The Stovebolt Site Forums The Shop Area Engine Shop Engine turning but no spark

Hi there,

Let me start off by saying thanks to anyone who has ever replied to my posts, the people on this forum are great.

I am working on a project truck that has not run since I bought it a year ago, and I have no experience working on vehicles. It has been a fun project and I am seeing the finish line.

I finally have a working engine, trans, and almost working brakes. I am trying to fire it up and I am able to turn the engine but there is no spark. I know this can mean any number of issues, so I was hoping there is a proper order in which to check the following to trouble shoot:

good spark plugs

Points/condenser

spark plug wires

Solenoid


Am I missing anything from the above list?

Thanks in advance for your suggestions.

Carlos

Hy Ruckin Chevy, why don't we start this discussion by you telling us what year, size, and make [Chev or GMC]of truck you are asking for advice on, also is the truck stock or modified?

Don't get tempted to use the "shotgun" approach and try to fix everything at once. You're going to need to approach the problem with a little logic and patience. There are two separate paths to the ignition system, and both have to work properly before a spark can happen. You haven't told us if you're working with a 6 or 12 volt system, but with a few minor differences, the troubleshooting procedure is similar. First, be sure you have a well-charged battery that will crank the engine at normal speed. One that turns slowly due to a low battery can keep the ignition system from working, or give a very weak spark.

The low-voltage part of the ignition system, called the "primary" circuit, consists of the battery, the ignition switch, the primary winding of the coil, the points, and an electrical path back to the battery known as a "ground". The battery current must flow through all these parts in turn to produce magnetism in the coil to generate the high voltage needed to fire the spark plugs.

The high voltage system known as the "secondary" consists of part of the coil, the wire from the center of the coil to the distributor, the distributor cap and rotor, the spark plug wires, and finally, the spark plugs. The high voltage (10,000 to as much as 50,000 volts in some situations)across the spark plug gap is used to fire the fuel and air mixture in the cylinders. The primary and secondary circuits are completely separate, but both of them must function properly to make the ignition system work. (Confused yet?)

You'll need a voltage-testing device such as a probe-type test light or a voltmeter, but if you're an electrical newbie, stick with the test light. It's harder to make a mistake using it. Begin by taking the distributor cap off (Release the two spring clips on the side of the distributor) and while looking at the rotor, have someone spin the engine with the starter. The rotor should turn as the starter turns the engine. If that does not happen, you've got merchanical problems such as a stripped timing gear, broken distributor shaft, or some other mechanical disaster. If the rotor turns, we've eliminated mechanical failure. As the distributor is turning, the points should open and close. The gap between them will be small, about the thickness of two business cards stacked together, but it must be there. If the points do not open and close, loosen the adjusting screw on the point that's attached to the base plate, turn the engine by hand until the insulated block on the movable point is on the highest part of one of the six cam lobes, and adjust the gap until a feeler gauge blade about .016" thick will slip between the points. Snug the adjusting screw(s) down. Turn the ignition switch on and spin the engine, and see if the big wire at the center of the coil will jump a spark to the engine block or cylinder head by holding the wire about 1/2" from the engine. use some well-insulated pliers to hold the wire- - - - -you're dealing with a potential of several thousand volts. The distributor cap and rotor do not have to be reassembled to do this test- - - -just pull the center wire out of the cap and use it to test for spark. Obviously, leave it plugged into the coil. If adjusting the points gets the spark going, you've solved the "no spark" problem. Try this much of the process and get back to us with the results- - - -I don't want to overload you with information, and we're only about 1/10 of the way through a total ignition diagnosis!
Jerry

About 9 out of ten engines that have set for a long and have no spark the points will be the culprit. Before sanding, filing, or replacing pull the coil wire from the distributor cap and place the end 1/4" or so from a good ground. Now use a screwdriver to open and close the points but don't try to be precise about it--just rattle them around. Even if the contacts are corroded the screwdriver will act as a breaker and you'll get spark. If you do the points need cleaning or replacing and it you don't then it is another problem.

Bingo! That's where and how I start. Fresh battery, make sure you have a good ground at the engine and make sure the points are working. Oh yeah, make sure the key is on Glad to hear I am not the only one that uses a screwdriver to test the old points.

Carlos, if that's a 1920s through 1960's Chevy a modern Delco D105P point set will fit.

Sorry about that. it is a '54 Chevy 3100. 12V, stock.

Nice read - thanks. My 41' half ton has been sitting since 1980; just got to the point of checking fire last night. The coil had a broken post so I took one off my 56' 6 volt tractor. Test light shows juice on both sides of that coil, and at, and thru, the points, and lawnmower test shows all the plugs fire blue. Can't get any Ohlm reading on the wires, and no spark with plug connected. I didn't have much time so stopped there. Will try coil wire spark test this afternoon! It was driven into the storage facility in 1980. All thoughts WILL BE APPRECIATED!

So how does the engine ground play into it. I see a ground on the side of the engine that has the wire missing - so maybe no ground? I am not getting the plugs to fire. Can the lack of that ground wire be my problem.

It is circuit. The power comes from the battery and has to go back in. If you don't have ground you can't complete the circuit. Without getting all complicated about it the negative is the frame and engine block. If you look at the spark plug you will note the one contact that you adjust is connected to the threads. The threads complete the path to the engine block and then if you have a ground strap to the engine block back to the battery you can complete the circuit.

Farmone, if you lacked a ground on the engine it wouldn't crank, the starter wouldn't work .... if the "lawnmower test shows all the plugs fire blue", then the plugs are firing, maybe just not enough, try jumping it with a 12V battery

Bill

Thank you. I assumed that if the starter would spend the engine, the engine was adequately grounded. But I'll go back and make sure it is from block to frame.

I assume I need to bypass the 6 volt battery so as not to damage it? I've got a new coil,wires, and condenser coming After all, it has been stored for 33 years!Thanks for your reply. I'll post the big moment.

I found the problem - ground wire from distributor to the engine. Couldn't really tell until I out an ohm meter on it. So, the engine had a good ground, but the distributor did not. Problem solved.