I am stumped. My son's car has an HEI from a mid 70's GM truck. Dang thing has no spark. We replaced the module with a new one and had it tested to make certain it is good. The pickup tests out/ohms out in the range it is supposed to. New cap, rotor and coil. It has battery voltage 13.2 at the battery wire to the distributor while cranking or just on. Any ideas? Thanks in advance, Chip.
after you put in the new module, did you crank it over with any of the pug wires disconnected? sometimes that'll blow out a module. also did you check the coil, and make sure it has the ground wire/strap, and the ****on in the middle of the cap, etc?
x2, also verify the distributor is actually turning when cranking, I've seen it happen more than once...
My first test was to pull the cap to insure the rotor was turning. The coil does have the ground strap connected. The module was tested after the initial problem and is good as is the other module I have. These were tested at Slo Reilly yesterday. The ****on in the middle of the cap is good as well. It is part of the coil test and tested out fine. The tests I performed were with a digital multimeter. The tests were all per the Autozone website HEI troubleshooting section. Thanks for the quick responses.
How about the output from the pickup coil?? It should put out an ac voltage signal to the module. It might check ok as far as resistance but it needs to produce that ac signal or it won't trigger the module. You should see about 1.5 volts ac at 200 rpm (cranking speed) and if you use something with a pattern display you will see an AC sine wave build and drop off as the reluctor spins. I think the pickup coil resistance is about 900-1200 ohms.
Maybe a stupid answer, but check to make sure you have juice to the dizzy in the 'start' position. I have learned the hard way to check the obvious first.
I own nothing so elaborate as a meter with a display like you described, mine is a Radio Shack special that has served well for most everything the last ten years or so. Can I test the pickup with no power to it? Does it generate the ac signal or convert the dc to ac somhow(Which I can't imagine). I do have power in both the run and start position. I think this car hates me, it knows it is sold as soon as it is running and we get done painting it.
You can check the pickup with it unplugged and no power on. Just use the AC volts scale on a low setting and spin the dizzy.....should be 1.5-2.5 volts. If you want to make sure the module and the rest of the system are ok,leave the wires from the pickup unplugged from the module. Then take a plain old nothin' fancy test light and hook the clip to the battery + post or another 12v source. Now take the test light probe and rattle it between the two prongs of the module where the pickup usually plugs in. The module will see this as a pulsing pickup and will fire the coil rapidly. Have a ground wire near the center ****on of the cap for the spark to jump to.....a test lead with alligator clips will work fine.Be sure to have the power wire hooked up and the ign on when you do this test. Oh....make sure the tach isn't shorted out and causing this. Just unplug anything hooked to the TACH terminal to make sure. chicken
another thing to check, make sure you have the correct module, if it has an extra wire connection then it won't work, needs to be for a 70s vehicle. Also check the polarity of the pickup coil, if it's backwards wierd things happen, believe it or not. one more: it's possible to plug the pickup in wrong, so the terminal is not making contact, this is another side of the road discovery I made
I don't know how you have the 12v to the coil connected, but I don't have a tach, so I used a female spade connector. If you did that, just make sure you have it hooked up to the BAT connector and not to the tach connector. Don't ask me how I know.
I learned that from a buddys truck that wouldn't run after he put a new cap on it. He hooked the spade connector to the tach terminal and it wouldn't run. I probably spent an hour trying to get spark on the danged thing til I figured out what he did. He also had the plug wires all jacked up.
Double check other people's work. Somebody had put the wires on the wrong spots. Black to starter and red to ground, then they hooked the wires to the battery red to positive and black to ground. Everything operated but there was no spark. Straightened out the wires and had spark immediately. Tonight we try to start the car after we put on a new upper radiator hose. Sheesh stupid stuff causes so much irritation. Thanks for all the help on this major irritation, Chip.
Another thing to check is the small metal strap that slips into the cap and acts as a connection from the incoming leads to the ground at the coil when the cap is put on. Some distributors used a small black wire that bolts to the coil case using one of the 4 mounting bolts, but many used a strap instead. If you forget to pull the metal strap from the old cap and put it in the new cap, it can cause problems. Look inside the old cap and see if you left it behind by accident, or make sure there is a ground wire on one of the coil mounting bolts. One way to make the control module last a whole lot longer is to get it out of the distributor. On my Stude pickup with 259 engine and homemade HEI, I used to have to change the module every 2 years or so, usually at a bad time in a parking lot somewhere. Wanting to avoid the embarr***ment of being seen working under the hood of the most noticable car in town in a Wal Mart parking lot, I wired TWO modules to use under the dash so I could simply flip a switch to change to a new module when one would fail next time. Won't start? CLICK! Its fixed! A wonderfull thing happened-- In over 10 years I haven't had to flip that switch EVEN ONCE. I guess getting the module away from the engine heat is what made all the difference. It hasn't failed once in over 10 years so far. I did the same thing with my electric fuel pumps. (UNDER the car of course) TWO in parallel with tee-fittings, and a switch I could flip instead of crawling under the car on the side of the highway for an emergency repair in my good clothes. Whether they last two years or ten years, no more emergency highway fixes. CLICK! its fixed!
One more important thing- Some HEI coils were very slightly thinner than others. If you use the coil-screws from one coil onto a different coil that needs shorter screws, there is a possibility that you could have a screw that slightly and unnoticably cracks the cap inside near the high voltage terminals and could provide a hard-to-find pathway for the high tension current to jump to the ground via the coil mounting bolts. Look inside the cap and see if there might be tiny cracks or a small bulge inside where the coil bolts might break thru if they are a tad too long. If that happens, it is usually ALMOST invisible and you have to look closely. If there is even a small crack there, it can be a pathway for the spark to ground itself thru the coil bolts. Also make sure that the tiny spring that connects the bottom of the coil to the center "****on" that touches the rotor is in place. The spark can usually jump that small gap if the spring is missing, but it also invites the spark to go elsewhere if the resistance is high and you have a weak spot somewhere. Also- watch out if you like to run large plug gaps like the .060 in many GM manuals. HEIs in good shape can handle huge plug gaps, but any weakness anywhere can invite bad misfires. A cheap coil with less internal insulation, or a dirty rotor, or a light film of dirt inside the cap... Too-high of resistance in the circuit - big gaps, or cranking the engine with plug wires not hooked up, or ??? can make any coil, not just HEI coils, spark internally instead of following the path. Sometimes that can eat coils from the inside, or jump thru the rotor to eventually weld on the timing mechanism to make it stiff operating or even sieze it up if neglected long enough. The HEI rotors had to be redesigned slightly in the center areas, but there are still many old style ones still being sold out of old stock at parts stores. The old style rotors are still good ones, but not as resistant to neglect as the later rotors. It's just something to remember to look at when you check to see if you need a tune up. Whew, three posts. I am all talked out for this week.
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