VPC acts as a FCD - HOW?

[HKS_TRD]

I read through the manual for the VPC about the "option out" knob for the FCON, but I don't see the difference between this is the gain knob. It states it allows for additional fuel above stock fuel cut off. Does this mean that the regular gain knob only adjust fuel up to the stock fuel cut off (and that the VPC DOES cap the AFM signal to prevent fuel cut, answering this thread's questions), but the option out allows for fuel trim adjustment AFTER fuel cut off?

The FCON has a dial inside it that lets you adjudt the fuel curve the FCON creates past the stock cutoff point. THE option out dial on the VPC controls this feature of the FCON and allows you to leave the FCON internal dial at the middle setting and adjust without opening it.

I cant offer any more info in this thread till I sell some of my JDM parts :sarcasm:

 

[87witmoreboost]

The FCON has a dial inside it that lets you adjudt the fuel curve the FCON creates past the stock cutoff point. THE option out dial on the VPC controls this feature of the FCON and allows you to leave the FCON internal dial at the middle setting and adjust without opening it.

I cant offer any more info in this thread till I sell some of my JDM parts :sarcasm:

HAH. <<damnit, he's trying to trick me into buying stuff and knows I love this thread>>

Should this option out be adjusted to make a generally AFR-happy fuel curve after stock cutoff point before the GCC is used? Or should it be ignored and tuning should all be done via GCC?

 

[crisp]

HAH. <<damnit, he's trying to trick me into buying stuff and knows I love this thread>>

Should this option out be adjusted to make a generally AFR-happy fuel curve after stock cutoff point before the GCC is used? Or should it be ignored and tuning should all be done via GCC?

I run mine CENTRAL (12 o'clock position) on the OPTION OUT, and "TRIM" with the GCC +- accordingly.

My understanding is that IF the GCC "TRIM" is creating the (interpolated) curve at the points you have control over, the OP OUT will move the ENTIRE MAP (trim curve) incrementally by the 2% per "notch" of adjustment thereafter.

WithOUT the GCC, you are at the "mercy" of the map inherent the chip, with SOME control over just the on/off throttle and idle, which is incremental and NOT really changing the "MAP SLOPE" as the GCC does. Also, unless I am mistaken, the GAIN is controlling a "non-linear" slope rate, not a pure OP OUT percentage... but I forget what my HKS tech response to this understanding was... been a long time! DOH!:cry:


-crisp

 

[HKS_TRD]

The gain adjusts the entire output map generated by the VPC up or down, crank the gain and you will hit fuel cut eventually, but it will have no implication on map post fuel cut. NO interception of an ECU input can do this, I cant over-emphasise this point.

HOWEVER

The option out will dial the map generated by the FCON up or down. The FCON map takes over the factory map afer a certain injector duty (point of fuel cut), so the option out would be adjusting the fuel deliver post the stock fuel cut point

 

[87witmoreboost]

That's awesome. Makes sense and that is some very high resolution tuning. The more I learn about these HKS piggies, the more I like them.

Glad I got the FCON now. Makes me wonder what would happen in boost levels after stock fuel cut without the FCON. I'd still like to know how it caps the signal without starving fuel. Maybe everyone always runs FCON with the vpc to get that post-cut-off fuel map.

 

[HKS_TRD]

You would still starve of fuel eventually

A friend runs one of my OLD VPCs and 550s with a stock ECU and he runs out of fuel at 20psi on his modded CT-26

I had a Mines ECU, and running VPC and 550s I ran out of fuel and had to go to 720s with the 35R

The whole reason for the FCON is to not starve for fuel past fuel cut

Not all fuel cut defenders are created equal, my Brother used an adjustable type and found it very touch to either cut fuel or run lean

Got a HKS one and it worked alot better. THe HKS one also had an input for the rpm signal the other one didnt

A VPC wont be able to give you any more fuel than if you use a Lexus AFM

 

[87witmoreboost]

Right, all makes sense. I get your point about not being able to control post-fco stuff with ecu inputs. This is why FCON works before and after ECU. Now, I read a second source mentioning hooking the GCC to the vpc and not FCON, but how will this help after stock fuel cut off if vpc caps and map after the cut off is in the hands of the FCON???.

 

[HKS_TRD]

Right, all makes sense. I get your point about not being able to control post-fco stuff with ecu inputs. This is why FCON works before and after ECU. Now, I read a second source mentioning hooking the GCC to the vpc and not FCON, but how will this help after stock fuel cut off if vpc caps and map after the cut off is in the hands of the FCON???.

As the FCON is only controlling a small part of the fuel curve, the point where the stock ECU stops onwards, the GCC if you hook it up to the FCON is only going to be able to control that part of the fuel curve. If you hook it up to the VPC, which is controlling the rest of the fuel curve, you can then tune the parts where you need more precision, such as the transition from vacuum to boost.

Basically, the FCON sits silent till the point of fuel cut then takes over with its own fuel map past that point. With the 550 chip when used with stock AFM the FCON would only be applying a fixed scaling factor to injector signals up to fuel cut and then continuing the fuel map past this

These old units can work OK if you take the time and right approach to tuning them

 

[87witmoreboost]

As the FCON is only controlling a small part of the fuel curve, the point where the stock ECU stops onwards, the GCC if you hook it up to the FCON is only going to be able to control that part of the fuel curve. If you hook it up to the VPC, which is controlling the rest of the fuel curve, you can then tune the parts where you need more precision, such as the transition from vacuum to boost.

Basically, the FCON sits silent till the point of fuel cut then takes over with its own fuel map past that point. With the 550 chip when used with stock AFM the FCON would only be applying a fixed scaling factor to injector signals up to fuel cut and then continuing the fuel map past this

These old units can work OK if you take the time and right approach to tuning them

Makes sense, except it sounds like the GCC won't be doing anything after the stock cut if thats when the VPC stops knowing what to do and FCON takes over. Does this mean tuning after stock cut must be through option out, or would changes on the GCC affect the fuel curve after the cut off?

 

[87witmoreboost]

So... I decided hardwiring my FCON was gonna SUCK and I got ambitious. Called all around to see who has one and of course, nobody. They have been discontinued for a while.

Got a hold of some people at Dynamic Autosports in Cali (good people!), and they called HKS. They found me the last 87-88 FCON harness known to the HKS computer system. FOR $119 SHIPPED! WOOT!

Now all I need is a legit VPC harness and I can avoid this resistor hardwiring crap. Anyone have any tips for finding one?

 

[peter551984]

HOw much can i Make with a FCD with stock head gasket and without?

 

[martin p]

I found fuel cut on mine today, with the vpc fitted, it was just over 1.1 bar, mind you that was at 4500 rpm, so time to invest in a 440 chip for my Fcon and fit it, As it includes a fcd in the pnp harness.

 

[Mike Morris]

Been running the HKS stuff for years(GCC,Fcon,VPC,F con fuel mixture switch etc....)
No problems running a TT pump and 550cc since 2001. Car runs 11s on pump gas.

 

[erics3000]

How did it go. Do you get it all going? Any pics? This is a great thread.

I have been getting my car back up and going after sitting for about 10 years and still have a bunch of old school stuff. Back in the day I just ran the lexus AFM and 550 cc. I think as soon as I work ou the bugs I am going to drop a vpc gcc that I have had for about 5 years sitting on the shelf. I also am going to go the fcon route.