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Hi,

I brought a Fuel Cut Defender (FCD) for my 1989 Legacy RS. The idea is to not cut the fuel over 12.5 psi, which sounds great!

But then I started thinking and not so sure its a good idea. The boost pressure in my car is control electronically by the ECU, but has been reset to 14psi by an eprom chip in the ECU. I not 100% sure on how the FCD works, but I think it lies to the ECU to tell it that the boost pressure has not gone over 12.5 psi.

If this is true, the ECU will have no idea the boost is over 12.5 psi and will not fuel cut but it will also not stop the boost pressure from increasing at 14 psi. Therefore the boost would never stop! well, not untill the engine stops

Is this right or wrong?

If I'm right, I guess you could still use a manual boost controller. eg: boost tap or dual stage controller????

Thanks
Hayden

Don't the chips you guys can get also raise the fuel cut, to account for the increased boost? You might want to give a look through http://www.rslibertyclub.org/forums/index.php, as they have experience with reprogramming the ECU.

Basically you are right. The FCD is wired inline with the map sensor output wire to the ecu. The FCD does this by clamping the voltage to the ecu. Therefore the ecu never see's boost over 12.5psi(or equivilant map voltage). By doing this you eliminate the engine's only protection, the ecu. It is recommended to install a boost gauge first, so you dont over boost and cook your engine. Also a good boost controller is a given. Dont be too disheartend though, it can be, and has been done successfully by alot of the people on this board.

http://bbs.legacycentral.org/viewtopic.php?t=14620

Don't forget to intercool.

Tleg93 wrote:Don't forget to intercool.

He has an RS. His came with an intercooler, would have save us some work if our version did

Thanks for your comments.

Yes, my RS has AWIC and it seems to work pretty well.

The car is acting like it is getting fuel cut at the moment. It should run at 14psi, but spikes to 13psi and then drops to 11psi (thats what my boost guage says anyway). I also have a air/fuel guage running of the O2 sensor. When I hit 11psi the mixture leans a little but not too much.

Could be fuel cut, or that I have a completely standard fuel system (pump, filter, reg, rails, injectors).

Your comments please!!!

You KNOW when you hit fuel cut

It feels like you suddenly hit a brick wall or something. It's quite jarring.

hmmm, no sudden change in the engine. But the power sort of dies out, it continues to accelerate but not as angry about it

Maybe not fuel cut. Just the limit of the turbo/fuel system?

mikec,

went to the http://www.rslibertyclub.org/forums/index.php link but there are no posts in any of the threads. I have been to this site before and it has been like that every another time as well. There are people viewing the threads but no posts to view???? weird!

Does anyone else have this problem?

http://www.rslibertyclub.org/forums/index.php


Ask there. They'll know exactly what you need.

RallyRS wrote:Hi,

I brought a Fuel Cut Defender (FCD) for my 1989 Legacy RS. The idea is to not cut the fuel over 12.5 psi, which sounds great!

But then I started thinking and not so sure its a good idea. The boost pressure in my car is control electronically by the ECU, but has been reset to 14psi by an eprom chip in the ECU. I not 100% sure on how the FCD works, but I think it lies to the ECU to tell it that the boost pressure has not gone over 12.5 psi.

If this is true, the ECU will have no idea the boost is over 12.5 psi and will not fuel cut but it will also not stop the boost pressure from increasing at 14 psi. Therefore the boost would never stop! well, not untill the engine stops

Is this right or wrong?

If I'm right, I guess you could still use a manual boost controller. eg: boost tap or dual stage controller????

Thanks
Hayden

Yeah, you're right. If you are still running the stock electronic boost control based on the pressure sensor signal, then you don't want to do anything to screw with that signal or else obviously the boost control would also be screwed.

Running manual boost control would fix this problem, because the boost control would no longer use the pressure sensor, and therefore you could have your way with the pressure sensor signal. But then the chip was kinda of silly

Mikec has an interesting point. It seems like their chip would have to adjust the fuel cut at the same time that it adjusts the boost. Otherwise, you're screwed and the whole chip doesn't make sense.

RallyRS wrote:Maybe not fuel cut. Just the limit of the turbo/fuel system?

Thats what it sounds like to me. You're probably running extremely lean at high boost, you'll probably want to look at bigger injectors ASAP

RallyRS wrote:mikec,

went to the http://www.rslibertyclub.org/forums/index.php link but there are no posts in any of the threads. I have been to this site before and it has been like that every another time as well. There are people viewing the threads but no posts to view???? weird!

Does anyone else have this problem?

I just checked - you have to register and login before you can see anything. I guess they're not as friendly as us

Oops, I didn't see that you had already posted the link Mike.

Splinter wrote:

RallyRS wrote:Maybe not fuel cut. Just the limit of the turbo/fuel system?

Thats what it sounds like to me. You're probably running extremely lean at high boost, you'll probably want to look at bigger injectors ASAP

Or it could be fuel starvation. Like Splinter said bigger injectors, BUT without the proper management bigger injectors can only do so much. I would say get a walbro pump too. check all of your vaccum lines also.

I think you are all right! I need a better fuel system if I want more power.

And the EPROM chip thing, just confuses me. No idea what is it doing?

I have a fuel/air guage (LambaLink) and Knock sensor display (Also Link), and these show things to be fine, as I said a little lean at the top but not bad.

Everything cost money and more power is on the bottom of the list at the moment. The car is mostly a rally car now just needs a trip meter and turbo restrictor, then lotsa tyres .

I hope to rebuild the fuel system and fit a Link ECU during the off season. I also plan to get some head work done and I have some Pro-Drive cams to put in. Hoping for over 300Hp with the restrictor in???? but we will see what happens.