Getting wet feet....junkyard TBI

[Bruce]

From: <WEG1192 at aol.com>
> In a message dated 5/29/2001 11:04:29 AM Eastern Daylight Time,
> John.Janssen at SomervillePackaging.com writes:

> <<  Am I overanalyzing things? What you guys are working at doing is
>  tuning your ECMS for MAX performance correct? but in my case just hooking
>  everything up (closed loop - will do timing as well) should work fine
>  correct? Will I have to do any programming?
>  One part I need yet - the 5 prong chip that I have to swap out the GM HEI
>  distributor to run closed loop timing - anyone know an application that I
>  can order this from? >>
> John,

> For starters, get the ignition module mentioned recently and wire it to
> trigger from the pickup coil in your distributor. Then disable the
mechanical
> advance in your Jeep distributor by removing the springs and weights, but
> reinstall the springs to hold the timing steady.

Disable advance and use springs to hold it steady.
Ugh, OK, and I'll turn off my PC by using start.

Others on this list advocate
> tack welding the rotor mount to the distributor shaft so that there is no
> slop, but I have just put the springs back in and have had no problems.
The
> only time I can think you would have any slop is when decelerating hard in
> gear, and in this case the rotor mount would have to outrun the
distributor
> shaft with the spring tension fighting this motion. Again, I think its not
a
> problem.

Rotor mount outrunning the distributor shaft.
Similiar to Doc out running Sleepy.

 Disabling the vacuum advance is done by simply leaving the rubber
> vacuum line off and plugging the line.

Whew, a trinket.

> For spark tuning on a non-GM vehicle, I start by getting a copy of the
> factory manual showing the vacuum and mechanical advance curves. I then
> program Excel spreadsheets with the vacuum portion alone, the RPM portion
> alone, the static timing alone, and the fourth sheet being the sum of the
> first three. This sum sheet will be a table with MAP (same as inverse of
> vacuum) as the x axis, RPM as the Y axis, and the spark value as the entry
in
> the table. This is a 3 dimensional table since you have two independent
> variables. This table is then programmed into the chip as a starting point
> for say a Jeep. If you want to tweak it after that, its up to you, but the
> spark table fine tuning is where the hidden power lies, that and getting
the
> WOT fueling right.

Yep, and if you want to ignore the timing during overrun, that fits in here
to.   But if the rotor mount is out running the distributor shaft then ya
just gotta call Doc and Sleepy for an instant replay.   If your going to use
the distributors mech/vac settings then just leave the ignition alone other
then using it for a reference pulse.
   No thanks,

By the way, there is no closed loop spark tuning. This
> part of tuning is feed forward only.

feed forward, is probably the uncontrolled part of the timing curve
controlled by the rotor mount doing it's thing with the distributor shaft.

What you program stays that way even if
> the engine runs crappy. The exception to this is the knock sensor system,
but
> this only retards timing. It doesnt add timing when a timing increase
could
> probably help.

Whew, been worrin about the retard adding timing,  maybe the rotor mount,
never mind...

 The only feedback for spark tuning is in the seat of your
> pants (or an accelerometer for performance tuning).

Whew, we definetely don't want to measure anything, and calibrated
buttometers are a dime a dozen, goes with guessing about the rotor mount
slippage.

> As for fuel adjustments, start by getting a scantool and seeing where your
> BLMs are at hiway cruising speeds on a flat road. Then adjust (ie
reprogram)
> the Base Pulse Width constant to get your BLMs around 124-128. Then check
the
> BPW constant to make sure its not too far off from what it should be.

Wow, that saves all that work with looking at the VE table, and trying to
actually get it right.

What I
> mean by that is the BPW constant is calculated from the injector flowrate,
> the engine cubic inches, and a units conversion constant (see Tunercats
help
> file for the 1227747 ECM at www.Tunercat.com). Since the cubic inches
ain't
> gonna change (258 ci right) and the conversion constant is a constant, the
> only variable in the BPW constant is the injector flowrate.

When at tunercat.com, see if the link to the ecmguy is still there and go to
Bruce's page, and you'll get some good 747 info..   Might try getting a copy
of tuning.doc at the DIY_EFI FTP.

 The 4.3L
> injectors were rated for 45 #/hr based on what I've learned and found with
> actual injectors. However, some flow more and some less. So if the BPW
that
> gets you a good BLM is back calculated and the injector constant is more
than
> 10% away from the 45 #/hr number, then you either don't have 45#/hr
injectors
> or your engine has a problem (in my case, my engine was worn out causing a
> very high injector size to be calculated; what I think was wrong was all
the
> blowby I had required more gas than a fresh 360 engine would require;
> therefore I needed a very high BPW to make my Jeep run; 139 should have
done
> it whereas my Jeep with AMC 360 needed a 170 BPW constant to run well with
61
> #/hr injectors).
>
> Now assuming that the BPW that gets you a decent BLM range also yields a
> reasonable flowrate for the injectors you are supposed to have (the color
> bands on the top of the injectors tell you the flowrate), you now have two
> choices. You can tune the hell out of it like most on this list insist has
to
> be done, or you can drive it awhile and let the GM closed loop logic tune
the
> system for you. I have found that on a stock engine for a daily driver,
that
> I don't have to do much of anything at this point except watch my BLMs
with a
> scantool for a few weeks just to make sure the values aren't too far off.
> What the closed loop logic does is maintain a 14.7 AFR at all times by
nature
> of the O2 sensor design, and it adjusts the fuel tables via the BLM (block
> learn mode). So no matter what the fuel table says, the BLM will steer the
> system towards an AFR of 14.7. The exception to this rule is at WOT when
the
> closed loop logic is turned off. In this case, the logic looks at the
highest
> BLM cell, which is assumed to yield a 14.7 AFR at WOT, and recalculates
the
> AFR based on a WOT RPM vs. AFR table. For performance gurus, the WOT RPM
vs.
> AFR table and the spark table are where all their efforts go. It takes a
real
> good tuner and probably a dyno ( or good spark plug reader) to fine tune
> these tables for performance. But again, I have found that for a daily
driver
> where MPG is more important than MPH, the closed loop logic will take care
of
> everything. I don't plan on racing my Jeep Grand Wagoneer. I just let the
GM
> stock WOT settings govern here.
>
> In summary, this is the basic start for reprogramming a GM EPROM just to
get
> the system running well. To get it running perfect, you have to go much
> further. Also, keep in mind that this is a simplified explanation and not
all
> exceptions to the rules are covered here. JW

Running or running well?.
I'm still not clear on the rotor mount outrunning the distributor shaft.
Oh, and plug reading is only for WOT?.
And why not get WOT right?,  it doesn't hurt anything to do it right.
Gads,
Please don't respond, I'll find the meaning of rotor mount out running
distributor shaft on my own
Bruce



----------------------------------------------------------------------------
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