Diagram of EGR/Smog?
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Joined: Apr 2000
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From: Stillwater, OK
Car: 1991 Formula
Engine: 355 DFI Superram w/ R-Trim
Transmission: Probuilt 700r4
Diagram of EGR/Smog?
I was wondering if anyone had any drawings of the egr passages and schematics of the EGR system and the smog system. I would like to see this either on L98 or Lt1 intakes...or even the differences among these. I'm collecting information so I can implement the egr in the LT1. Thanks for your help!
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Joined: Sep 1999
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From: Philly, PA
The LT-1 EGR system uses an external tube coming off one of the exhaust manfiolds to supply EGR gas to the valve which sits on the back, driver's side of the intake manfiold. The valve then passes the EGR gas into passages in the intake manfold. Not sure where they end up- never went looking for them- somewhere inside the plenum I'm sure but not exactly where.
The L-98 has the valve down on the lower intake roughly in the center of the intake. It draws EGR gas from the exhaust crossover that runs between the heads. It is fed from the valve up to the plenum where it is fed into the plenum not far behind the throttle blades.
Both are controlled in a similar manner. Full manifold vacuum is fed from the intake manfold to an EGR solenoid which opens and closes under ECM control to determine how far to open the EGR valve. It does this by cycling the solenoid rapidly between open (venting vacuum to atmosphere through a small filter) and closed
(supplying vacuum to the EGR valve. The higher the duty cycle the more average vacuum is fed to the EGR valve and the further it opens.
I am not sure if L-98 and LT-1 EGR solenoids are interchangable, or if the signal from an L-98 computer could run and correctly operate an LT-1 EGR solenoid or valve. I'm sure there's some combination of aprts that could work but I don't know what that combo would be.
Smog pumps are different animals. LT-1 uses an electric motor driven air pump that is turned on and off by the ECM via a relay, fuses, etc. It has only 2 entry points to the exhaust system (at least on my 94)- one tube to each exhaust manifold. The L-98 has a belt driven air pump with a pair of ECM-controlled diverter valves that can do several things with the pump's output: Vent it to antmosphere, supply it to the exhaust manfiolds, supply it to the cat or both.
That's just from casual observation on my part. Others may be able to supply more detailed information.
The L-98 has the valve down on the lower intake roughly in the center of the intake. It draws EGR gas from the exhaust crossover that runs between the heads. It is fed from the valve up to the plenum where it is fed into the plenum not far behind the throttle blades.
Both are controlled in a similar manner. Full manifold vacuum is fed from the intake manfold to an EGR solenoid which opens and closes under ECM control to determine how far to open the EGR valve. It does this by cycling the solenoid rapidly between open (venting vacuum to atmosphere through a small filter) and closed
(supplying vacuum to the EGR valve. The higher the duty cycle the more average vacuum is fed to the EGR valve and the further it opens.
I am not sure if L-98 and LT-1 EGR solenoids are interchangable, or if the signal from an L-98 computer could run and correctly operate an LT-1 EGR solenoid or valve. I'm sure there's some combination of aprts that could work but I don't know what that combo would be.
Smog pumps are different animals. LT-1 uses an electric motor driven air pump that is turned on and off by the ECM via a relay, fuses, etc. It has only 2 entry points to the exhaust system (at least on my 94)- one tube to each exhaust manifold. The L-98 has a belt driven air pump with a pair of ECM-controlled diverter valves that can do several things with the pump's output: Vent it to antmosphere, supply it to the exhaust manfiolds, supply it to the cat or both.
That's just from casual observation on my part. Others may be able to supply more detailed information.
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