Snook

iTrader: (12)

If the stock ecu Fuel cuts around 12psi and the stock fuel system is good for 13-14psi could this work in place of a piggyback ecu like the M2/Pettit etc?

Or does the stock computer not have maps for anything beyond 10 or 12? I've never seen this product before for a RX-7, I know they are one of the first things supra guys do on their way to going BPU - Boost Cut Controller. Anyone ever seen this product or used one?

http://www.ebay.com/itm/RX7-FD3S-Knight-Sports-FCDF-d4-Fuel-Cut-Defencer-fcd-1996-UP-jdm-/171903347022?hash=item28063ce94e&vxp=mtr

DaleClark

iTrader: (55)

FCD's are a bad idea. It limits the output of the MAP sensor to the ECU so it doesn't "see" into boost that would make it cut out.

Of course, now the computer doesn't know how much boost you are actually running, so you don't get fuel and timing for that boost level.

FCD's are a 90's hack - you put that on, then you put on additional injectors, or bump fuel pressure, or some crazy crap. It's a mess to tune and you get sloppy results.

Chipped ECU's go used for VERY cheap, go that route or get a PowerFC. The PFC is one of the best things I ever did for my car, and you can get them for $600-700 easy.

Dale

Sgtblue

iTrader: (16)

^ agree. I think if you use some patience and shop around NEW PFCs are very reasonable these days... As long as you don't insist on having one of the new style commanders.

Snook

iTrader: (12)

I currently have a pfc but was curious what this did.

So what exactly does the stock ecu do that makes it bad for anything but stock boost levels? I read it fuel cuts at 12psi right? It has no fuel map for above 10psi?

So the pettit and m2 piggybacks remove fuel cut until higher boost or all together and have richer maps for the higher boost?

Natey

iTrader: (19)

Raise the boost, mess with the AFR...Richer maps all around.

Only the Pettit Unlimited does away with the fuel cut.
I think the problem/danger with raising the boost on a stock ECU is running lean and going zoom zoom boom.

Out of experience, when I went from the Pettit Unlimited to a well tuned PFC.. WOW. Bang for the buck champ>

Snook

iTrader: (12)

I'm just trying to familiarize myself with what the details are with stock ecu characteristics.

I remember that if you keep the boost at 10 the AF is fine even with all bolt on mods.

So maybe you could either raise the boost a little or put some flow mods on but not both.

SA3R

PFC has no knock-spark retard. If it knocks, it goes boom with the PFC.

Stock ECU can pull back timing if the knock sensor senses knock.

This may be the ultimate benefit to using a chipped stock ECU as I do, rather than the PFC, which I'm not a fan of (and I have all the datalogit stuff here, but I refuse to use one in my car).

Montego

iTrader: (1)

This statement just sent us back 20 years. There is a reason why the fd got the reputation of eating motors... Which basically boils down to is sufficient fuel. The three mod rule took years to eradicate but the reason that rule came about was because of all the people blowing motors.

Wade performed lamba tests on the stock ecu and through him it was proven that the stock ecu runs rich enough for flow mods @ stock levels. However he also proved that it's the elevated boost that kills motors on the stocker because it doesn't supply enough fuel to support that.

In terms of cfm: increasing boost is not the same as adding flow mods.

j9fd3s

iTrader: (3)

we know a little about the stock ecu, and it doesn't work quite like an aftermarket ecu, like the PFC. the stock ECU actually comes up with a calculation based on RPM and MAP, and then it has corrections for, knock, coolant and air temp, and a bunch of other things. then there is also a small correction table. so it comes up with a base duty cycle, adds the corrections, looks at the correction table and then outputs accordingly.

timing is just an rpm x boost table, with knock feedback.

the stock fuel cut starts around 12-13psi depending on the rpm (its higher during the transition), and then the fuel cut actually stops, and then the fuel comes back on, and the ecu will keep outputting until the CEL comes on for the MAP sensor.

my friends car has a boost control problem on the 1st turbo, and if you just mat it, it will hit 20psi on the first turbo, and so it blows right through fuel cut, and then over 17psi the CEL comes on for the MAP sensor...

as pointed out, the fuel cut defender goes between the MAP sensor and the ecu, and keeps the signal the ecu sees under fuel cut, which is actually bad because the ECU is actually working up to the limit of the MAP sensor.

the chipped ecu's just have the fuel cut turned off in the software. depending on which chipped ecu* they can have more boost, different timing and fueling, or actually be single turbo.

*back in the day we used to run the M2 ecus, and we didn't have any way to measure it, but it seems like they just had the boost cut turned off and the boost set to 12psi. i have an RE Amemyia ecu now, and i can tell they tuned a lot more, it runs way differently than the stock ecu.

j9fd3s

iTrader: (3)

BTW the chipped ECU's usually sell very cheap, as everyone wants a PFC.

HDA

iTrader: (2)

So if I put a downpipe and High Flow Cat would I have boost problem and need to upgrade the ECU? Stock everything else.

