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MG MGB GT V8 Factory Originals Technical - No Spark
I am currently working through electrical issues with my 1978 MGB V8.
I have a gear reduction Starter, GM alternator, Accel Billetproof electronic distributor and a pertronix Coil (needs no ballast resistor).
Starter works great and sounds good too. Ignition light comes on so I assume the alternator curcuit is good.
I have twelve volts at the "+" side of the coil, but no spark anywhere.
I have the white and black wires going to the "-" side of the coil and I ran a wire from the fuse box (white and Brown spade) to the "+" side of the coil. The distributor has three wires, Red, Green and Brown. The red is on the positive side, green on the Negative side, and Brown is grounded to the manifold.
Everything looks good, but no spark.
Please help.....I am really excited about getting this 3 year project running. Would make my wife happy as well.
Thank you all for your time,
|Is there no spark coming out of the coil, or at the plug wires? You may have a bad coil. Double check all your wiring and verify your ground wires are truly grounded. Make certain the engine has a functional ground strap as well. Is the rotor installed in the distributor? Does the old coil provide spark under the same conditions?|
|I have an extra coil from a running engine that I swapped out with and still no spark. Distributor is ready to run and brand new. Complete with rotor. There is no spark from the coil or any of the plug wires. I do get a 12V reading to the positive side of the coil. I will look into grounding additional straps as a safety precaution. I will get back to you with my progress, but it may have to wait until the weekend. Thank you Jeff for your time.|
Like Jeff, I suspect the coil (haven't met accel billetproof) - You might try either a continuity test on the coil or its resistance if you still have the manufacturer's data. The point is; there should be something on the negative side of the coil as well.
Three points, the OE groundstrap is prone to wear - many of us have a second one in the engine bay where we can keep an eye on it. The second concerns your new starter, if my memory serves me right, the OE V8 had a coil feed from the starter to ensure sufficient current while cranking. The suggestion being the current at the coil might otherwise be too low - it may be worthwhile checking that out before you start to worry about amplifyers etc.
The last point concerns static ignition timing - Should we assume you are certain that you have hit about 8 degrees btdc ?
Happy New Year
|If your distributor isn't switching the current through the coil on and off you won't get a spark. Normally this is done by switching a ground to the coil -ve, but I don't know your distributor. If you see the same constant 12v on the coil -ve as the coil +ve when cranking the distributor isn't grounding the coil. If there is a constant ground on the coil -ve then it *is* grounding the coil but isn't disconnecting the ground when a spark is required. You should be able to get a weak spark out of the coil by disconnecting the wires that are already on the coil -ve and flashing a known good ground onto the terminal instead, that at least will prove the coil. After that it is down to the distributor and its connections. The problem with electronic units is that the only way to test them is by substitution. At least with points you can diagnose many of the problems with nothing more than a simple voltmeter. Have you double-checked your distributor connections with the manufacturers information? A ground wire sounds uneccessary as the body of the unit should get a good enough ground through its mechanical fixings.|
If the cranking speed is OK then the engine groundstrap is OK. If the coil primary measures between 2.4 ohms and 3 ohms then it is a 12v coil and you have connected it correctly. If it measures about 1.5 ohms then it is a 6v coil which will need the ballast or it can overload the distributor switching circuit, and may also require the distributor electronics to be connected to a 12v source and not the coil +ve.
|Thanks Jeff and Paul for you valuable input. The accel billetproof distributor is a lot like a mallory unilite.|
The gear reduction starter only has one spade fitting instead of the two the the OE starter has. Can I tie both wires into that one spade fitting on the starter and try to get back to original wiring?
Also, this engine has never been run and I am trying to install distributor at TDC. I will try the above mentioned wiring and pull the distributor and double check that I have everything where it should be.
The coil is a brand new Petronix model 40001 with 1.5 ohms. The instructions to the coil states no resistor needed.
I will go through this on Saturday or Sunday and get back with you on my findings. I really hope that it is just a wiring or timing issue as I purchased these parts new about a year and a half ago and you all know how these warranties work. But that is all part of doing these types of projects.
Thank you all for your time and may you all have a happy New Year.
|Daniel, also double check that your coil has 12v while cranking. Have someone turn the key while you check the voltage.|
I changed the new accel distributor out with an old and very used pertronix and hooked everything up and all I can say is WOW....
I do not know if it was the Accel distributor being bad or maybe I had just put it in wrong. I will try this distributor again next week just because it is brand new and looks a lot better then the stock distributor in the buick 215.
Thank you all for your help with this,
|Daniel - I'd be concerned about your coil resistance. It is the same as the 6v factory coils, which if used without ballast cause the points to rapidly burn. Even with an electronic trigger in place of points you will be getting double the current through it, which may be OK or maybe not. I'd check with the distributor manufacturer as to what resistance coils it can be run with. It also doubles the current in the coil and the how hot it will get. |
*Don't* connect the light-green/white to the brown/white at the solenoid. If the other end is still connected you could upset the ignition voltage and/or get the solenoid sticking on hence continuous cranking, at best you will be drawing an extra 10 amps or so from the alternator and dissipating about 130 watts of heat in the loom. The light-green/white should be insulated and tied back out of the way at the solenoid and coil at least.
This thread was discussed between 30/12/2004 and 01/01/2005
This thread is from the archive. The Live MG MGB GT V8 Factory Originals Technical BBS is active now.