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Tech Reference Page #5


& HEI installations

Authored by Wes Vann, last revised on January 21, 1997

I had to remove the links to Schurkeys e-mail due to his getting off the net. (he is missed and hopefully will return soon)

The "Diagnosis of HEI" section at bottom of page written by Schurkey Swanke and was added 10/22/97

PLEASE NOTE: Any time that you work on the electrical system of your car, disconnect the battery! (I like using a SCCA approved battery disconnect switch)

This is written with the idea of a Chevy V8 engine's distributor. But then, basics are basics.


I don't want to bore (or insult) anybody, but, there are a bunch of items that should be said.

The firing order on a Chevy is; 1-8-4-3-6-5-7-2

If you view the top of the distributor cap, the spark plugs should be in a "clock-wise" order.

The spark should occur at the "top dead center" that is at the end of the compression cycle. The other "top dead center" is at the end of the exhaust cycle. Keep in mind that we are talking four stroke engines here and there are two rotations of the crank for every one rotation of the cam or distributor!

Vacuum advance is the canister that is mounted on the side of the distributor. It has a line that is hooked up to a fitting on the carb. It controls the advance based on engine load. You can get adjustable canisters.

Centrifical advance is done by the set of weights and springs inside the distributor. When a distributor is "recurved", it's the weights and springs that are changed.

You can rotate the distributor body to any position you want, as long as the spark plug wires are positioned so that the rotor is pointing to the terminal with the #1 wire at the correct engine time. Keep in mind that the terminals on the cap are evenly spaced (except for that weird odd-fire V6!).

How to find the correct "top dead center" for #1 firing;

This assumes that you trust your timing marker is correct. Depending on the history of the engine, you may not want to make this assumption.

You should remove the spark plugs so that it's easier to rotate the engine. You will also have to remove the valve cover on the drivers side of the engine.

The valve that is the closest to the radiator is the #1 exhaust valve. The second is the #1 intake valve.

Always rotate the engine in a "clockwise" direction as you look at the harmonic balancer. Rotate the engine while watching the #1 input valve. The first time that the timing mark comes up to "top-dead-center" after the input valve closes is when the time when the spark should occur!


A friend told me about a "whistle" tool that screws into the #1 spark plug hole that will tell you when on the compression cycle. I've never seen one, but it sounds like a handy little tool!

If you don't trust the timing mark;

You will have to use a piston stop in order to do this. A piston stop is a hard item limits how high a piston can go. I made one by welding an extension on a sparkplug that would go into the cylinder chamber. If you hit the starter, you will turn a piston into a screen door!

Once the piston stop is installed, you have to rotate the engine clockwise until the piston hits the stop. Put a mark on the balancer where the timing pointer is pointing. Then rotate the engine counter-clockwise until the piston again hits the stop. Make another mark on the balancer where the timing pointer is pointing.

The point between the two marks you made on the harmonic balancer is "top dead center"!!

Distributor installation;

This is if you didn't note the position of rotor when you pulled it out or just rebuilt the engine.

You first have to make sure that you are at the TDC that is at the end of the compression cycle (see above).

One of the biggest headaches in installing a distributor in a Chevy is that not only does it have to engage the gears at the end of the cam, it also has to connect to the oil pump.

Due to gear on the cam, the rotor will rotate a few degrees (counter-clockwise) as you slide it down. If it doesn't go down all the way, it's due to not engaging into the oil pump shaft correctly. Don't try to force it!

If it doesn't engage correctly into the oil pump shaft, you have to use a long screwdriver to rotate the pump a little. Then retry installing the distributor. It's just a matter of playing with it!

Converting a "points" distributor to "non-points";

I'm currently getting together data to fill out this section, but here is some basic information.

Converting to "non-points" or electronic ignition requires that you remove the points and replace them with a magnetic or optical sensor.

The nice thing about this is that the points don't wear out plus you still have the look of a stock distributor.

Notes on wiring for a "points" distributor;

1. There are normally two wires on the "+" terminal on the coil. One is the "resistance" power wire. The other is a power wire from the starter.

