[Gmecm] TBI and EFE

Sat Dec 2 15:31:42 UTC 2006

 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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