I have a s5 tII and recently installed an autometer boost gauge and an apexi power intake. My boost gauge is only getting up to around 6psi. My car has 126,xxxk on it. Do you guys think it is boosting properly?

 

Stock boost level for an S5 is 5.5 PSI. Check the exhaust, your cats are probably glogged.

 

reference my other question:

https://www.rx7club.com/forum/showth...threadid=94483

 

Are you SURE? I thought people were saying like 7 PSI for S4's, and 8 or so for S5's?

 

I'm sorry........please disregard my previous post. S4 hits fuel cut at 5.5, stock S5 boost is in the 8's. I'm sorry again.........I'm trying to think about too many things at once.

 

ok, just wanted to make sure that I wasn't backwards or something..

 

S4 doesn't hit fuel cut at 5.5. I have a S5 core/turbo and a S4 ECU, and my fuel cut is about 8.5 psi.

 

It's got nothing to do with the turbo, only the ECU. Both turbos have the same wastegate and will boost to 6.6psi, but the S5 has a bleed solenoid controlled by the ECU that raises boost to 8.25psi. Without the ECU control, an S5 turbo on an S4 will boost the same as the S4 turbo. Both ECU's cut fuel at 8.6psi.

88gxl, you probably have clogged cats.

 

I would kinda doubt the clogged cats if it hits exactly 5.5 psi like he says it does.

 

I was talking to 88gxl. His boost is supposed to be 8psi...

 

NZ, thats strange, because I have a S4 ECU, and yet I boost 8-9 PSI always, although I've been hitting fuel cut now.

 

So do I, but my cars modded and I bet yours is too.

 

Hm... well, it has always boosted over 6 psi when I had the stock exhaust. Actually, the previous owner had a midpipe on. He *said* it was an 89 Jspec engine, but I know it isn't now, because of sensors and everything else. When I got the catback on, it boosted more, then the downpipe, even more. Didn't think the wastegate was being overrun.. but oh well

 

My TII hit fuel cut at a little over 5 lbs on my aftermarket gauge. I built my FCD and now my boost goes up to 9 PSI.

 

I'd get that gauge checked against another one. Fuel cut is at 8.6psi for all models (it varies a bit but it's never under 8psi), so you may have a gauge error. If it was reading ~5psi at 8-9psi, what's the actual boost when your gauge says 9psi...

 

I swear, every single person says fuel cut is different for S4 TII's. This is my second boost gauge in the car and they both hit fuel cut at the same PSI, a little over 5. After I got my second gauge I unplugged the FCD to see if it was reading the same as my first one and it was.

 

This article say 8.6psi: http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm I have a 87 turboII that hits it at approx 8.6psi, and I have monitored the volatge signal from the pressure sensor when it hits fuel cut and that figure matches the graph in the above article.

Is there the smallest chance that you need an orifice in the vacuum line b/t the boost sensor and the intake manifold???????? Maybe your spiking without the orifice.

 

I have searched and searched for that freakin' orifice(it's supposed to be there stock, right??)and I can't find it. I guess I could put one in there and see what it does. I've heard that using a nipple from a solenoid is just about right. Any truth to that?

 

Im having problems boosting too. The s4/s5 gates are diffrent, though the actators maybe the same. Heres how mazda says to check the actuator. Im pretty sure it takes more than 6 psi to open, its probally only part way.

 

The fuel cut point is part of the ECU’s programming, so that should be consistent between cars. The variances would come from the pressure sensor (minor) and the gauge used to read the manifold pressure (could be anything!). 8.6psi is the generally agreed number.
Do you still have the restrictor pill in the pressure sensor line? If the is removed, fuel cut can be hit earlier due to pressure spikes.

 

is there anything he could use (substitute) because i think he doesn't have the pill in there.

 

No, there is no pill, I have switched to all silicone vac lines. I did not find a pill in the old line. Could I use a solenoid nipple as mentioned above as a restrictor pill?