2. The "resistance" wire on a GM isn't anything that can really be seen. It looks like just any other wire. (on some other manufactures cars, the resistance is in a block)

3. The wire from the distributor goes to the "-" terminal on the coil.

Notes on wiring for an "HEI" distributor;

1. If you are converting from a points type distributor, you have to make sure that the "resistance" power wire is bypassed! It's best to just run a new wire from the fuse block. This wire goes to the terminal marked "batt" on the distributor cap.

2. There is no need for the power wire that comes from the starter.

3. On most HEI's, there are three wires that come from the base of the distributor and they plug into the cap. It's a connector block and can't be plugged in wrong.

Additional notes on HEI distributors;

1. Not all HEI distributors have the coil in the cap.

2. Over the years, there have been several different configurations of HEI's. In most cases, you will want to use one that has both vacuum and centrifugal advance. It wouldn't do you any good to have one that is set up for computer advance control if you don't have a computer!

This next section was written by Schurkey Swanke (best known just as "Schurkey") and I'd like to say thanks! All that I (Wes Vann) have done is some minor editing.

Diagnosis of HEI Ignition Systems;

Got the HEI No-Spark Blues? Don't worry, be happy. HEI's are as easy as pie to fix. You don't even need kilobuck 'scopes, module testers, or computer interfaces.

The Usual Legal Disclaimers And Stuff.

This is NOT the official factory diagnostic procedure. This is shorter and simpler. It requires fewer special tools. It is a little less thorough, but a lot faster. This is not designed to locate everything that could possibly go wrong with an HEI. It will locate the common problems.

General Assumptions:

You "know which end of a screwdriver to hold onto". You've even replaced a distributor cap and rotor and timed an engine at some point in your life, and the engine ran after you completed the job.

You have basic hand tools.

You have a non-computer controlled HEI (the module has only four terminals) with the coil built into the cap. If you have a separate ignition coil, the basics are the same, but the details are a little different.

You don't have a pacemaker, 'cause we are dealing with 50,000 volts and I don't want anyone to have their ticker "vapor lock", if you know what I mean. You do not want to "catch a spark" even if you're completely healthy. It hurts, especially if you are leaning over the fender and the spark grounds through your pants zipper. Damn, I hate it when that happens. Whenever I tell you to crank the engine, I'm assuming the ignition is ON and the car has the park brake engaged and the trans is in "Park". Your necktie is not wrapped around the fan blades.

Special Tools:

The most important special tool is a fully functional brain. Be sure yours is completely engaged. If the clutch plates of your mind are slipping, press "BACK" on your browser.

Spark tester: K-D tools 2756 (also available from Snap-On), A-C Delco ST-125, Mac ET 760H, or equivalent. Cost is about twelve dollars. Available at any well stocked auto parts store. This looks like a spark plug with an alligator clip soldered to it. If you're a low budget dude, you can make your own, but I don't recommend it. The real thing has a calibrated spark gap that will properly load an HEI coil whereas the homemade unit won't present as much of a challenge to your coil. I have seen weak coils that would allow the engine to run at idle and light load, but could not produce a spark at the HEI spark tester like those I've listed. Toss the coil! If you do make your own, be sure to remove the side electrode from a new spark plug, as you don't want false readings because your spark tester is oil fouled.

A spark plug boot: Needs to be a straight one. You'll cut it so that when you slip it over your spark tester, it extends about ½ inch beyond the tester.

Jumper wire: Plain old 14 gauge primary wire about three feet long, with alligator clips on each end.

12 Volt test light: A cheap one is OK, but test it every time you use it. If the wire is connected to ground, (the usual arrangement) touch the probe to a power source and make sure it lights up. HINT: Use the alternator positive terminal if it is easier to reach than the battery positive terminal. On those occasions that the wire is connected to a power source, touch the probe to ground and make sure it lights up. It's very frustrating to have to re-do an hour's work because the bulb in the test light burned out and has been giving you false readings.

Ohmmeter/voltmeter: Even a ten dollar Radio Shaft unit will work. (but NOT for module testing!)


