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LAST EDITED ON 24-Oct-01 AT 07:43 AM (PST) There was a discussion on this over at ASOG, but I thought it was worthwhile over here to make the same post since there are so many turbo'ed peeps.
I had a probem about a month ago with my air-fuel ratio as I was mysteriously going lean at WOT. After a few calls with Bill Hahn and doing a bunch of sensor checks, buying a new fuel rail with injectors, a new map sensor, changing fuel filters, new spark plug wires, and two sets of spark plugs, I FINALLY found out what caused my leanness. My HRC fuel mapper(or FCD) was clamping my voltage at 3.3-3.5 volts thereby sending an extremely low map sensor voltage to the ecu and it in turn sending a low voltage to my fuel injectors. The HRC fuel mapper apparently worked properly for over a year, but for some reason failed me as of late. HRC was happy to take it back, bench test it, and send me a new one. The new one clamps at about 4.35-4.5 volts. I'm not sure I'm happy with this voltage clamp level, so I've looked into alternatives.
I've seen what some other turbo owners use, and many either go by way of HKS fuel cut defensers or what's called a Zenier Diode. Both of these items also clamp your map sensor/MAS sensor voltage so your car won't freak out upon seeing too much boost (or any boost in our cars). The Zenier Diodes go for about .10-.20 cents while the HKS FCD's are about $70 and up.
The thing is now, I want a voltage clamp that will not only be reliable, but not fluctuate every time I start the car, much less as an ordinary side effect of its operation.
Split Sec is of course the company that supplies the VC-1 to individuals who run the STAR turbosystem. After a conversation with those folks, they told me that their product, the VC-1 clamps the voltage at 4.75-4.85, but it was a "soft clamp," so again, fluctuation would be a normal by-product of its operation. They did tell me, and I've heard from a second source, that a VC-2 was coming out very shortly (possibly within a month) that would be a "hard clamp" and not fluctuate and also be adjustable.
That sounds most appealing to me, so I can set the voltage clamp myself, and hopefully find the highest level of voltage my car will allow, before freaking out. I'm just wondering what level of map sensor voltage activates the injectors to operate at maximum fuel cycle. (I'm also wondering if the Spli Sec product may be more reliable since it has its own 12v power feed and ground as opposed to the more simply installed HRC fuel mapper that merely takes the output Map sensor voltage and its ground.)
I just don't want a large amount of fluctuation that will effect the tuning of my car everytime out. Am I supposed to build in a large amount of safety for a fluctuatiing voltage clamp? Am I supposed to tune my S-AFC every time I get in my car to account for a fluctuating voltage clamp?
Just seems important to me if people out there have disfunctional voltage clamps that could or might cause a dangerous amount of leanness in your car. Do your "check sensors" on your S-AFC screen at WOT and see what voltage you get. I'm sure many (or most) are fine...but if not, watch out for leanness caused by a fluctuating or failing voltage clamp.
Jason
98' Eagle Talon ESi-T
Mitsu Super 16g Turbo(HRC)/Custom FMIC
http://springfielddsm.homestead.com/JasonsPics.html
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Jason ESi-T
04' BMW 325Ci
91' Nissan 240SX
98' Eagle Talon ESi (sold)
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The VC-2 sounds like a much better product. 
