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Hey all... I recently was tooling down the road in my 81 and noticed the tach was cutting out for split seconds. I know it's the entire engine cutting out not just one cylinder. I pretty much believe it's an ignition problem it doesn't act like it's starving for fuel and it doesn't happen under acceleration. The engine cuts out for split seconds here and there when I'm holding a steady cruising speed maybe 2100 rpm. I can ride for 10 minutes to 1/2 hour with no problems. The car will be running perfect then this miss out of no where? 3 to 5 times in a row then it will be ok for a little bit but it seems to be getting worse. Any thoughts before I start tearing things apart would be appreciated.
 

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My best guess would be the HEI module. Maybe the leads where they connect, or just a bad module.
That's a good guess but what I don't like about it is that I've usually seen the module die when trying to start the car. One day it runs fine, the next, totally dead. I've not known one to get sick and die. Doesn't mean that it can't happen though.

How about the MAP sensor? I honestly don't know how much this sensor affects an 81 via the CCC, but on my Saturn, I had one fail with similar symptoms.

Have you tried to check the computer for error codes?
 

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That's a good guess but what I don't like about it is that I've usually seen the module die when trying to start the car. One day it runs fine, the next, totally dead. I've not known one to get sick and die. Doesn't mean that it can't happen though.

How about the MAP sensor? I honestly don't know how much this sensor affects an 81 via the CCC, but on my Saturn, I had one fail with similar symptoms.

Have you tried to check the computer for error codes?
Mike, I say HEI because his tach is also affected. I think Noonie had a similar symptom.
The Map regulates timing advance.
His main problem is "intermitant" failure. Always a bugger to diagnose.
 

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I agree with the HEI module.

I've also seen a coil go bad (leak) and once in a while it'd drop a spark to ground- but that's usually on an external coil HEI too.

:cheers:
 

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Here is a test procedure for the hei.
also check your wiring connectors for continuity.

HEI Test

1. With the ignition on, connect a test light to the coil positive (+) post or HEI BAT terminal.

LIGHT ON: Go to step 3.

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 the coil positive (+) side or HEI BAT terminal, including any aftermarket ignition modules or ballast resistors. On conventional ignitions, also check for continuity in the bypass wire from the solenoid R terminal. Repair or replace as necessary.

STARTS: Stop—you’ve found the problem.

NO START: Go to step 3.

3. Remove a spark plug wire and insert an extension. Using insulated pliers, hold the spark plug wire ¼-inch away from the engine block while cranking the engine.

SPARK: The problem is not the ignition system. Check the fuel system, spark plugs, timing, and internal engine condition.

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. Check the coil.

CONVENTIONAL COIL: Go to step 6.

HEI (IN-CAP COIL): Go to step 9.

6. Set an ohmmeter to the low scale. Connect the leads across the primary terminals. Coils requiring ballast resistors should have about 1-2 ohms of resistance. Those not requiring a ballast resistor should have about 4-5 ohms of resistance.

OK: Go to step 7.

NOT OK: Replace coil.

7. Switch the ohmmeter to the high scale. Connect one lead to either coil primary terminal and the other lead to the secondary cable tower. A stock-style coil should read between 4K and 8K on the scale. Some aftermarket coils may have lower values; consult the appropriate specs.

BELOW 4K OR OVER 8K: Replace coil.

WITHIN SPEC: For points systems, go to step 8. For electronic systems other than HEI, consult the system manufacturer for further troubleshooting steps.

8. Using a voltmeter, connect one lead to ground and the other to the distributor side of the coil. Remove the high-tension wire from the coil and ground it. Bump the starter switch to open and close the points; the voltmeter reading should be 1/3 to ½ the battery voltage during cranking as the points open and close.

READING AT OR NEAR ZERO: Replace the points and condenser.


9. 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 11. 0-1 OHM: Go to step 10.

10. Switch the ohmmeter to the high scale. Connect one 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 11.

11. Remove the green and white leads from the HEI control module. Connect the ohmmeter from ground to either lead.

INFINITE:
Go to step 12. LESS THAN INFINITY: Replace the pickup coil. If the engine still won’t start, replace the module.

12. Connect the ohmmeter across the green and white module leads.

READS 500-1,500 OHMS: Repeat Steps 11 and 12 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.
:D
 
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