[Gmecm] TBI 350

[Jared Ryan]

I have a problem that I am at my wits' end about.  I've tried to research it and
experiment and I just can't figure it out.

I have a Chevrolet El Camino that used to have an LG4 305 (5.0L) V-8 with 8.6:1
static compression ratio when new (though this engine had seen better days; it
ran smoothly but burned oil).  I converted that 305 from a QuadraJet carburetor
to TBI with a stock intake manifold and throttle body from an F-body.  The ECM
is a 1228746.  I had a programmer make a custom chip for the LG4 305, and it
ran very well on 87-octane gasoline.

Recently, I swapped engines.  The new one is a brand-new GM 350 with a Crane
Cams 2032 roller camshaft and high-swirl TBI heads.  The static compression
ratio is 9.2:1, and the dynamic compression ratio with that camshaft should be
about 8.7:1.  I changed the fuel injectors from the 40 lb./hr. units to 55
lb./hr. units like a 350-equipped half-ton pickup truck would have.

I changed the ESC module and knock sensor when the new 350 went in.  They are
brand-new GM units specified for a 350.

>From the beginning, I have had a pinging problem.  It would run fine on
93-octane gasoline.  I would really like it to run on 87-octane.  I got the
programmer who made the chip I used for the 305 to make a new one for the 350. 
It was better, but it still pinged on 87-octane.  He made another revision, and
this time I logged data using a notebook PC and WinALDL.  It still pinged some,
and after reviewing more data that I logged, the programmer said it looked like
it was running too lean, and he suggested changing to an adjustable fuel
pressure regulator and increasing the pressure a little bit.

That is when the problem *really* got bad.

I installed a JET adjustable FPR.  I have watched while the engine is running
with the air cleaner housing removed so the injector pod is not shrouded, and
there are no leaks.  The problem at this stage is that even with the screw on
the AFPR turned to reduce the pressure as far as it will go (should be 10PSI),
the engine just does not run well at idle.  It puts out black smoke and runs
very rough, and sometimes surges.  The car accelerates fine, and there is no
smoke at mid-range to high engine speeds, but coming away from a new green
light, it can take several seconds for black smoke to stop coming out of the
tailpipes.  It looks like the engine is really loading up with fuel.  Even
though it runs very, very rich at idle, the engine does still ping some,
especially on light acceleration.  There is very little pinging under highway
cruising, but a lot from off-idle on up during light to moderate acceleration.

So I really don't understand what happened.  It idled *perfectly* with the
stock who-knows-how-old non-adjustable FPR that came with the throttle body
(that was salvaged off a wrecked F-body).  Doing the IAC reset and minimum idle
speed adjustment does not help.  The TPS on this throttle body is
non-adjustable.  The base ignition timing is set at 0.

To make things even worse, for three days in a row, I have tried to log a lot
of data with WinALDL, and the program has shut down, apparently causing a GPF
(in Windows 98), so I don't have hard data on the current state of things.

So there are only a few things I can imagine.  These are hypothoses I formed,
and feel free to disprove them.  I need ideas.

1. The stock FPR was worn-out and weak, or never correct from the factory, and
set a much lower fuel pressure than really needed, in which case the correct
fix would be to simply get a new stock FPR.

2. The adjustable FPR gives the pressure that this setup really needs, and the
chip is not programmed for the higher pressure.  The only situation in which I
can imagine this is that there is a certain minimum and maximum duty cycle for
the injectors, so the ECM cannot reduce the fuel to the point that it is lean
enough at idle.

3. This setup might really need a GM vacuum-adjustable regulator, so it can run
a low pressure at idle and a higher pressure at higher engine speeds.

4. I have some mismatch of the FPR and the spring that is installed with it.

Does anyone have some insight, and have some ideas for a systematic way to
figure this out without throwing money at it?  I want to learn.  I enjoy
tinkering with things.  I just really need to figure this out because gas
mileage has dropped from an average of 19.2MPG to 15.5MPG since installing the
adjustable FPR.

One interesting thing I noticed is that after installing the JET adjustable
FPR, the engine started MUCH faster than with the old stock regulator, even
though it doesn't idle smoothly.  It still cranks and starts very, very fast,
which makes me wonder if hypothesis #1 may be close to the truth.

I'm open to any ideas, discussion, arguments, etc.  Thanks!

--
 - Jared Ryan [jryan at caminofx.org]