Sorry I can't answer your question, but I do wonder about that ECON button... early Jeep XJ's had the same type of thing but instead called it comfort and power settings. Jeep XJ's use the same valve body as the A340 but possibly different programming/TCM boxes. But, the comfort setting was known for getting worse gas mileage.

The only idea I have about your question is if your ECON mode keeps it in higher gear longer, perhaps the engine gets more load for longer, more exhaust energy, more spool. Let's say If you're accelerating from 30 to 65 in 2nd vs 3rd, my hunch is that the 3d gear pull would put more load on the engine and spool the turbo more. I'm sure someone here will chime in with a more knowledgeable answer.

 

My understanding of those buttons is it changes the shift points in the transmission. Mine sometimes when cold would have difficulty with the first gear and behave like you describe. I normally baby it until it warms up. It would act funny and spool up GO TIME but the transmission hasn't shifted out of first yet.

 

I usually drive my car in Economy mode. There is a place I have to enter the freeway each morning and sometimes I will floor it to make a gap. When I do this, once I get into the higher rev ranges the engine will cut out as the turbo overspools. I know where it does this so I can just relax the pedal slightly, let it upshift and then press on the gas. Recently, I pushed in the PWR button and have been driving in the less efficient mode. This morning when I floored it the turbo never over spooled or cut out, accelerating smoothly all the way from zero to eighty. I thought that ECO vs PWR merely changed shift points. Clearly that is not the case, though I had also assumed that PWR would supply more fuel. Since more fuel = more exhaust, it was my guess that this would make it more likely to overspool, not less. The exact opposite happened.

What am I not understanding here?

Thanks as always for the education.

Do you have a boost gauge installed? If so, how much boost is showing when it hits this 'cut out?'

I suspect this has nothing to do with the transmission, and is in fact boost cut. You will hit boost cut at a lower boost level than most other 7M-GTE's because of the BC 264 cams you have installed. Bigger cams = more airflow at a given boost pressure.

Since boost cut is done by AFM reading, you're likely to hit boost cut at a significantly lower boost pressure with your setup.

Calling it 'turbo overspool' is a misnomer at best, because there's no 'spool' value for a turbo, it's not an empirical measurement of any kind. You can over-speed the CHRA itself (see my avatar for what that looks like) and that usually happens one of two ways:

-A boost leak that's just big enough to force significantly higher CHRA rpm to compensate for the boost leak and maintain targeted boost, this will usually also have noticeably more lag than it should.
-Targeting too high of a boost pressure at higher Density Altitude (empirical measurement of how the air gets thinner at higher physical elevations) - thinner air needs more turbine/compressor wheel rpm to move the same mass of air. This is how I nuked several stock CT26's while trying to run 14-15psi with fuel system changes and piggybacks.

In both cases, you'll see additional lag and reduced power, but you won't hit any direct 'boost cut' or hiccup sorts of events from the engine. At least, until the CHRA itself fails and the turbo looks like my avatar, in which case you'll suddenly have zero boost and likely a cloud of oil smoke coming out of the exhaust.

 

higher Density Altitude

This is very funny, btw. I live in Texas and can be standing in the waters of Gulf of Mexico in about 60 minutes drive. I live my whole life below 100 feet elevation.

 

Hey final,
Not dick holing your thread but…
What is Econ & Power selection?
I saw you have an mkiii.

 

He's talking about the auto transmission's switchable shift mapping. It's a button typically labeled 'ECT PWR' next to the AT shifter. 5MT Supras never had any of that.

 

Tanks Wreckless...
Did not know that.

 

In econ the transmission will shift early. My arm-waving guess is the car is shifting at a lower rpm where the CT26 is more efficient and that is resulting in a boost spike that is causing fuel cut. When an auto shifts the throttle stays wide open and the suddent drop in engine rpm will cause a boost spike since the turbo is still fully spooled. I see it on my car in cold weather.

 

Thanks to everyone for the replies. I meant to write “overboost” instead of “overspool” though I guess the situation is the same: too much boost pressure.

I do have a digital boost pressure gauge installed. I’ll do some tests watching it when I intentionally push it this hard and report back.

 

You are referring to fuel cut where the check engine light flashes (code 34) and the car loses power?

 

Yes. When my rebuild was complete one of the mechanics showed me how to cause this and explained what is happening. He said the check engine light would come on but would clear on its own. He said normally I wouldn’t be flooring the gas but wanted me to know what would happen when I did.