HKS VPC with S-afc help!

Can anyone explain the proper way to wire up my SAFC to be used in conjunction with the HKS VPC. Or maybe refer me to a site that explains it. I cant seem to find anything. Thanks!

 

web page

web page

 

Thanks so much I googled for over an hour with no results.

 

[85tr]

A few more questions. Do I run the safc in pressure mode? I have a blue and a gray wire coming out my vpc is the gray one the right one to hook up to the input of the safc?

 

[atc250r]

Check the links. They either give you the answers you're looking for or show you where to go to find them. Whether you set it to "Pressure" or "Karman" depends on how you hook the SAFC into the VPC.

John

 

[85tr]

I have checked ALLL the links and they were helpful. But slightly unclear in some areas the vpc I have has a gray wire and a blue one and I dont know which is which I wired the safc to run pressure and set it to presure but it wont run, as soon as I switch from pressure to karman without rewiring it will run decent.

 

[atc250r]

You're absolutely right. This is the link to the way that APEXi wants the SAFC interfaced with the VPC:

LINK

What it comes down to is where do you have the SAFC connected? In the air flow signal wire that goes from the VPC to the ECU or the pressure signal wire that comes from the VPC's MAP sensor and into the VPC?

That is what determines your SAFC's settings. It sounds to me like you have it in the wire between the VPC and the ECU in which case you want to set it to karman since the ECU reads karman and thats what the VPC sends to it. Techniacally, that is NOT the way that APEXi wants the SAFC connected but either way works. I've tried both and while the driveability is better the way APEXi wants it, the maximum signal that can go into the ECU is limited that way. Does that make sense?

John

 

[85tr]

this is making more sense now wich way is better in your opinion between the vpc and the ecu or between the sensor and the vpc? I have it between the vpc and the ecu at the moment.

 

[atc250r]

That way will extend the limits of how far you can push the VPC. Here's my thinking behind it:

If the VPC's MAP sensor is maxed out (5V output) at 27psi (totally theoretical) then anything above 5 volts is probably not recognized by the VPC. If you're running the MAP to its limit and want to add more fuel solely based on RPM and TPS you can't because that would require the signal into the VPC from the MAP to exceed 5 volts, thus the karman output of the VPC and into the ECU is not going to change. If you hook it up the way you have it now, you can add fuel because the VPC isn't being a "limiter" anymore.

For whatever reason, the driveability in my set up was a little better with the SAFC in the MAP wire but then you run into what I mentioned above. I would just leave it the way you have it now.

Keep in mind, this is all THEORY and its possible that the VPC unit will recognize a signal above 5 volts and continue to increase the output hz above that.

John

 

[85tr]

There is a gray wire coming out of the vpc near the wiring harness is that the wire that needs to be hooked into the ecu to feed the pressure info to it? There is also a red, blue black and white wire going to the ecu. I assume blue is throttle signal, white is rpm and red/black are power and ground.

 

[atc250r]

The ECU cannot read pressure so don't worry about that.

Are you trying to hardwire the VPC into the ECU without the big ECU harness that the VPC comes with?

John

 

[85tr]

no I have the full harness but the gray wire was cut, I am asuming that it was on accident by the previous owner.

 

[atc250r]

The second link in Ducktape's post has the purpose for each of the wires. Just look in the "files" section on the VPC digest.

John

 

[85tr]

this thing will not run with this setup yet do you think I need a different Keydiver chip in my ECU? Right now it is for 780s that I have with a 2g maf.

 

[atc250r]

Unfortunately I can't tell what chip you'd need. It sounds like you might have a problem in the wiring or the ECU harness that comes with the VPC. If all the wiring you did is correct then it sounds like you might have a problem with that harness. Just to confirm, the way you have it hooked up now requires that you set the SAFC's "sensor type" to KARMAN.

John

 

Quote:
this thing will not run with this setup yet do you think I need a different Keydiver chip in my ECU? Right now it is for 780s that I have with a 2g maf.



If you are using a 1G VPC chip its going to emulate a 1G MAS, which is WAY different than a 2G MAS. If you had a 2G 450cc VPC chip it *might* work OK, but I can't say for sure.

 

yes it is set at karman right now and no matter what I do wether before or after the sensor it wont run. The chip in the vpc I have says 660vpc, the chip in my car is for 780s and a 2g mas. I have some pretty big cams and it has always idled rough.

 

No way that is going to run. The VPC660 chip is removing ~30% airflow. The 780cc chip is removing 40% fuel. The only thing you have going for you is the 2G MAS compensation is going to add ~29% more fuel at higher airflow levels, but almost nothing extra at idle. You are going to be WAY lean.