Coolant bypass
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Joined: Feb 2001
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From: Lenhartsville, PA
Coolant bypass
Do I have to hook up coolant lines to my throttle body? I know a lot of people don't, but doesn't it have something to do with the EGR? I noticed there are passages all the way through the plenum into the runners, and into the intake.
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Joined: Dec 2000
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From: Philadelphia, PA USA
Car: 1989 Firebird Formula
Engine: 350
Transmission: 700R4
You don't need to have the coolant line run through the plenum. As far as I know it doesn't effect the EGR. GM did this so the throttle wouldn't freeze open or shut in extremely cold weather. Most people bypass this so the throttle body will stay cool and not heat the air coming in up.
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Run the line from the intake manifold into your heater control valve or into the heater, however your car is setup. If you are just bypassing it, you can just put a splice in the line. I would just replace the hose, cheap stuff. Probably costs less than the splice.
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Joined: Jul 1999
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From: The Bone Yard
Car: Death Mobile
Engine: 666 c.i.
Actually, a TB bypass DOES affect the EGR, but not the way most people think about. If the MAT detects a temperature below +5*C (+44*F), it will disable the EGR's functioning. This will result in decreased gas mileage and an incorrect calculation of the injector pulse width as the GM "MAT Delta Multiplier Inverse Tables" were defined with the idea that coolant would flow through the TB and heat up the plenum.
When the ECM sees a large difference between the MAT and CTS, it thinks the engine has just been started and still warming up. It therefore adds more fuel to help with the "warm up".
This is not much of a concern if you live in a hot climate, but if you live in a climate where the temperature can fall below 32*F, this is a concern.
The good news is, I have discovered where these tables are and how to correct the eprom's calibration so it will calculate the correct injector pulse width if you live in a colder climate. I now get gas mileage that meets and exceeds my summer gas mileage and so far, no matter what the temperature gets down too, I get a good "correction" factor for the injector pulse width.
Go to the PROM Board and read my post about "MAT correction" and it tells you how to modify the calibration tables.
When the ECM sees a large difference between the MAT and CTS, it thinks the engine has just been started and still warming up. It therefore adds more fuel to help with the "warm up".
This is not much of a concern if you live in a hot climate, but if you live in a climate where the temperature can fall below 32*F, this is a concern.
The good news is, I have discovered where these tables are and how to correct the eprom's calibration so it will calculate the correct injector pulse width if you live in a colder climate. I now get gas mileage that meets and exceeds my summer gas mileage and so far, no matter what the temperature gets down too, I get a good "correction" factor for the injector pulse width.
Go to the PROM Board and read my post about "MAT correction" and it tells you how to modify the calibration tables.
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