engine cuts out at high boost/revs

[mattsavage]

Hi. This maybe a similar question to the boost cut question, but I am pretty new to the RX7 so I\'m not sure what my problem is.
I have just bought (with your helpful advice!) a 1991 gen 2 turbo. It had the engine rebuilt about 6000 miles ago. It has had slight porting done and it has a sports stainless steel exhaust with the cat removed. I think the ECU is standard.
It goes very well. But sometimes when I put my foot to the floor the revs go up, the boost gauge goes up, the car accelerates but then at about 4500 revs it stops for a split second then carries on. If I am a little more gentle it doesn\'t do it.
It seems to only do it when the turbo boost is very high (right near to the top of the gauge)
Any ideas what could cause this and how I can fix it.
Cheers,
Matt

[Prof]

Revs seem a little high to be this problem, but check this out all the same:
 
http://fc3spro.com/TECH/FAQ/3800.html

[mattsavage]

Hi. Thanks for the reply. But like you say I don\'t think that this is my problem. My problem only happens on full throttle and only at higher revs. I can\'t make it do it all the time, but it seems to only be at high boost and high revs. I\'ve only had the car a few days, but 4500 revs seem to be the most often for the cut out, but it can be higher, like 5500.
But, as I said, if I am just a little more gentle (i.e. not just flooring it) then it doesn\'t do it.
Let me know what you think.
Cheers,
Matt

[ramirez]

I was / am having a similar issue with my T2 and the general consensus was that it could be plugs / leads. I haven\'t got round to fixing it yet but it sounds similar.

Have you got a fuel cut defender / boost controller at all? Also have you tried higher octane fuel?

Any particular gear?

[Prof]

That almost sounds like fuel delivery - although I would check out the bit about earthing in the link I sent - earthing issues can cause all sorts of funnies.
 
I found the wiring to the boost sensor on my very to be a little dodgy - intermittent readings - but you would see that because the boost gauge would falter.

[mattsavage]

Hi. Thanks for that.
What is a fuel cut defender? And what is a boost controller?!
As I said, it only seems to do it when the boost gauge is right at the very top, so I guess some sort of sensor is cutting power (fuel?) to stop it going too far. It only cuts out for a split second, the boost goes down a bit, then it carries on.
Many thanks,
Matt

[mattsavage]

Oh, I just noticed you asked if it does it in any particular gear, well, it can do it in any gear, but only when there is full boost, so it is mainly 2nd and 3rd. But that\'s just because there is more boost then, especially if you are going up hill.
Cheers,
Matt

[mattsavage]

Hi. I just tried it with no air filter and it was worse!
Any ideas?
Cheers,
Matt

[grinder]

sounds like you are hitting boost/fuel cut to be honest

have you got a after market boost gauge on the car ??

if not - get one and see what its boosting to when it cuts off

the stock ECU cuts the boost/fuel about 7-8psi

so in theory - you should beable to rev to the red line ( OFF BOOST ) but once you hit 7-8psi it should cut out

is this about right ??

Stu

mine did the same thing on the 1/4 mile - i didnt half panic when it happened - yeah im convinced now its fuel/boost cut

[mattsavage]

Hi. Yes, that sounds like my problem! It can rev to red line (buzzer) and works fine, but it is only when the boost goes right up to the top of the gauge that it cuts.
I\'ve only just bought the car, the gauge is the standard factory one. The needle goes right to the top (45, 10 x mmHg) (what is mmHg?).
 
So to fix the problem, do I reduce the boost, or let the ECU cut it off at a higher pressure?
 
Please let me know what you think. Oh, and could you let me know how to do it!!
 
Cheers,
Matt

[grinder]

if you are hitting the top of the stock boost gauge - then you are over boosting

this is down to a straight thru exhaust and filter usually

the way i fixed mine was to get a FCD - this stops the cut

its about a 3 second job to fit

1 - remove plug to pressure sendor ( driver side strut tower )
2 - plug that into the FCD
3 - plug FCD into the pressure sendor

job done - just need need to get one now ( most of the tuners will have them )

just make sure you get the correct one ( S4 or S5 )

Stu

[mattsavage]

Thanks. Yes, the car has a new exhaust with no cat and not many silencers!
What\'s an FCD?!
Cheers,
Matt

[mattsavage]

Hi. Sorry, but what is S4 or S5? Engine type?
I\'m new to these Mazdas!!

[mattsavage]

Got it!! Fuel Cut Deffender!
Where can I get one from?

[grinder]

if yours is a 1991 - then its a S5

the FCD - its full name is :

Fuel Cut Defence ( i think ! )

it stops fuel cut - which sounds like is happening to you

it fools the ecu into thinking that its running lower boost

mine pulls all the way up to .9 Bar ( and is still running rich )

so thats what i would get

what happens at the mo - is that the ECU cuts the fuel to the rear rotor when you hit 7-8psi as a safety measure - it stops you over boosting

so you can either get a boost controller and limit the boost to 7-8psi or get the FCD

this is my opinion anyways - speak to a tuner for more info ( or a better explaination !! )

Stu