I know what the fuel cut is but what does that boost sensor do. My car has the exhaust and filter and I need a fuel cut defender. My car is spiking but then it starts cutting out ( stock and it's boosting to 20 pounds). I thought maybe my boost sensor might be bad or unhooked. Or my waste gate is messed up. Or everthing and a vacuum problem. Help plz

 

Bout 4500 rpms is when it does it or bout half throtle, runs great until then.

 

20psi is a lot. Is the pressur line hooked up to the wastegate?

Joe

 

lol 20lbs doesnt sound right, the stock wastegate spring would leak bad. Are you looking at the stock boost gauge when this occurs?

Based on your description, its a consistent anomaly, not necessarily a spike. Assuming you haven't moved or changed anything when this started.

So with larger exhaust, without a FCD you will be experiencing fuel cut around those rpms. Before i would go any further finding the "spike" address your fuel cut problem first with a FCD. Then post your issues as they occur. Unfortunately for many of us, to properly diagnose your car we have to get a accurate and detailed description of whats happening due to the lack of being present when your spike happens.

Good luck

 

My car has been doing the same thing aswell. it's hard to describe but it's basically i can't ever go more than half throttle or i will instantly overboost regardless of rpm. i have looked over and replaced every vac line on manifold and as far as i read in FSM they should all be correctly hooked up.

I was also thinking it was my WG aswell but it doesn't seem to be the WG as far as i can tell.

I don't know if any of this helps but my vac lines on back of UIM are

Top - plugged
middle - Vac spider
Bottom FPR

and i can't remember exactly off top of my head what the 3 up front are going to i will have to take a peek tomorrow. i know one is going to crankcase vent .

 

you can definitely hit around 20psi from boost creep in cold weather. I've done it.

 

yeah, I hit over 20 psi with my stock S5 turbo... with an S4 you could probably easily do it much more.

you fix it by getting your waste gate ported, do not get a FCD until you port your wastegate or you'll just blow your engine with that amount of creep.

 

i hit 20 all the time in the winter in my drag s4... would not advise it (blew the engine)

im gonna go against what ^he^ said
you need to get a fcd now BUT you also need a boost controller just a shitty manual one

 

It sounds like Fuel Cut is saving your engine from blowing up. I would say address the real problems you have. Meaning upgrading the fuel system and the control of that fuel system. If you don't you will blow your engine. You can't run tons of boost without giving the engine more fuel. Do some research on this site and it will pay off for you.

 

ur right, i think a few years ago i tried to install a MBC on my S4 turbo and it was cold as **** out and i do recall seeing a huge 20psi boost spike.

 

Boost controllers CANNOT lower boost. If the wastegate is overwhelmed, and you stick a FCD in there, the engine will instead go extremely lean and blow. The fuel cut is harsh, but it's keeping this engine alive for now.

If you need a temporary solution to boost creep, put the stock intake and a cat back in the car. That'll restrict the system enough to keep boost within reasonable levels.

 

i am runnin stock intake/turbo with ported WG and still have stock exhaust right now.

I have yet to see 20psi creep but i am able to hit 10-14 consistently at under 3k rpm if i go anything more than half throttle. I am planning on swapping in my S5 turbo/manifold this weekend and see if there is any change.

 

The S5 turbo wastegate should be fairly stable with a stock exhaust. The S4 turbo wastegate is tiny, but it's surprising that you are hitting 10-14 psi. When you say stock exhaust, is that 100% stock (precat & main cat)? The only time I ran a S4 turbo was with the stock precat and main cat, and it never spiked over ~7psi.

 

I bought the car the way it is. But doesn't have cat and does have bigger exhaust pipe and aftermarket mufflers. It say for stage one to to do all that and buy a fcd. For stage 1. If I change waste to a external and manaully set it for 7-8 psi, I shouldn't have this promblem? So for now what can I do besides putting stock back on? Can I change injectors to 550 prim./750 2nd and help out? Before long I'll be upgrading everything, and going to need them in the long run right? Need all the help I can get.
I hooked up my aircompressor little air nozle to the vac on waste and with 8-12 pounds it opened real easy. Should it make any noises? What does it do when you grind the waste gate flap? Does it allow only so much boost and thats it or what?
Thanx alot guys

 

Just research more on how turbo's work, and about what other people do. What is happening is that with your open exhaust and intake your stock wastegate cannot let enough exhaust out it's tiny hole, so that exhaust goes into the turbo more and more; that is boost creep. When you port the wastegate it allows more exhaust to bypass the turbo helping to keep boost where it should be.

So you can either put a cat back on with airpump and/or get a stock intake which would be cheap and would help get your boost creep under control, or you can buy the required upgrades for fuel like clean 550/720 injectors, fuel pump, Rtek or other fuel control just to start with. Hope this helps, and just read up a lot and it will save you in the end.

 

I looked again and I still have a cat, my air pump is still hooked up. I was just going to remove and block off stuff I didn't need. There are some vac lines that I don't know where they go. The kid I bought it from had them blocked off. Since finding theses, I don't see any place for them. I'm going to set up pics and maybe someone can tell me where they go? Or show me detailed pics of your guys is motors? Two lines coming off the intercooler one snakes down to intake (bout 4 inch peice of pipe) and the other one is blocked off. And a couple of the rear hard lines to rubber are blocked off. I think I might found my promblem. Any full pics of the turbo side would be great. More than one pic plz. Need a few of them in different places to make sure my set up is correct. Thanx Alot Guys