mr-natural

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?

MrWillys

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.

mr-natural

Thanks a million Mr. ******. I didn't know about the VSS being so readily available and the Pin Out will be helpful too.

SunCr

http://forums.corvetteforum.com/c4-t...imary-fan.html

vetteoz

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

mr-natural

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?

ladystoy69

jump A and B in your aldl connector, key on engine off then test your c1 pin for ground out

MrWillys

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.

mr-natural

Ground was provided under this scienario. Ground continued for about 13 seconds after the ignition sw was returned to off. Does that mean the ECM is OK? What next?

mr-natural

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.

vetteoz

Should be checking the Ohms
http://www.corvettephotographs.com/c...nformation.htm

mr-natural

33 ohm @ 90 F and 63 @ 180 F.

vetteoz

Do you have the numbers reversed ?

CTS resistance (Ohms) should be reducing at the temp rises

http://www.chevythunder.com/cts_diagnostics.htm

Cliff Harris

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.

mr-natural

Mr. ******, I now have my VSS but the factory manual shows it going directly to the instrument cluster which, of course, I don't have. Where do I tie it into the ECM?

MrWillys

One wire goes to pin A10:
http://www.chevythunder.com/fuel%20i...ts.htm#1986-89 pinouts (ecm #1227165)
The other goes to ground.