helping my friend with his 1956 chevrolet 3100 that has a 250 6cyl with hei and no spark. the distributor is the "divorced coil" type. The coil,ignition module, pickup, rotor,cap are all new. I have a 12v lead from battery to coil going to leads towards front of engine and the 2 leads coming from hei to the 2 leads toward rear of engine. I have a jumper cable from negative post on battery to motor side on metal mount and no spark to plugs. i have put spark plug on coil lead and grounded still no spark. guys their isn't anything left in the hei but i believe is a ignition noise suppressor that we havn't replaced. this has he scratching my head and any ideas would be great. our next step is replace distributor with new one. the engine ran great before this i'm ready to solve this mystery. THANKS IN ADVANCE!
Do you get a "pulse" signal at the coil (using a test light) when cranking the engine? Have you closely examined the rotor for carbon arcing? the cap? The coil has to be grounded. checked for broken or cracked wires to the module? use the tug test, if it stretches the wire strands are broken.
coil has separate ground wire and rotor is installed. anyone else? the wires in and going to coil from distributor are new since module and pickup were replaced and both have new wires attached. have not checked for pulse.
This is from an article Tom (Langdon) wrote a while ago. I tried to upload as a .doc but the system didn't allow. I apologize for all the verbiage here! General Motors introduced the High Energy Ignition System (H.E.I.) on all engines beginning with the 1975 model year. The Chevrolet 250 and 292 six cylinder engines used this system initially with an externally mounted coil unique to the HEI system. Several years later the system was changed to incorporate the coil in the distributor cap similar to the V8 unit used since 1975. The internal and external coil versions have different internal components. To add to this confusion, two different four cylinder distributors were also used during this time period. These also used different internal components. The aftermarket rebuilders routinely mix these parts at random – a practice that frequently results in major mis-alignment of the rotor to distributor cap at the moment of firing. More on this later. This family of distributors can be modified to fit the older 235 type Chevrolet six by repositioning the gear and shaft length to properly align with the camshaft gear and oil pump. Articles have been written on this in previous issues of the 12 Port News. Today there is a better alternative, but I will leave this for another article. Based on disassembly of hundreds of these types of distributors, I have found the following problem areas: · Lower bushing wear on 1975-1976 distributors (do not have “flex-shaft” type design). · Non concentric lower bushing caused by rebuilder who is not knowledgeable in this type of work. · Distributor gear wear caused by high volume oil pump and heavy weight oil. · Advance weight plastic bushing wear · Internal parts mismatching (previously mentioned) caused by improper rebuilding procedure · Module failure & invisible module terminal corrosion (infrequent) · Pick-up coil wire failure due to flexing from vacuum advance action · Deterioration of vacuum advance diaphragm (easy to check) Lower bushing wear is virtually impossible to repair and a common result of poor quality engineering by aftermarket rebuilders. If you find this condition, the distributor should not be used. Installation of an unfinished bushing and line boring of the assembly is the only way to correct this condition. This is not common practice in the aftermarket industry. Distributor gear wear is usually caused by the use of high volume oil pump, heavy weight engine oils, or poor quality machining on (aftermarket distributor drive gear) camshafts. Keep these factors in mind as you build your engine. Distributor weight bushings are available at better auto parts stores (Borg Warner # DG13 or Niehoff XD13) but are getting expensive and hard to find. Internal parts mis-matching can easily be checked by noting the exact location of the rotor terminal when the internal and external tips are aligned inside the distributor (see picture). A terminal in the cap must align with the rotor terminal. If this check indicates mis-alignment, correction can be made by complete disassembly and re-alignment of the rotor plate and star with a 1 1/4” socket (see picture). Module failure & terminal corrosion can be diagnosed by your local auto parts dealer. This is usually a free service. Pick-up coil failure can be diagnosed with an OHM- meter while flexing the two output wires. A consistent reading of 400 OHMS would be correct. Vacuum advance diaphragm failure can be checked by simply sucking on its vacuum supply hose. If it is defective, it will not hold a vacuum and cannot be repaired. Replacement with a new unit (with a soft spring) can be easily done even with the distributor in the vehicle. There were hundreds of different vacuum advance units used by G.M., so there is a wide choice of spring rates and advance travel. Try for a unit that starts at about 4” of vacuum and has 20o of advance. By checking the above mentioned areas and supplying a direct 12 volt, 10 gauge wire power supply, you can easily and very economically have the best ignition system available and have immediate access to parts at auto parts stores anytime. In summary, I generally do not recommend purchasing commercially rebuilt distributors due to the previously mentioned rebuilding practices. A good used unit would be preferable with a good cleaning and inspection.
Had a similar problem with my HEI last summer. Engine was running, then out of the blue, just stopped! No spark. Did all the same stuff, replaced everything, still no spark. So in my frustrated state of mind I started from the beginning. Pulled everything back off, checked all the components again. Put everything back together again, engine fired right up, I had spark again. Then I noticed my Tach wasn't working. Took a quick look, I forgot to plug it back in to the "Tach" side of the coil. Plugged it in , engine shut off, no spark again. Disconnected it and got spark back. Turns out my tach went bad. Go figure . If you have a Tach, try disconnecting it from the coil.
Found this on the internet- Testing the GM HEI Distributor A no-spark condition is checked by checking the distributor for power at the connector on the side of the cap. If there is power, disconnect the electrical connector and remove the cap. Check the rotor and the cap for excessive wear. Check the coil tower for excessive wear. Remove the top plastic cap on the distributor cap. Use an ohmmeter and check the coil positive terminal to the metal case of the coil. The reading should be infinity. Check the coil tower and the negative terminal. The reading should be 900 ohms. Check the positive terminal to the negative terminal. The reading should be around 700 ohms. If any of these tests show drastically different readings, the coil is bad. If the coil is good, the cap and rotor are not cracked or worn significantly and there is no spark at any wire, replace the ignition module Read more : http://www.ehow.com/how-does_4809570_troubleshooting-gm-hei-distributor.html
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