[Gmecm] TBI and EFE

Sun Dec 3 17:04:42 UTC 2006

Have you checked for a vacuum leak, how old is the
throttle body gskt.
It sounds like a vacuum leak which would cause the
idle
problem and the smell out the exhaust.
Have you check any engine data?
Terry
--- Jared Ryan <jryan at caminofx.org> wrote:

> OK, here is what happened, from the beginning.  The
> exact sequence is  
> important.
> 
> I discovered the busted fuel injector O-ring that
> was the cause of the  
> too-rich problems I had been chasing since April. 
> (The lower O-ring on  
> the left-side fuel injector was mashed, letting fuel
> under pressure  
> down into the barrel).  I replaced that, and the
> engine ran perfectly.   
> It idled very slow (at the target idle speed
> programmed into the ANLU  
> chip, about 550 RPM) but very smooth.  Drivability
> was excellent.
> 
> Then, after a few days, I noticed it would sometimes
> idle faster than  
> it had been.  It was still smooth, but about 1000
> RPM.  It would flare  
> up when I shifted out of drive into Park or Neutral
> and not come down  
> as fast as it had.
> 
> All of the preceding is with the daytime highs in
> the mid-70s and lows  
> in the 60s.  Warm weather.
> 
> Well, I wondered if the IAC valve might be sticking.
>  I took out the  
> valve and cleaned it.  It wasn't very dirty, hardly
> any carbon, but I  
> sprayed Gum-Out on it and also sprayed it in the
> passage on the  
> throttle body.  I put the IAC valve back in.  I
> didn't drive it after  
> doing this.  Later that night, the arctic blast came
> through (well, for  
> Houston, TX; lows in the low 30s, highs in the 50s
> at the most).  Since  
> the day I cleaned the IAC valve, it has not idled
> well.  It acts like  
> it might be too rich, and it won't idle slower than
> about 700 RPM.
> 
> I've done the IAC reset, grounding the diagnostic
> pin to force the ECM  
> to extend the IAC plunger fully, and the slowest I
> can get it to idle  
> with the IAC valve unplugged is about 600, and it's
> rough.  It's rough  
> with the IAC valve connected, both cold and hot, and
> it idles faster in  
> Park or Neutral than in Drive.  In Drive it's right
> about at the target  
> idle speed, but still rough, but it won't idle down
> when taken out of  
> gear.
> 
> By "rough" I mean a bad smell from the tailpipes,
> car shaking, surging,  
> having to really hold my foot on the brake to keep
> it still at a red  
> light due to the surging.
> 
> So could I have damaged the IAC valve with the
> Gum-Out?
> 
> I broke the scientific method and changed two things
> at once (OK, so I  
> can't control the weather), and now I don't know if
> I have an acting-up  
> IAC valve, a fuel leak, or if it just doesn't like
> the chilled air.
> 
> The pintle of the IAC valve looks like it could
> possibly wear over time  
> and not seal against the throttle body, with or
> without carbon buildup.
> 
>   ---> Jared Ryan <---
> jryan at caminofx.org | http://www.caminofx.org
> 
> On Dec 2, 2006, at 9:31 AM,
> davesnothereman at netscape.net wrote:
> 
> >
> >  The TBI trucks w/ 7747 expect intake air temp
> around 90 deg F or  
> > greater.  The intake air heater is calibrated for
> this temp.  Most  
> > folks with older tbi trucks don't seem to know /
> care.  In an area  
> > where 10 year old trucks are rotted out due to
> salt, snow, and  
> > humidity it's not uncommon to see the few left
> running with no heat  
> > stove left on the manifold and no tube connected
> to the snorkel.
> >
> > The question you need to answer is "How good is
> good enough?"  I have  
> > open element air cleaners on my truck which used
> to run in temps well  
> > below zero without causing any issues which I can
> remember.
> >
> > The old carby 2.8 S10's had an electrically heated
> grid under the carb  
> > to prevent icing.  A 15-20 mile drive at highway
> speed at 50 deg temps  
> > could cause enough restriction to bring vehicle
> speed below 30 mph if  
> > the heater was inoperative.
> >
> > Zaphod
> >
> > -----Original Message-----
> > From: jryan at caminofx.org
> > To: gmecm at diy-efi.org
> > Sent: Fri, 1 Dec 2006 1:28 PM
> > Subject: [Gmecm] TBI and EFE
> >
> >
> > Do TBI engines typically need the EFE ThermAC
> setup to run smoothly in  
> > cold weather?
> >
> > I have an El Camino that has a heat stove on the
> passenger side, but I  
> > recently changed to a Camaro air cleaner that puts
> the snorkel on the  
> > driver side (this fits MUCH better with my Camaro
> serpentine belt  
> > setup). I will need to put a heat stove on the
> left-side exhaust  
> > manifold in order to use the ThermAC.
> >
> > I assume it wouldn't be there (on '88-'92 TBI
> F-bodies) if it didn't  
> > help. It made a BIG difference in cold-weather
> running when I had the  
> > QuadraJet carburetor, and TBI is also a
> wet-manifold system.
> >
> > The reason I ask is that the temperature has
> dropped into the 30s F,  
> > which is cold for Houston, TX, and the idle is a
> little rough.  
> > However, the cold weather moved in on the same day
> I removed and  
> > cleaned the IAC valve. It is entirely possible I
> just need to reset  
> > the minimum-air setting and the idle will smooth
> out.
> >
> > Off-idle performance has been perfect, just a
> little bit of a rough  
> > idle since it turned cold. I will do the IAC reset
> this afternoon, but  
> > I still wonder if making the ThermAC operational
> will help a lot.
> >
> > I notice that the TBI intake manifolds no longer
> have the exhaust  
> > crossover under the carburetor/throttle body
> mounting pad.
> >
> > I hear a lot about ThermAC, like "It only closes
> in *really* cold  
> > weather. When I had it set up properly with the
> QuadraJet, it would  
> > close at least a little bit on sunny warm spring
> days! It would open  
> > quickly, but it didn't only work on very cold
> days, for sure. On very  
> > cold days, like what we have here, it often
> wouldn't ever open  
> > completely.
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> 
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