Fuel Pump/FPCM/Relay
Fuel Pump/FPCM/Relay
Had all sorts of weird intermittent starting problems...thought it was the injectors cause I had good pressure to the rail...but lost it overnight. Thought it was the fuel pressure regulator...but I hear they usually don't go bad. Replaced the fuel pump 20k ago (car has 110K)...so didn't think that was the problem, no humming, no noise. Then disaster...dead Q and expensive tow....jumping the pump to ground wouldn't work! Supposedly it's a fried controller AND bad relay. BIG question....would the relay and the FPCM go all at once? Should I pop for a new fuel pump just in case. Why else would the FPCM or the relay go bad? Anyway I can test the fuel pump? Would Ohming (.5 spec) be enough? If so...I'm not quite sure which pins on the blue connector to check?
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Re: Fuel Pump/FPCM/Relay (Locknut)
EVERY dc motor on earth fails the same way when the commutators wear they slow down..............you can measure the rpm by looking at the current waveform and counting the pulses with an oscilloscope.
An ammeter doesn't show this since the readings are damped.
The 15 amp fuse is designed nor to blow unless a total short.
Ohms law says a 0.5 ohm pump should draw 26 amps at 13 volts and 18 amps at 9 volts. Since the commutator divides this into 8 pulses per evolution the pump is not drawing power 100% of the time as it comes off a winding the is a lull and then on to the next winding.
A frozen pump will blow the fuse or melt the FPCU transistors or solder joints depending how the FPCU fails it can pit the relay contacts and open the circuit.
Years of bad experiences have mandated that the dealer change the pump and FPCU as a pair to avoid warranty comebacks.
We still replace only the failed component but warn the customer in writing that the other could fail soon and they make have to pay additional to replace AND TOW................and that each could take out the other and there is no warranty unless both are changed simultaneously.
An ammeter doesn't show this since the readings are damped.
The 15 amp fuse is designed nor to blow unless a total short.
Ohms law says a 0.5 ohm pump should draw 26 amps at 13 volts and 18 amps at 9 volts. Since the commutator divides this into 8 pulses per evolution the pump is not drawing power 100% of the time as it comes off a winding the is a lull and then on to the next winding.
A frozen pump will blow the fuse or melt the FPCU transistors or solder joints depending how the FPCU fails it can pit the relay contacts and open the circuit.
Years of bad experiences have mandated that the dealer change the pump and FPCU as a pair to avoid warranty comebacks.
We still replace only the failed component but warn the customer in writing that the other could fail soon and they make have to pay additional to replace AND TOW................and that each could take out the other and there is no warranty unless both are changed simultaneously.
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maxnix
- Posts: 22627
- Joined: Mon Jul 22, 2002 8:11 pm
- Car: 1995 Infiniti Q45
1995 Infiniti Q45t
2000 Infiniti Q45
Re: Fuel Pump/FPCM/Relay (Locknut)
I would add that you need to change your fuel filter also. Inspect the tank and if it is not absolutely perfect (not even a film) then pull it and steam clean it. Blow air through the metal fuel lines and replace all the rubber ones. You should be good for another 10 -15 years if your fuel sources are not bad.
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Re: (Q451990)
Most FPCU fail via the melted solder joint which can be repaired...........which gives those at one with the car the warnings to get something repaired.
An electronic amp meter [with a 15 amp shunt in series with the fuses] would give lots of detailed info............as you could see the various speed modes.A shunt is a very low resistance calibrated resistor that allows one to measure the current by measuring the voltage drop across the shunt.
Nice 20 amp unit for $20 ebayhttp://cgi.ebay.com/20A-Ammete...wItem
Unfortunately a 10 AMP fuse is not large enough and might naturally open under WOT in Summer when you are doing an emergency pass and facing a semi.
Every pump will read a different ampere draw +-2-3% and increase with age.
An electronic amp meter [with a 15 amp shunt in series with the fuses] would give lots of detailed info............as you could see the various speed modes.A shunt is a very low resistance calibrated resistor that allows one to measure the current by measuring the voltage drop across the shunt.
Nice 20 amp unit for $20 ebayhttp://cgi.ebay.com/20A-Ammete...wItem
Unfortunately a 10 AMP fuse is not large enough and might naturally open under WOT in Summer when you are doing an emergency pass and facing a semi.
Every pump will read a different ampere draw +-2-3% and increase with age.