[Gmecm] Re: Big cap HEI on 7747

[dgilbert78 at juno.com]

EST timing. I once had a small cap problem that I fought for awhile with
erratic timing. I benched the dist in a vise, connected a few wires and
played with it a lot. used the timing light to watch the dist. Found that
had to much end play in the shaft. Could fire the dist by simply moving
the shaft up and down. Watch out for cracked magnet material, makes extra
poles i think. Shimmed shaft endplay so would not cause spark when shaft
moved vertically . It is truly amazing just how slow you can rotate the
shaft and still produce a spark. I think the internal coil module has 1
less pin, but is basically the same module. In bypass the ECM has no
control, it is all internal. If jumping timing it is the ECM telling the
module to fire when not in bypass. If you have a knock module it could be
detecting knocks and retarding the spark at random. Could be false
knocks. An O scope at times like this works wonders. I have a complete
break out box i made for the 1227747, I can scope any wire or measure any
voltage if i need to work on something that is giving me problems. I had
a small cap and augured the top of the cap out at each tower so I could
watch the spark inside the cap when running, that showed me a lot,
uncovered a timing error on my part. I do not know if you can do that on
the big cap with the coil in top (i assume you have the coil in top) Good
luck
Darryl...
On Mon, 5 Jun 2006 21:11:51 -0700 "Mark Romans" <romans at starstream.net>
writes:
> Hi DarrylAndrew:
> 
> We switched the wires on the module and it seems to have killed
> the module.  What's weird is that your description is so exactly 
> what the 
> symtoms are.
> Keep in mind this is a big cap HEI with an internal module.
> 
> The timing varies by huge amounts and greatly by engine rpm.
> 
> It idles fine in EST bypass.
> 
> Everything has been replaced.  One more thing is that this is an EST 
> HEI 
> modified to fit
> a 350 Buick running a 747 ecm.
> 
> Mark
> 
> 
> 
> 
> ----- Original Message ----- 
> From: "Andrew Gibson" <andrewsharyn at yahoo.com>
> To: <gmecm at diy-efi.org>
> Sent: Saturday, June 03, 2006 5:09 PM
> Subject: [Gmecm] Re: Big cap HEI on 7747
> 
> 
> >I wasn't talking about the 4 wires from the module to the ecm. I 
> was 
> >talking about the two wires from the ignition pickup coil inside 
> the 
> >distributor to the module. If the wires are switched the timing 
> pickup is 
> >coming off the curved section of the waveform instead of the 
> vertical slope 
> >in the center. This can offset the timing by as much as 40 degress 
> and will 
> >vary greatly by engine rpm. (See the piggyback igintion module 
> discussion I 
> >started a couple of months ago.) The wires should be white and 
> green (at 
> >least off the pickup coil) I don't remember which is positive and 
> which is 
> >negative.
> >
> >  Also since you are obviously having problems and must have 
> extended the 
> > pickup coil wires to have a external module: If you need the 
> module more 
> > than 1.5" away (The length of  stock pickup coil wires) the 
> spliced in 
> > wires need to be twisted for noise reduction. (If you peel the 
> insulation 
> > off a piece of network cable you will get the idea)
> >
> >  Good luck!
> >
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