Hitting FCO with Boost controler off

[rolman]

Hello everyone.
I am fairly new to this board and this is the first question I have had to ask.
I have read quite a few posts and am impressed with the knowledge some of you guys have.
My big question: I have a 92 turbo supra- (automatic with basic upgrades,
HKS intercooler with hard pipes, 3 in exhaust, greddy profec boost controller, upgraded turbo, etc). Until recently the car ran perfectly. Now I hit fuel cut when ever I accelerate hard. With the boost controller off I should be running stock boost limits and not hitting FCO. I have checked for leaks, found none. I checked timing per documentation, it is set to 10 degrees with e1/t1 jumpered. Unjumpered timing goes to about 5 degrees. Is this the issue? or could it possibly be a stuck wastgate? The car run good as long as I drive without boosting past stock limits. Problem is like having boost controller set on and being set to high.
Any help is appreciated...TIA

 

[GrimJack]

Actually, with the upgrades you mention, you should be running a fair bit over stock boost with the controller off. We've made virtually stock cars here hit FCO with only once of becauseican's divorced downpipes!

The timing will have no effect on FCO.

Did you just add something that would reduce flow restrictions to the engine? How did you check for boost leaks - did you pressure test the intake tract, or was it just a visual inspection?

If you've just hit the mod level where you are pushing too much air, then you'll need to ante up for some hardware that controls FCO, like a MAFT and GM MAF, or the venerable Lexus AFM / 550cc injectors combo.

 

[$pecialk91Turbo]

I have the same problem after I put on my DDP. I felt around under the turbo though and I think my actuator arm is hitting the flange on the ddp, which is not allowing the wastegate to open all the way. With the MBC turned all the way down my boost jumps to about 7-8psi and then creeps to FCO at the top of the gear. I dont know how to fix it though.

Anyway, check your wastegate actuator. Maybe the arm was bent somehow.

 

[becauseican]

Fuel cut is based on Air flow, not boost pressure. An upgraded turbo will flow a lot more air at the same boost pressure, which is why you are hitting fuel cut. The upgraded turbo will probably flow the same amount of air at 10 psi as the stock one does at 12-13 psi. Yes the actuator arm may be bent and hitting the downpipe flange, you could just tweak it a bit so it wont hit the flange if that is the problem.

 

[suprra_girl]

welcome to my world of 9psi
i fixed mine with a fcd but recommended is maft/lexus 550's etc

 

[rolman]

Thanks for the responses from you guys.
This weekend i will be critiquing some of the items you mentioned. There is something that has changed or gone defective recently though. I have had all these mods done for a while now (last mod was 3" CAT inline with HKS downpipe done a year ago)
This problem just started a couple of weeks ago. Previously with boost controller of under full throttle i wouldn't hit FCO, now i do.
Once i find the problem i will keep all in loop.

 

[Steve_N]

I would double check your hard pipe couplers. Make sure they are on snug & clamps are tight. 1st ones to check would be at the throtal body to 3Kpipe & at the turbo to IC. Replace any that has any small rips or tears. Even if they are small under boost they will expand & cause a leak.

 

[GrimJack]

Sounds like the evil boost leak to me. Pressure check that intake!