2007 Mazda 3, 2.3L, 5MT No spark

Hey everyone,

The car sat for a long time, but was running fine when I parked it. I went to move it and it started for a second, then died. I figured out that the VVT sprocket cratered, so I replaced the timing gear and pulled the head to verify that there was no damage to the valves and it has 200,00km on it so I figured it could use a good clean and new valve stem seals.

I did the head and new timing components, put it all together and then it wouldn't crank. Figured that out but now there's no spark at any cylinder.

I need a bit of help troubleshooting this problem.

I can't find any wiring diagrams, and honestly I am a bit over my head with this diagnosis.

I don't know how to tell if this is an immobilizer issue or what. The car does have an aftermarket remote starter that was professionally installed about 10 years ago.

Any help would be really deeply appreciated.
Charlie

Hey Wytbishop, happy to help.

No spark is actually a decent place to start as far as diagnostic direction goes. But before that, I'd suggest getting some kind of scanner on it if you haven't already. Nothing fancy is needed - all we really want is fault codes (if any) and the RPM data PID during cranking if possible.

The idea is to make sure the ECM is alive and talking, and hasn't flagged any obvious input issues. Any fault codes for critical inputs or immobilizer issues are gonna put us on a different path. No communication with the ECM would also change our direction.

Going back to no spark, I grabbed a bit of the wiring diagram for reference:



Two quick checks you can do is to use an incandescent test light to check for ignition coil power and ground during cranking. The green wire at each coil is 12V from the Engine 20A fuse in the passenger junction box. Black/blue is a constant ground. We're not interested in the individual coil control wires at the moment.

With a test light connected to B-, the green wire should light brightly with the key on or cranking. Test light to B+, the black/blue wire should also light brightly. Missing either one is a red flag.

Hey Tyler,

Thanks for this. I will start here.

I have verified that the PCM is alive and communicating. Prior to this issue I had a no crank problem that I had to figure out and in the process of that I was able to confirm that the brains are all good.

I'm about 95% sure that this is going to be something silly like a disconnected harness plug or broken wire that occurred in the process of refreshing the head and timing components. I just don't have enough experience doing this kind of troubleshooting to approach it systematically. I will look for power at the coils. Assuming that's not there...which I'm sure it won't be, what would be the next step in the process in your mind?

Thanks,
Charlie

Hey Tyler,

Would you be able to share a diagram of the path from the IGN switch to the coils? I know that power is being interrupted somewhere along the way but I am not sure exactly where to look.

thanks

Wytbishop wrote:

Hey Tyler,

Would you be able to share a diagram of the path from the IGN switch to the coils? I know that power is being interrupted somewhere along the way but I am not sure exactly where to look.

thanks

So to confirm, you did NOT find power at the ignition coil connectors during a starting attempt? Is the Engine 20A fuse in the passenger side fuse box good? Does it have power on both sides during cranking?

I've attached the power distribution diagram that covers the circuit from the ignition switch to the Engine 20A fuse.



Keep in mind that the Engine 20A fuse powers other components as well, like the fuel pump relays, the downstream O2 heater and the fuel injectors.

Hey Tyler

Sorry for the long delay. Christmas, then new years...you know.

Thanks for the power distribution diagram. That helps. I got back to the car today and here's what I can tell you...

- I was probing the coils incorrectly. I do, in fact, have power to the coils with the key On. That suggests to me that the fuse behind the passenger dash is good.

- I do not seem to have any power to the fuel injectors. I had previously checked, and confirmed today that there is fuel pressure in the rail, but I disconnected a harness plug and there is no power at the injectors.

Correct me if I'm wrong, but both the injectors and ignition coils should have constant power when the key is ON and are controlled with ground by the PCM. So I should be able to put a test light on the +ve battery terminal and probe the control wire on either a coil or an injector and it should flicker when cranking right?

I am pretty certain that if I can figure out where power is being interrupted from getting to the injectors, I will solve my problem. I will get back to the car in a couple of days and I'd love it if you could help me figure that out.

Does power go directly from that 20A fuse behind the dash to the main fuse box in the engine bay?

Thanks for helping.

power to the fuel injectors does not appear to come from the same fuse as the one for the ignition coils. there is a dedicated fuse in the main fuse block labeled something like EGI INJ or fuse # F34. ((It gets its power from the MAIN relay which is powered up by the ECM))... I`d start by checking to see if there is power on either side of the EGI INJ fuse #34 in the main fuse block with key on or cranking... I believe the main fuse block is the fuse box under the hood on the driver side... make sure theres not a bent pin in the injector harness connector too. I attached a couple wiring diagrams that may be helpful.

Ok that's good to know. I have verified that all the fuses in the main fuse box are good. I do not know if there is power to and from that fuse though. That is the next step I guess.

thanks.

Wytbishop wrote:

I was probing the coils incorrectly. I do, in fact, have power to the coils with the key On. That suggests to me that the fuse behind the passenger dash is good.

OK, good to know. We can probably leave that alone for now, because...

I do not seem to have any power to the fuel injectors. I had previously checked, and confirmed today that there is fuel pressure in the rail, but I disconnected a harness plug and there is no power at the injectors.

No power at the injectors would definitely be an issue. :silly: But, to make double sure, you found no power at the green/blue wire at an injector connector? I grabbed a screenshot from ptebo1's provided diagram:



Checking the EGI INJ fuse for power on both sides, key on AND cranking, is a fantastic idea. If you find no power at the EGI INJ fuse, check ENG BAR 1, 2 and 3 while you're there:

Correct me if I'm wrong, but both the injectors and ignition coils should have constant power when the key is ON and are controlled with ground by the PCM.

That, I'm honestly not sure about. Coil power is controlled directly by the ignition switch. Injector power is controlled by the Main Relay and the PCM. I really doubt Mazda would control their main relay like Chrysler does with their ASD relays (closed only during cranking or engine running), but I can't say for certain. That's why I'm suggesting checking for injector power during cranking as well.

Tyler wrote:

But, to make double sure, you found no power at the green/blue wire at an injector connector?

Correct.

Also, when I say there is constant power at the Injectors and coils and they are controlled by ground, I mean that they are both triggered by ground through the PCM. I feel like there should be power at the injectors when the key is on like there is at the coils.