[Gmecm] Help with unusual BLM's

Tue Apr 4 03:38:23 UTC 2006

This may not be correct, but the few times I have had a jumping (or
dropping) tach, it has been an ignition module problem.   Its only been on
GM V6 motors with DIS, but have done it with both a  3.1 and a 3.8.
Replacing the module has solved my problem.    Just food for thought...

Scott
----- Original Message ----- 
From: <ahuxtable at sola.com.au>
To: <gmecm at diy-efi.org>
Sent: Monday, April 03, 2006 7:01 PM
Subject: RE: [Gmecm] Help with unusual BLM's

> Thanks for the extra info Dustin.
>
> The misfire is really intermittent.  Plug gaps were triple checked and
> the coil has also been replaced.
>
> Along with the misfire there is also a violent act of the tacho dropping
> down.  This leads me more to thing that it could be something like the
> coil/ignition module losing power (or the ECM altogether).  It's a sort
> of CBF factor as it's ok most of the time.
>
> On a slightly different note however - It seems to be *almost* perfect
> over the last few days while I've had the 10k resister in the ALDL
> connector (logging or not).  Maybe it is the ECM after all...Then again,
> it could be complete coincidence since the weather here has just taken a
> bit of a cold snap.
>
>
> Ahh, I love cars...
>
> Andrew
>
> -----Original Message-----
> From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On
> Behalf Of Dustin Lof
> Sent: Wednesday, 29 March 2006 10:49 AM
> To: gmecm at diy-efi.org
> Subject: RE: [Gmecm] Help with unusual BLM's
>
> Your misfire problem will cause low block learn
> numbers. Less than 128 the ecm is subrtracting fuel
> more than 128 it is adding fuel.
>
> Just because the cap rotor, wires etc. is all new does
> not necessarly mean it is good, what is the spark plug
> gap at every plug, how many kv is the coil able to
> produce, what is available at the wires. Invest in an
> adjustable spark tester, one that is marked in kv, and
> check each wire.  Set it to about 20,000 connect it to
> one wire, start the engine, make sure the spark is
> jumping the gap of the tester and not somewhere else,
> shut the engine off and move the tester to the next
> cylinder and repeat the process. also check the spark
> plug gaps, maybee one got smashed shut, or to .010
> when it should be .035, if one is .010 less than the
> rest it will idle like a top but under a load at light
> throttle it will misfire like crazy. especially a
> small 4 cylinder
>
> Dustin Lof
>
> --- ahuxtable at sola.com.au wrote:
>
> > Thanks for that Gene (and Steve - See further down)
> >
> > As for your problem Gene, that was some of the first
> > things I checked on
> > this engine because oddly enough, it has a misfire
> > problem.
> >
> > I changed all plugs, leads, Cap, Button ignition
> > module and ECM and it
> > still does it.  It's not all the time, generally
> > when hot and I rev over
> > 4k RPM.  It sorta sounds as if I'm hitting rev limit
> > but I'm not.
> >
> > Still trying to find the cause of that one (which is
> > also partly why I
> > hooked up the lappy)
> >
> > Steve, I get it now.  The BLM's being low is not
> > that it's physically
> > rich at that point, moreso that it is removing fuel
> > because it 'was'.
> > Makes so much more sense now that fuel is getting in
> > somewhere else (As
> > Dave mentioned). Will have to play some more.
> >
> > Thanks for your help guys!
> >
> > Andrew
> >
> > -----Original Message-----
> > From: gmecm-bounces at diy-efi.org
> > [mailto:gmecm-bounces at diy-efi.org] On
> > Behalf Of Randy & Gene
> > Sent: Tuesday, 28 March 2006 11:10 AM
> > To: gmecm at diy-efi.org
> > Subject: Re: [Gmecm] Help with unusual BLM's
> >
> >      Hi Andrew, today I solved a 3 year mystery as
> > to why my 1993
> > Pontiac
> > Sunbird with a 3.1 V6 did exactly what your engine
> > is doing. I had taken
> > it
> > to a dealer and Mr. Goodwrench charged me close to
> > $1300 Cdn and
> > couldn't
> > fix the problem in 13 hours. I took it to another
> > fellow who had worked
> > for
> > GM and he changed the upper and lower manifold
> > gaskets citing there was
> > a
> > vacuum leak..$500...and another emissions shop
> > charged me close to $200
> > for
> > telling me it had a vacuum leak near the back of the
> > engine because when
> > he
> > sprayed a liquid in that area the engine sped up a
> > bit......this car has
> > a
> > full body kit installed otherwise I would have towed
> > it to the wrecking
> > yard...anyway...I bought a 1992 Sunbird with the
> > same engine for
> > $350....bought a manual and laptop from E Bay and
> > proceeded to swap
> > parts
> > out...O2,EGR,TPS,MAP,ECU and even checked every mile
> > of cable harness
> > for
> > resistance...everything including injectors were
> > swapped, throttle
> > body.........nothing helped...then I decided to
> > start over with
> > basics....a
> > simple compression test was first.....pulled all of
> > the spark plug boots
> > first then took out the 3 front plugs and number one
> > from the
> > back....number
> > 3 was missing....or at least half of it was...part
> > stuck in the boot and
> > the
> > other in the head......compression was good on all
> > and when I supplied a
> > plug from my parts car the 3.1 lit up like it was
> > new..........you can't
> > imagine my joy........the only code I ever got was a
> > 45....rich O2...it
> > had
> > been replaced...a broken plug........make sure your
> > basic stuff is in
> > order
> > first and good luck.....Gene
> >
> > ----- Original Message ----- 
> > From: <ahuxtable at sola.com.au>
> > To: <gmecm at diy-efi.org>
> > Sent: Sunday, March 26, 2006 8:04 PM
> > Subject: [Gmecm] Help with unusual BLM's
> >
> >
> > Hi all.  I've been trying to work out why for some
> > reason my car has
> > been running rich.  I just always assumed that it
> > was the O2 sensor
> > playing up - Until yesterday that is...
> >
> > I logged some data and the highest BLM I saw was
> > 120.  Most being around
> > 115 so my engine is running fairly rich. So, the
> > computer thinks that
> > it's running rich and it actually is = not O2
> > sensor.  Next I thought it
> > might be the CTS or MAT sensors but logging them,
> > it's all normal.  CTS
> > reports running temp of ~85DegC (184DegF) and MAT is
> > reading as expected
> > too.
> >
> > What else could be forcing the engine to run rich?
> >
> > Thanks
> > Andrew
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