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GM HEI 5-7 pin timing control...

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GM HEI 5-7 pin timing control...

Postby F1Fever » Mon Jan 11, 2010 10:37 am

In reference to another post here ..

I have looked around and cannot verify this, has anybody dealt with this before?


http://speedtalk.com/forum/viewtopic.php?t=19785#216400
Use a 5 pin module I beleive 87 olds v-8 is the application the extra pin gets hooked to a toggle switch with 12v when activated it will pull approx. 10 degrees timing out of the engine making it easier to hook up on a slick track.


I am thinking if this infact works i can use it triggered off my starter wire to pull 10* out with a locked out HEI to ease in starting. and if it does work how are the dwell setting with this module, good for power and rpm?
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Postby dieselgeek » Mon Jan 11, 2010 3:22 pm

Any HEI that has external timing control (computer equipped engines) can be set up. Although, it retards the timing to a "fixed 10 degrees total" not "retards by 10 degrees"

There's good detail on the various HEI modules and how they work, in the megamanual or on many megasquirt forum posts.
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Postby barnym17 » Mon Jan 11, 2010 4:40 pm

This pin when triggered by 12 volt input pulls 10 degrees out it was used on carbed engines with ccc control.The knock sensor detected knock wich triggered the 3c system to pull timing to control detonation .It was acrude system compared to todays but worked to prevent engine damage.As far as dwell and high rpm capability , we always used the module to trigger an msd via the white wire so the module was only providing a signal not carrying the amperage for the coil.There are Ford modules which can be used for this same purpose duraspark 2 if I'm not mistaken the white wire from the module was hooked to the starter soloniod terminal and retarded timing during cranking.
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Postby dieselgeek » Mon Jan 11, 2010 4:43 pm

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Postby F1Fever » Mon Jan 11, 2010 8:17 pm

dieselgeek wrote:it retards the timing to a "fixed 10 degrees total" not "retards by 10 degrees"

Scott, that is different than what barnym said. how would it (or could it) possibly know where 10* total would be?
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Postby dieselgeek » Mon Jan 11, 2010 9:01 pm

F1Fever wrote:
dieselgeek wrote:it retards the timing to a "fixed 10 degrees total" not "retards by 10 degrees"

Scott, that is different than what barnym said. how would it (or could it) possibly know where 10* total would be?


The module assumes that you have the OEM distributor on an OEM application in the OEM position. So while it may have idled with 20-25 degrees total when the +5 signal is online (telling the HEI module to get it's timing info from the external computer). The 10 degrees was so that, if the computer or electronics or wiring failed, the HEI would operate in a limp mode and keep the engine running.

Ford TFI modules do the exact same thing, except their signalling is a different. Pull the "SPOUT" connector (which disconnects the spark-output of the computer from the transistor inside the module) and the unit defaults to 10 degrees advance, assuming the distributor is rotated in the correct position. On the Fords, it's also how you set the base timing.

Since both modules are reading the trigger signal (coil pickup inside the dist) they simply fire the transistor (thus the coil) a fixed spacing between the teeth that they're sensing. Which works out to 10 degrees BTDC on each firing event, if the distributor is in the right place. This 10 degrees stays fixed at ALL rpm's, that's why it's not quite accurate to say "the module retards timing 10 degrees" because, at 6000rpm the engine might have 34 degrees total, but in "limp" (or no-spout) modes, they'll run at 10 degrees BTDC all the time.

I agree with what's said about using an MSD or other CDI ignition, though. Dwell is a non-issue if you're using an external CDI box.
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Postby F1Fever » Mon Jan 11, 2010 9:26 pm

but if I'm locked out at 34* initial/total
it is going to pull it to 24* right.. would be better if it could set itself to 10* but I don't see how, only wishing...
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Postby dieselgeek » Mon Jan 11, 2010 9:31 pm

F1Fever wrote:but if I'm locked out at 34* initial/total
it is going to pull it to 24* right.. would be better if it could set itself to 10* but I don't see how, only wishing...


that depends on what the OEM application called for. If I remember right, most of them idled around 25 degrees total, so it'd pull about 15 degrees. Maybe 20, max, from your idle timing. BUT - it's VERY important to realize it won't just pull a fixed number, it's going to run a fixed number at all RPM's. So, that 15-20 degree retard at idle might be a 25-30 degree retard at WOT...
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Postby F1Fever » Mon Jan 11, 2010 9:45 pm

gotcha 8)

barnym17 thanks for the idea, and Scott, thanks for the specifics, I owe you both a beer!
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Postby Schurkey » Mon Jan 11, 2010 10:28 pm

There are at least two styles of FIVE pin modules; the fifth pin on each is used to retard timing.

One is set up to retard timing based on a + voltage going to the fifth pin.

The other is set up to retard timing based on grounding the fifth pin.

I don't have application information; except to say that 5-pin modules were used on Olds and Buick engines BEFORE full computer-controlled timing came in in '81 1/2. Therefore the distributors using the five-pin modules still retained centrifugal advance and vacuum advance.

Five pin modules were used for:
HEI-EMR (Electronic Module Retard)
HEI-ESC (Electronic Spark Control)
HEI-ESS (Electronic Spark Selection)
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Postby barnym17 » Tue Jan 12, 2010 6:24 am

The best way is to hook up a timing light and check all can be different.Some ford modules retard 3degrees, some 10 it really depends on many factors.Experiment with some junkyard modules to get what you need.
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Postby Socrace » Tue Jan 12, 2010 9:33 am

Used on early non-efi HEI vehicles for detonation control such as 1980 Pontiac TransAm Turbo (301 olds), retards BY 10 deg when 5th pin is grounded.
Can be combined with knock sensor + esc module from same vehicle to make a crude sort of knock control, winds up being too sensitive for most as I remember.
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Postby dieselgeek » Tue Jan 12, 2010 9:37 am

Socrace wrote:Used on early non-efi HEI vehicles for detonation control such as 1980 Pontiac TransAm Turbo (301 olds), retards BY 10 deg when 5th pin is grounded.
Can be combined with knock sensor + esc module from same vehicle to make a crude sort of knock control, winds up being too sensitive for most as I remember.
Bob D


I am unfamiliar with the older modules, this is good info. Do the versions you speak of, include their own advance curve within the module then? or were they used with mechanical/vac advance distributors?
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Postby Socrace » Tue Jan 12, 2010 10:58 am

These distributors were more or less standard looking 4pin HEI with mechanical/vac advance, they just had the extra 5th pin.
Evidently used some kind of analog retard method within the 5pin module, probably about as accurate as a dial back timing light was back then, but probably ok for what they did.
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Postby F-BIRD'88 » Wed Jan 13, 2010 9:35 pm

To aid hot starting with a locked out HEI you'll probabily find that a SPST 15Amp rated switch on the 12V+ feed wire is just as effective and a lot simpler.
Make sure you have the rear support bracket/brace on the starter motor.
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