HEI IGNITION Problem

[Staci Newsom]

I have a 1978 GMC Sierra Grande with a 350 ci engine. I believed I had a blown head gasket and got that all done but now I have no spark at the plugs. If I tested right I connected my volt meter to the tach connector as suggested to see if there was voltage. I thought I would get a steady voltage after putting the key in the on position. I got voltages all over the place. What could that mean? When I try to check the continuity across the yellow and center and red and center of the coil I get no reading. I don't know if I am testing that part correctly.

I haven't checked the pu coil or the module. I wanted to make sure the coil is working. My instinct is to just replace all three but I want be sure.

Any help would good?

 

[SirRobyn0]

Ok so in a way that is good because the tach terminal should receive a pulse from the distributor. The tach in your vehicle (if it has one) translates the frequency of those flashes into the reading on a gauge.

What you should have. With key on you should have 12volts at the wire on the + terminal on the distributor. You should have spark at the end of ignition wires, you did not specifically say you checked, so if you didn't you should, but I will assume you have.

Next if it's been a while you should replace the cap and rotor.

This article gives a really good testing procedure and is basically how we would go about it at the shop. https://www.chevyhardcore.com/news/hei-distributor-troubleshooting-with-performance-distributors/

I will add this, if you test the power and ground, the coil and pickup and all of that tests good, you'll want to replace the module. FYI the module is probably the most common failure, but given the recent head work I'd look really close at a possible power or ground issue. All though some guys will disagree with me on this, if you find that the pick up is bad I'd recommend a new distributor, it is fairly time consuming to replace and setup the pick up properly so to me if time is valuable do the entire distributor at that point.

Hopefully that article will help.

 

[SirRobyn0]

I'm not complaining merely trying to help. I see most of the ignition system problems in the engine performance section and wondering if a moderator should more it there so more people might see it and be able to provide Staci with additional feedback on her problem.

 

[Matt69olds]

Read this.

https://www.gmcmi.com/wp-content/uploads/2014/05/HEI-Testing.pdf

 

[Staci Newsom]

These were all what I needed. Thanks, I knew you guys would know.

 

[dvdswan]

1. With the ignition on, connect a voltmeter (or test light) to the + post or HEI BAT terminal located on the distributor cap.
+12 volts or Test LIGHT ON: Go to step 3.
No voltage or Test LIGHT OFF: Go to step 2.

2. Check for continuity or voltage drop in the ignition switch and in the circuit from the switch to HEI BAT terminal. Fix missing +12 volt problem.
STARTS: Stop—you’ve found the problem.
NO START: Go to step 3.

3. Remove a spark plug wire and insert a HEI spark tester ($2.99 from Harbor Freight) in line. Crank the engine and observe the light in the tester.
3a. Alternatively remove a spark plug wire and insert a metallic extension in the end of the wire. Using insulated pliers, hold the spark plug wire no more than .25 inch away from the engine block while cranking the engine. If you use the alternate method be very careful to hold the wire no more than .25 inch away from the engine. Greater distances can cause damage to the ignition module.

LIGHT FLASH IN TESTER or SPARK JUMP TO ENGINE BLOCK: The problem is not the ignition system. Check the fuel system, spark plugs, timing, and internal engine condition.
No light or NO SPARK: Go to step 4.

4. Remove and inspect the distributor cap for cracks and carbon-tracking. Visually inspect the distributor mechanism for moisture, corrosion, or burns. Repair as needed.
STARTS: Stop—you’ve fixed it.
NO START: Go to step 5.

5. Set an ohmmeter to the low scale. Connect the leads across the HEI’s “BAT” and “TACH” terminals.

ABOVE 1 OHM: Replace coil. If vehicle still doesn’t start, go to step 6.
0-1 OHM: Go to step 6.

6. Connect one ohmmeter lead to the “BAT” terminal and the other lead to the coil contact in the inside-center of the cap. Switch the first lead to the “TACH” terminal and recheck.
EITHER TEST READS 6K to 30K: Coil is OK. Go to Step 11.
BOTH TESTS READ INFINITY: Replace the coil. If the engine still won’t start, go to step 7.

