VSS importance

Mike Hoenes MHoenes at dhr.state.nc.us
Mon Sep 28 16:14:26 GMT 1998


anyone figure out how to get a 730  with a 91 L98 eprom to accept input from
a 2000ppm vss?
 ----------
From: Jake Sternberg
To: diy_efi at esl.eng.ohio-state.edu
Subject: VSS importance
Date: Monday, September 28, 1998 10:59AM


the following text is from:
http://www.jagsthatrun.com/Pages/SpeedSensors_Speedometer.html

 -------- quoted text from webpage ------------

Without a VSS, the Chevrolet Fuel Injected engines will not run correctly,
and they will not pass a smog test.

Basically, the VSS tells the ECM how fast the vehicle is going. Most
people think the VSS is only used for the lock-up torque converter. The
VSS is also used to control the EGR valve, the charcoal canister purge
valve, the electric cooling fans, idle speed, and air/fuel ratio. This is
all explained in the Chevrolet shop manuals.

It must be emphasized that the VSS is used to control the idle speed when
the vehicle is moving. Without the VSS, a vehicle may have stalling
problems under certain conditions.  Needless to say, this is dangerous.
Raising the minimum idle speed with the adjusting screw can eliminate
stalling, but the engine will still not run optimally without a VSS.

A lot of people think that running "closed loop" is best for fuel mileage.
Closed loop simply means that the oxygen sensor is being used to monitor
the fuel/air ratio. Some of the Chevrolet fuel-injected engines are
programmed to run lean under certain conditions (called "highway mode") to
improve fuel mileage during steady cruise conditions. Without a VSS, the
engine computer (ECM) will not get the correct signals to run the engine
for best fuel mileage. There are a lot of programs in the ECM that depend
on the VSS. For best operation, the VSS needs to be connected and
functioning.

 -------- end quoted text from webpage ------------




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