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Discussion Starter · #1 · (Edited)
All,

Since we received our UTecs, David and I have been struggling with boost-induced fuel cuts even when utilizing the UTec FCD disable feature. It was traced to the MAP clamp implemented by the UTec which is actually of a higher voltage than that which the ECU sees as 'overboost' when running at high altitudes. David opted to pay for the external TurboXS FCD device, but I decided to seek out an alternative (lower cost) solution.

Henceforth I have constructed a prototype of an adjustable FCD which will be tested on my WRX this weekend after I return to Colorado. Assuming that the device functions as designed, I intend to initially produce these in small volume batches. Since each unit is assembled by hand, there will be a small markup over the raw component cost. This is to help offset my assembly time and effort, as well as the R&D of locating an appropriate schematic and asserting its application to the WRX ECM.

Some loose details:

- Adjustable clamp-type FCD.
- Professional black-box packaging.
- Requires splicing into ECM harness (3 wires).
- Installation instructions included for UTec'd cars, as well as for those with no aftermarket EMS.
- Pre-configured clamp voltage with instructions on adjustment (should not be necessary).
- In-built circuit protection from voltage spikes.
- To be priced under $50.

The aftermarket FCD is a necessity for high-altitude cars running UTecs who wish to boost in excess of ~18psi, as well as any WRXs (at any elevation) which do not have an aftermarket ECM capable of clamping the MAP signal.

Given that I have some testing to perform, and documentation to assemble, the first batch of five should be ready to ship the last week of April or first week of May. If you are tentatively interested, please post here. I know that the overboost fuel cut is of particular concern to high altitude owners as a number of you have been dealing with this on a daily basis, as I have. Nobody likes paying $150 for a $50 device.

Best regards.

-Pace
 

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Discussion Starter · #4 · (Edited)
Mad WRX said:
At what boost levels do you experience fuel cut?
I'm told that the ECM adjusts the overboost MAP threshold according to elevation (ambient barometric pressure). Essentially there is some elevation where the overboost voltage drops below the UTec clamp voltage. Once that happens, you are fully at the mercy of the stock computer.

At 10,000ft I can trigger a fuel cut at about 1 bar of boost. At 8,500ft I am good to about 1.2 bar of boost. Down in the foothills I have managed to push about 1.3 bar before experiencing problems.

If you have a UTec and only drive around Denver at 18-19psi then you will likely never encounter the fuel cut. Start pushing some serious boost or drive up into the mountains, and you'll trigger the cut.

Honestly, if conservative boost settings mean you never encounter this issue, then there is no point fitting an FCD.

-Pace
 

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interested

well i hit my cut on the way to cripple creek today, not sure of the exact elevation i was at, but i was boosting to about 1.2 bar.

keep us posted on your progress


cnstman
 

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I wish I paid more attention in HS physics, but do Bars translate directly into PSI? If so, what is the conversion?
 

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Thanks.

Interesting how 1 bar = 14.5 psi and I think stock WRXs max at about that level.

Isn't barametric pressure relative to elevation though? Or is 1 Bar = to 1 barametric pressure at sea-level and every Bar figure relative to sea-level Bars?
 

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Discussion Starter · #10 · (Edited)
WTypeRogerX said:
Thanks.

Interesting how 1 bar = 14.5 psi and I think stock WRXs max at about that level.

Isn't barametric pressure relative to elevation though? Or is 1 Bar = to 1 barametric pressure at sea-level and every Bar figure relative to sea-level Bars?
1 Bar != 1 atm. But it's really really close. ;)

Don't try to confuse yourself with elevation. Bar is just another pressure scale like psi or kg/cm3.

-Pace

p.s Semi-interesting sidenote. The WRX MAP sensor is a 2.5 bar unit, but this is quoted as absolute. Hence, at this altitude it can read to approximately:

2.5 * 14.5 - 10.5 = 25.75psig (+/- 1psi for elevation variation).
 

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Discussion Starter · #12 ·
The prototype evaluation was successful. I think I have determined an optimal clamp point; at least for the kinds of elevation I drive at. I have been pushing 1.5bar at >9,000ft elevation with no triggered fuel cuts. A cut would likely occur at some higher altitude as the ECM safety threshold voltage drops below my clamp voltage, but in that event the adjustability of the FCD allows the clamp point to be lowered further. Essentially the clamp is adjustable down to zero volts, so this device can be configured for any boost/elevation scenario.

A number of people have expressed interest in this. Over the next couple of days I am going to be investigating fabrication options to determine the cheapest method of small batch assembly, and will also be ordering the necessary components. The first batch should be ready within a couple of weeks.

-Pace

p.s My car feels mean at 1.5bar. Too bad the VF22 won't hold up to that kind of abuse. Hence, the 20G. :)
 

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Discussion Starter · #15 ·
I found a low-volume PCB fabricator and this morning I sent the PCB artwork off for a quote. I am pretty confident it will prove to be a cost-effective approach, but if not then I'll just lead-wire all the component connections instead (as I did with my prototype).

Stay tuned.

-Pace
 

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Pace -

What does the '-10.5' represent in the following equation?

2.5 * 14.5 - 10.5 = 25.75psig

I understand the other numbers...

2.5 (2.5 bar senson)
14.5 (1bar)

TIA.

-p
 

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Discussion Starter · #18 · (Edited)
aussieinstlouis said:
I reckon 10.5 is the approximate barometric pressure at 10000 ft??
Correct. 10.5psi is the approximate absolute barometric that I see at my house, ~9000ft ASL.

AFAIK, when they spec MAP sensors as (for example) 2.5bar, it is quoted as absolute (not referenced to sea-level). Therefore to convert to approximate relative boost you need to deduct your local ambient barometric.

On another note: The design was accepted, and an order has been placed for the first batch of PCBs. They should be here within a week or so. It will then take a few days to assemble all the FCDs.

-Pace
 

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Thanks for the info, guys.

Pace - I would be interested in buying one of these. I have to crank my boost WAY down to avoid fuel cut when I'm heading west out of Georgetown. Cheers.

-p
 

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Discussion Starter · #20 ·
Dizzy said:
Thanks for the info, guys.

Pace - I would be interested in buying one of these. I have to crank my boost WAY down to avoid fuel cut when I'm heading west out of Georgetown. Cheers.

-p
Ok. Will put you on the list. They should be ready in a couple of weeks, and I can set the clamp especially low for you if you do a lot of very high altitude (>9,000ft) driving.

-Pace
 
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