Soldering gun rated at 450 watts: Yup, that's a big'un. (wv - a soldering gun is different from an iron in that it looks like a "gun" and has trigger that is used to cause it to heat up)

10 MEGOHM input impedance Voltmeter: This is required for module testing.

Remote starter switch: (or a buddy to crank the engine while you're inspecting parts from over the fender) If you use a remote starter switch, be sure the ignition is ON when you're cranking during testing. You'll waste a lot of time if you crank the engine with the ignition off.


You have an engine that won't run properly, or won't run at all. When you look down the carb throat and work the linkage, you can see fuel squirt out of the accelerator pump nozzle. The engine cranks at it's usual speed. (wv - you may want to charge the battery over night, so that there is a full charge)

STEP ONE: Verify No-Spark.

Select the easiest to reach plug wire and remove it from the plug. (on an inline six or four cylinder disconnect the coil wire from the cap and use it for this test) Connect it to spark tester and ground tester to any convenient chunk of nearby iron, such as a header bolt or the alternator bracket. Hint: face the sparking end of the tester so you can see it from the driver's seat.

Crank the engine with the car in "Park". If you have a good spark, check other plug wires. The HEI is OK, but perhaps your distributor cap or some of your plug wires are defective. If you have no spark, test a couple other plug wires. Still no spark? Reconnect the plug wires and go to step 2.

STEP TWO: Verify power supply to HEI.

Disconnect the power wire to the ignition coil. If the coil is built into the distributor cap, this wire will plug into the cap, at the "Batt" or "C" terminal. Probe the connector on the power wire with the test light or the voltmeter. With the ignition ON, but not cranking, you should have within one volt of battery voltage, or a very bright test light. With the engine cranking, you should have a minimum of seven volts on the voltmeter or a medium brightness on the test light. Poor voltage? Repair wiring from ignition switch. If you have good voltage, reconnect power wire. Go to step three.

STEP THREE: Exploratory Surgery

Remove the distributor cap and rotor from the distributor. If it is easier, label and remove the plug wires from the cap, but leave the other wires connected! Flip the cap upside down. Push the "Special tool" plug boot over the spark tester, and then push the open end of the plug boot over the center post of the distributor cap. This is the post with the carbon doohickey that rubs on the top of the rotor. The tip of the spark tester will be touching the center post of the cap, held in place by the cut-down rubber plug boot. Use your jumper wire to connect the spark tester to a good ground.

If you have a separate ignition coil (inline six or four cylinder) disconnect the cap and rotor, but just install the spark tester in the coil in place of the coil wire. Use the jumper wire to connect the tester to ground.

Make sure the advance mechanism of the distributor will clear the upside down cap. Crank the engine with the ignition ON. Watch the distributor so you know it turns when the engine cranks. This is a repeat of step one, but without the plug wires, rotor and cap in the circuit. If you now have spark, start looking at the wires, rotor and cap. If you have no spark, LEAVE THE SPARK TESTER IN PLACE and go to step four or five.

STEP FOUR: (only if you have the big soldering gun)

THIS IS IMPORTANT - don't hold the hot tip of the gun next to the pickup coil, and most definitely don't touch the tip to the pickup! You want to hold the "body" of the soldering gun near the pickup. The idea here is that the pickup will sense the electrical "goings-on" (non-technical term!) inside the body of the soldering gun and cause a "trigger". YOU ARE NOT TRYING TO SOLDER ANYTHING! IF YOU DO THIS RIGHT, THE TIP OF THE SOLDERING GUN WON'T EVEN GET HOT.

Plug in the soldering gun, and with the ignition ON, hold the body of the soldering gun as close to the pickup coil as you can. Keep your arm away from the spark tester. Pull the trigger on the gun. (one second is enough) look for sparks at the spark tester. This is a repeat of Step three, but with the pole piece (reluctor) out of the equation. The alternating magnetic field in the body of the soldering gun will induce voltage in the pickup coil which should trigger the module, which should trigger the ignition coil. If the soldering gun is not big enough, or is held too far from the pickup coil, you won't induce voltage in the pickup coil and the test is invalid. Experiment with this on a known good system, it's a real time-saver! If you're sure you've done this right, and you get no spark, LEAVE THE SPARK TESTER IN PLACE and go to step five. If you get spark here and you didn't in step three, the pickup coil is defective in a way that is not common. Re-do step three to be sure.

