PraxRX7

Yea, those 4 things are exactly what I am doing for now.

Nothing more needs to be done really until I am running on a new engine with a new aftermarket turbo.

JarrardB

That's exactly what I needed to hear....

Just one more little question....

Will my car be safe with just a FCD until I can afford/find a new fuel pump/injectors etc?

And what is a SAFC? (...... Air Fuel Comp?)

PraxRX7

not 100% safe.

I mean right now you really have no choice from the sounds of it. Just take it easy on the throttle until you do have more fuel.


Although my car is fine @ 10.5 PSI without an FCD...

These cars sure are good at confusing people.

If you can't afford it, get an FCD AND an aftermarket boost gauge along with either a/f ratio gauge or exhaust temp gauge. That way you can throttle it and "try" not to go over 9 PSI. (Although from the way my car is looking, you could safely run @ 10psi, but don't quote me on that, I suggest staying under 9...I don't know your car, but an A/F and/or exhaust temp gauge would "help" you make sure nothing bad happens.

Good Luck with your Car

Oh yea, and S-AFC if APEXi's Super-Air/Fuel Controller or something along those lines, it basically allows you to add more fuel based on RPM (or boost if you get creative with the wireing.), however, the reason were all talking about more fuel is because the injectors should not really run over 70% duty cycle, and anything over I think about 85% can make the injector go static (get stuck on methinks). Bigger fuel injectors and pump allow you to run more fuel at 70% duty cycle...

I don't know to much, I m learning a lot still from Ted and the others.

BlackDragon

AHH! You guys are scaring the hell outta me. Basically it's like this. I just bought a T2 (which I may be keeping, it's a HUGE ORDEAL that I don't want to get into again) and it currently has a full 2.5" exhaust with a K&N filter and NO FCD. This is BAD. I don't know why the motor hasn't blown yet, thats why I had the compression tested. Anyway, I was just about to order a RB FCD because I figured that would keep me safe. However, if buying the FCD will only complicate things more by allowing the car to reach a point where it runs lean and IS NOT corrected by the ECU (i.e. fuel cut) then thats even worse. So basically, how about this idea to solve both our problems Jarrard. (Because we're both short on cash) What about if we bought an aftermarket boost gauge (autometers are cheap) and a manual boost controller. That way we could set the boost to the stock boost setting without having to worry about it cutting fuel or running lean. Since it looks to me like if you don't have an S-AFC with new injectors and pump, then you're engine is running bad. What do you guys think?

PraxRX7

Well from my lack of experience in the matter:

Well, I would suggest the FCD and just be nice to the throttle for a while, get 2 gauges (autometers are cheap) boost, a/f and/or egt.

That will keep you safe and good until you can afford more fuel.

Manual boost controllers can only turn up the boost from my knowledge, at the lowest setting your car would still make as much boost as it could squeeze through without a manual boost controller.

But I could be wrong.

Just go with the FCD and the gauges, after that you should have no excuse for blowing your engine (unless you get that adreneline rush and stomp on it and the boost goes up to 13 PSI....that could be bad.)

All it will require is a little self control. I am doing the same thing right now, just taking it easy, nothing past 8 PSI except when I was testing @ 10.5 psi without cuttoff

NZConvertible

The thing is, I doubt the ECU would cut fuel part way through an injection cycle. That just doesn’t make sense. As I understand automotive ECUs, they look at each input sensor once per cycle to calculate its outputs. So if you look at each chamber cycle individually, the cycle immediately before boost exceeds the cut point would have the correct amount of fuel injected and normal (hopefully rich) combustion. The next cycle (about 10ms later at 6000rpm!) the ECU sees boost has exceeded the cut point and would have no fuel injected, and hence no combustion. This causes boost to drop, and on the cycle the ECU sees boost has dropped below the cut point, fuel is injected normally and the cycle starts again.
I’m not doubting fuel cut is bad for the engine, I’m just trying to get what’s happening straight in my head. I’m not entirely convinced it’s actually lean combustion that’s doing the damage. Like I said earlier, other cars seem to use this method with less disastrous consequences.
Oh well, I guess it doesn’t really matter coz I’m not planning on going there! Testing to destruction! Now that’s commitment to the cause!

