Miniram Backfire Update II

[Bob]

Jason, what did you find when you checked the throttle position sensor? I
believe these sensors are basically a potentiometer and can wear producing
intermittent failures (i.e. the scratchy noise on a worn volume control). If
you haven't already done it, I would suggest checking it through it
operational range.

The throttle position sensor is the accelerator pump.

Bob

-----Original Message-----
From: owner-gmecm at diy-efi.org [mailto:owner-gmecm at diy-efi.org]On Behalf
Of JN
Sent: Monday, November 13, 2000 9:21 AM
To: gmecm at diy-efi.org; Romans, Mark; Walter Sherwin;
timsiford at hushmail.com
Subject: Miniram Backfire Update II


Good Morning,

    I have worked and worked this weekend to chase this problem burning over
12 chips in one day.  First I have basic question before I go any further.
Do you have to clear the ECM (disconnect the battery) every time you change
the chip?   Anyway, the only table GMEPro has for Acceleration fuel is:
AE fuel vs change in LV8
AE fuel vs coolant temp
AE fuel decay rate

I have been fooling with the first one.  I popped in the new 30 pound
injectors and set the constant to 33lbs for double and single fire modes.
At idle I was a little rich with 45 psi (vacuum line off) at the rail.
Block learns at about 110.  Pulse widths at 1.3 or so at 800 RPM.  Anyway,
the stock values for this table are:
LV8            Factor
0                .125
64              .125
128            .156
192            .203
256            .203

    I increased these numbers by 25%, 50% etc, until I just jammed the
maximum allowed (.99) in the first 3 slots (0,64,128) just to see what
happened.  Well that was too rich or course but at least it didn't backfire.
I backed them down to .750 and then I get the hesitation again.  I tried
values in between but when I cover the initial opening, it created a whole
other problem.  The problem is two fold.  First during initial opening, the
flat lean condition is covered but as you keep the throttle moving down, it
hits PE (50% TPS) and BIG TIME richness!  Motor runs like crap and black
smokes.  Second,  and this one is interesting.  Advance the throttle in say
4th to say 1.75 volts,  O2 volts stay up and no lean condition.  All of a
sudden, while keeping the throttle in a fixed position, the AE seems to
decay out and it goes way, way lean and backfires to beat hell.  Why?  Well
while in AE mode the ECM is yanking fuel out like crazy because its rich.
After the AE decays, the Block learn is like 108 and the INT climbs skyward
to try and add fuel and within a few seconds it gets enough in there to stop
the backfiring.  ????????

So it seems I need a table that is TPS related and not LV8 related.  Just
like this car needs and accelerator pump.  Does Tunercat have a table like
this?  I was also thinking of decaying the AE much faster so as to not
affect the fuel trims so drastically.  Any thoughts or suggestions?

Thanks,
Jason Norris


----- Original Message -----
From: <timsiford at hushmail.com>
To: "Walter Sherwin" <wsherwin at home.com>; "JN" <jwn at sgi.net>
Sent: Sunday, November 12, 2000 8:27 AM
Subject: Re: New Spreadsheet


> I absolutely agree.
>
> The only other idea that just got mentioned on the list (but I have also
> been thinking of) is changing the delta TPS that is needed to enter PE
mode.
>  What do you think Walt?
>
> Tim
>
> At Fri, 10 Nov 2000 17:31:24 -0800, "Walter Sherwin" <wsherwin at home.com>
> wrote:
>
> >
> >To me it looks like the throttle gets opened suddenly, the mixture falls
> >flat on its face, and she probably backfires as a result?  I'd guess
> >and say
> >that a whole bunch more initial tip-in AE fuel is needed.
> >
> >I'm not sure what you have at your disposal in your MAF cal,  but I
> >know
> >that in the MAP stuff I play with there are usually two components of
> >AE
> >fuel, each with their own set of tables and modifiers.  The first
component
> >is TPS based, and gets dumped in right away to cover the initial bog
> >hole.
> >The second part is MAP based and gets blended in as the TPS based stuff
> >decays away.
> >
> >I'd say you need much more "TPS" type AE fuel.
> >
> >The secondary ignition system is in good working condition right?
> >
> >Take Care;
> >Walt.
> >
> >
> >
> >----- Original Message -----
> >From: <timsiford at hushmail.com>
> >To: "JN" <jwn at sgi.net>
> >Cc: <wsherwin at home.com>
> >Sent: Friday, November 10, 2000 7:16 AM
> >Subject: Re: New Spreadsheet
> >
> >
> >> JN,
> >>
> >> This new spreadsheet is very interesting.  I have highlighted a few
> >sections
> >> in ORANGE.  These sections show you opening the throttle and the O2
> >volts
> >> going down to zero indicating a lean condition.  You said that you
> >have
> >> modified the pump shot.  Which table are you referring to?  Are you
> >using
> >> TunerCat?  What ECM definition file are you using with TunerCat?
> >If you
> >> want - you can always send your BIN to me and I'll take a quick look
> >at
> >> it.  I CC'd Walter on this one because he was interested in your first
> >XLS
> >> file.
> >>
> >> Tim
> >>
> >>
> >> At Fri, 10 Nov 2000 09:59:47 -0500, "JN" <jwn at sgi.net> wrote:
> >>
> >> >
> >> >
> >> >Tim,
> >> >
> >> >    Take a look at this new spread sheet. At the bottom there is
> >a
> >recording
> >> >where the backfire happened.  Get a load of the O2 volts.  Interesting
> >> >huh?
> >> >
> >> >Jason
> >> >
> >> >
> >

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org