Primary fan control by ECM
Thread Starter
Instructor
Joined: Feb 2004
Posts: 141
Likes: 4
From: Scottsdale AZ
Primary fan control by ECM
L98 in a 58 vette w/no A/C and no speed sensor. C1 of the ECM provides ground to the primary fan (I am using two aftermarket fans). 12 VDC to B8 of the ECM emulates the A/C being turned on which should ground C1 and turn on the fan. Is that correct or am I missing something? Also the stock fans shut down at 35 MPH if temp is under control. Is that because the fans actually restrict airflow above 35 MPH?
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
L98 in a 58 vette w/no A/C and no speed sensor. C1 of the ECM provides ground to the primary fan (I am using two aftermarket fans). 12 VDC to B8 of the ECM emulates the A/C being turned on which should ground C1 and turn on the fan. Is that correct or am I missing something? Also the stock fans shut down at 35 MPH if temp is under control. Is that because the fans actually restrict airflow above 35 MPH?
http://www.chevythunder.com/fuel%20i...ts.htm#1986-89 pinouts (ecm #1227165)
A VSS circuit should be used, and is really quite simple to hook up. See here:
http://www.jagsthatrun.com/SpeedSensors_Order.html
You need the first one for a 7165 ECM, and it screws on to your speedometer output. Keep these wires away from other ignition wires as much as possible.
You should consider having a competent programmer redo what you have to optimize your vehicle.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
There are well documented problems resulting from no VSS input
http://www.thirdgen.org/techboard/di...-cell-4-a.html
http://www.thirdgen.org/techboard/po...162-post2.html
Thread Starter
Instructor
Joined: Feb 2004
Posts: 141
Likes: 4
From: Scottsdale AZ
First, if you're using pin C1 you must have a 1227165 ECM? Pin C1 is the primary fan relay only, and does not turn of at 35 mph like the later model speed density units do. Pin B8 sends a signal to the ECM that says AC has been turned on, so add 50 rpm to idle to make up for an additional load.
http://www.chevythunder.com/fuel%20i...ts.htm#1986-89 pinouts (ecm #1227165)
A VSS circuit should be used, and is really quite simple to hook up. See here:
http://www.jagsthatrun.com/SpeedSensors_Order.html
You need the first one for a 7165 ECM, and it screws on to your speedometer output. Keep these wires away from other ignition wires as much as possible.
You should consider having a competent programmer redo what you have to optimize your vehicle.
http://www.chevythunder.com/fuel%20i...ts.htm#1986-89 pinouts (ecm #1227165)
A VSS circuit should be used, and is really quite simple to hook up. See here:
http://www.jagsthatrun.com/SpeedSensors_Order.html
You need the first one for a 7165 ECM, and it screws on to your speedometer output. Keep these wires away from other ignition wires as much as possible.
You should consider having a competent programmer redo what you have to optimize your vehicle.
Burning Brakes
Joined: Jun 2003
Posts: 849
Likes: 1
From: dubuque iowa
While I'm waiting for a VSS to arrive and install I'm still thinking my ECM is kaput. I'm not getting ground on C1 when B8 is getting 12 VDC. Switching the 12 VDC on and off causes the idle speed to change as it should. Is there anything I'm missing to get C1 grounded?
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
What BCC (broadcast code) are you using? IE: ARAP? In a stock memcal the fans won't be called for until 108 C or 226 F. GM manuals show 228 F, but the programming and my conversion says otherwise. Are you not getting a ground signal after it reaches this temp? This can be lowered if you like. Call me at (775) 530-5892 if you'd like to discuss.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Thread Starter
Instructor
Joined: Feb 2004
Posts: 141
Likes: 4
From: Scottsdale AZ
Thread Starter
Instructor
Joined: Feb 2004
Posts: 141
Likes: 4
From: Scottsdale AZ
Correct I'm not getting ground at C1 when the engine is up to temp - even when applying 12VDC to pin B8. I'm reading 2.5 volts out of the temp sensor at the front of the intake. I don't have a scan tool but from what I understand that voltage is higher than normal at operating temp.
Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
Thread Starter
Instructor
Joined: Feb 2004
Posts: 141
Likes: 4
From: Scottsdale AZ
Should be checking the Ohms
http://www.corvettephotographs.com/c...nformation.htm
http://www.corvettephotographs.com/c...nformation.htm
Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
Do you have the numbers reversed ?
CTS resistance (Ohms) should be reducing at the temp rises
http://www.chevythunder.com/cts_diagnostics.htm
CTS resistance (Ohms) should be reducing at the temp rises
http://www.chevythunder.com/cts_diagnostics.htm
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
I like this chart from the FSM (simple):
The only temperatures you really care about are cold and hot, which would be somewhere around 70° and somewhere around 200° (depending on your thermostat and how good your cooling system is).
You can remove the connector on the CTS and simulate the extremes: open = -40°. Shorted = 300°F.
The only temperatures you really care about are cold and hot, which would be somewhere around 70° and somewhere around 200° (depending on your thermostat and how good your cooling system is).
You can remove the connector on the CTS and simulate the extremes: open = -40°. Shorted = 300°F.
Last edited by Cliff Harris; Aug 29, 2013 at 02:31 AM. Reason: Clarified CTS temperature extremes.
Thread Starter
Instructor
Joined: Feb 2004
Posts: 141
Likes: 4
From: Scottsdale AZ
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
One wire goes to pin A10:
http://www.chevythunder.com/fuel%20i...ts.htm#1986-89 pinouts (ecm #1227165)
The other goes to ground.
http://www.chevythunder.com/fuel%20i...ts.htm#1986-89 pinouts (ecm #1227165)
The other goes to ground.