[Gmecm] TBI and EFE
jryan at caminofx.org
jryan
Tue Dec 5 14:19:17 UTC 2006
Today was another cold morning (30 F) and it ran well. (I know cold
in Houston is not the same as in other parts of the country.
Fortunately, when it freezes here, there is almost never
precipitation. Right now it's 38 with a dewpoint of 29, relative
humidity 70%, which is more humid than it has been.)
I haven't been letting it idle and warm up at all in the mornings. I
just start it and go. It comes up to operating temperature much
faster in normal driving than idling, anyway. Even so, with the iron
block and heads, I'm on the freeway before it comes up to thermostat
temperature.
This morning I noticed that when I parked at work and moved the
gearshift from OD to P, the idle speed stayed high, about 1000 RPM. I
moved the lever back to OD, then back to P, and it settled down to the
speed set in the PROM. Could this be a misadjusted Park/Neutral
switch? I have seen this on occasion on this car, and it seems like
every time, putting it back in gear and then back in park makes it
settle down.
I'm actually very surprised at how well the 1989 9C1 PROM works,
considering I'm using full-size pickup injectors, which to my
understanding are 61 lb./hr. while the 9C1's might have been 68
lb./hr. When there are no fuel leaks at the throttle body (and I hope
that is cured for good), the drivability is overall excellent.
Quoting Rick McLeod <dunvegan at sbcglobal.net>:
> J, good news. It was kinda as suspected, something amis from the
> work being done. Since you have an IAT sensor, it appears to be
> compensating adaqately, goodness.
>
> I'd suspect a minor tweak on mechanical min idle will cure the hunt,
> you may have a sensitive setup that it's between counts for correct
> idle on the IAC and it's trying to settle, which mechanical min
> idle setting might correct, try just a little bit backed off of min
> idle to see if that cures it, or maybe add just the slightest bit.
>
> Good luck, stay warm
>
>
> ----- Original Message ----
> From: "jryan at caminofx.org" <jryan at caminofx.org>
> To: gmecm at diy-efi.org
> Sent: Monday, December 4, 2006 2:49:06 PM
> Subject: Re: [Gmecm] TBI and EFE
>
>
> Well, once again, apparently I fail.
>
> It turns out that the injector cover gasket was leaking. I took a
> look at it with the air cleaner lid off, and I noticed that the
> left-side throttle plate was wet, but the right-side plate was dry,
> and the part of the gasket on the left side was glistening. I have a
> dual-plane intake manifold (Edelbrock 3704), so one-half of the
> cylinders were getting a very rich mixture, while one-half were
> getting a lean mixture, apparently.
>
> So I went to the parts store and got a TBI gasket kit, and I replaced
> everything I could without taking the throttle body off the manifold
> (no reason to suspect the base gasket). I changed the injector
> O-rings, injector cover gasket, IAC valve gasket, etc.
>
> I don't know if this is a best practice but I used petroleum jelly on
> the injector O-rings to try to protect them during installation, as I
> have mashed a lower O-ring in the past by accident, causing a
> super-rich running condition.
>
> At any rate, I started it up and it ran fine, much smoother. After it
> warmed up, I had to do the whole minimum-air reset procedure, because
> it idled much too fast (due to the mixture being much leaner).
>
> For what it's worth, I actually do have an IAT sensor. I have a
> strange hodgepodge of components. The serpentine belt system, 1228746
> ECM and air cleaner are all from a Camaro. The intake fits under the
> hood of the El Camino nicely and looks like it belongs there.
>
> The other thing the 1228746 has that the '747 seems not to is a
> control for the vapor canister solenoid. Cars seemed to have a
> solenoid, while pickups did not seem to. This may also play into your
> thinking - truck owners may not be as sensitive to small variations as
> car owners.
>
> It was 30 degrees F when I started out this morning, and it ran fine -
> no stumble, no rough idling, no black smoke (lotsa white stuff out the
> pipes though!), so apparently it is not critical to preheat the intake
> air. With the Camaro air cleaner, duct and scoop, it's getting cold
> air from right behind the driver-side headlight, not heated by the
> engine compartment or radiator.
>
> There is one small issue left, and this may be because I'm using the
> ANLU (9C1 350) PROM with a camshaft a little bigger than it was made
> for. It idles very nicely at all times, very smooth, very close to
> the target speed set in the PROM, but it does something a little funny
> after I have been driving a while and I shift from OD/D to P. The
> idle jumps up slightly due to the decreased load, then the tachometer
> needle does kind of a pendulum thing, going up and down about 100 RPM
> total. After about five or six cycles, it stabilizes and stays at the
> set idle speed. It only does this when shifting from OD/D to P, not
> from P to OD/D.
>
> It acts like it's chasing the target idle speed, but it's such a small
> variation that many people might not notice it happening. I wonder if
> I should get a scantool and watch the IAC counts, and try fine-tuning
> the throttle plate opening based on the IAC counts.
>
> Thanks to everyone for all the advice. I am enjoying learning how
> this system is really supposed to work, and starting to really enjoy
> driving the car.
>
> Quoting Carl Rumberger <perfdyn at cwnet.com>:
>
>> I have read a number of replies to your cold drivability issues that
>> address throttle body icing. Though icing may indeed be a real
>> concern, especially from a safety standpoint and may contribute to
>> your cold run issues, it is at least equally possible the problem is
>> related to the "747" TBI system not having any Intake Air Temp.
>> (can you say air density) sensing.
>>
>> GM choose not to use IAT sensors in Pick-Up applications where the
>> typical owner wasn't likely to be very picky about slight running
>> issues . . . combined with the fact that in these engines the intake
>> and coolant temperatures closely follow each other under most
>> operating conditions (a coolant temp. sensor and single temp. table
>> could substitute for both sensors and tables).
>>
>> The truth is these engines can be sensitive to cold intake air /
>> lean A/F ratios. Of course the A/F: vs. Coolant Temp. table can be
>> adjusted richer under cold operation but then you would likely run
>> into slightly rich cold running when the weather turns warm. And yes
>> a TAC system will tend to minimize intake air temp.(air density)
>> variations. I have had the misfortune of tuning a TBI "747"
>> conversion that the customer choose an Edelbrock Performer RPM Air
>> Gap intake manifold combined with a cold air intake system on a
>> Chev. 350 with a mild cam. Trying to get the fueling correct was
>> frustrating not only because of the cold air system but with this
>> intake manifold the changes in IAT no longer even remotely followed
>> the changes to coolant temp.
>>
>> It is also interesting to note that in those applications where GM
>> thought the owners were more likely to be picky (Caprice / F body)
>> they used a IAT sensor and the 1228746 ECU.
>>
>>
>> ----- Original Message ----- From: Jared Ryan <jryan at caminofx.org>
>> To: gmecm at diy-efi.org
>> Sent: Friday, December 1, 2006 12:28:24 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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