High Altitude FCD issues...

[farfrumwork]

So I finally installed the version 1 VRG FCD I bought used a year ago.

I turned by boost up a bit more for a test run (14.5 peak in 4th), and I still went into fuel cut in said 4th gear (vf12, TBE, A/W IC). It did seem to push off the fuel cut from where it was, but I REALLY want to run 14-15psi and NOT have fuel cut at ALL I think as it stands it may run 13-14psi without cut, but ?

I am certain that I installed it correctly (it's not that hard). I saw *some* references to high altitude problems with the FCD, but no conclusions.

Has there been some dicovery related to this. Any theories? Maybe the FCD just needs some different resistors to function "right" at atltitude? BTW it's 5500ft ASL here.

Any input would be appreciated!

-Chad

[biggreen96]

I had the same probs, and ended up going with an adjustable turboXS.

I you were to add mile high functionality with another resistor or something once you took a trip to lower levels it would let you boost higher than you might want to.

[farfrumwork]

Thanks Biggreen

Maybe I'll look into some of the adjustable units, (I just liked the cheap FCD! - oh well)

I am kind of wrestling with the concept though. I don't quite understand why higher altitudes change the function of the voltage clamp...? I read of many people running 16+psi at lower altitudes when using the VRG FCD

We have a lower starting pressure than at lower altitude (sea level), so I would *think* that there would be a larger window above that before boost cut occurs. Say we are at 12.5psi (~atmosphere at 5280ft) vs. 14.7psi at sea level, and the MAP sensor reads up to 27psi, I should be able to run 14.5psi and not see fuel cut (even with NO FCD). Vs. sea level, where it should cut at 12.3psi (or so).
But I can't - I was seeing cut at 13psi or so in 4th/5th before the FCD install. Maybe the MAP sensor works differently than I thought....

[Legacy777]

In theory, you're right.....but something else is going on. Probably the fact that the ECU is taking account for the atmospheric pressure difference and may be lowering fuel cut.

Remember the MAP sensor also provides atmospheric conditions as well.

[farfrumwork]

Thanks Josh,

That makes sense, as the MAP may recalibrate the fuel cut based on atmospheric readings.

I'm going to test my wiring as well. I turned boost down a bit but it still cuts in 4th with ~13.5psi. Maybe it's me

If I don't get it to work, I'll probably try out some mechanical system (pressure relief valve) so the MAP doesn't ever see >10-12psi.

[vrg3]

I know it's been a while, but I just posted in the electronic FCD thread about a way to lower the threshold of the FCD. If the ECU is in fact lowering the pressure at which it cuts fuel, my suggestions there will solve the problem:

http://bbs.legacycentral.org/viewtopic. ... &start=130

[farfrumwork]

Cool, I'll check it out. although I have a 10psi pressure release valve performing my FCD duties at the present time...

Someday the electronic FCD may be necessary again though as the mechanical device has flow limitations and I will be pushing more boost in the future

And hey, Vikash is BACK!