Tim Burgess

I'm trying to get a '90 truck which came with a 5.7 & TBI system (1227747 ECM)
to work with a Chev ZZZ crate motor - which is a 350, as well, but has a
GM ZZZ (10134334) cam which has 0.480" lift, 235 degrees duration @ 0.050 &
336 degrees duration @ 0.004", for both int & exh. This is the first TBI
system I've worked on & so far I've tried just increasing the target idle
to 1000 rpm & also increasing the target idle to 1000 rpm & leaning out
(reducing) the two VE tables by 30%, but the thing does not want to run
unless I give it lots of base advance at the distributor. From the HC & CO
readings, it actually appeared to run lean, so I'm going to try & increase
the VE tables by 15% & see what happens. Any recommendations on what to
modify, or am I doomed in trying to get this thing to run with that cam in
there? The VE tables only go to 3200 rpm & the spark tables only go to
3600 rpm, so I'm wondering if this ECM is really capable of running this
motor......

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Tim

1992 Z28, 305 TPI 5 speed, 12.1 sec @ 114.7 mph

1984 Berlinetta 305 TPI Auto, 13.8 sec @ 99.7 mph

Brent

iTrader: (1)

VE #2 controls the fueling up to 6400rpms.

Sounds like ALOT of duration. The ZZ4 cam would be much easier to work with.

What MAP does it idle at?

Tim Burgess

It idles roughly @ between 2 - 3 volts (13.5" - 8" HG). It only idled @ 750 - 800 rpm, even though I had it set to run @ 1100 rpm & the IAC counts were stuck @ 145, so I think that the IAC is out of flow & maxed out, so I'll have to manually open the throttle plates a bit more. I'm going to try for an 800 rpm idle & add a bit of fuel @ idle on the next cut. What's async mode? (Displayed on the Auto Xray.) It was going in & out of async mode @ idle.

Thanks for the help......

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Tim

1992 Z28, 305 TPI 5 speed, 12.1 sec @ 114.7 mph

1984 Berlinetta 305 TPI Auto, 13.8 sec @ 99.7 mph

Brent

iTrader: (1)

13-8 in hg MAP or Vacuum? If you mean vacuum its gonna need major spark table work. Right now it's idling at 70KPA which is a moderately heavy load for a stock truck. Thus a bunch of timing is pulled out.

Definitely go to www.thirdgen.org/gmecm/ and www.thirdgen.org/diyefi/ and search for tbi programming 101, etc. There are hordes of good info there.


Autoxray? They don't show MAP in KPA do they? I highly recommend checking out the software in this link. https://www.thirdgen.org/messgboard/...ML/002113.html

It makes it one step more complicated when your scantool doesn't show MAP in KPA.


Async is a injector firing strategy. Here is a blurb I saved.
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Sync is when the injector(s) fire coinciding with a distributor reference pulse. Async is when the injector(s) fire at an 80Hz rate. This coincides with the ECM minor fuel loop code.

Sync is used 99% of the time. Async is used when the desired sync pulse is too short to be accurately metered. The pulse widths for min's, max's, switching between the two are all in the code (or data tbls).

Then there is the quasi-async pulsing. This is when both sync and async are taking place together. Such as pump shot.

This is how the '747 & '8746 handle it. Others may vary.

BobR.
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Grumpy

For openers get a early BBC TBI throttle body. Running the stock throttle body on that is going to be like breathing thru a straw. Look at the tuning.doc at the DIY EFI Site, it was all about tuning a 224 @ 050 TBI engine

Tim Burgess

Couldn't find the file in the FTP site index on diy-efi. Where is it located?

I converted the MAP readings from the Xray to "Hg (gauge) using a calibration chart I made up - it has MAP voltage to KPA & "Hg - from the shop manual - and also a column for "Hg (gauge) - which corresponds to actual "Hg @ my location (3000 ft.) at the various MAP voltage output levels. The voltages listed are from the Xray & the "Hg are what a gauge would read @ 3000 ft.

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Tim

1992 Z28, 305 TPI 5 speed, 12.1 sec @ 114.7 mph

1984 Berlinetta 305 TPI Auto, 13.8 sec @ 99.7 mph

Grumpy

Arrgh, try here
http://www.diy-efi.org/gmecm/papers/
Poke around, lots of related good stuff there