Fuel Pump Output problem MS1 V2.2 29Y4

[efims]

Fuel pump doesn't prime intermittently

At times, it doesn't prime when ignition is turned ON.(usually will prime about 1 sec before cranking).

I measured Fuel Pump Output voltage vs +12Vdc(ignition) but got about 5-6Vdc(with relay connected). It should be 12V, right?

At this voltage, the relay coil MAY energize sometime and the fuel pump will prime.....at times, the relay coil doesn't energize, therefore the fuel pump will not prime.

Could this be due to failure of Q3 or D7 or something else?

Thanks in advance for helping.

[SymTech Laboratories]

How is the relay connected to your MegaSquirt ECU? The fuel pump output connects or disconnects the relay's coil to ground, so there is no voltage to measure without the relay. The other side of the relay's coil should be connected to a switched +12V source. With the relay installed and when the fuel pump output is off, you should measure close to battery voltage, otherwise you should measure close to ground.

It's possible there's a problem with Q3 or D7. Make sure D7 is inserted in the right orientation, and check the solder joints around both components. Probe R13 with a digital multimeter, and check for a 5V signal when the fuel pump output should be on.

[efims]

Thanks for giving me something to work on.


I measured Fuel Pump Output voltage vs +12Vdc(ignition) but got about 5-6Vdc(with relay connected). It should be 12V, right?


Instead of giving OVdc to energize the relay, the Fuel Pump relay output gave +6 to 7Vdc, thus the voltage across the relay coil is not sufficient to energize the relay(to power the Fuel Pump).

[SymTech Laboratories]

Thanks for giving me something to work on.


I measured Fuel Pump Output voltage vs +12Vdc(ignition) but got about 5-6Vdc(with relay connected). It should be 12V, right?


Instead of giving OVdc to energize the relay, the Fuel Pump relay output gave +6 to 7Vdc, thus the voltage across the relay coil is not sufficient to energize the relay(to power the Fuel Pump).

Where is your negative multimeter lead when you're taking these measurements?

[efims]

DMM Positive probe on Igntion 12V+ while Negative probe at Fuel pump output(ie 85 and 86 of relay coil) with relay fitted.

[SymTech Laboratories]

DMM Positive probe on Igntion 12V+ while Negative probe at Fuel pump output(ie 85 and 86 of relay coil) with relay fitted.

Keep your negative lead touching ground, then measure everything again using your positive lead.

[efims]

Replaced Q3 and got fuel pump relay to run activate as required.

Thanks for helping

Problem (not)SOLVED.

Next day, problem came BACK.

[SymTech Laboratories]

Great news, thanks for updating us with the solution!

[efims]

Problem came back...started the car...and after about 30sec, the engine stalled....fuel pump refused to activate.

Measure output and found insufficient 12V(about 4 Vdc only) to activate relay coil.

Could it be the firmware?

Or could it be defective D7(is it true that D7 is to protect flyback for the relay coil)?...could a defective D7 lead to(failing to protect flyback) damage of Q3?

[SymTech Laboratories]

Problem came back...started the car...and after about 30sec, the engine stalled....fuel pump refused to activate.

Measure output and found insufficient 12V(about 4 Vdc only) to activate relay coil.

Could it be the firmware?

Or could it be defective D7(is it true that D7 is to protect flyback for the relay coil)?...could a defective D7 lead to(failing to protect flyback) damage of Q3?

Have you measured everything like we suggested? It's possible that D7 has failed.

Keep your negative lead touching ground, then measure everything again using your positive lead.

[efims]

Have you measured everything like we suggested? It's possible that D7 has failed.

Besides the fuel Pump output, what else should I measure?

TQ

[SymTech Laboratories]

You should measure the voltage on both sides of the relay coil with your negative multimeter lead touching ground. Or you can replace D7 and see if that fixes the problem; there aren't many components in this circuit that could fail...

[efims]

You should measure the voltage on both sides of the relay coil with your negative multimeter lead touching ground. Or you can replace D7 and see if that fixes the problem; there aren't many components in this circuit that could fail...

With negative DMM lead on grd, I got 12V at ignition side of the relay coil

With negative DMM lead on grd, I got 8-9V at fuel pump output(from MS ECU) side of the relay coil

The relay doesn't activate

I replaced the Q3(again) and D7...hope this will solve the problem...will test out the ecu for the next few days

[cmaid]

I replaced the Q3(again) and D7...hope this will solve the problem...will test out the ecu for the next few days

Solved?

[efims]

yup...solved after replacing Q3 and D7.

Thanks

[cmaid]

Same problem here - same solution!

Thanks!