89 Iroc Z

I have a 730 ECM in my car now. Why is there a constant for the second cooling fan in the bin if the ECM does not control it? Can someone who has gone through the 8D source code tell me if this constant is even linked to anything else in the code? Has anyone edited the code to ground an output to be able to use the second fan control?

I know the V6 cars that use the 730 have second fan control and the corvette 727 ECM does also. Would it be possible to transfer over this bit of code from the corvette bin and change the output to one on the 730 ECM?

Any information would be greatly appreciated.

91L98Z28

Here is my uneducated, I didn't look at the schematics, I didn't look at the sourcecode, guess:

All the code to control the fan is probably in the $8d / AUJP code.

The pin might even exist on the outside of the '730 (if you say v6 cars using '730 have two fan control, then it MUST exist on the outside of the '730). In which case its just a matter of wiring the pin to a relay and to the second fan, and setting the enable/disable temp points in the prom to reasonable values.

Grumpy

I looked thru the code, and saw that there is some code for operating it. The easy thing to do would set the values to some real world values, and then run it on an ecm bench.

I was trying to find a wiring diagram, but for some reason nothing related to images is working. Does any of your wiring show a hook up for the second fan?.

Just FWIW, on my car I have the ecm control the low temp fan, and then a mechanical sender for use just in case the ecm fails to trigger the fan on

Speartech

The secondary fan control for the 730 ECM is controlled at pin F8.

There are almost no 730 applications that use an ECM controlled secondary fan, so it took some digging to find the pin. Knowing the 727 DOES use the sec. fan control; and that the 727 and 730 are basically two configurations of the same circuit, it just took a little probing and the right schematics!

Putting the ECM in control of the secondary fan works great and lets YOU decide what temp it comes on at!

89 Iroc Z

Speartech, Have you tryed this. Are you saying it really does work. Thats awesome, I'll check it out with a DMM.

Speartech

It really works!
I forget which car we did it on. It was either the 91 Z28 before I pulled the TPI, or on the 91 454 Caprice wagon (730 ECM). Whichever one it was, the function worked fine.

91L98Z28

hey speartech,
haven't seen you on here before, welcome to the board. by the way- love your white 91!!! :hail:

Z_Ghost

Thanks for the info Speartech, I will have to try that on my car.

jonarotz

iTrader: (26)

Hey Speartech,
I re-pinned my fan 2 to pin F8 now when I turn on the AC the primary fan (fan 1) comes on, is this normal? I took My fan 2 wire (from pin D12, "AC pres. fan switch") and grounded it to make sure I got the right wire and sure enough the secondary fan came on. So is the primary fan supposed to come on when AC is on? Thanks

89 Iroc Z

That’s the pin used by the ECM to know when the A/C is on. You need to run a new wire from the second fan relay to the ECM.

jonarotz

iTrader: (26)

Cool,
thanks 89

Speartech

Thanks! The 91 LS1 has been a fun project!

I don't get to spend much time on the different boards; but I like to drop in when I can.

John

Speartech

I thought just the secondary fan came on with the A/C, based on head pressure.

Since D12 is tied to the secondary fan control line, you could do a jumper wire from D12 to F8. That would keep all of the functionality of everything else the same, and allow your programmed temperature to activate the fan.

jonarotz

iTrader: (26)

Thanks speartech,
Thats what I was thinking too. At least I have someone who is thinking the same way I am. It just seems so much easier to run a jumper instead of running a wire to the fan relay.

TRAXION

I jumpered the pins as you mentioned awhile ago. Now when the ECM controlled primary fan turns on ... they both turn on. I love it that way. My next mod to this circuit is to bridge in a switch so that I can activate both fans whenever I want ... like when you are in the staging lanes at the track!

Tim

SATURN5

Tim... Not sure if you have seen it but Willie has a Total Fan control article in Tech..


BW

TRAXION

Yea - I've definitely seen it. But, I love simplicity. One temp turns on both fans. One switch turns on both fans. It doesn't get much simpler than that. Extra wiring? Not much. Just gotta jumper the two at the ECM and run a ground wire off of it. Very easy, very simple, and works for everything that I need.

Tim

SATURN5

Since I had to rewire so things fit into the Malibu I just jumped the relay trips together and set the bin to 175*. Have to see how temps are once summer is in full swing but <180* is typical temp.

Ed Maher

I like having my fans on seperate switches. I did consider making it a common circuit, but decided against it figuring there isn't a point to putting extra load on the electrical system for no reason. Also, the start up load especially is pretty significant, so swicthing them simultaneously just seems like a mean thing to do to my alternator. And we all love our CS-130s. ****, i'd walk on broken glass if it told me i'd never have to drive 300 miles looking at a dropped voltmeter again. So letting the fans hit seperately was the least i could do.

But really, i almost never need my secondary fan anyway. Only in the worst of traffic on the beltway in 95' 98% humidity august did it ever really prove useful.

TRAXION

Ed - no offense but some of us need the secondary cooling fan to cool our motors You are very right about the spike necessary to powerup both fans at one time. Some people have blown fusible links doing it. But, it works fine on my car and I NEED to have both running. Plus, it's the quickest way to cool the car down in the staging lanes.

Tim

89 Iroc Z

I think I am going to jump a wire from pin F8 directly to pin D12. Instead of moving pin D12 to F8. That way the ECM will know when the second fan is been turned on by the A/C cooling fan pressure switch via the “Fan request signal”, pin D12. I will leave the factory secondary cooling fan temperature switch and wiring to act as a backup.

For a master override, I will hook a switch up to D12 to allow me to turn on both fans manually.

I have read the total fan control article also but I rather not spend any money on aftermarket parts when I can do it for free and have more control.

