, Plug Wire, problems...
01-17-2008, 04:17 PM
#16
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For your ignition situation test this way. On a very dark night, allow your vision to adapt to darkness for 15 minutes. Then, with no lights on from the car, turn on the engine and in the dark look at the ignition wire loom carefully. If you see small blue or white 'halo' effect around the ignition wires where they route to the plug holes, they are breaking down and need to be replaced. You will want to take off the intake tubes first to get a good look. Get close to the wire and look carefully for a kind of glow around the wires. Sometimes it is easy to see, sometimes it is not.
Roger can supply you with an economy set of wires that are very easy to replace. Simpy unscrew the plug extender from the wire, clean the extender and seal and screw on the new wire. Route one at a time and it's very easy.
Roger can supply you with an economy set of wires that are very easy to replace. Simpy unscrew the plug extender from the wire, clean the extender and seal and screw on the new wire. Route one at a time and it's very easy.
docmirror, I've just make this test, and there is no small blue or white 'halo' effect around the ignition wires or anyware else in the engine bay, do you thing that I can leave this for a few months and save $500 or so for now?
Thank you
Lefteris
01-17-2008, 04:18 PM
#17
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Here's a thought on the practice of "pulling" a plug wire to test for spark.
The coil works as a transformer, an inductive electrical device that depends on a magnetic field inside to store electrical energy. The feild is forced to collapse when energy is discontinued to the "primary" or low voltage side. That energy is 'transformed' to higher voltage into the secondary winding of the ignition coil. The voltage increases in the coil secondary until it reaches a level sufficient to jump the gap in the spark plug. If the plug wire is disconnected, that voltage can continue to rise until either a new path is found at a higher voltage, or the magnetic field from the primary side is completely dissipated. When one plug wair was removed, the voltage continued to rise until the energy "leaked" through the other plug wires and the insulating supports to ground.
Possible problems are that the next path-of-least-resistance may be through the pliers you used, through your body, to the car chassis. Since we often hold the pliers in one of our hands, that high voltage path to ground could easily be through the heart, and cause the heart to get confused to the point where it stops pumping adequate blood. At the same time the ignition pulses through the arm and hand can easily prevent one from letting go of the pliers.
Assuming that the electrical pasth isn't through your heart and/or brain, there's the next path to ground through internal insulation in the ignition coil. The internal arcing will quickly melt the enamel insulation used on the wires that make of that little transformer inside the coil. If that new area with no insulation happens to be lower resistance now than a spark plug with the plug wires and all, your spark energy will forever more choose to go that "shorter" route rather than through the plug. No more spark, therefore no more car run. The only solution at that point is to replace the damaged coil.
Bottom line-- Don't even THINK of pulling a plug lead from a 928 engine that's running or even cranking, without providing a suitable low-resistance path to ground for thr spark energy. Want to test to see if a plug is firing? Try attaching an inductive timing light, which depends on current flow through the plug wire to get a trigger signal. If you must use the primitive method, stick a plug into the end of the wire, and make sure the plug body is securely grounded to the chassis or frame. Crank the motor and observe the spark in the end of the plug.
The coil works as a transformer, an inductive electrical device that depends on a magnetic field inside to store electrical energy. The feild is forced to collapse when energy is discontinued to the "primary" or low voltage side. That energy is 'transformed' to higher voltage into the secondary winding of the ignition coil. The voltage increases in the coil secondary until it reaches a level sufficient to jump the gap in the spark plug. If the plug wire is disconnected, that voltage can continue to rise until either a new path is found at a higher voltage, or the magnetic field from the primary side is completely dissipated. When one plug wair was removed, the voltage continued to rise until the energy "leaked" through the other plug wires and the insulating supports to ground.
Possible problems are that the next path-of-least-resistance may be through the pliers you used, through your body, to the car chassis. Since we often hold the pliers in one of our hands, that high voltage path to ground could easily be through the heart, and cause the heart to get confused to the point where it stops pumping adequate blood. At the same time the ignition pulses through the arm and hand can easily prevent one from letting go of the pliers.
