Piranha

Hey guys, well, I had just made a do-it yourself FCD a few days ago, and it checked out pretty well with the multimeter. Welllll, I was hooking it up as per the instructions on the DIY page to make sure nothing messed up when it was really hooked up, and I think I shorted between the 12v and the ground going to the boost plug.

There was a constant tapping when I had the key on and I was jimmying with it (yeah, duh). All of a suden it stopped. Well, I had a dream last night saying my car wasn't going to start. And this afternoon it DIDN'T!!! So I thought, well, maybe it is flooded. I pulled the plugs, they were dry, and when I turned the motor I heard the pulses pretty strong. I put ATF fluid in anyway, and no start.

My tach needle isn't jumping like normal either.

Uhm... HELP!!!

MIKE-P-28

iTrader: (1)

? try checking fuses? i dunno on a fC, but most EFI cars have a fuse right on the body of the computer

Piranha

are there fuses right on the ECU?

mazdaspeed7

Check the codes. If the check engine light stays lit without flashing, the ecu is toast. If there are any stored codes, and check engine light will flash, and if there are no codes, it will not light up at all.

Piranha

yeah, thats another problem... I have an '88, and I made a code checker, but it doesn't work. the LEDs light up when I turn on the car, but that is it. And I know I have at least 1 code.

mazdaspeed7

Have you checked your code checker on a known good car? Same principle, if theres a code, it will flash. If the ecu is fried, it will be constant on. No codes, no lighting up at all.

Piranha

no, I haven't. I can try it on my buddy's car tomorrow, he is coming back from school. Well, the LEDs light up for the first 3 seconds after I turn the ignition. Someone else told me that sometimes the code checkers just don't work. (??)

HAILERS

Go to your boost/pressure sensor and take the plug off. See if you have any voltage on the brown/white wire. If memory serves, I think you should have about 5v ref voltage there. If you do then the ECU seems to be doing something positive. Also on the codes. You'll only see a code flash on that model, I believe, if a connector is off. Take the boost sensor off and see if you get a flashing light. If not that one take off the tps and look for a light. You should also be able to go to the tps and look for 5v at its brown and white wire. If there, thats good. You have gotten rid of your homemade fcd by now for sure. A fellow on this forum grounded out the brown/white wire at the boost sensor and the car would not start. He ungrounded the wire and all was well. Oh , on your fuel pump jumper near the right hand strut tower. Do you have 12v at one of the two sockets? If yu do thats a positive sign.

Piranha

Thanks Hailers, I will definately try all those tomorrow, since it is Mother's day (and its raining).

What happened when they grounded the Brown/white wire? Was their ECUs fried?

I think my Code checker doesn't work because my coolant temp sensor on top of the water pump housing's wiring broke. My ECU runs my electrical fan constantly now, and I think that warrents a code. But I'll try what you said anyway.

HAILERS

The fellow who grounded the brown/white wire(86-88) killed the reference voltage to several sensors. When he saw what had happened, he reversed his mistake and the car started. Now that part where you said the coolant fan now blows all the time....I remember someone having this condition and it turns out, believe it or not, there is a fuse burnt out. I'll look see and see if I can remember which one. That fuse box in the cabin. Look at all the fuses, but in particular, count the rows from the bottom, and the forth row from the bottom going upwards, look at the third fuse from your left on that forth row. It should be labled ENGINE. That feeds 12v to your ECU. No 12v, no start the car. Also look in the engine compartment at all the fuses in the black rectangular box. One of those fuse feeds the afore mentioned fuse on the forth row from the bottom. I'd do the fuse check prior to doing anything else, even if you've already looked. That broken wire does not warrent a code, I don't think. The boost sensor does, tps does, afm plug does, air temp sensor on the left side of the dymanic chamber does. This car if 86-88 has no memory of a tripped code(said HAILERS with some uncertainty). Only shows a code if the condition exists at that moment. Mostly just tells you there is a plug off or an open circuit. Not if a tps is out of range etc.

Fingers

you know what's an easy way of determining your problem? Try someone else's ecu. Do you have any buddies that have an rx7? if not, there's alot of guys on this forum that will gladly send you an ECU from a parts car for a minimal fee

Piranha

Hailers, how did he reverse his mistake (killing the reference voltage)? I did already check all my fuses in the cabin, and they all seem to be good

HAILERS

The fellow reversed his mistake by undoing what he had done. He had accidently grounded the brown/white wire on the boost sensor. When he ungrounded it, the car ran. I have no idea why the ECU circuit didn't go **** up. I ain't gonna experiment. If you will, check the brown/white wire on your boost sensor and tps to see if you have 5volts approx there. That would give us an idea if the ECU is working.

Piranha

Yeah... I think that may have what I did instead, but mine DID go **** up. I haven't checked the power by the fuel pump yet, but I did check the voltage at the wire for the boost sensor, and I didn't get 5v. I did talk to someone about getting another ECU and its on the way. Live and learn

Piranha

So I got my "new" ECU, threw it in, Bam, WHITE SMOKE EVERYWHERE! I put ATF fluid in because I thought it was possible it was flooded. Time to switch the plugs. Thanks for all the help though guys.

HAILERS

Do you have an interest in selling your old ECU? Fifteen bucks and I pay the shipping?

mazdaspeed7

HAILERS, I have a dead 89 n/a ECU if you want it.

HAILERS

MAZDASPEED7 ...thanks for the offer, but I think your ECU is too different from my 87. I *think* your ECU has just one large plug, the best I can tell. The 86-88 have three plugs on the ECU. I was going to either try to repair his turbo ECU and if that did not work, use the electrical jacks to make a more professional breakout box to moitor the ECU signals(read:make a toy to play with).

mazdaspeed7

The S5 ones have 3 plugs, but I think they are a little different than the S4 ones. Ill check later tonight, I have a spare S4 harness in my garage. You interested it if fits?