7. Remove the green and white leads from the HEI control module. Connect the ohmmeter from ground to either lead.
INFINITE reading: Go to step 8.
LESS THAN INFINITY: Replace the pickup coil. If the engine still won’t start, replace the module.

8. Connect the ohmmeter across the green and white pick up coil leads.
READS 500-1,500 OHMS: Repeat Steps 7 and 8 while moving the vacuum advance with a screwdriver. If reading is still OK, replace the module.
DOES NOT READ 500-1,500 OHMS: Replace pickup coil. If the engine still doesn’t start, replace the module.

That is it. You will notice that there is really no diagnosis of the module. When everything else reads correct the module is replaced by default. In my case the coil read open. replacing it did not fix the problem so I had to replace the module also. BOTH items were bad and I assume the coil took out the module

 

[SirRobyn0]

1. With the ignition on, connect a voltmeter (or test light) to the + post or HEI BAT terminal located on the distributor cap.
+12 volts or Test LIGHT ON: Go to step 3.
No voltage or Test LIGHT OFF: Go to step 2.

2. Check for continuity or voltage drop in the ignition switch and in the circuit from the switch to HEI BAT terminal. Fix missing +12 volt problem.
STARTS: Stop—you’ve found the problem.
NO START: Go to step 3.

3. Remove a spark plug wire and insert a HEI spark tester ($2.99 from Harbor Freight) in line. Crank the engine and observe the light in the tester.
3a. Alternatively remove a spark plug wire and insert a metallic extension in the end of the wire. Using insulated pliers, hold the spark plug wire no more than .25 inch away from the engine block while cranking the engine. If you use the alternate method be very careful to hold the wire no more than .25 inch away from the engine. Greater distances can cause damage to the ignition module.

LIGHT FLASH IN TESTER or SPARK JUMP TO ENGINE BLOCK: The problem is not the ignition system. Check the fuel system, spark plugs, timing, and internal engine condition.
No light or NO SPARK: Go to step 4.

4. Remove and inspect the distributor cap for cracks and carbon-tracking. Visually inspect the distributor mechanism for moisture, corrosion, or burns. Repair as needed.
STARTS: Stop—you’ve fixed it.
NO START: Go to step 5.

5. Set an ohmmeter to the low scale. Connect the leads across the HEI’s “BAT” and “TACH” terminals.

ABOVE 1 OHM: Replace coil. If vehicle still doesn’t start, go to step 6.
0-1 OHM: Go to step 6.

6. Connect one ohmmeter lead to the “BAT” terminal and the other lead to the coil contact in the inside-center of the cap. Switch the first lead to the “TACH” terminal and recheck.
EITHER TEST READS 6K to 30K: Coil is OK. Go to Step 11.
BOTH TESTS READ INFINITY: Replace the coil. If the engine still won’t start, go to step 7.

7. Remove the green and white leads from the HEI control module. Connect the ohmmeter from ground to either lead.
INFINITE reading: Go to step 8.
LESS THAN INFINITY: Replace the pickup coil. If the engine still won’t start, replace the module.

8. Connect the ohmmeter across the green and white pick up coil leads.
READS 500-1,500 OHMS: Repeat Steps 7 and 8 while moving the vacuum advance with a screwdriver. If reading is still OK, replace the module.
DOES NOT READ 500-1,500 OHMS: Replace pickup coil. If the engine still doesn’t start, replace the module.

That is it. You will notice that there is really no diagnosis of the module. When everything else reads correct the module is replaced by default. In my case the coil read open. replacing it did not fix the problem so I had to replace the module also. BOTH items were bad and I assume the coil took out the module

If I had to lodge a complaint about this forum it would be this. We need some sort of a data base of knowledge, where write ups like yours could be stored and then pulled out as needed. Someone suggested that to me when I did a write up about rehabing window regulators. On this forum good write ups like that, and like yours on this ignition issue. They stay in whatever thread they are written and scroll down and down and eventually get lost unless they get stickied. Which is great but that's the entire thread, there needs to be a place to store a post like this, like what was said to me a "data base of knowledge" that we could point people to later.

 

[dvdswan]

AGREED^^^