Assuming that the electrical pasth isn't through your heart and/or brain, there's the next path to ground through internal insulation in the ignition coil. The internal arcing will quickly melt the enamel insulation used on the wires that make of that little transformer inside the coil. If that new area with no insulation happens to be lower resistance now than a spark plug with the plug wires and all, your spark energy will forever more choose to go that "shorter" route rather than through the plug. No more spark, therefore no more car run. The only solution at that point is to replace the damaged coil.
Bottom line-- Don't even THINK of pulling a plug lead from a 928 engine that's running or even cranking, without providing a suitable low-resistance path to ground for thr spark energy. Want to test to see if a plug is firing? Try attaching an inductive timing light, which depends on current flow through the plug wire to get a trigger signal. If you must use the primitive method, stick a plug into the end of the wire, and make sure the plug body is securely grounded to the chassis or frame. Crank the motor and observe the spark in the end of the plug.
Thanks for this
Lefteris
01-17-2008, 05:55 PM
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Yes, I would say that your ignition wires are okay for now. Your vibration is almost certainly from motor mounts. My opinion is that this job is not technically challenging, but it is very dirty, messy and you will work with several heavy components on your back. Take your time, and there are several other things to check and maintain during the motor mount job. Do a bit of searching for 'motor mount' and you will get a good idea, or Roger will guide you as well.
01-17-2008, 09:39 PM
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Yes, I would say that your ignition wires are okay for now. Your vibration is almost certainly from motor mounts. My opinion is that this job is not technically challenging, but it is very dirty, messy and you will work with several heavy components on your back. Take your time, and there are several other things to check and maintain during the motor mount job. Do a bit of searching for 'motor mount' and you will get a good idea, or Roger will guide you as well.
Thank you for all!
Regards
Lefteris
01-17-2008, 11:27 PM
#20
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Yeah What BOB said! Be Safe , Keep em flying!
01-18-2008, 12:12 AM
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There are also 'plastic' pliers manufactured for such tests...........as Bob suggets have the spark plug removed from the engine but fully connected to the rest of the ignition system and grounded to the cylinder head/valve cover as far from the spark plug hole as possible. Have a friend crank the engine and observe the spark plug 'spark'.
Extreme care must be excercised as both combustion and fuel exist in the cylinder............should the spark get close you'll have the resultant explosion which may lead to the other issues described above.
Extreme care must be excercised as both combustion and fuel exist in the cylinder............should the spark get close you'll have the resultant explosion which may lead to the other issues described above.
01-18-2008, 12:56 AM
#22
Lefteris,
Once you start a good thread on Rennlist forum the help is tremendous.
I would suggest that the 'halo' effect around the hight tension ignition leads is ozone formed by the high voltage flow through the leads and is not really a breakdown of insulation. High voltage flow, flux density and magnetic field can produce the ozone. If you have a breakdown of insulation you will get arking and the destinctive "crack" of the spark discharge over the point of least resistance. Dr Bobs description of what is goin on in the ignition system is fabulous. You can also get tracking without sparking.
When dark it is easier to see the blue spark when tracing faults in the system, but don't go sticking you hands in when engine is operating. The old magneto ignitions were safer and an old trick played on me when I was a boy was for this chap to grab my ear and the spark plug at the same time. Pretty hard to forget the feeling! I have great respect for ignition systems.
Within the WSM the ohm resistane values of the wires and the connections, the distributors and the rotors etc., are given. A good maintenance procedure is to remove all the high tension ignition system, clean and inspect on a regular basis, look for corrosion, errosion, tracking, cracks, insulation cracking mindful that the wires are very low resistance copper core wires and the resistance is contained withing the connectors, as this design allows for a consistant spark to be delivered to each cylinder.
If the system test out OK you can let it go for the present. If it ain't broken don't fix it, unless there is a specific requirement to do so.
With regards to the motor mount replacement, when you have to replace the cross member after the mounts have been replaced, machine or grind a conical end on each of the through bolts for ease of location into their respective holes. There are a lot of other good tips on this forum especially relating to how to support your motor, how to drop the power steering and tyre rods (if necessary).
