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Discussion Starter #1
Greetings all. First of all, let me say this site is the shiz........
I have be trying to figure a way to raise the fuel cut on my 91 automatic. I am trying to safely boost 12 psi. I have an apexi intake with a 3" exhaust (3" from the flex back) and the primary cat removed. I also have a dawes devices dual stage MBC and a blitz turbo timer w/ boost guage. My headgasket is new OEM torqued to 70 ft-lbs as of January.
I am hitting fuel cut right at about 9.5 psi. On cold days I can slowly accelerate and boost up to about 9.5 psi before FC. However, if I floor the pedal, sometimes I almost immediately get FC. If FC does not come on immediately, I almost always get in on the second gear shift.

From what I read on another site: "Especially the cars equipped with automatic transmission will suffer from fuel cuts because of too high boost pressure.", I'm thinking the fuel cut at such low psi (on cold days) is because I have an automatic transmission.

I have checked for boost leaks and have not found any. I also re-tighted all my clamps. I also re-adjusted the AFM screw, but it had no effect on the car.

From what I've read, it seems my other options are:
1. do the lexus AFM mod with 550 injectors
2. get a fuel cut defender
3. introduce extra air into the accordian hose downstream of the AFM

Are there any other methods available to raise fuel cut and what do you all recommend as the:
1. safest way
2. least expensive way
3. best balance of cost and safety

Any help provided is greatly appreciated.

Note: This is my first post and I've only had my supra less than 5 months, so I'm a newbie in the worst way. If I've said something way out to lunch, refer to the previous sentence.
 

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I'm not sure how you would do #3 on the options list, but it wouldn't work.....you don't want unmetered air entering/exiting the intake.
The easiest way would be to put on a fuel cut defencer, the HKS one is about $65 iirc.
That is not the safest way though, fuel cut is there for a reason.
Beyond that there are several options from the Lex/550s, to a MAFT setup, or a VPC. (search on those 2)
Those would all depend on what your goal with the car is as each has its pros and cons. Whichever of the 3 above you choose, you will need will to get upgraded injectors, fuel pump, and a fuel pressure regulator to do right.
 

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There is something else up if you are hitting fuel cut at 9.5PSI, even on an auto. I could make over 12 easily on my auto. Another thing to do would be to pressure test your system, there are some old posts that tell how to do that. I wouldn't think of making any modifications until you correct that. And Dawes Devices rules :)
 

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I agree with kirk. Check your IC pipes for holes, rips,cracks, loose conections. Check the one from turbo to IC. That is usualy the 1st to go bad. Also check the coupler that connects the 3K pipe th the Throtal body.
 

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For starters, take the stock AFM and drill out the adjustment screw cover. Take the screw all the way out to the end of it's adjustment. That should get you a few more psi before F/C.

Fuel cut is there for a reason though. You should really be using a wideband when playing with boost w/out fuel cut.
 

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Wade said:
For starters, take the stock AFM and drill out the adjustment screw cover. Take the screw all the way out to the end of it's adjustment. That should get you a few more psi before F/C.

Fuel cut is there for a reason though. You should really be using a wideband when playing with boost w/out fuel cut.

:werd:





you probably do have a boost leak though.... there's a crack in a hose, a loose clamp or one that's on crooked. check the plastic one in the fender, that tends to crack as these cars are now 15+ years old
 

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Discussion Starter #8
Sounds like I do have a boost leak that has gone undetected. Since I spent last weekend looking over the hoses and re-tightening clamps, I guess my next task will be to replace the hoses. I guess now only to decide whether I should go OEM, PVC, aluminium, or standard exhaust tubing from a muffler shop.
Ray, regarding option 3 in my first list, I got that idea from here: http://www.supras.nl/mods.htm under CHEAP FCD.
I have done a search on this site trying to find someone who has done the mod, but no luck.

Anyway, thanks all for the replies. Looks like I got some more research to do.
 

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yup yup 10 psi is too low for fuel cut

if it's a stock turbo you can get away with at least 12 before fuel cut, give or take..
 
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