Fuel/Boost Cut at 85-90mph in 4th gear

[MConte05]

So I was out on my little stretch of gravel road doing testing for the upcoming 100AW in my Legacy Turbo rally car. Very cold outside, and anytime I was doing a long pull and doing sustained speed in 4th gear once I got around 4500-5000 RPM's it would fuel/boost cut on me. I kept getting out and turning down the MBC that the car has till it was practically about to come off, as low as it could go, and it would still keep on fuel cutting at sustained pulls.

Any ideas?

Stock VF11, stock engine, 3" full turboback, MBC. Boost gauge was around 12-13 and kept rising as more load was put on it in 4th and 5th gear. Pulls strong at lower gears.

[alexandermf]

If your boost gauge kept rising check the hoses running from your mbc to the turbo. Make sure they aren't ripped or blown off the compressor nipple. Mine does it every once in a while and my boost gauge always shows a little higher boost in 4th and 5th versus 1, 2 , and 3.


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[robertpaige]

Double check your wastegate and housing lines. Make sure they are really on there and have a snug fit.


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[Legacy777]

I would agree with the others; check the MBC and vacuum/boost lines. The ECU is kicking in fuel cut at the right spot, so it's likely something where the MBC isn't limiting the boost enough or vacuum/boost leaks.

[MConte05]

You guys were spot on.

I visually checked the lines, didn't see any problems. It wasn't until I went to pull them off to see if there was a restrictor pill in it did the line break about 1/2" from the compressor nipple. I suspect that it was cracked just enough that it bareeeeely allowed for 13-14psi in 4th and 5th gear. Even when I had the MBC cranked full off it would still boost that high.

Replaced the lines, put good clamps on them, and now the MBC is functioning properly and boosting correctly. Now to dial in that boost for 100AW....

Thanks guys!

[Legacy777]

Good deal! Glad it was an easy fix.