SaabGuy

I think my ECU is shot. I have been trying to figure out why I get fuel cut...

I unplug my boost sensor plug and my FCD. Turn on the ignition and my stock boost guage points straight up. What the heck is wrong with this picture? is this normal? can comeone go try this out on their car so I know if this is right or wrong? thank you.

Eric

N1XRR

Well, my car was doing something similar when I was having problems with it. First off my ECU went bad. Then when I got it running again my TPS went bad and it ACTED like it was hitting fuel cut. Try unplugging your TPS and driving. If that works then you know its your TPS.

Michael

Scott 89t2

the boost gauge should work the same with and without the FCD. it just means the gauge will never go over 8psi, even if you are over. so it should be at 0 either way, on in vacum with the car running.

maybe you got a series 5 FCD by mistake? don't know if the plugs are the same or not. but the FCD's are not.

SaabGuy

well I took the FCD out of the equation. I unplugged my fcd and my boost sensor and took the car for a spin. the stock guage was pointing straight up and the car DID NOT hit fuel cut. Can comeone with a TII please go outside and unplug their boost sensor and then just turn the key to the on position? Hopefully someone elses stock boost guage will point straight up, otherwise I may have a shorted wire, or a bad ecu.

I want to know if things arelooking good for my rx7, so I have to rule out the wiring and the ECU before I go on to the boost sensor, fcd, and restricter pill.. Im not going to drive it again cause I really dont wanna blow it up.

I purchased the FCD used from a person who has a 1988 tII, he had his ecu reprogrammed.. Not sure if the FCD is ok though...

SaabGuy

BTW, in my first message I said that I unplugg BOTH my fcd, and my boost sensor... so my successful run (9psi, not cutoff) was with the boost sensor unplugged, (NO FCD) and the stock guage pointing straight up.

HAILERS

I have seen what you describe. I can duplucate it(the boost gauge sticking straight up). One day I put my n/a boost/pressure sensor on the turbo just to see what the gauge would do(with the key on the stock unit installed, it does not reach zero). Well the n/a boost/pressure sensor makes the gauge go almost straight up. Really stops short of straight up. What do you think. Got the wrong sensor on your car? Like I tried to say earlier, with the stock gauge in the car, the key to on, the needle rest halfway b/t zero and dead bottom. And a note: I hit fuel cut at approx 8.5 psi. Pretty much on the whole a stock car. Except for the downpipe and presilencer and someother stuff.EDIT: Another tack on this subject: do the checkout of the boost sensor found on page 4B-77 of the 88manual. Pull 3.9 in-hg on the sensor and then check the output which should be 2.0-2.5V for a tubo model. The same test on a N/A sensor will give you 2.5-3.5V. Output wire is the brown and red one. Or if you have no MITTYVAC just turn the key on and see what the reading is on that wire and we can compare readings.

Josepi

Hey, I did that on my 91, the gauge didn't point straight up. It seems like the gauge is getting a signal from somewhere.

Josepi

Have you tried adding a new ground to the boost sensor?

SaabGuy

with the sensor unplugged. I turn on the key and BOING!?!?!? the stock guage goes straight up so fast that it actually wobbles back anf forth for about a second due to its own inertia.

SaabGuy

but when I plug the sensor in, it seems to read the correct boost while driving.

Josepi

That's odd, I can say this, that when I turn the key to the ON (not start) position, it (the boost gauge needle) rises slowly to a little bit below 0. Then after the car is started, it drops down to the bottom of the gauge.

SaabGuy

Heres something else to add... if I leave my FCD plugged in, and unplug it from the boost sensor, my sock guages reads a constant 40 with the ignition on.

Can someone please replicate all this stuff so I can say, good.. my ECU isnt fried?!?!??!?! PLEASE!?

SaabGuy

OK this is very strange... this morning, I unplug both the fcd and the boost sensor, and the guage stays flat at -20, which by my volt meter is -.4vDC

Josepi

This may sound like a shot in the dark, but i'm the only one awake around here for now . Do ya think that if it's reading the max amount before fuel cut, that the FCD is sending the high volt signal to the boost gauge?

SaabGuy

Josepi,

My guage does the same thing when either or the fcd and sensor are plugged in.

SaabGuy

Please disreguard my last post. When everything is plugged in, it reads 0 inches. when only the sensor is plugged in, it reads 0 inches. When I plug in ONLY the fcd to the stock wiring harness, it reads about 40 inches, and I get a voltage reading of 3.2ish accross the fcd output and ground.

man I can tell that Im confusing the crap outa people now.

The Ace

Dont know what you have done wrong, but the same thing happened to me when I was trying to install my FCD: at some point in time the boost gauge would shot straight up and stay there. There was also a noticeable "ticking" sound from the engine bay.

That was a short-circuit. Dont know why or how, but this is clearly a sign of a short-circuit. Dont drive your car like this. The ECU is getting all sorts of wrong signals, and probably settles for the safe-mode. Check and re-check every wire and connection you have. In my case, the +12V wire of the FCD was somewhat loose, and as soon as it got slightly out of place, the gauge would shot up and stay there.

Only one way to check: get the multimeter, set for Short-Circuit Check, and start checking all connections...

Scott 89t2

why would you only hook up the FCD? you need the boost sensor. and when the boost sensor is pluged in it seems fine to me with and with out the FCD. what's the problem???...

SaabGuy

The main problem I am trying to solve is Fuel cut.

My car hits fuel cut WITH the fcd connected, but does not hit fuel cut when I disconnect both the fcd and the boost sensor (this is VERY bad to run like that, I know, but I had to make sure I was hitting fuel cut and not something else).


I am just trying to troubleshoot my fuel cut problem. Seems as if my boost sensor and ecu are acting OK though. Tomarrow I am getting the inline restricter pill from my local Mazda dealship, I dought that is the problem, but hey, its only 4 bux.

Thank you for all of your help.

HAILERS

I see I misread your post. Sorry 'bout that.