My fuel pump ('92 Q) has gotten a little noisy in the past few days with cooler weather. Comes and goes. Can hear at start up and at highway speeds if stereo is off. Full tank of gas shuts it up.
Got out service manual and it says to test resistance of pump with multimeter. So got a $15 multimeter.....
Was having trouble getting a consistent reading, but the average reading was around 0.7 ohms. Per service manual it should be 0.5 ohms. Should I be concerned?
Any tips on using the multimeter? Says not to hold the device and to have your feet on the ground (was wearing running shoes). Tried to lay inside the trunk but got all kinds of different readings....
:thinker
fuel pump resistance
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greg_atlanta
- Posts: 1111
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- Car: 2008 G35 Journey Sedan, silver/black (no sunroof), 1992 Q45 (in a past life)
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Q45tech
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- 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
Like any dc motor the current varies with load and wear [and brush wear [carbon] filling in the gaps of the commutator].
The 15 amp fuse inside left dash compartment is the place to measure whats happening! Good engineering practice says use a fuse twice the expected current but with 10 or 15 amp sizes to chose from we don't know if the design goal was to protect a 5.5 or 6.0 or 6.5 or 7.0 or 7.5 current maximum [the cold engine sart fuel boost current or the 15-60 second WOT speed run.With a 10 ampere meter and fuse adapeter [some spade lugs that emulate fuse pins] you read start and running current.
A brand new pump is 2.2 to 3.2 amperes, a worn noisey pump is 4.0-4.2 amperes [mine that started noise about a month ago].
What is the maximum safe current is being determined:It willl vary with ambient temperature inside the controller.
Start up current can be as high as 7.0 amperes [used/worn] 5.0 amperes new.
We are zeroing in on the numbers but we need more samples.
I feel that doubling the current is a dangerous level but what the average new current is is still unknown..........is it 2.2 or 3.2.
IS 4.4 or 6.4 the dangerous level?
Each solder joint in the controller module will be different as to the exact diameter and thickness of the solder so its current vs melting point will be different.
We all know you can live with some pump noise till one day it fails!
I am ordering a pump next week to do the replament before Christmas.
What would be interesting would be to measure the current before/after a fuel filter change to see the restriction effects on the pump.I changed my filter and the noise subsided a little [changed pitch] but returned after 3 weeks [600 miles]............never know if you have excess dirt till you look in the tank bottom.
The 15 amp fuse inside left dash compartment is the place to measure whats happening! Good engineering practice says use a fuse twice the expected current but with 10 or 15 amp sizes to chose from we don't know if the design goal was to protect a 5.5 or 6.0 or 6.5 or 7.0 or 7.5 current maximum [the cold engine sart fuel boost current or the 15-60 second WOT speed run.With a 10 ampere meter and fuse adapeter [some spade lugs that emulate fuse pins] you read start and running current.
A brand new pump is 2.2 to 3.2 amperes, a worn noisey pump is 4.0-4.2 amperes [mine that started noise about a month ago].
What is the maximum safe current is being determined:It willl vary with ambient temperature inside the controller.
Start up current can be as high as 7.0 amperes [used/worn] 5.0 amperes new.
We are zeroing in on the numbers but we need more samples.
I feel that doubling the current is a dangerous level but what the average new current is is still unknown..........is it 2.2 or 3.2.
IS 4.4 or 6.4 the dangerous level?
Each solder joint in the controller module will be different as to the exact diameter and thickness of the solder so its current vs melting point will be different.
We all know you can live with some pump noise till one day it fails!
I am ordering a pump next week to do the replament before Christmas.
What would be interesting would be to measure the current before/after a fuel filter change to see the restriction effects on the pump.I changed my filter and the noise subsided a little [changed pitch] but returned after 3 weeks [600 miles]............never know if you have excess dirt till you look in the tank bottom.
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greg_atlanta
- Posts: 1111
- Joined: Tue Jul 23, 2002 4:37 pm
- Car: 2008 G35 Journey Sedan, silver/black (no sunroof), 1992 Q45 (in a past life)
So I can't check anything in the fuse box with my new $15 toy? Oh well.....Q45tech wrote:The 15 amp fuse inside left dash compartment is the place to measure whats happening! ......With a 10 ampere meter and fuse adapeter [some spade lugs that emulate fuse pins] you read start and running current.
Today the pump is whisper quiet (full tank of gas + warm weather helps). I'll try readings at different temperatures and before/after use and see if it changes. Really not too worried about it. No roadtrips planned anytime soon.
Fuel filter was replaced 1 yr/15k miles ago, so I'll replace it again on next oil change. Same pump has been in car since I owned it, so at least 60K miles on current pump. I always fill up at 1/4 tank or more.
I noticed instructions for MMO (marvel mystery oil) say it can help lubricate the fuel pump. Any truth to that?