[Gmecm] TBI 350

[DV Fagan]

Jared,
What is the fuel pressure at idle?
What is the fuel pressure at WOT?
Until you measure these numbers with a guage, you and
the guy burning your chips are guessing.  This can
take a while.
Dennis

p.s. I use the GMPP vacuum modulated regulator.

--- Jared Ryan <jryan at caminofx.org> wrote:

> 
> 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]
> 
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