TechnoViking Posted April 14 Share Posted April 14 Decided to perform the sacrilegious act of installing a new HEI to replace a factory coil & distributor setup to chase down a miss and a broken vacuum advance. I suppose the idea of cleaning up some extra spaghetti out of the engine bay was also a bonus. Matched timing (~10 degrees BTDC initial) up by spinning engine over until old rotor was pointed to #1 and clocking new HEI distributor the same. Tested red/green coil wire to have power on key and crank and wired to the BAT terminal on the HEI. Left green/yellow coil wire and 3-wire distributor plug disconnected. After install it now fires up and idles when cold without complaint and runs noticeably smoother. The first test drive unfortunately revealed that it now intermittently stalls when shifting into forward/reverse from P or N (C6 auto) or coming to a complete stop in any forward gear. It will immediately re-fire and idle & rev like clockwork in P or N. Once moving in gear, it runs like a top. Full disclosure - my kick-down linkage needs love so for now it is disconnected and gears are shifted manually from the column. No issues driving this way before HEI install. Hoping someone more familiar with these ignition systems can chime in if I am missing anything obvious. From the questionable information I've gathered on YouTube, the HEI seemed essentially plug & play with just the 12v source from the coil. (Please excuse the jank wiring; cleanup to come) Cheers! Link to comment Share on other sites More sharing options...
mat in tn Posted April 15 Share Posted April 15 im not sure that the dist. is the issue. the previous might have had an issue. et the intermittent stalling seems odd. you say that the kickdown linkage is a little needy so its disconnected. however, the c6 is shifted by way of a vacuum modulator. it is mounted at the back of the transmission beside the tail shaft housing facing rearward. it is connected to manifold vacuum by way of a 3/16" hose about 6-8" long and then a 3/16" steel line reaching up at an angle and then again by a hose. possibly connected to a vacuum tree on the firewall but only if it is a factory ac truck. Otherwise hooked to a vacuum tree below the carb. i say this as stalling after let oof of the throttle is commonly a vacuum leak. and this could also keep the trans from shifting properly. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted April 16 Share Posted April 16 Is the advance hooked to a manifold or ported vacuum source? Link to comment Share on other sites More sharing options...
TechnoViking Posted April 16 Author Share Posted April 16 Is the advance hooked to a manifold or ported vacuum source? It's hooked up to the "distributor spark port" (labeled in similar YF/YFA style carb diagram below) the same as before the HEI swap: Next chance I get I will double-check all vacuum lines and try to reproduce the issue with the vacuum advance line plugged to make sure there isn't a leak in the new unit. Probably wouldn't hurt to test with the brake booster & vacuum modulator lines plugged as well. I did try setting the idle a tad higher but it would still occasionally die when stopped in gear. Giving a little more RPM when shifting into gear seemed to reliably keep it from cutting out. Still idles perfectly fine with no load in P or N. Appreciate any other ideas to help narrow this down. Link to comment Share on other sites More sharing options...
viven44 Posted April 16 Share Posted April 16 It's hooked up to the "distributor spark port" (labeled in similar YF/YFA style carb diagram below) the same as before the HEI swap: Next chance I get I will double-check all vacuum lines and try to reproduce the issue with the vacuum advance line plugged to make sure there isn't a leak in the new unit. Probably wouldn't hurt to test with the brake booster & vacuum modulator lines plugged as well. I did try setting the idle a tad higher but it would still occasionally die when stopped in gear. Giving a little more RPM when shifting into gear seemed to reliably keep it from cutting out. Still idles perfectly fine with no load in P or N. Appreciate any other ideas to help narrow this down. Really thinking you have a voltage problem. How does the charging voltage look while idling ? And when headlights are on ? Any major fluctuations in voltage when the turn signal is flashing ? How about with AC on ? Link to comment Share on other sites More sharing options...
1986F150Six Posted April 17 Share Posted April 17 Really thinking you have a voltage problem. How does the charging voltage look while idling ? And when headlights are on ? Any major fluctuations in voltage when the turn signal is flashing ? How about with AC on ? Have you tried slightly increasing the idle speed to compensate for the additional load when in gear? Link to comment Share on other sites More sharing options...
mat in tn Posted April 17 Share Posted April 17 Have you tried slightly increasing the idle speed to compensate for the additional load when in gear? elegant solution, and may help diagnose further. Link to comment Share on other sites More sharing options...
TechnoViking Posted May 16 Author Share Posted May 16 Have you tried slightly increasing the idle speed to compensate for the additional load when in gear? Belated update in case anyone else goes the HEI dizzi route: Increasing the idle speed most likely would've been a work around to mask the issue. After studying Duraspark II ignition wiring diagrams and getting a better understanding of the START/RUN current path I realized that the coil + lead that is commonly suggested to power an aftermarket HEI distributor is running through the ballast resistor. Came to find out that the coil + wire will show a full 12V in the run position but the voltage will drop through the resistor with the engine running enough to cause the HEI to lose spark. Ended up using the main power for the DSII box (W/LB wire from ignition switch that goes into red on the 2-wire DSII connector) that provides a direct 12V from RUN & START. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted May 16 Share Posted May 16 Belated update in case anyone else goes the HEI dizzi route: Increasing the idle speed most likely would've been a work around to mask the issue. After studying Duraspark II ignition wiring diagrams and getting a better understanding of the START/RUN current path I realized that the coil + lead that is commonly suggested to power an aftermarket HEI distributor is running through the ballast resistor. Came to find out that the coil + wire will show a full 12V in the run position but the voltage will drop through the resistor with the engine running enough to cause the HEI to lose spark. Ended up using the main power for the DSII box (W/LB wire from ignition switch that goes into red on the 2-wire DSII connector) that provides a direct 12V from RUN & START. There's no way either of those wires will provide enough current to run a GM ignitor. You should read the tutorial under Bullnose upgrades to learn how to wire a relay and fuse into the system. Link to comment Share on other sites More sharing options...
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