Here is a fan control schematic of the 90-92 camaro with a 730 if anyone wants to see the stock wiring setup: ftp://ftp.diy-efi.org/pub/gmecm/manu...730v8tpi-4.jpg

87_TA

Being that I am not using A/C I could just repin D12 to F8 and have no worries,correct?

yellow73bb

Does anyone know what book/manual that schematic came from?

SATURN5

More than likely the wiring service manual for a 90-92 F-body. Check Ebay... manuals are always listed.

edit: Complete service manual for a 90 Camaro.

http://cgi.ebay.com/ebaymotors/ws/eB...category=34214

yellow73bb

Thanks for the link. My Haynes manual for my 90 van has drawings just like the link above, given by 89 Iroc Z, for the 1227747, probably copied from the Chevy manuals. I don't mind buying the Chevy manual if that is the only way to get the drawings, but since I don't own a camaro (I'm retrofitting into a 1973 vette 454), if I can get by with the cheaper Haynes manual that is what I would prefer.

Does anyone know if those schematics are in the Haynes manual?

SATURN5

Do you need just the EFI harness diagrams?

The link to the FTP site has schematics for both F-body and vette.

ftp://ftp.diy-efi.org/pub/gmecm/manuals/1227730/

yellow73bb

Yup. I got them. Those will probably do the job.

Thanks,

LBSZ28BLOWN

Just did the Fan 2 mod on my car this week end and it works
great.
I did the jumper from D12 to F8 and then set the operating temps for my fans in the .bin (awsome)

Scott_92RS

Diggin up an old post here. I did this mode the other day, along with wiring up a manual override switch. The manual override switch works great, but for some reason my fans wont come on at the defined temps. I burned a chip with fan1 and fan2 on temps set to 23 degrees, just as a test. Datamaster reported a temp of 17*C, so I busted out my sisters hair dryer and heated up the sensor. The temp rose to over 25 degrees, and the fans never came on. I was heating the sensor on the intake manifold, does the ECM use another sensor for the fan temps? I know there is a sensor for the gauge, and a fan switch to turn on the secondary fan (driver side head), but what about the one on the pass. side head? Is that the one that would trigger the primary fan at the temp specified in the ECM? Thanks!

Scott

jonarotz

iTrader: (26)

The ECM uses a different switch, It is on the pass. side head, towards the rear. Near the dipstick.

Scott_92RS

I figured it probably used that sensor. I tried heating that sensor too, for a longer period of time that I heated the other sensor, and I still got nothing though. Maybe the sensor is bad? Its brand new, but that doesnt mean anything. Now that I think of it, my fans haven't really worked correctly since the motor swap, so maybe that sensor is at fault. Does the body of the sensor have to be grounded? I have teflon wrapped around the threads, so maybe there is just no electrical connection between the sensor and ground? Cant wait to lose all my coolant again, thats so fun!

1bad91Z

iTrader: (1)

I dont think the sensor is bad Scott. I think it's that POS firebird harness and or those relays on the firewall.

Scott_92RS

The relays work. The switch I wired up enables the relays, both relays "click" and both fans come on when I flip the switch. I even swapped the relays for known-good ones and there was no difference in functionality. The harness is not a POS, it just required a few mods to make it fit in the car. At least my car starts on the first try! My money is on the THREADS of the sensor. I'm going to take it out and spread some red RTV on there. That'll allow the sensor to contact the head, but still be sealed.

Actually, first I'm going to attach a ground wire the the sensor somehow, and see if that makes it work. If it works, I'll take the sensor out and seal it differently, if that still doesnt work, I'll get a new sensor.

TRAXION

Wrong. The ECM uses one and only one Coolant Temp Sensor ... and that is the one on the front of the intake manifold. The one in the passenger side head is nothing more than a fan switch that creates a ground once a certain temp is reached. This switch is not ECM controlled. It is just a mechanical switch.

The fans operate as follows ...
GE8 (DK GRN/WHITE - circuit 335): The primary fan is ECM controlled and its relay gets a ground via the ECM
BD12 (GRY - circuit 731): The secondary fan is not ECM controlled and gets a ground via either the temperature switch in the head or via the A/C pressure switch. The link to the ECM is only for checking a ground to see if the fan has been kicked on by either one of those switches.

The operation of these two fans are clearly described in the manual...
http://www.eecis.udel.edu/~davis/z28...730v8tpi-4.jpg

Basically, you want to find a way to take BD12 (GRY - circuit 731) and have a way for the ECM to pass a ground along this ciruit. I did it by jumpering this circuit with the primary fan on pin GE8 (DK GRN/WHITE - circuit 335). However, according to what Speartech said you can jumper this wire to F8.

Tim

Scott_92RS

Well, if thats the case, then what would cause not even my primary fan to come on when the temp. set in "Fan 1 On" was reached? I put a wire into the blank spot on F8 (Secondary Fan Enable), and attached that wire to D12. Then ran 1 wire from the jumper wire to a DPST switch, and that switch goes to ground. I then spliced into E8 (primary fan enable), and ran that to the other switch post on the DPST. The other side of the switch has 1 ground wire that splits into 2, to hit both posts. The fans should operate normally since E8 and F8 are still seperated, except when the switch it ON. I'll disconnect all my jumpers and see if the primary fan comes on when its supposed to.

1bad91Z

iTrader: (1)

Ok, then what the heck does the driverside head temp sensor do or control?

TRAXION

Your temperature gauge behind the steering wheel

Tim

1bad91Z

iTrader: (1)

Thats pretty damn gay that GM needed 3 sensor's to do all that!

The ECM should be able to control all temp related stuff with just one sensor.

Oh well!