Roger, I believe also sell silicone rubber sump pan gaskets, which are far better than the cork ones installed or supplied by Porsche. If you fit a cork gasket just nip it up and at each yearly service go around each set bolt and just nip them up again. I they are over tightened they will splay out the gasket.
Best of luck with the GT.
Tails 1990 928 S4 Auto
Once you start a good thread on Rennlist forum the help is tremendous.
I would suggest that the 'halo' effect around the hight tension ignition leads is ozone formed by the high voltage flow through the leads and is not really a breakdown of insulation. High voltage flow, flux density and magnetic field can produce the ozone. If you have a breakdown of insulation you will get arking and the destinctive "crack" of the spark discharge over the point of least resistance. Dr Bobs description of what is goin on in the ignition system is fabulous. You can also get tracking without sparking.
When dark it is easier to see the blue spark when tracing faults in the system, but don't go sticking you hands in when engine is operating. The old magneto ignitions were safer and an old trick played on me when I was a boy was for this chap to grab my ear and the spark plug at the same time. Pretty hard to forget the feeling! I have great respect for ignition systems.
Within the WSM the ohm resistane values of the wires and the connections, the distributors and the rotors etc., are given. A good maintenance procedure is to remove all the high tension ignition system, clean and inspect on a regular basis, look for corrosion, errosion, tracking, cracks, insulation cracking mindful that the wires are very low resistance copper core wires and the resistance is contained withing the connectors, as this design allows for a consistant spark to be delivered to each cylinder.
If the system test out OK you can let it go for the present. If it ain't broken don't fix it, unless there is a specific requirement to do so.
With regards to the motor mount replacement, when you have to replace the cross member after the mounts have been replaced, machine or grind a conical end on each of the through bolts for ease of location into their respective holes. There are a lot of other good tips on this forum especially relating to how to support your motor, how to drop the power steering and tyre rods (if necessary).
Roger, I believe also sell silicone rubber sump pan gaskets, which are far better than the cork ones installed or supplied by Porsche. If you fit a cork gasket just nip it up and at each yearly service go around each set bolt and just nip them up again. I they are over tightened they will splay out the gasket.
Best of luck with the GT.
Tails 1990 928 S4 Auto
01-18-2008, 02:03 AM
#23
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Lefteris,
Once you start a good thread on Rennlist forum the help is tremendous.
I would suggest that the 'halo' effect around the hight tension ignition leads is ozone formed by the high voltage flow through the leads and is not really a breakdown of insulation. High voltage flow, flux density and magnetic field can produce the ozone. If you have a breakdown of insulation you will get arking and the destinctive "crack" of the spark discharge over the point of least resistance. Dr Bobs description of what is goin on in the ignition system is fabulous. You can also get tracking without sparking.
Once you start a good thread on Rennlist forum the help is tremendous.
I would suggest that the 'halo' effect around the hight tension ignition leads is ozone formed by the high voltage flow through the leads and is not really a breakdown of insulation. High voltage flow, flux density and magnetic field can produce the ozone. If you have a breakdown of insulation you will get arking and the destinctive "crack" of the spark discharge over the point of least resistance. Dr Bobs description of what is goin on in the ignition system is fabulous. You can also get tracking without sparking.
I used to work in high energy field, and studied long term affects of high voltage on the breakdown of various types of insulation. An actual break in the insulation is easy to see and hear as you said it's a snapping sound, that can be hard to distinguish from injector ticking. This is generally found in vehicles where the ignition wires run close to the exhaust system such as the Dodge V8s and early Chevy V8s. The temps of the Porsche do not cause this effect. They also have a sheath that prevents the mechanical breakdown of the wires, but the electrical breakdown will occur on these vehicles. If a car has an open circuit in the plug extender for a while, that will cause a reflection of the ignition pulse, and this is really, really causative, but rare.
01-23-2008, 06:44 AM
#24
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MM's are $35 each and the Silicone Oil Pan Gasket is $42.
They can ship today if you email me your address.
Roger@928sRus.com
They can ship today if you email me your address.
Roger@928sRus.com
I just received the package!
I will put them on the car this Monday.
Thanks for the great service and prices!
Regards
Lefteris