SaabGuy

Mods on 1987 Mazda RX7 (Built June of 1986)

Racingbeat Turbo Back Exhaust
Racing Beat FCD (Had a Stoaks FCD)
Walbro Fuel Pump (actually took it out cause I thought it posed a problem)
Rewired Fuel Pump
Boost guage, A/F guage, Volt guage(on fuel pump, reads 10.5 to 14)

Tuneups;
Basically every filter, wires, plugs, some hoses, idle adjustments, timing adjustment (I retarded it a bunch to help diagnose this cutoff), TPS adjusted and actually swapped for no difference, Belts, 90% of vacumm lines, disconnected all the electronic connections and sprayed contact cleaner to clean them ALL, resoldered every circuit board that I could get my hands on, reground boost sensor, combed the car for crossed wires (tried) and intake leaks... if its not listed here, I prolly tuned it up.

Engine analysis;
I do not have a compression tester, BUT the car does read between 17-18 inches of vacum at 800 rpm. The car idles smooth and pulls just as smooth. very smooth. 143k miles on motor. Hot start is not a problem, it always starts and never ever floods. I never have to tap the gas to start the car.

When the engine was stock, the car ran flawless. no cut off.

What the car is doing;
I suspect Fuel cut. My FCD was purchased used BUT I was able to test it using the method for testing the Stoaks FCD. I had a Stoaks FCD and the cutoff was just the same, which is why I bought the Racingbeat FCD.
The car boosts to 8-9psi of boost and it seems to hold that boost until 5400-5600 rpm at which point it will die like someone hits the key. IF I UNPLUGG MY BOOST SENSOR and run the car, it will not hit this cutoff (I know, very dangerous, but what else can I do.) ALSO, I can freely rev the motor to 7k in neutral, or run any gear up to 7k as long as I keep the boost down. I opened up the RB FCD and noticed that it has a trimmer, so I tuned it to choak at about 35 on the stock boost guage (thats about 6.7 psi) and it still cut out.
I checked engine codes to no success.

Please help me!

Could an administrator please stick this up top so everyone can have a piece of my problem? I cant afford a new motor right now.

ATVmasta1 on Aol Aim
supertegrs@yahoo.com

SaabGuy

oh ya, I bought a new restrictor pill which goes inline with the boost sensor. that did jack ****.

Scott 89t2

is it possable that the FCD is for a series 5?

or maybe you have the wrong boost sersor for your car??

SaabGuy

The FCD? it could be possible, but the RB number matches the one they sell for the 87-88.

The incorrect sensor?? That could maybe be a posibility, seems kinda strange though.

SaabGuy

people, please I need a lot of help over here. Im about to park my car and forget about it cause this is so frustrating. If anybody has any clues as to why my car is being a little bitch, please respond.

Thank you.

HAILERS

Maybe the knock sensor?? Sounds like the fcd is doing you no good, just as you said. I hit fuel cut at approx 8.5 without a fcd. To be sure its fuel cut, why not get a wire tap and tap one of the injector wires and see what is happening to the injectors when you hit this barrier? With the knock sensor maybe you can unscrew it and lay it in someplace where it does not contact the engine or maybe something as simple as disconnecting it and having a go. By the way, when you turn you key to on, where does your needle on your boost gauge rest. On zero or possibly below zero?? What brand boost gauge are you using????? EDIT: Here's a better idea. Why not monitor the signal from the boost/pressure sensor at the ECU with a meter and wire tap. See what the voltage is when you hit this barrier that seems to be fuel cut. That should tell you if the fcd is doing its job or not, which seems to be the problem. But you've probably already done that. Right?

SaabGuy

I was actually considering splicing into each wire at the ecu and monitoring its signals. i will do this in a few days because right now I really do not have the time.

The knock sensor? OK... I will try that but you know, some of these tests are really pretty dangerous with my kind of miles. Thank you Hailers for the new ideas that I will try.

Anyone else??