NZConvertible

No, you’re dead right. Boost controllers (manual and electronic) cannot lower boost below the level that would occur without it. Those people that want to buy boost controllers as a first mod, with the idea of keeping boost down will be quickly disappointed. And when they realise how easy it has become to raise their boost, human nature will take over and you can guess the result...

RETed

This would be fine and dandy if the fuel injectors can stop on a dime, but in real life, we know that's impossible.

At 6,000RPM, the eccentric shaft does rotate a full revolution, but the unique rotor face has only gone 1/3rd of a revolution...

We don't know how quick the ECU samples the boost sensor, or how it's control algorithm is in terms of the overboost fuel-cut, but I've blown motors pushing it against the overboost fuel-cut.&nbsp That's good enough result to tell me the whole thing is "bad".


Yep, 1987 Turbo II (black, if it matters), 61k miles on the OD.&nbsp BONE STOCK exhaust system - pre-cat intact; main cat intact; rest of the exhaust is all stock.&nbsp Using a "bleeder valve" to control boost on the stock turbo, I hit overboost fuel-cut on the freeway...once.&nbsp I thought it was a hiccup in the motor (it was a very light hesitation), so I clutched-in and let the revs drop to idle - idle was still fine at 800RPM.&nbsp I got back on it to see if it was overboost fuel-cut - *buck* yep, it sure was - clutch-in, the engine died while rolling.&nbsp I popped the clutch out to get it to "roll start" (at 60mph!), and the engine caught.&nbsp I went back into the garage, pull the compression checker - front all 110's; rear 80-0-0 *oops*.

Now, for the obvious question:&nbsp what the hell was I doing trying to deliberately hit the overboost fuel-cut?&nbsp My original (blue) '87 Turbo II had gone through an engine fire; the car was almost rebuilt and running at this point.&nbsp I "lucked out" with this black '87 Turbo II I bought as a "daily driver", since a used car dealer sold it to me for $4,000 cash out the door; the car has a hideous idle problem when cold - it just would not idle at all.&nbsp It turns out it was missing an intercooler clamp. Lucky me - this happened back in 1996, so a $4k Turbo II with 60k miles was a pretty good find; I had paid $9,000 for my blue '87 Turbo II just 6 months prior!

Sorry for the long saga!


-Ted

BlackDragon

So a full exhaust and a K&N filter will reach past stock fuel abilities? So basically I can't take it to the races next friday and humiliate the integras??? ****! So now I've gotta come up with about $750 for fuel mods and an S-AFC and an FCD and a Boost gauge and an A/F gauge......dammit dammit dammit....

JarrardB

Thanks Guys,

You've been very helpful....

Have any of you had experience with the DIY FCD from teamfc3s.org?

I'm probably going to sit down and make it tonight...

rx7_turbo2

No. A 2.5" exhuast and intake should be OK. Once again it depends a little on the car. I had both those things and ran fine with no FCD, no gauges, no fuel mods. If you want to run with your current mods then get a cheap Autometer boost gauge and install it. This will tell you what level of boost your running with your current mods. If you give it a rip and the boost looks like it's going to hit 10psi then lay off the throttle and make a mental note that you will infact need to address some fuel issues. Then baby foot it around till you get the $$$.

I have a similar problem. I have a hybrid turbo on my S4 car and even with the wastegate wired wide open my boost is still out of this world, and yes it's ported to the max, i am in the proccess of finding a permanent solution.

JarrardB

I got my car back from the exhaust shop yesterday...

I have mandrel bends and stainless all through 3inches from the turbo into a 3inch hi flo cat.....into 2 x 2 1/4 pipes into two straight through mufflers....

I hit fuel cut at 5500 rpm in second....boost is about 8-9psi...

