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The Audi Doctor
The Audi Doctor, Technician
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Maserati 3500 gt: I have a 59 Maserati 3500 with a 3.5l engine.

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I have a 59 Maserati 3500 with a 3.5l engine. Have no/ weak spark. Won't light a timing light. When I put a auxiliary ground to the end of the spark plug I get good spark and timing light flashes. Did a voltage drop test to the block from the battery and read .2 volts. Think I have a good ground but am spinning in circles. Any suggestions?

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.2 volts would be the maximum voltage drop provided you did it correctly. How did you perform the test? What is the battery surface voltage? What is the voltage across the battery when the starter is cranking?

Are you saying that when hook a ground directly from the spark plug to the battery negative terminal the spark is strong? How about if you hook a jumper battery cable from the negative terminal of the battery to the block. Does the engine start?

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Jake “The Auto Doctor”
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Customer: replied 4 years ago.
Test was performed by using a Dvom and running from battery neg to eng block. While cranking I have .2 volts. Across battery I have 12.4 v and while cranking across battery I have 9.9 v. I know 9.9 is a little low but that's do to many failed attempts to get spark. I have a charger on Battery now.
You actually know how to do a VD test. I am amazed how many Techs don't know how or use them. Yes, .2v is acceptable.

First off what's going on here? Was this a running vehicle that died? was it stored or restored and you are trying to get it running? What's the situation?

Also, let me get something straight when you take a spark plug, plug it into the secondary wire, hold the plug against the block and crank it (cranks at normal speed) the spark is weak and won't fire the light, but when you add a jumper from th negative terminal to the spark plug spark is strong and the timing light fires. Is that correct?

If you hook a "jumper cable" from the battery to block and is the spark ok and will the spark plug and timing light fire?

Thanks Jake
Customer: replied 4 years ago.
The car was running and then stopped. You are correct with the spark situation. I have run auxiliary ground from Battery to distributor base then to head. Feel I have a good ground at head but still weak/ no spark. Someone mentioned to run a tap thru the spark plug holes. I also tested my coils I have open loop between positive and high tension and negitive and high tension. I do have good resistance between positive and neg terminals. Tested a new coil from parts store to compare and have same values. Also ran a ground from battery to coils to make sure they have proper grounding. Have external resistors and I am getting proper voltage to coil during cranking so am assuming resistors are good. It is a dual coil system so I do have dual plugs, points, coils, and resistors.
I believe the system should bypass the ignition coil resister during cranking, and then run through the resister for running. This way it allows full battery voltage during starting, and reduced voltage for reduced wear on the points. Try jumping straight battery voltage to the positive side of the coil when cranking.

I have never heard of cleaning the spark plug threads to correct a ground issue, but by all means clean all grounds and connections. Be sure to put a smear of anti-seize on the threads before re installing or replacing the spark plugs.

Start with cleaning both battery terminals, then follow both the positive and the ground paths, and remove, clean and secure all connections. Then do a VD test of the complete system.

Thanks Jake