Tach and fuel pump issues...

[Phish]

Well i am having a few issues with the fuel pump and the tach. It all started when driving the other day the car just shuts off. The fuel pump was not working. Long story short, when i jumped the fuel pump directly, it works and it was able to drive it home. Once back home, i wired up the fuel pump as it is supposed to be and now the fuel pump stays on constantly with the key forward. It does not prime for two seconds then shut off as it should.

So to recap that issues, Pump stopped working - worked when wired driectly -when wired up correctly it now stays on and does not cycle with key forward and engine not running.

Now, when diagnosing the fuel pump issue, i now notice that the tach is not working. The tach has always worked in this car and i have never had one issue with it. It also worked on the drive home when i had the fuel pump jumpered so the car would run. I also have a RPM window switch that is tapped into the white wire out of the ecu. Its connected right at the ECU and it as well is not getting an RPM signal. This makes me think that the ECU is not putting out a signal for the RPM switch nor the dash tach to be reading. (when i try to start the car initially the tach does jump a touch meaning it has power) The car fires right up and has no starting issues what so ever.


Relevant info about the car: 1990 Mazda RX7 - LQ4 - 1998 ECU - fuel pump is ran off a relay but uses the green/white ECU trigger wire to activate the fuel pump.

[sparkles]

Unhook the tach driver and see if the pump works. A long time ago (like in my Focus days) I had a similar problem with my tach driver going bad and the ECU not sending out a signal for the pump. It's worth a shot.

[AutoMods]

weird issue, did you hook your fuel pump to the same wire it was hooked up to before? i'm sure you know already but the 98 has different pcm pinouts then the other years.

I'm just guessing but maybe the cam sensor or crank sensor is having issues. check those sensor wires to make sure they aren't damaged/pinched. check for engine codes, i read code P0343 is related to the cam sensor and turns the tach off. also see if the rpm signal is visible in the computer with the scanner. even if you don't have hptuners and efilive, someone can hook up their tuner to your car for free to scan. only flashing/tuning requires an extra vin license.

[AutoMods]

Unhook the tach driver and see if the pump works. A long time ago (like in my Focus days) I had a similar problem with my tach driver going bad and the ECU not sending out a signal for the pump. It's worth a shot.

there isn't an external tach driver. just an rpm out signal wire from the pcm

[Phish]

I read that if its the cam sensor that the car would be hard to start. This cranks and fires first istantly. However I think that the scan tool will be my next step in diagnosis