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#26 |
Registered User
Join Date: Apr 2010
Location: So Cal
Posts: 1,437
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Re: HEI issues?
from above
>>If the resistance wire from the ignition switch to the distributor is still being used then he won't have 12v. Likely nearer 7v which causes undue heat in the module.<< Absolutely and completely false. To begin, you should be starting with 14Volts, not 12v, assuming you have a working alternator. That dreaded ballast or ignition resistor wire measures 1.6 Ohms. (1.8 ohms on the inline six) If you would insert an Ammeter in the B+ wire feeding YOUR HEI, if it is an original GM HEI, you will measure 1-2 AMPS. GM actually list it as 2 Amps in some spec sheets and sometimes 1.5 Amps. OHm's Law states; Voltage = Current x Resistance This will give you Voltage drop across the Resistance Wire. I.E. the voltage you are fearfull of losing from the 14Volt supply voltage. The dreaded 1.6 ohms X GM's 2 Amps = 3.2 Volts dropped across the resistance wire. MAX 14 Volts - 3.2 Volts = 10.8 Volts at the HEI BAT terminal. In reality the stock HEI with stock coil will draw less than 2 Amps and through an original resistance wire you will still have between 11 and 12 volts at the HEI Bat terminal. It is also true that the stock HEI when supplied with anything from 8-16 Volts will still supply adequate secondary voltage from idle to 6,000 rpm. A points ignition and a HEI ignition are both called Induction Ignition systems. You need to understand that the 10V or 12V or even 14V flowing through the ignition coil does not generate the secondary voltage that fires the spark plug. 12volts flowing through a primary winding of the ignition coil generates a magnetic field around the primary and secondary windings. It isn't the 12Volt generated magnetic field that causes current to flow through the secondary winding to the plugs. IT"S WHEN YOU REMOVE THE 12 VOLTS. When the points open and the 12 volts stops pushing current through the coil, The magnetic field COLLAPSES. When the magnetic field collapses. it generates as much as 300 Volts across the primary winding. This voltage is called Back EMF. Coil advertisements often include information such as a winding ratio of 100:1 300 primary volts X 100 = 30,000 secondary volts, potentially. When the 20k-30k is being generated in the secondary winding, you do not have 12 volts on the primary winding, you have 200-300 Volts. That arcing you see across the points on a points ignition isn't the 12 volts, it's the 200-300 volts looking for a place to go. Most of it goes into the condenser and later discharged when the points close again. The points ignition can't maintain dwell time as rpm increases. The magnetic field doesn't have enough time to be fully saturated and the 300 volt number drops. The point closed is the Dwell time and is mechanically linked to the points open time by the shape of the lobe. That's where the HEI comes in. It can control dwell time at higher rpm. If you don't understand any of that above, you should stop expounding the crap about having to have a FULL 12VOLTS for the HEI. If you're going racing that's a different story. You should know that there are circletrack racers out there that run a racing HEI without an alternator. Starting a race with 12.5 battery voltage, they still have plenty of high rpm ignition, 40 laps later when the Bat may have dropped below 10 volts. For the street, I can tell you I installed a coil-in-cap HEI in my truck more that 25 years ago. 10 years ago when I installed the AC, I switched it to an external coil HEI. The original Resistor Wire is still in place. I read 11 Volts at the distributor. The truck gets 15-16 mpg on the highway and it can run 70-75 mph for a couple hours at a time and never skip a beat.
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'67 GMC 2500, 292, 4spd, AC |
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#27 | ||||
"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,940
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Re: HEI issues?
Quote:
That's the one! Quote:
Gary
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'cuz chicks dig scars... My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread. The Rebuild of Creeping Death after the wreck Quote:
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#28 | |
Msgt USAF Ret
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Location: Kalamazoo, Michigan
Posts: 8,714
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Re: HEI issues?
Quote:
The level of exasperation you exhibit equals my own when it comes to posters who forget to give details even as simple as the year of their trucks. Points to add. You are correct about the 12 volts not generating the 20K to 30K volts on the induction side of the coil. I believe the boost comes from the discharge through the condenser (points), or the ignition module (HEI) what say you? You didn't address the module heat caused by low voltage but I think this is in error and the heat is caused by the engine temperature transferred through the distributor so an insulator is used. Resistance also produces heat so it may need to transfer to the distributor so either theory is possible. It has been stated that using the external voltage regulator, which generates voltage spikes, is often the module killer in HEI ignitions since the modules do not like voltage spikes. Most digital equipment follows that rule. Your last paragraph bears out the original post where he states that his engine ran fine until it died and again after he got it restarted. I'm open for discussion.
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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 | |
Senior Member
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Location: Tucson, AZ USA
Posts: 7,276
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Re: HEI issues?