I really down want to go through the hassle of tuning it, I just want to keep things cooler and go zoom zoom sometimes. Without the boom

j9fd3s

iTrader: (3)

with the stock cat back it would probably still be ok, but yeah a chipped ECU is probably a good next step. with the JDM ones they have the thing pretty fully unlocked, and as such they are able to offer stock without speed cut all the way up to big single turbo tunes. if buying used it is important to know what the tune is, or buy one you can send back to japan and get the right tune in it.

Re Amemyia usually puts a sticker with the tune on the ECU, and then they have the menu on the website, so its pretty simple. knightsports also labels their ecu's well too. both companies will rechip an ecu if desired, although they do not speak english, so you either need a translator or go between.

there are many other JDM shops that tune ecu's, so i mention the two that we know about. Blue Tii had his knightsports ecu retuned

Snook

iTrader: (12)

The stock ecu sounds pretty good. If the car came with bigger injectors and a better fuel pump from stock and the stock computer supported that I bet the car would have had a completely different reputation. And I bet bigger injectors, fuel pump and map sensor would have cost mazda another 200 per car if that. The stock ecu should have supported the max boost levels that one would reasonably run on pump gas and with the stock turbos, common sense...otherwise there should have literally been check engine light warnings and limp mode in place when a car ran a lean condition once, so the dealer could explain the deal to customers

Snook

iTrader: (12)

So stock ecu will fuel cut starting at 12-13psi to warn you that you're overboosting.
But up to that point its using maps that look at boost, rpms, and knock to adjust the timing, so it's exactly what you need just doesn't go up to higher boost because thats all the weak stock fuel system could support and seems like the maps were lean at anything above higher boost.

The piggypack or chipped ecus fuel cut later and try to maximize the stock fuel system to its fullest, what the stock ecu should have really done that I posted above.

The pettit ecu is fully tunable but only doesnt look at knock sensors in its calculations. if you dont have an experienced tuner and detailed tune you are screwed and if you overboost enough you are screwed as it doesnt see knock

Isnt there a newer ecu that looks at knock and tunes itself as you drive? What are the success rates there?

Correct me if I'm wrong as I try to pick this stuff back up.

Montego

iTrader: (1)

Would you have a boost issue? No one will be able to tell you for certain. However if you did have a boost issue, you would need to fix it or get an ECU that can supply enough fuel at whatever elevated boost your car is at.

There are countless threads addressing this issue. Just search under boost spike and boost creep because those two issues are caused by mods. By the way the two are completely different from each other and thus have different fixes so don't think that they are one and the same.

Snook

iTrader: (12)

You will need to have a boost controller and make sure to keep the boost at 10psi. You should be able to do that with those mods. If you put a straight through midpipe on and a catback you probably wouldnt be able to keep it at 10psi because the wastegate on stock twins is too small.

HDA

iTrader: (2)

Thanks guys - as you see I am a newbie to the FD world, I have lots of reading to do and this forum is great to get advice from users like you.

Natey

iTrader: (19)

The rule of thumb with an FD is you get three "airflow" mods before you gotta deal with throwing more fuel at it.
Intake/downpipe/exhaust is cool, but if you add a midpipe and things begin to get dangerous.

Also, a cheap mechanical boost gauge can save you endless headaches and guess work. If you're new to FDs, congrats on your new toy! Buy a boost gauge and an aluminum AST now.

Snook

iTrader: (12)

Boost and Temp Gauges for sure. And definitely don't install a midpipe. That's the kiss of death on this car, even with aftermarket computer, makes boost control difficult on stock turbos that have not been removed to modify and enlarge the wastegate. Not for amatuers for sure!

Monsterbox

iTrader: (6)

You can get away w midpipe if you install a restrictor. Installed plate, cut to diminsions of the flange but kept hole size in center at only 2.25", this brought boost spike/creep back to stock, back in the day on stock setup w midpipe

Snook

iTrader: (12)

Hmm that's interesting, good to know. I would think I wouldn't want a midpipe if I'm restricting it. Probably a high flow cat would be good at that point, if I'm going to be restricted in flow may as well have the exhaust not stink like gas at the same time.

What about FDs that run rich and shoot flames (seems like all with a straight through exhaust). If you're resticting it at the midpipe could the unburned gas explode at the midpipe with restrictor instead of exiting the exahaust? kind of a weird question but thats where my head went. likely extra unburned gas is in the form of gas not liquid and would still exit the catback.

I know the silencers in my dual n1 have always made a huge difference in how much boost I see, the car feels like crap with them in, like a banana in the tail pipe haha

Monsterbox

iTrader: (6)

lol no, the flames will still exit out of the tail pipe. There's no issue to running a restrictor besides the smell. I ditched the stock cat years ago and swapped to a resonated midpipe for the sound and power and utilized a restrictor until there was a chance to pull the turbocharger assembly and port the wastegate.