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350matt, Engineer
Category: Mazda
Satisfied Customers: 21707
Experience:  Mechanical Engineer BEng Hons22 years experience
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2007 mazda cx7 with a 4cyl. turbo. won't start. has spark

Customer Question

2007 mazda cx7 with a 4cyl. turbo. won't start. has spark but no injector pulse!
Submitted: 1 year ago.
Category: Mazda
Customer: replied 1 year ago.
The vin: JM3ER293170107192
Expert:  350matt replied 1 year ago.


If there is a spark and its still not starting then its likely that the ECU isn't opening the fuel injectors, if the injectors are working you can hear them click - its difficult to hear them with background noise so use a long screwdriver like a stethoscope, placing the handle end in your ear and the metal tip against the body of the injector whilst your assistant turns the engine over.

If you can't hear anything check the ECU power is present by measuring voltage at the fusebox and on its relay socket if OK then check the connections to the crank speed sensor and consider replacing this sensor if the wiring / connections look OK

If the car will start using a squirt of quick/ easi start into the intake then this confirms the problem is lack of fuel

Customer: replied 1 year ago.
There's no power to injectors and no pulse signal from Pcm either. According to the diagram on alldata the injector relay is controlled and the power side of the relay runs to the Pcm. Therefore there's no direct link between injector relay and injectors. I checked the input and output on the relay-Ok. I also replaced this relay with a good known relay. When cranking the Scanner indicates RPM reading!
Expert:  350matt replied 1 year ago.


OK there's power to the ECU

and there's engine speed signal

its just not injecting?

in which case there must no load signal into the ECU to generate a fuel injection pulse

this comes from the MAF meter on the intake so check the state of its connection and wiring for damage and corrosion and also try cleaning the sensor element inside by removing itfrom the car and spraying the exposed sensor wires inside the tube with a brakeor switch cleaner - ensure that the cleaner is one of the old fashioned, nonEco type that does not leave a residue

On no accounttouch the sensor wires with anything physical as they are extremely fragile

Customer: replied 1 year ago.
I click tested injectors (disconnected). They clicked!
Customer: replied 1 year ago.
Well in off right now. I'll get back to you tomorrow in the morning about 9 CST. Thanks.
Customer: replied 1 year ago.
Good morning!
Customer: replied 1 year ago.
I checked the MAF. It reads according to specs. <0.6v static. I cleaned it anyway but no difference!
Customer: replied 1 year ago.
Expert:  350matt replied 1 year ago.


OK if the injectors are clicking then they're OK mechanically, it just means that the ECU isn't opening them and if the MAF is reading OK then I'd say its time to send the ECU off for repair / testing

try these firms

Customer: replied 1 year ago.
As at now I'm convinced the PCM isn't controlling the injectors. I'm gonna look for that and let you know. In the meantime if any other clue, just let me know. It's worth trying anything!
Expert:  350matt replied 1 year ago.

the only other thing to check is to remove the ECU plug and do a continuity test between the injectors and the ecu

this will check out the wiring loom