Sounds good. I'll give it a stab tomorrow after work and report back.

 

Pulled the UIM and pulled the connector off the rear primary injector and blasted it with air and inspected it for damage. Reinstalled everything and started the car. Still no voltage to that injector. Should I just pull the stock wires off the harness and ECU harness and just run my own 2 wires? What's the injector driver?

Is the wire just grounded somewhere stopping the injector from getting voltage or is it something more complicated?

 

BUMP

 

Man, youre making this more complex than it has to be.

You say youre not getting voltage at the injector. I'd like some clarification on that actually. Measured at the injector, do you get 12vdc on one pin, and ground trigger (when the CAS is rotated) on the other? IF not both, which is missing?

IF you're not getting 12vdc constant, there is a break in a wire somewhere, and you can get by with running your own to make up for it. IF you're missing the ground trigger from the ecu, and you measure again at the ecu and still can't get it, you're gonna need another ecu, plain and simple.

The ONLY 2 devices in question here are the wiring and ecu.

 

Ok I tested the voltage from the injectors today and got 12V constant from the injector harness. Is the trigger ground the pin in the ECU? I dont understand the parts about the missing ground trigger while the CAS is rotated. Care to elaborate. I'm going to try and test the resitance.

So it looks like I will need another ECU and possibly have to run my own wires to save me some headaches later on.

 

How the injector circuits work:

The main relay provides 12vdc+ through a large wire that splits into 4. IF you have any 86-7 car, the wire splits into 4, runs through the injector resistor pack, and then each of those 4 out to each injector. IF you have an 88+, it runs from the one main wire, splits into 4 in the harness, and runs directly to each injector. OF course, each injector needs ground to open. The ecu handles this. IT looks at the CAS for engine position (don't wanna inject fuel at the wrong time, you know) and completes the circuit with ground when necessary...the ground wire comes from the ecu and runs directly to each injector.

A short in the harness somewhere (either to ground constant or positive) can kill the section of the ecu (I call them injector drivers, Im not sure of their actual name) that handles this trigger output.

IF you find that youre not getting the trigger ground (I use a spare CAS, unplug my stock one, plug in the spare, turn on the key, turn the gear on the CAS, and check the injector to see if it opens or not, or using a noid lite check to see if it gets voltage) then you either have a break in the supply wire, or a bad ecu. Perhaps cut the afflicted wire near the ecu, and test again at the ecu...a break in the wire could have affected your results in the engine bay.

Noid lites are available at autozone for about 5 bucks. A spool of 100 foot of 14 gauge primary wire is about 9 bucks at autozone...you can get 25-50 foot for less. This could cost a maximum of (besides the ecu, if damaged) 25 bucks to fix. You're talking about running one, maybe 2 6 foot lengths of wire, worst case scenario.

 

Bump for u cause im on my way over to your house

 

Thanks for the detailed explanation. It really cleared things up for me. I have traced the wire from the ecu through the harness and the harness is in mint condition with no damage at all. I dont see any possible way that there is a break in the wire but I am not discounting it.

I checked the resistance of the injector harness in question per Wayne's method and the resistance jumps all over the place. I think I will just run my own wires from the injector and get another ECU to cover all bases.

 

IF you're going to do it, it wouldn't be a bad idea to run all 4. You're in there anyway. Theyve all seen the same number of years, heatcycles, and miles. Also, I'd start with 4 new injector clips, you can get replacements from fuel injector shops or autozone (there is a gp sorenson part number on my webpage tech section regarding injectors).

 

Thanks for the advice.

One more question, is there any potential damage I could have done by driving the car in this condition for about 30 miles. I had to keep the revs high and alot of throttle to keep up with freeway speed to get it home. Boost did not go over .3 bar (under 5psi).

 

No, assuming you were driving with no fuel to one rotor (unless you got above the cut-on point for the secondaries). To have detonation, you have to have combustion that heats the chamber too much...with no fuel, you can have no combustion, so you can have no detonation. The afflicted rotor was just freewheeling around, not doing anything to help the engine make power, but not hurting anything either. An engine does the same thing, mechanically, whether or not combustion is actually occuring inside. All it was doing was pumping air in and out. No issues there.

 

Its not like a vac leak or a busted AFM or something is it? I'm paranoid about these things recently...

 

No vac leak and AFM is fine.

Just wanted to ask if the bouncing resistance is a sign of some malfunction in the wires?

What should I do to shield the new wires I am running?

 

The only shielded wires on the FC are knock sensor and 02 sensor. Very low voltage ones. INjector leads, just like everything else, are regular 16/14 gauge wire.

 

Bump

I'm having trouble tracing the wires from the injector. I understand that it gets power from the 100amp main fuse but where do the 2 wires (on the injector) meet. One wire goes to the ECU but I cannot find where the other wire goes without cutting open the harness. I couldnt find a wiring diagram anywhere. Thanks again.

Wayne88N/A I sent you a PM also.

 

Bump

I really cannot find where the wires run to. Do the 2 wires on each injector ever connect? If so where? Anybody?

 

I'd like to suggest an alternate problem. Make sure your coils are ok by another means other than resistance.
I had the same symptoms with my 89TII (gas soaked plugs, no power, excessive smoke after boost, etc)....

pulled one of the leading plugs and had my uncle crank the car while I watched for spark.... nothing.....
swapped the leading coil with one from my 86, and BAAAM! she ran like an animal

 

I have traced the power leads down on an s4 car, but not an s5...I assume it'd be similar though.

IF you trace the engine harness in towards the ecu, you'll find 2 large yellow/orange plugs not going to the ecu, but they both plug into the dash harness which snakes over towards the drivers side. ON the s4, the power wire(s) are found on the smaller of these 2 large plugs (engine harness side). They are 2 black/yellow wires adjacent to one another...about 9 inches up into the harness they merge into one. This is the power supply wire that goes out to the injectors (or resistor pack if an 86-7 model) and gets split into 4 power wires there.

 

buy new spark plug wires. I had the same problem.

 

mabey new spark pluygs too

 

 

Stan- the two injector wires do not meet each other, except at the injectors...

Kevin- I've always wondered where the "one wire" splits into 4, you're saying it's about 9" from the orange (or yellow) plug inside the cabin, near the firewall?

RX7.0- so you're saying that you had a coil that read out good with a meter, but was bad on the car? Did you swap the whole ignitor/coil assy to "fix" your prob, or just the coil?

 

There are 2 power supply wires, identical in size and color, that come from the dash harness. I have not traced them back from there. Where this smaller yellow/orange plug connects to the dash harness, both of these wires carry across, adjacent to each other. About 9" up the engine harness, they join TOGETHER for one wire. This one wire carries through the engine harness. IF you deal with an 86-7 car with a resistor pack, it goes to it, and gets split into 4 seperate wires there, each of which go directly to the injectors. IF you're dealing with an 88+ car, this one wire gets split (somewhere in the engine harness near the oil filler tube) into 4 wires. I actually cut back into one to find all this out. I have a pic I'll try to find.

 

Swapped the whole thing....

By watching the plugs I could see a nice spark on both trailings, but none on the leading, and all 3 tested fine for resistance.

 

Cool, thanks...So it's actually in the engine bay then...

Why do the power wires from the main relay go through the dash harness though? I could see for the ignition system, but the injectors???

All I see on the schematic is the front harness to the emission harness plug connection (and there are two identical wires, like you described). I think Mazda expected bad connections at their plugs, sooner or later, because of the way they designed that...

And this plug is in the cabin, to the right of the ECU?

Not trying to hijack your thread, Stan, lol