Fuel Pump Output problem MS1 V2.2 29Y4

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Fuel Pump Output problem MS1 V2.2 29Y4

Postby efims » Tue Mar 27, 2012 4:43 am

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.
Last edited by efims on Tue Mar 27, 2012 7:03 am, edited 1 time in total.
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby SymTech Laboratories » Tue Mar 27, 2012 6:54 am

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.
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby efims » Tue Mar 27, 2012 7:06 am

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).
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby SymTech Laboratories » Tue Mar 27, 2012 7:20 am

efims wrote: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?
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby efims » Tue Mar 27, 2012 2:31 pm

DMM Positive probe on Igntion 12V+ while Negative probe at Fuel pump output(ie 85 and 86 of relay coil) with relay fitted.
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby SymTech Laboratories » Tue Mar 27, 2012 2:50 pm

efims wrote: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.
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby efims » Sat Mar 31, 2012 5:28 pm

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

Thanks for helping

Problem (not)SOLVED.

Next day, problem came BACK.
Last edited by efims on Mon Apr 02, 2012 8:35 pm, edited 1 time in total.
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby SymTech Laboratories » Sat Mar 31, 2012 5:48 pm

Great news, thanks for updating us with the solution!
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby efims » Mon Apr 02, 2012 8:34 pm

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?
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby SymTech Laboratories » Mon Apr 02, 2012 9:14 pm

efims wrote: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.

SymTech Laboratories wrote:Keep your negative lead touching ground, then measure everything again using your positive lead.
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby efims » Tue Apr 03, 2012 5:20 am

SymTech Laboratories wrote: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
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby SymTech Laboratories » Tue Apr 03, 2012 8:16 am

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...
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby efims » Tue Apr 03, 2012 8:03 pm

SymTech Laboratories wrote: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
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby cmaid » Wed May 30, 2012 6:56 am

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


Solved?
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby efims » Wed May 30, 2012 7:39 am

yup...solved after replacing Q3 and D7.

Thanks
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Re: Fuel Pump Output problem MS1 V2.2 29Y4

Postby cmaid » Sun Jun 03, 2012 11:19 pm

Same problem here - same solution!

Thanks!
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