HAILERS

After thinking a bit, I'd skip the knock sensor for now. Later maybe. I read the paul Stokes article. He says if you hit fuel cut, turn the trimmer down even more until you don't hit fuel cut. But that can't be your problem because you have Racing Beat???? FCD and it should have been good to go at the beginning. Wire taps are cheap items at Radio Shack and you avoid soldering and splicing. Can put the meter where the idiot lights are and run a long wire to the output of the boost sensor or the rear injectors to see what is happening. Whenever you get a chance.

SaabGuy

the FCD that I have (rb) actually has a trimmer inside of it.

I knocked it to the lowest setting (3v which is like 6.8psi) and the car still hits this cutoff.

I'll get some connectors from Radio shack. spark plugs are pretty black and they are new. i wonder if this could be an ignition problem.

SaabGuy

By the way, My car does not shoot any flames. it does not make the gunshot sound and I have no cats. Somthing to think about..

SaabGuy

I bench tested my FCD and boost sensor...

cymfc3s

what intake do you have right now? stock?

SaabGuy

Stock paper filter with stock ducts

cymfc3s

try removing your stock airbox tonight and see if you still get "fuel cut."

SaabGuy

ok I will try that ASAP.

But right now I have the ECU out of the car. I was checking things out. 2 resistors are fried but they are not part of the engine system, they are part of the emissions side. I am going to replace them tomarrow cuse I had to order them. I really highly dought that these reistors cause a fuel cut symptom cause they are for the relief solenoid valve, which a lot of people just rip out. Since the ECU is out I amcreating a test connector so i can monitor 21 different sensors/signals and maybe I can find out why my car fuel cuts, as well as has black spark plugs. A sensor migt be bad.

Still, I need more input on this issue, not gonna let this thread fall until I fix this problem.

After I test the ECu and it checks out OK, Im going to replace my ig coils and after that, im gonna rip off the upper intake and investigate the injector wires and PD, then Im going haltech if all else fails.

jspecracer7

The first night I had my FC, I ran it and hit fuel cut. I had the stock intake...stock EVERYTHING...

...so I checked all the hosing, and watched my boost...

...same thing happened, and boost was the same...

...so I bought intakes and installed them that day...

...NEVER hit fuel cut again...

...well, actually I'd hit fuel cut when I took out my knightsports FCD, but other than that...never hit fuel cut again.

SaabGuy

OK that is a good idea to test it out with some kind of intake... hmm... that leads me to think about the airflow meter... I'll put "modify intake" on my list. I wish I could test all this crap out at once... I hate this risky testing.

HAILERS

Just some information. I notice that my 87 with very little modification, hits fuel cut at 3.4v output from the pressure/boost sensor. That figure is quite a bit lower from the figure given in the fcd article at http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm and I have repeated this several times, so its not a fluke reading. Always 3.4v. Makes me wonder about a lot of things. The Autometer boost gauge (which I have determined is about 2-3psi high) will read close to 10psi when the fuel cut happens and the 3.4v is displayed. So it would be interesting to see what the reading is on your car when you hit fuel cut i.e. higher or lower than 3.4volts. Today its about 55 degrees and I can hit fuel cut. Around 70 degrees you really have to work at it to hit fuel cut. I don't comprehend the post above where changing air filters cured his fuel cut. But, hey, if it worked, it worked. Just don't understand why it would.

SaabGuy

OK I am stopping at this point. I think I found my problems.

Today I put the ECU back in the car and wired up a 21 sensor test pin to the ECU. I found that the Air Bypass Solenoid Valve has the wrong voltage(Supposed to be 12v but actually 4.8v). The solenoid operates when I test it with a battery. This will probably solve my lack of 3k rpm startup but I really do not wish to fix this problem..