The Ace

OK some nice info in here....so I just HAVE to contribute

First of all, I didnt know that some TIIs -supposedly- had a 11.2psi fuel-cut....I always assumed 8.6psi. If thats the case, then I might try mine for a while without the FCD...

As for the DIY FCD, I was/am one of the guys that actually sat down, made it, and installed it into their cars. I also talked to Paul about some issues with the FCD and the boost levels. As long as you dont mess up the wires AND secure all connections, the custom FCD will work just fine -in fact better than most aftermarket ones Its clamping circuit is much better and follows the signal much more closely...

As for the detonation and the particularity of the wankel engine, I think that other cars are able to "afford" fuel-cut because if they DO meet with "pre-detonation" the most damage they can sustain is the valve cover (valves shooting out the back due to the detonation) or a piston (due to the heat). Both are very easy, albeit not so cheap, to replace. The same situation on a rotary means rebuilding or new engine

As for what causes fuel-cut and what happens next, I'm not TOO into the rotary's combustion cycle, so I cannt commend, but it seems that forcing the rotary engine to hit fuel-cut again and again and again is what does the trick. Hitting fuel-cut once shouldnt be THAT bad....

Finally, I agree that there is no set amount of mods that will "allow" the engine to overboost. For some cars all it took was a DP or mufflers, others have installed full exhaust and intake, and still run without hitting fuel-cut. If it helps, I have 2,5" catback and intake (but probably badly clogged pre-cat) and I'm nowhere near fuel-cut boost limits (my FCD is not installed right now).
In general, you could say that a) a DP, b) a nice catback, and c) a nice AND cold intake, will each add about 1psi to your boost levels. So all of these *should* add about 3psi to your stock boost, so in theory combined they could send your engine over fuel-cut....

Just my 0.02 euro


EDIT: Oops, forgot to rate...

PraxRX7

I went from 7 - 10.5 PSI just from changing out my exhaust to a custom straight pipe of stock diameter back to a custom Y-pipe and on through stock mufflers.

I wouldn't dream of opening up my intake right now, not until I get some more fuel pumping into there. (I might even loosen my BOV tightening screw so that it begins venting boost past 8 PSI, I wonder if that is safe.

NZConvertible

A big vacuum leak isn't really a good idea!

rx7_turbo2

Probably not a good idea.

RX7GT

Some really great info. Answered a lot of q's that I had too about what exactly is needed to avoid leaning out on an overboost. I have hit the fuel cut point several times (right around 8.6) and I have only cleared my factory exhaust (no intake or fuel mods). I guess the old saying of "the faster I go, the broker I get" is very true. I definitely want to go MUCH faster so I'm looking at spending some serious money. I don't like to spend money because I am cheap, but I also don't like to go slow because I am a rotary owner. I'm off to go shopping! ---Jeremy

JarrardB

OK.....I have the option to buy/make a FCD or buy a Blitz Access ECU.......

does anyone know anything about this Blitz Access ECU and what would you suggest I get....A FCD or the new ECU?

BlackRx7

I just bought my 88 white TII and on they way back from missouri (where I bought it) driving back to TExas, I took the FCD off my car because of all I'd heard about the ill affect, well just so happens theres a superchaged GTP grand prix trying to race me and every time I hit 5,500 rpms I would hit the fuel cut, major hestiation so I back off and when I stop to get gas, I slaped the FCD and power was smooth all to 7000, that was when i didn't know how much boost I was running and no a/f gauge.

Now I have my FCD installed with an autometer boost gauge and A/F gauge, I've only hit 6-7 psi max boost, all the time the a/f gauge reading rich.

my question how did I hit the fuel cut if I'm only hiting 6-7psi?

my mods are in my sig
should I be hitingg the fuel cut?

The Ace

With your mods you are only hitting 6-7psi ?
Man something's wrong...you should MOST definetly be hitting fuel cut without any fuel mods to the ECU and injectors....