Quote:
But intermittent on the Tach line shouldn't have affected ignition. That's what threw me off. By ''wheel house'' do you mean the engine bay, at the bulkhead terminal block? Or the cab. [Kind of a salty nautical handle for a truck cab if it is. lol] I'm referring to pulling a tap off the inside-cab fuse block. Just easier to get to. Yes, a female terminal taps into a recessed positive terminal in the fuse block. Without getting obsessively technical-- the 20 ga. Orange/White/Purple wire coming out of the bulkhead connector on the drivers side firewall, feeds nominal 12 VDC at start, then, being a resistance wire, increases resistance as it heats up and cuts down to 9 - 7 VDC, to keep from burning up the points. HEI modules fed voltages under 12 VDC heat up and fail. At the other end of the resistance wire it splits into two 20 ga Yellow lines, one to the Coil positive terminal and the other to the starter. No longer needed in the HEI system.
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Every 25 years I like to rebuild that 292, whether it needs it or not. Last edited by '68OrangeSunshine; 09-13-2017 at 08:03 PM. |
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#30 | |
Registered User
Join Date: Jun 2017
Location: Cincinnati Ohio
Posts: 51
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Re: HEI issues?
Quote:
So I checked, that black Batt power wire already runs to the fuse block. Would pushing that multi meter almost through that power wire possibly cause new issues? The truck started again, but sounds like it's trying to suck too much air when you tap the throttle, to the point if you press it too hard it will stall out. Seems to idle alright for a bit though. I have a video but have to get it uploaded since the photobucket BS. |
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#31 |
Registered User
Join Date: Jun 2017
Location: Cincinnati Ohio
Posts: 51
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Re: HEI issues?
https://flic.kr/p/YGxnqR
Here's a link to the video couldn't get it to embed. |
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#32 |
Registered User
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Location: Mohnton pa.
Posts: 208
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Re: HEI issues?
I did the Hei conversion on my 350 a few months ago. I used the old resistor wire as a 12v + trigger for a 30amp relay on the fire wall. I ran a dedicated 12gauge wire from a spare fuse box I installed in the cab to power up the contact side of the relay, then over to the Hei.
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#33 |
Registered User
Join Date: Jun 2017
Location: Cincinnati Ohio
Posts: 51
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Re: HEI issues?
Another longer version. It didn't start doing this until last night/today. So that's why I feel like this may be something I caused possibly?
https://flic.kr/p/XsABzr |
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#34 |
Registered User
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Location: 2nd left past the stump on a dirt road.
Posts: 2,629
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Re: HEI issues?
The way that engine backfires and chuckles along seeing the carb fumes coming back out makes me think the timing is Way Off.
But to check it you have to get it idling. Do you know how to set your timing working it backwards? Or all in by 3000 rpm? |
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#35 |
Registered User
Join Date: Jun 2017
Location: Cincinnati Ohio
Posts: 51
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Re: HEI issues?
Which would make me curious how the timing could be so far out. I don't know how to set the timing working it backwards. At this point I think it's going to my buddy's shop to get sorted, as I just simply don't have time to keep chasing this. As hard as it is to "diagnose" on the forums, thanks for all the tips so far guys!
Last edited by zachste; 09-14-2017 at 09:42 AM. |
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#36 |
Registered User
Join Date: Jun 2017
Location: Cincinnati Ohio
Posts: 51
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Re: HEI issues?
Wanted to circle back and post the fix. Put a new DUI module in, and all is well.
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#37 |
laying low
![]() Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 13,265
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Re: HEI issues?
Thanks for the final update.
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Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross |
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#38 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,642
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Re: HEI issues?
Thanks for the follow-up. I'll admit I had to Google DUI module, it has always just been HEI to me. Glad you fixed the problem!
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#39 |
Registered User
Join Date: Jun 2017
Location: Cincinnati Ohio
Posts: 51
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Re: HEI issues?
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#40 |
Registered User
Join Date: Apr 2010
Location: So Cal
Posts: 1,437
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Re: HEI issues?
You purchased an ICM, Inter Continental Missile?
It would make sense that many don't know what DUI means. It's not clear that DUI does. http://performancedistributors.com/ Their web address says "performance distributors" and their home page says the same. You have to blow the Home page up 400% to read Davis Unified under the D.U.I. logo. You got a new HEI Module. That is the term used by everyone. The only question anyone might ask, is it a 4 pin, 5 Pin, 7 pin or 8 Pin.
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'67 GMC 2500, 292, 4spd, AC |
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#41 |
Senior Member
![]() Join Date: Feb 2002
Location: Tucson, AZ USA
Posts: 7,276
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Re: HEI issues?
Davis Unified Ignitions custom makes their distributors for each application. They have to know the vehicle, engine size, vintage, type of driving done, and then they build their distributors... I looked at one in a Jeep pickup. It's an overbuilt HEI with heatshrink on the wire ends of the plug and cap boots. Quite expensive. They even make a GM-style HEI for Fords.
The ambiguity of their initials is no coincidence. The company makes its major money off supplying court-ordered ignition breath-a-lyser interrupters for drunk driving offenders.
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
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#42 | |
Registered User
Join Date: Jun 2017
Location: Cincinnati Ohio
Posts: 51
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Re: HEI issues?
Quote:
Yea I actually googled them to find more info on their parts and at first missed their website due to it's name. Weird business model if you ask me. But supposedly make great parts. |
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