Re: teknickle difikulty

["Walter Sherwin" <wsherwin@home.com>]

Hi Carl,

Distributors of that vintage had more goofy problems (that would affect
normal operation) than you can possibly imagine, especially once they had
accumulated a few miles.  Take a good look at the reluctor assembly on the
mainshaft.  The magnets had a tendency to either swell or crack, and the
reluctor housing has been known to jump/slip on the mainshaft.  Holding the
distributor assembly in your hands, you should be able to feel 8 very
distinct "tugs" as you rotate the shaft with light effort.  Forget about
swapping internal parts, the cheaper solution is a complete new assembly
from GM (1103952).   Below is a little blurb that I sometimes share with
folks who are faced with diagnosing suspect distributors.  It's pretty much
applicable to all the popular SBC and BBC GM HEI/EST external coil ECM/PCM
setups.  Internal cross-over was a big problem too.  Here goes........

_____________________________________
10) Try disconnecting the EST Bypass line (same thing as the set timing
connector that you disconnect when setting the base ignition timing) and
driving the truck. If the situation seems improved, then you definitely
have either a distributor problem or a problem with some portion of your
EST system wiring.  If the operation does not change, then you also have
a problem.

11) Lastly, my favourite pet peev???.?.get on your distributor?s case and
make it prove to you that it is ?Okay?. Warm-up your engine. With a
timing light connected to plug wire #1, watch the timing mark on your
harmonic balancer with the engine at idle speed. Does the mark seem
relatively steady, give or take a few degrees? If it appears that pulses
from your timing light drop-out occasionally, or if the mark is wandering
wildly all over the place, then there is definitely something wrong with
your distributor. I?ve seen distributors that intermittently jump 30-90
degrees out of phase, at or just off idle, that worked ?okay? most of the
time on the road. However, in those same vehicles all of the driveability
concerns were 100% resolved by installing a known good distributor. What?s
a known good distributor? It?s a distributor that has proven to work well
in a real world truck application. I have one that I guard under lock & key
in my work bench. If it works okay in the subject vehicle, then I know
enough to go buy a new distributor assembly. This test has not been wrong
to date, and the recent service replacement distributor assemblies that I
have examined have generally proven to have been adequate. Next, disconnect
the EST BYPASS connector to force the control system into backup ignition
timing mode. Effectively, this gives autonomous control of the ignition
timing to the distributor module, and bypasses the entire EST feature of the
PCM. Again, watch the timing mark on the balancer. With a stock SS chip,
the timing mark should appear steady at around 4 degrees BTDC (yours may
differ, depending upon the chip & settings you are running). Now, with your
other hand, slowly raise the engine idle speed towards 2000 RPM. The timing
mark should hold steady, plus or minus a couple of degrees to account for
cam chain slack, and then there should be an abrupt shift of 6 degrees more
advance (kinda like someone threw a switch). This is the backup timing
feature of the distributor module kicking in, and is completely normal and
desirable. What you want to note is the RPM at which this shift occurred.
If well before 2000 RPM (typically 1600 RPM), and if the previous tests were
passed, then your distributor is most likely okay. If the shift was
nearer 2000 RPM, or yeeeeee gads, past 2000 RPM then your distributor is
most likely FUBAR despite the fact that the previous tests may or may not
have passed. If your distributor is FUBAR, you can gamble with replacing
select internal components such as the mainshaft/pickup, but see earlier
comments relative to complete assembly replacement.
_____________________________________







-----Original Message-----
From: Carl Summers <InTech@writeme.com>
To: gmecm@diy-efi.org <gmecm@diy-efi.org>
Date: Friday, August 18, 2000 3:57 AM
Subject: RE: teknickle difikulty


>Hi Shannen,
>    Verified the 10 degree jump the module provides at ~1600rpm with wire
>unplugged.....Locked e-brake and loaded throttle with and without the wire
>plugged and diacom was accurate with the timing light....This is why I
>brought up this question....I don't generally do diagnostic stuff so
thought
>some of you guys might have seen it and know why....As soon as I get the
>vacuum leak fixed(next week) I'll delve into it a little deeper....Tried
for
>that 80+ million yesterday in the CA lottery....didn't get it...crap,
>shoulda worked on this truck yesterday.  :)
>-Carl Summers
>
>
>
>-----Original Message-----
>From: owner-gmecm@diy-efi.org [mailto:owner-gmecm@diy-efi.org]On Behalf
>Of Shannen Durphey
>Sent: Friday, August 18, 2000 3:27 AM
>To: gmecm@diy-efi.org
>Subject: Re: teknickle difikulty
>
>
>Somewhere around 1800-2200 rpm the module will advance timing if it's
>not getting 5V from the ecm.  It's very sudden.  Disconnect 5V line,
>start at 800, bring rpm up.  Watch for timing to jump.
>
>Timing matching with EST unplugged is a coincidence.  Prolly pretty
>rare, too.  You might want to buy a lottery ticket since you're
>beating the odds today.
>
>With the EST disconnected  I'd bet it wouldn't take much to find an
>rpm/vacuum where Diacom and the timing light don't agree, if you were
>trying.
>
>Shannen
>Carl Summers wrote:
>>
>> Hi All,
>>      Working on a 94 Chev Pu here with Blower and TBI, 7427 4l60E....has
>> been running well for about 4 years...Runs really poor now...I start with
>> the basics and check timing and fuel pressure....fuel pressure is good
but
>> timing is 22degrees with est plug disconnected(should be 0)....so I
>attempt
>> to move it back and it doesn't like it...dies every time....I notice on
>the
>> diacom that the IAC counts down to 0 AND the diacom shows 22 degrees
>advance
>> with the EST unplugged....hmmmm....unhook the IAC motor and hook up my
IAC
>> tester/driver and close the IAC completely and engine still idles at
>> 800.....anyway bottom line on the iac stuff is I have a vacuum leak
>between
>> the blower and the intake manifold...My question is: Have any of you seen
>a
>> spot in the code that increases timing back to what is in the table if
IAC
>> will not lower the rpm enough???? Kinda seems backwards....I was thinking
>I
>> had a bad ecm at first since I had an IAC code, EST code and some
>> others....The timing with and without the EST wire plugged in always
>matches
>> what the diacom says so seems as if all is well with the ECM....Oh well
>just
>> checking with Y'all if you have seen this before....ttyl
>> -Calr Summers
>>
>
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