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#26 |
Cluster King
![]() Join Date: Nov 2012
Location: Junction City, OR
Posts: 5,263
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Re: Trouble with underhood harness with HEI conversion
This has got me so curious that I went out and checked my own truck (1972 Chevy 350 w/HEI and external regulated alternator (factory config)
Using a DVOM, I have 12.4 volts with key on engine off. During the crank which is very short, I see a voltage drop to 10.8. While running, I see between 13.6 and 14.1 volts at idle with no acc on or lights. The battery voltage on the hot wire to the distributor for an HEI should be whatever the alternator is putting out at any given time. I believe it is possible for a weak ignition module to require more than 10 volts to light the engine up. Is it 10 or 10.8 and is that enough to make a difference?? Normally when an HEI ignition module goes bad it is due to heat and not voltage. I am curious to see what the fix is for you. |
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#27 |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
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Re: Trouble with underhood harness with HEI conversion
The specification for starter motor operation is a maintained 9.6 volts at the battery.
It would not be unusual to only see 9 volts at the HEI under those circumstances. (cranking the engine)
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My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
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#28 |
Msgt USAF Ret
![]() ![]() Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 8,713
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Re: Trouble with underhood harness with HEI conversion
I'm late to the party here but if you just want to get 12 volts to the Hei to start it you can just run a 16 gauge wire from the "R" terminal on the starter to the HEI BAT and you'll get battery voltage during the start. That's what the points ignition does. That will solve your problem until the module goes tango uniform.
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VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. |
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#29 |
Registered User
Join Date: Jun 2013
Location: Somewhere
Posts: 3,073
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Re: Trouble with underhood harness with HEI conversion
Duh, what does back probing mean? Measuring Voltage while cranking? That being the meaningful measurement.
The OP mat want to measure the resistance from the junction block by the battery to the connection at the HEI, and from the same spot to the firewall connector. Of course, measuring resistance doesn't give an indication of current capacity. Tango uniform. Funny... Interesting. I guess the R terminal gets 12V when the solenoid engages. The S terminal I guess means start. What does R mean? Last edited by franken; 08-18-2013 at 12:34 AM. |
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#30 | ||
Msgt USAF Ret
![]() ![]() Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 8,713
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Re: Trouble with underhood harness with HEI conversion
Quote:
here is a picture for anyone who cares.
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VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. |
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#31 | |
Cluster King
![]() Join Date: Nov 2012
Location: Junction City, OR
Posts: 5,263
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Re: Trouble with underhood harness with HEI conversion
Quote:
This is very simple. You need battery voltage on the "BAT" terminal of the distributor when the key is in the on/start position. If the connection is good, wiring is not the problem. I would try a different distributor or ign module. Is the dist you have 100% new including the pick up coil? Even new parts are prone to premature failure. |
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#32 |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
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Re: Trouble with underhood harness with HEI conversion
No, the copper washer is only hot while cranking. It will see battery voltage. Your's was 10.8v which indicated a healthy battery. The minimum specification is 9.6v. However, I've seen, many-many times, a vehicle start even when the battery voltage drops lower than that.
Since the OP said he only had 8-9 volts at the HEI connector (I assume unhooked) andd he can run the HEI connected directly to the battery indicates excess resistance in the ignition circuit. It could be on the power side or the ground side. It could be junction block, ignition switch, or any number of connectors or connections.
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My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
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#33 | |
Msgt USAF Ret
![]() ![]() Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 8,713
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Re: Trouble with underhood harness with HEI conversion
Quote:
One guy has been running his that way for years and he claims his truck runs perfect. Digital electronics are funny critters, they are more sensitive to voltage than analog stuff. The old stuff would run on less than 12 volts but slower, such as a fan or a motor. His pickup coil in the distributor probably needs more voltage because of greater resistance or the module won't switch just like the fellows have said. My post is only a band aid fix and was not meant to be the correct way to do it.
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VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. |
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#34 |
Senior Member
![]() Join Date: Aug 2008
Location: Cedar Park, Texas
Posts: 7,496
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Re: Trouble with underhood harness with HEI conversion
I started the morning off by swapping in a known good ac delco coil. Still no fire at the plugs. I then swapped in a module out of the same dusty crusty dist thT has been on a shelf in my barn for at least 15 yrs. It has "GM" stamped on it. Put it all back together, hit the key and she fired right up! The generic black module with no i.d. Went sailing across the garage in the general direction of the trash can.
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#35 |
Senior Member
![]() Join Date: Aug 2008
Location: Cedar Park, Texas
Posts: 7,496
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Re: Trouble with underhood harness with HEI conversion
I have had trouble with junk chinese modules in the past, but this is the first time i have had one not make it to the end of the driveway!
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#36 |
Registered User
![]() Join Date: Dec 2012
Location: Chandler AZ
Posts: 1,149
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Re: Trouble with underhood harness with HEI conversion
good troubleshooting..... I had an Accel super duper module do that to me. I was able to drive around the block and it stalled right before my drive way.....I don't know if you've ever tried to push a Longhorn UP a drive with a good slope to it by yourself in AZ in the summer...
Consider yourself lucky it didn't make it out of the drive.
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1970 Longhorn, Front Disc, 350/4 bolt, 882 heads, HEI, Edelbrock, 700R4, HO-52/4.11. 1996 Corvette, Collector Roadster, LT4, 396, 450RWHP, 6sp, 4.11/Dana44/posi 5 point roll bar And let us not grow weary of doing good, for in due season we will reap, if we do not give up. Gal 6:9 |
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#37 |
Senior Member
![]() Join Date: Aug 2008
Location: Cedar Park, Texas
Posts: 7,496
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Re: Trouble with underhood harness with HEI conversion
I am now getting 10.5 volts when back probing the pink HEI power wire at the dist while cranking. I'm not sure if the low voltage ruined the original module or what.
Thanks everyone for the input. It was a big help! Now to get the brake bled and start on the exhaust! Posted via Mobile Device |
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