Fast XFI - and using A/C and second fan control

[GregWeld]

I'm helping a buddy with his 'last mile' - Fast XFI - and he wants to be able to control TWO fans independently. He wants one fan to come on with the ECT control - that's easy..... but looking at the instructions and pin choices - the A/C control and second fan is a bit confusing to me.

I see AUX # 3 (ECU Main pin 3 output) has a couple of controls for this output. Easy - %TPS and ECT

I also see there is a A/C "enable" pin B11 - that can hook to the NEGATIVE side of a relay... but this is a pin OUT I assume and has a 2 amp capacity.. plenty for switching a relay.

What I don't see is an A/C INPUT.... in other words - how would the ECU know the A/C has been turned on... I can't find this anywhere in the instructions.

HELP! I hate calling the tech lines....

[camcojb]

usually the ecu controls the fan by grounding the fan relay as you said. The a/c has a binary or trinary pressure switch inline and on mine it has a ground output which I tied into the fan relay ground, along with the ecu ground wire. That way the ecu will command the fan on at a certain temp and regardless of temp whenever the a/c is switched on the trinary switch will ground the fan relay to run the fan, which should always run if the a/c is on.

I turn on both fans at the same time, but you could run one off the ecu, and run the other one or both off the a/c pressure switch. I am not familiar with the XFI but if it has two fan controllers then set one ground wire to each fan relay for the ecu control, and then tie in the a/c pressure switch to the relay ground of one or both fans, depending on your preference. If there is an a/c input wire for the XFI then you'd run the ground or 12v off the binary/trinary pressure switch there, instead of directly to the relay. I do not know if it does though.

EDIT: I downloaded the XFI manual. The a/c control they give you is to override the a/c relay and let the ecu shut off the a/c by temp or throttle percentage. You can set max temp to operate, so it will not come on if the coolant temp is beyond where you set it. It also lets you set a tps setting so once beyond a set % of throttle it shuts off the a/c (like full throttle) to reduce load on the engine. There is no input, you just hook the output wire (B11) to the a/c relay ground terminal and let the ecu control it. It doesn't need an input as it only shuts the system off by temp or tps % through ungrounding the a/c relay. It will not affect or control the fans off this circuit.

To get the fan control do what I outlined above. The XFI system can only control one fan, so you'll need the a/c pressure switch ground output to ground the second fan relay, or use a fan controller like the preset ground switches that screw into the intake or block and ground the circuit at a certain temp, like say 200 degrees, and run the second fan relay ground to that switch.

Jody

[GregWeld]

Thanks Jody!!

You confirmed what I thought... Your instructions/ideas - is exactly how I run my Accel DFI system - but it has an A/C input - so was trying to see if the Fast EFI used this as well.

Living in the great Pacific NorthWET we have very few cooling issues... and I've been using the Accel to control both fans with a stepped / overlapped ECT. But using the ECU to only control ONE fan on with the A/C... but maybe I should be turning both fans on when the A/C comes on and will look into that. That might help the cooling (A/C) when the car is in Reno (Hot August Nights) and we're just tooling around town in stop and go traffic.

Right now - his system is using a Binary switch - but I have to make him all new A/C hoses anyway - so will put in a Trinary switch when I do. :)

[wedged]

there are several programable outputs that you could use to control relays. they could be used to control fans, if you wanted. Eventually I am going to use 2 of them to control converter lock up and overdrive engagement.

[GregWeld]

there are several programable outputs that you could use to control relays. they could be used to control fans, if you wanted. Eventually I am going to use 2 of them to control converter lock up and overdrive engagement.

I actually FOUND - their instructions actually kinda suck - that B3 in the 25 pin (grey) ECU connector is a controllable fan output (goes to NEGATIVE side of the relay #86). There is software parameters for setting this pin out....

I also am using the A/C "enable" function - which goes to the NEGATIVE leg of a Tri-nary switch in the A/C line. There is a wire in the harness labeled as such.

FYI - there is already a Torque Converter Control (TCC) output with wire provided in the main harness.

Now here's the giggle juice for you.... Fast does not provide additional pins (spares) in order to access these additional functions in the ECU harness. A trip to the automotive store to search for some provided no relief. BUT! There are a couple of spare outputs with a length of wire that if one could get the pin out of the harness - he could move it to where needed. I have a full set of cute little tools for removing such pins from various connectors.... and after 30 minutes or so... finally gave up on every tool I had to poke and prod the damn pin loose (they're a push in and lock type so you have to be able to get to the release).... Stick with me here....

So as I'm examining the dang connector -- and trying to discover how to correctly unseat the pin -- I noticed that the connector has a WHITE stripe running through it - which is obviously a different "piece" from the grey body (of the connector) that it's in... and it appeared to have a slot (damn small) which a guy could insert a small flat blade screw driver (or?) and pry the WHITE strip. I ever so gently tried this and to my delight - it loosened about a 1/16th of an inch away from the connector (I had to pop it up from both sides) - IT IS A LOCK THAT HOLDS THE PINS IN THE CONNECTOR - once this was 'popped up' - the pin and it's wire came right out... and I was able then, to do the same thing to the connector I wanted to use (stole the pin with it's wire length from connector A and put it in connector B at B3) and bada bing, bada boom, I was done!

So -- when you start working on your setup -- remember this little 'tip' should you need to do the same thing.

[wedged]

My car...er truck... has been running with FAST EFI for about 3 years now. I bought the harness kit that was the universal type- only terminated at the ECU end. I removed all of the wiring I was not using to neaten things up a bit. The connectors were no mystery to me, but I guess you could say I cheated a bit since I've been fixing cars for over 20 years. The wiring job was fun in a slightly sadistic way since I was combining the stock harness of a 94 Dodge Dakota with the FAST harness so that all of the stock neccesities would work.

edit: almost forgot- if you need more pins, sockets or the connector bodies, try Digikey. I bought some various items from them for the project including the parts to create a 5v reference source so the speedometer would work.

http://www.bigblockdakota.com/images/newrad.jpg

[parsonsj]

I've got my V/A, FAST XFI, and DC Controls Fan controller all working now.

Here's a thread about the process:

http://www.pro-touring.com/forum/showthread.php?t=53755&highlight=FAST

One thing to know: the B11 input is backwards in the documentation. It's a 12V (not ground!) signal that tells the FAST ECU that the A/C is on.

jp