[Diy_efi] rich/lean and O2.

[mbelloli at speedymotorsports.com]

Roger,
     What are the BLM (Block Learn) and INT (Block Integrator) readings
when cold and then again once warmed up?  If it hesitates cold and
then seems to be better warm - sounds to me like you are running too
lean.  Once in closed loop The BLM will tell you whether the computer
is trying to compensate.  A lot can be done with the fuel pressure on
the GM TBI.  1/2 either way can make a very big difference.  stock
setting is 12psi and it is absolutely critical.  Any deviation and
foget everything else.  The computer cannot compensate for it.  The
window that it works well is on about 1/4 lb either way from 12 psi. 
Do you have the stock cam that came with the engine that had the tbi
on it?  Any changes in CAM with throw everything way off.  You'll
have to make a chip with a new fuel map.  Also what kind of MAP
readings are you getting?  Is it a very steady reading?  You know a
good thing to do if you can is get a CO reading at the tailpipe and
use that to see if your o2 readings are making sense.  a good running
engine at 2500rpm should go to about .5% CO before the Catalytic, and
the air injection off.  So if the O2 is crossing rapidly, and your
reading is much lower, or higher something is really wrong.
     I have a 350 chevrolet with a 89 TBI off a Chevrolet pickup in my
1970 Toyota Landcruiser.  It runs great now, but took a lot of
playing with the fuel map in the computer after I got everything else
correct.  The computer works great when you have everything on the
money.  But when the fuel trim map is off, the computer just doesn't
have the ability to correct for it.  At least that has been my
experience.

Marcello







> Have a problem I just can't get a handle on! Just installed 5.7L
> TBinjected chevy into my Cherokee and can't get the engine to run "closed
> loop". O2 sensor appears ok, but output at idle is .800+ volts, steady,
> and rapidly drops to .o25v, steady, above idle. I'm experiencing "lean
> stumble" until engine is completely warmed up. My O2 readings are the same
> at 140* engine temp as well as at 195* temp. My temp sensor (CTS) reads 1v
> at 190*. My fuel pressure holds steady across the rpm test range (625rpm
> to 2000rpm).
> My throttle position sensor reads .65 at idle and 4.8v at WOT. I can drive
> the O2 reading up from .025 to .8+ by injecting propane into the TB, and
> can get the .8+ reading at idle to drop to.45v by pulling the pwr brake
> booster hose loose. The O2 signal from the ECM is .39v with the O2 sensor
> disconnected. The ECM and PROM are new and appropriate for the application
> (entirely stock).
>
> What have I overlooked? Any thoughts would be appreciated.
>
> Roger_______________________________________________
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> diy_efi at diy-efi.org
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>

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