Second MAJOR problem is that the terminal on the ECU for the Boost Sensor is reading 0 volts at all times. It is supposed to be 2.4ish volts depending on boost and altitude (3.2v is about 8-9 psi of boost.) So basically unless I fucked up on my soldered wire tap-ins, my ECU is running at an EXTREMELY high altitude (maybe) which would explain why I only get about 15 Miles per gallon and most likely why I am hitting fuel cut. The thing I do not understand about this new found problem is, Why does my stock boost guage work? It taps into the same wire (BrR off the sensor) so there must be a break somewhere in the car or behind the guage cluster.

Can I have some input please?

SaabGuy

Hailers, what ECU do you have? the N332???

HAILERS

I have a N332. Sorry, lost track of this post. Yeah, something is odd here. Gauge works but no input at the ECU. I don't think that can happen, can it. I'll stare at a diagram sometime this morning. Oh! I see where you say that 3.2v is 8-9 psi of boost. I'll have to look at that graph from that fcs3 whatever site again. I must be reading it wrong. Also yeah. Screw the airbypass solenoid. My wiring is broken down in the solenoid, so I know it does not work. What I did find strange, is my car was reving to 3000 in the morning, and one morning I said to myself *wait a minute, it can't rev to 3000rpm at startup!*. Thats when I realized the bac works in conjunction with the airbypass solenoid to produce the high rpm at startup. So I consider that airbypass solenoid useless along with the solenoid on the back of the engine that has something to do with powersteering that I also don't have. Later after I look at the schematic.

HAILERS

Hey. Back. On the wiring diagram, page 50-25 of the 88 manual online, I see that you look at the pressure sensor. It has the Br/r or brown and red wire leaving the sensor. On the way to the ECU there is a splice off the brown and red wire, with a L/W or blue and white wire going to the boost sensor. The Br/R wire continues to the ECU. So, there you have it. You have a broken wire going to your ECU from that splice area. Thats why the gauge reads but the ECu isn't picking up the signal. That make sense??? It does but brings up another set of questions, like why do you hit fuel cut????? If the ECU does not see the signal, why would it cut???? Check the wiring b/t the pressure sensor and the ECU. You've probably done that by now. Hows it coming?????? EDIT: The way I just read that graph from the article on FCD, is that fuel cut is at a max of 8.6, and on the graph that should be about 3.7v. Right??? Or did I miss something? I just gotta buy a good gauge or just drive that darn car and forget about little needles going up and down.

Kahren

iTrader: (13)

hey saabguy, u do blow flames, u just never got teh exhaust hot enouf, i saw one flame when i was gettign off rt9 and u passed by me, small little flame inside your muffler berely comming out, so if u kept beating on it u woudl eventualyl blow big ones. and btw, MAKE SURE your piping diameter to the PRESSURE SENSOR is exact same as stock and MAKE sure u are suing the STOCK pill. and do as they said take off teh cover completely. it sounds like u are runnig too rich, which also can expalin your car smelling like *** more then mine talk to u soon, my f***ing internet is down at home teh cable modem **** the bed...
good luck

SaabGuy

hailers, I actually had the test connector hooked into the wrong wire, so my ECU is in fact seeing about 2.4v with the ignition on. ******* pisser man. I need a haltech light right now cause this ecu blows goat cheese.

HAILERS

That's great, the finding of the wire not quite right. I get the same reading with my meter. I get 2.37v with the key just on. I hope you can drive it sometime and see what the voltage is when the fuel cut hits. I used a better meter today and it cuts at 3.5 consistently on my car. I have it mounted or laying near the idiot lites so I don't have to look down while driving into on coming traffic. This way I can look straight ahead while driving into on coming traffic. humor, please. Just some notes you might comment on. With the key just to the on position, my factory gauge reads b/t the very bottom and the zero. How about yours? When I hit fuel cut, the factory gauge is hitting the two top hash marks. I mean those thin, last two hash marks. Not the fat ones. The very, very last ones. I don't talk about what my autometer gauge reads. Well not much. It shows cut at a whisker(what ever happen to **** hairs?) below the 10psi mark. Its too high by about 2 to 2and 1/2 psi. I'm going to work on my factory gauge. I think with some effort I can make it read zero with the key on. Bad solder joint somewhere.