Please tell me how you did this? I have a GN fan switch that kicks the second fan on at a lower temp. But still a little late for my tastes in heavy traffic? The car cools right down when both fans are running.


Mike

 

My guess would be that he utilized an unused grounding output to drive the secondary fan relay, and patched a threshold comparison into the code right after an existent coolant temp. lookup.

I'd like to know for sure though.....would be nice if there's a simpler way for those like me who can't really work with the code yet.

 

Well...I spoke to soon..I did a search and found some things. IM wondering about the draw on the alternator with both fans kicking on at the same time. Have it wired up just have to give it a try with the car up to temp.

Anyone have any problems doing this?

 

You need to either "swap" the pin from BD12 to GF8 (my preference) or just "jump/tie" a wire from BD12 to GF8. I prefered "swapping" because then when you initiate Fan 2, it doesn't report it as "High A/C Pressure" through BD12 to the ECM which will happen if you "jump/tie" BD12 & GF8 together and Fan 2 turns on.

I haven't checked if there are any ramifications in the code when the "High A/C Pressure" switch is detected by the ECM. But, I don't feel like "finding out the hard way" whether there is. So, just "swapping" BD12 to GF8 will avoid the possiblity of some code being invoked with the "High A/C Pressure Switch" is detected.

Second thing, which I have never seen discussed is a discussion on the what is the best way to engage the fans. With the small mod above enabling ECM control of Fan 2, I prefer to engage Fan 2 BEFORE Fan 1.

I do this so IF my engine is already hot enough to turn on a fan when I turn on A/C, I will have both fans going instead of just one. I have encounter hot temps in the summer where I live that when the A/C is turned on, it causes the engine to continue to get hotter even though Fan 1 is on. This is especially true in "stop n go" traffic when the temperature is > 100*F.

Also, because Fan 2 will have the "first threshold", should the A/C cause the engine temp to rise higher than the single Fan 1 can cool, Fan 2 will turn on sooner to assist in cooling.

Lastly, Fan 2 has seldom/never been turned on, on my engine. Electric motors don't last forever, so I figure that since Fan 2 has seldom/never been used, it will probably last longer than if I engage Fan 1 first.

This is just my preference, so you can do what you wish. I prefer the engaging the fans independently and Fan 2 first. I have concerns with engaging both fans at the same time due to possible the spike/surge in electric current. It is easier on the electrical system to have the fans come on at slightly differeent times than both at the same time.

 

Well it was just a guess, after all.

 

Aren't you glad it is even simpler than you thought? The toughest part for a lot of guys is pulling the wire out from BD12 if you have never done it before. I use a small jewellers screwdriver to press down on the 'lock" so I can pull the wire, but you need to be careful and the "first time" is always the toughest.

For that reason, a lot of guys prefer to just "jump/tie" a wire from GF8 to BD12 rather than risk ruining the "pin".

If you have never done this before, you may wish to consider going to a wrecking yard and "cutting" a couple connectors (with approx 6" of wires) and practice pulling out the "pins" first.

 

I fix cars for a living. I've done my fair share of re-pinning connectors, often ones that have melted for one reason or another (*cough*shadetreewiring*cough*) so that shouldn't be an issue.

I have a dental pick just for this purpose.




Thanks for the info though.

 

That is why this board is called DIY*cough*shadetree*cough*PROM

 

This is not shadetree work. I'm in the kitchen.

 

https://www.thirdgen.org/techbb2/sho...hreadid=182538

EDIT:
This is a link to a thread that tells how to jump a wire on the ECM to control both fans.

 

Eventually all of us DIY'ers must get under the shadetree. But, a lot of the "eprom/ECM" stuff can be done elsewhere.

 

Oh I spent a few years under the tree alright...but now I have access to a 6-bay shop so those days are in the past.

Lucky me, eh? Air tools....2 lifts....Mitchell database....good stuff.

 

My wife won't let me install a lift in our garage (Heck there's no room either) DOUBLE

 

I'd invite you to come use ours, but I fear it's a bit of a drive.....

 

Be careful of what you offer, you never know who may take you up on it.

 

Bring it on, Cletus.


Just call and let me know before you pull in the drive so I can put my pants on.

 

Idle increase.

 

Glenn your way sounds better to me, i just jumped the wires at the relays. IM afraid of blowing out a fuesable link. Dont want that to happen at rush hour.

I dont really understand how you did it. Did you pull the BD12 wire from the pigtail at the fan relay? And connect it to the GF8 wire at the other fan relay? Sorry, I dont know alot about wiring. But I can get by when I need to do it.

yeah it gets pretty hot here in the summer. I need all the help I can get. keeping this thing cool in heavy traffic. With the air going.

So how did you get the fans to come on at different times? In tunercat there is two settings for fans. when swapping the pins both settings will work for each fan?

Thanks for the reply!

Mike

 

I did it at the "connector" to the ECM under the dash. It's cleaner and easier. Then you just need to reburn your eprom.

 

Not sure if this will help or not.

https://www.thirdgen.org/techbb2/sho...hreadid=231080

 

Yes thanks that did help!


Well I swapped the BD12 pin over to GF8... Have to see how it works on the drive into work. I changed the settings in the eprom like you suggested Glenn. Starting with fan 2 on first.

Thanks Glenn!!!!!!!!!!

 

Well....I was stuck in heavy traffic and she never went over 195.

 

Just to make sure it is working, let the car sit idling and get hot enough to turn Fan 2 on. Then, turn on the A/C and watch both turn on. In the summer, I never saw the temperature creep up with the A/C like I use to before I did the re-pinning and altered the settings to make Fan 2 my "first threshold".

 

Works great Glenn!....... the car runs so cool now. I always hated watching the gauge creep up so high in temp. It would aways cool right down with both fans going. Now I can set them to turn on at the temp I need. With just a simple change in the eprom.

I have the car running better then ever in openloop. And it stays nice and cool even in heavy traffic.

 

So what did you actually connect to where?

Detailed instructions, please!

I can do the prom side of it......


- Vern

 

Vern look at the pic here.
ftp://ftp.diy-efi.org/pub/gmecm/man...7730v8tpi-4.jpg

You will see the 3 plugs on the back of the computer are lettered, the 24 pin plug is A & B the black 32 pin plug is C & D and the green 32 pin plug is E & F.
Now each side is also lettered and numbered.
I did what Glenn did and swapped the pin from BD12 to GF8.

Next time I have Matilda at the GTG you can check it out.

 

The first letter is the plug and the 2nd letter and # is the wire in that plug.

 

Great - THANK!, Phil!!!!