STEP FIVE: Eliminate the pickup coil.

Disconnect the two very fine wires from the module. Connect the wire on your test light to a voltage source such as the alternator POSITIVE terminal. Touch the probe of the test light to the module terminal labeled "G". (Its the smaller of the two terminals that you disconnected the pickup coil wires from) The test light will not light up on this test. If you get no spark, go to step six or seven. If you get a spark each time you remove the test light from the module, but got no sparks in the other tests, your pickup coil is defective. Replace it, connect the pickup coil wires to the module and repeat step three. If step three produces spark, the problem is fixed. Put it all back together and go cruising.

STEP SIX: Only if you have a voltmeter/ multimeter with 10 megohm input impedance.

Unplug the connector from the "TACH" terminal, if there is one. Usually there isn't. Set meter to lowest voltage scale that will accommodate 15 volts. Connect the positive voltmeter lead to "TACH" terminal on distributor cap (or separate coil) Connect the negative lead to ground. With ignition ON, repeat step five, except watch the voltmeter not the spark tester. The voltage reading should read high, but spike downward when you remove the test light from the module terminal. If it does, replace the ignition coil and repeat test five. If it does not, replace module and repeat test five. If you get sparks in test five, the problem is fixed. Put it all back together and go cruising.

STEP SEVEN: test ignition coil.

Remove the spark tester and all wires from distributor cap. Lift the cap out of the engine compartment for testing. Use ohmmeter set on a "high ohms" scale. First test: Connect between "Batt" ("C") terminal and "Tach" terminal. Resistance should be very low. If not, replace coil. Second test: Connect ohmmeter between Batt terminal and the carbon button in the middle of the cap. Read ohmmeter. Connect ohmmeter between ground terminal (the middle one of the three parallel blades) and the carbon button. Read ohmmeter. If BOTH of the readings in the second test are infinite, indicating an open circuit, replace coil. If you replace the coil, repeat step five. If the coil passes both of these resistance tests, replace module and repeat step five. Step five should produce spark, and the problem is fixed. Put it all back together and go cruising. If not, go cruising in your buddy's car to clear your head, then start from Step Two and re-check all your work, making sure you have good connections at the spark tester, test light and volt/ohmmeter. Then verify that the wiring that connects the components is sound. If you're ABSOLUTELY sure that everything tests good, and you still have no spark, replace the module and retest.

Other HEI problems:

A. Insufficient wire gauge to "Batt" or "C" terminal. You must have 12 gauge wire or thicker. GM knows this, but often cars get converted to HEI and thin wire or the old resistance wire is used. This will produce weak spark, especially at higher RPM.

B. Module MUST have dielectric silicone grease between bottom of module and distributor housing. WHEEL BEARING GREASE WON'T DO! The module transfers heat through the silicone grease so it doesn't toast itself.

C. Windings in pickup coil open when underhood temperature rises. Car runs great cold but dies when hot.

D. Windings in ignition coil open when hot. Same symptom as C above.

E. Wires that connect pickup coil to module break inside the insulation. (they don't look broken) When the vacuum advance moves the pickup coil, the broken wire opens the circuit, the engine dies. Vacuum is reduced, the vacuum advance relaxes, the wire reconnects and the engine runs. Cycle repeats.

F. Centrifugal advance doesn't get lubed and wears out the holes in the weights and the pins that the weights pivot on. In addition to screwing up the advance curve, all the metal dust from the worn out weights and pins is now stuck to the inside of the cap and rotor, making a possible path to ground for the spark.

G. V-6 cars that run really erratic may have mis-matched reluctor and pickup coil. If you have an odd-fire reluctor and an even-fire pickup coil, (or the other way around) the engine may run, but three cylinders are going to have timing that's really screwed up. I even saw a V-8 with a six cylinder pickup coil. Count the number of teeth on the reluctor and pickup coil. There should be one for each cylinder. The teeth will be unevenly spaced for odd-fire V-6, evenly spaced for everything else.