Tonight I was bored (and motivated by my car that’s tuned like a drunk monkey because of a deteriorating missing link) so I attempted to reverse engineer the HRC black box, seeing as how I could probably design and build a better one myself.

I didn’t even bother contacting HRC to ask for a schematic, because they’d think that I just wanted one so I could build one, sell it, and hurt their business. Damn proprietary intellectual property. Truth be told, I’d want a schematic so I could fix the damn thing myself and be done with it.

So what’s inside this mysterious device? After my little temper tantrum with this thing which resulted in it’s inevitable destruction, I still have no clue.

Upon getting the outer case open, I discovered that it was filled with potting material. Whoever designed it knew that someone trying to copy the technology and improve upon it (me) would try to open it at some point. The engineer who designed it had some idea of what they were doing, but obviously weren’t smart enough. If they were smart enough, the circuit would never fail under normal operating conditions and no one would try to improve upon a circuit that was already perfect.

I tried all of my tricks that I've learned over the years at my work to try to reverse engineer this thing. Once potting material sets, it can’t be worked with. It’s like epoxy. If you try to fool with it, it will just chip off. It doesn’t melt, solvents don’t affect it, etc... Anyways, I could identify 2 components:

1. What seemed to be some sort of variable resistor, which wasn’t completely shrouded by the potting stuff. I think when the device is built, it is calibrated using this little thing.
2. What seemed to be a piece of a .01 microfarad 50v tantalum capacitor (very common for a output filter) that fell out of one of the chips of the epoxy

That’s all I could figure out about it. Everything else was so well covered with that black epoxy crap I couldn’t identify anything else. I’ve been owned, yet again. Looks like I’m starting out on my electronic FCD solution from scratch... I’m thinking about using a similar version of my TPS override circuit to switch the MAP sensor wires coming from the ECU to a perfect 4.5 volt reference so long as the actual MAP sensor voltage is greater than 4.5 volts. Hmmm, that would probably work pretty well, but I might have to use a high speed solid state relay (expensive) to make sure it works fast enough and provide a smooth transistion.

is potting when they fill it with something that dries/hardens?

Just make one of these....
http://www.fwdmopar.com/sites/dennis/howto.html

It works better, it's tuneable, and costs way less money.

eh, i already thought about a design like that, but that's just a variable resistor and a generic high speed switching diode that drops the MAP sensor voltage kind of like how an AFC works. that design will trick the ECU into thinking that X psi of boost is 0 psi of boost. this design (when applied to an aftermarket turbocharged 420A) ensures that the timing will be advanced and closed loop will be maintained until you hit that pre-set boost level. it might work well for cars with a MAF like a 4G63 or something, but for a boosted 420A application it's a bad idea IMO...

Perhaps you don't understand how it's being used.
You adjust the pot so that the ECU reads as normal when you go beyond 0 psi boost. It's a voltage clamp just like the HRC black box, except you can adjust it yourself so you can fine tune it closer than the HRC box. It doesn't affect the timing unless it's turned down too far. The ECU reads the varying voltage until it gets to your preset clamping position, So the car behaves like stock until you get into boost. Then, it behaves like its in WOT at 0 vacuum, or the richest portion of the fuel map. It works well, trust me. It eliminates the boost stumble during the transition from vacuum to boost perfectly. I didn't invent it, I just use it.

I don't get it.

Originally posted by ner947
...that design will trick the ECU into thinking that X psi of boost is 0 psi of boost.

Isn't that what HRC's black box does. Thats the trick - Make your computer think your just below cutout. Maybe I'm mistaken :shrug


95 Eclipse RS : 5 speed
15.7 @ 87.9mph
Jeep TB writeup - http://www.dimensia.com:81/jimbo/JeepTBfor2gnt.html

No, the hrc box attempts to hold the voltage at a certian level, and does a very bad job of it. Basicly its tring to always keep the voltage below a certan point.

My custom FCD is simple, just a diode and a resistor...

Keeps the MAP reading from getting above a pre-determined value... ;)

Works perfectly.