Open Loop / Close Loop ??????????????
Safety Car
Joined: Oct 2008
Posts: 4,022
Likes: 30
From: Los Angeles CA
Drifting
Joined: Jun 2010
Posts: 1,853
Likes: 8
From: Westerly RI
"Open loop" operation occurs before the engine has warmed up. In open loop, the ECM ignores real-time voltages from the various sensors, other than the CTS (coolant temp sensor) in favor of default values. When the engine warms up, as determined by the CTS, the ECM goes to "Closed loop" and begins metering fuel, adjusting timing, etc. based on inputs from the sensors.
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
When cold (open loop), calculations are used to determine fueling requirements. To make sure it never goes too lean, those calculations err on the side of running rich. So, during open loop operation, you're probably burning more fuel than closed loop. Once it hits closed loop, oxygen levels can be monitored to compensate. And, slices of data are taken every few milliseconds.
This trim data is stored in volital (eraseable) computer memory. It's a version of memory that helps better anticipate how the car "needs" to run for best economy/emissions compliance.
Associate open with "open circuit" or closed with "closed circuit" so you can remember which state has the ECM monitoring performance.
One final note: operating parameters can be changed. We call it tuning.
Thread Starter
Intermediate
Joined: Mar 2009
Posts: 29
Likes: 0
The reason I posted this thread about the Open & Closed loop systems is that I just had to have all three cats replaced on my 91 and it only has 36K on it. Exhaust guy said the pre-cats where " melted " < his words > and that it was due to it running to rich. I bought a new O2 senors and he installed it prior to me leaving his shop. SailorSteve mentioned the CTS sensor controlling the fuel metering in the Open Loop. Where is that located on the engine and could that be something I need to replace / clean also ?????
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Drifting
Joined: Jun 2010
Posts: 1,853
Likes: 8
From: Westerly RI
The reason I posted this thread about the Open & Closed loop systems is that I just had to have all three cats replaced on my 91 and it only has 36K on it. Exhaust guy said the pre-cats where " melted " < his words > and that it was due to it running to rich. I bought a new O2 senors and he installed it prior to me leaving his shop. SailorSteve mentioned the CTS sensor controlling the fuel metering in the Open Loop. Where is that located on the engine and could that be something I need to replace / clean also ?????
The CTS is located on the lower front side of the water pump, screws into the pump casting, has an electrical connector on it. Codes 14 and 15 are associated with this sensor.
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
CTS=Cold Temp Sensor
There must be a difference in the early vs late C4s. On mine, the CTS is mounted in the head near the dipstick. There's another one in the front of the intake. One sends info to the dash display. The other is used for the ECM to determine engine temp.
If your CTS was bad, and you were always running in open loop, it should have smelled super rich -- before you melted the cats.
There must be a difference in the early vs late C4s. On mine, the CTS is mounted in the head near the dipstick. There's another one in the front of the intake. One sends info to the dash display. The other is used for the ECM to determine engine temp.
If your CTS was bad, and you were always running in open loop, it should have smelled super rich -- before you melted the cats.
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
It's the one it that screws into the front of the intake manifold (just above the water pump).
FYI: I have seen posts where the sensor wasn't bad, it was the ECM not getting it's signal. That info was posted in this thread....http://forums.corvetteforum.com/c4-t...old-start.html
FYI: I have seen posts where the sensor wasn't bad, it was the ECM not getting it's signal. That info was posted in this thread....http://forums.corvetteforum.com/c4-t...old-start.html
