So I bought this 93 recently and it looks stock. It does not run and thats how I got it so cheap. 4 "mechanics" have looked at it and cant figure it out I don't want to be the 5th. I'll Megasquirt it before I give up! 141K on it 5spd. Here is the story that I know from previous owner:


Car overheated and the engine cut out and it hasn't started since. Replaced timing belt, fuel pump, spark plugs, gaskets, had the head milled and checked for cracks. Here's the strange thing if the injectors are unplugged, and we spray starting fluid, it starts and runs as long as the starting fluid is being sprayed but as soon as we plug the injectors in it floods car and nothing! The problem seems to be that the fuel injectors are constantly firing and flooding the engine. The spark plugs get soaked in fuel. Anybody have any thoughts about what might be telling the fuel injectors to dump fuel constantly?

Items replaced:

CAS
ECU
Plugs
Timing set, head milled and checked
water pump
Temp sensor on back of head
New injector relay
fuel pressure regulator
Fuel pump has been jumpered on (no difference)


I have verified excellent spark and everything seems to be hooked up right. It does run on starting fluid with injectors unplugged. Plug them in it stumbles and then wont start and if you pull plugs they are soaked. Power is present in injector wire when it is KOEO but ground is not.

I dont have a NOID light and I cant see the test light blinking (jumped between an injector connector) when turning it over.
???

Ideas?

 

What about the injectors themselves? Maybe they're static? Just a guess

 

I'll try anything....im sure I got a set here somewhere. I just cant believe that all 4 just froze at once.

 

See what the singal from the ECU back to the injectors looks like. Determine first, if the injectors are going to ground constantly with just power on (they always get 12v from the white/red wire, the ECU rapidly grounds them to spray fuel). If not, see if that's happening during cranking--unplug an injector with the connector going to DMM in diode mode to ground...do you have a constant buzz or a morse code like chime?

 

Any way you can borrow a MS or other known good ECU.

 

Injectors are not going to constantly. They do have power on r/white but no ground with KOEO.

I will try the "diode mode" never heard that before. Unplug injector and exactly what do I connect DVM to?

 

Got it. Ran ground side of injector to continuity tester on DVM and it beeps constantly as soon as key is in on position. So problem found now what caused it and how do I fix it.

I have another ECU here swapping now...

 

one to yellow wire another to ground. dmm should brobeepwhen grounded

 

New ECU. Same issue grounds as soon as KO.
So this would eliminate the problem being in the harness because it only does it with KO right?

 

So checking the wiring diagram yel/blk are grounds to ECU for cyc 2-4 and Yel is ground to ECU for cyc 1-3. I checked both and both ground as soon as KO? As far as the wiring diagram says they are completely different wires all the way to the ECU. So leads me back to the ECU that I just swapped again....no change.

 

These 1.6L batch fire all 4 cyc or 1-3 than 2-4?

 

?

 

Daily WTF bump

 

beats me bro.

something might be causing a short with key on which is causing the injector outputs to go low.

 

Wow stumped you I am in trouble.

I'm going to borrow a PNP today and see if it runs on that. I dont know what that will prove but at least if it runs I can buy a PNP and sell it running....lol

 

Got your PM, afraid I'm a tad stumped as well. Normally, this is the point where I'd start directly observing things with the oscilloscope.

All I can tell you at the moment is the answer this this question:Under normal operation, the 1/3 and 2/4 injector pairs alternate, with each pair squirting once per engine cycle. I have never scoped a 1.6 ECU during cranking to see if the pattern changes during that time.



If you unplug the ECU, do the injector lines still ground with the key on?

 

reverant has a video of the odd pattern at startup.


n/m video was from 2002+ miata.




1.6L notes:

 

Ah, yes. Good ole' pin 1C.

Quick-n-dirty test:

Let the ST SIG fuse be removed from the main fuse block, and let the F/P connector within the diagnostic box be jumpered to ground.

Verily, shall then the starter be engaged- for while it may be a total bitch to start, worketh ye the throttle that normal operation be attained.

 

:bowr ofl:


Ok so here the deal. With the ECU, CAS and ignitor, unplugged it still beeped showing the injector on full open. WTF So I did as told....

I plugged all back in jumpered the FP and took out the ST fuse and after some cranking it started. Now what did I do? What exactly does the ST fuse disable?

Again, you sir have proven your worth on this earth.


EDIT: looks to be the starter signal fuse? But what it do to the ECU and why did removing this work.

EDIT #2: Found this: If you have the ST SIGN fuse removed the car won't give the fuel pump the quick cycle that it usually does when you move the key from OFF to RUN. The pump will run while cranking though, and when the ECU sees the crank signal. So is that all it does.... pressurize the fuel system?

 

Close-ish.

The ST SIG fuse takes voltage which has been applied to the starter soldenoid by the keyswitch (when held in the START position) and conveys it to two places:

1: The fuel pump relay (circuit opening relay) to drive the fuel pump despite the fact that airflow is too low to reliably trip the switch contact in the AFM which normally engages the relay, and

2: The ECU, on pin 1C, which informs the ECU that the starter is engaged, and it should be in cranking mode. (Trigger-return timing, fully-banked injection, crank enrich, etc.)


If your car normally blips the fuel pump when switching from OFF to RUN, then something is wrong. The fact that pulling the ST SIG fuse stopped this should give you a clue as to what.