Cause of fuel pump failure
08-14-2018, 09:52 PM
#1
Rennlist Member
Thread Starter
Cause of fuel pump failure
Apologies for going OT but I think it’s relevant to many (I replaced my Porsche fuel pump a few years back) and I was hoping to tap the wisdom on this board for a deeper, more educated understanding.My other car is a 98 Subaru Outback, 250k miles, and I just had the second fuel pump failure in 5 years. The original one lasted 15 years and I replaced it with a Genuine Subaru replacement from the dealer for the tune of $500 so I’m wondering if there’s something else going on that’s causing the fuel pumps to fail. Like, could the fuel pressure regulator be a bit leaky such that the pump has to work harder maintaining a high flow rate to reach operating pressure?
When the original pump failed, I replaced all the filters and checked the FPR operation per the manual and it checked out OK so I didn’t replace it.
Was that a mistake?
Anyone have any experience or done any flow rate experiments?
When the original pump failed, I replaced all the filters and checked the FPR operation per the manual and it checked out OK so I didn’t replace it.
Was that a mistake?
Anyone have any experience or done any flow rate experiments?
08-14-2018, 09:58 PM
#2
Rennlist Member
I would guess every car design is unique for fuel pumps. Porsche might have a more unique tank setup than most cars. It does seem that Porsche fuel pumps are more prone to fail than others, but who really know. Porsche still has a high level of reliability.
I know that, generally, it’s best not to run the tank empty all the time, as fuel in the tank keeps the pump cooled.
I know that, generally, it’s best not to run the tank empty all the time, as fuel in the tank keeps the pump cooled.
08-14-2018, 10:38 PM
#3
Rennlist Member
Thread Starter
Thats true of the Soob but not of the 993 at least. The pump has its own compartment under the car - so could be an issue for our cars, more heat and only cooled by the fuel through the pump. But not a factor in the Soob.
08-14-2018, 10:57 PM
#4
Rennlist Member
In my 50 year experience with things mechanical and automotive, I've found that component replacements generally only have a life of 50-70% of the original component. So, if an original component lasted 10 years, you should be happy if the replacement lasts 5-7 years. This isn't true for every replacement component, but you'd be surprised how accurate it is for most. Two fuel pumps in 250K miles is actually pretty excellent.
08-14-2018, 11:14 PM
#5
Wonder if there is any correlation of fuel pump failures and DME relay burnouts. My original pump lasted 103k if I recall correctly. It was whining and making all sorts of sounds that led me to believe it was failing. Replaced it just to be sure. Bosch unit wasn't expensive and relatively easy to change. DME relay had failed about 1 month prior to my replacement. Would be nice to know the current draw delta between old and new....
08-14-2018, 11:21 PM
#6
Rennlist Member
Thread Starter
My experience has been that cheap autoparts store aftermarket parts are trash and don't last more than 10% of genuine parts. But genuine OEM parts do last as long. You'd hope that design and manufacturing improvements would outpace cost reductions with a reputable manufacturer but I know there's lots of examples where that isn't true.
But fuel pumps are fuel pumps, they make 'em by the million. What is it about me installing one vs the factory installing one that makes mine last half as long? Did I fail to treat the root cause failure by treating the symptom?
But fuel pumps are fuel pumps, they make 'em by the million. What is it about me installing one vs the factory installing one that makes mine last half as long? Did I fail to treat the root cause failure by treating the symptom?
08-14-2018, 11:28 PM
#7
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Thread Starter
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08-15-2018, 12:00 PM
#8
RL Community Team
Rennlist Member
Rennlist Member
This may explain the service life issue you bring up. Something I learned while a product manager in the automotive parts manufacturing industry.
Andy
08-15-2018, 02:38 PM
#9
Do you run your tank to low? Low fuel levels cause in tank pumps to not be cooled enough by the fuel they are submerged, this can cause the pump to overheat and burn out early. Also when ran low, the pump is more likely to suck up the crud at the bottom of the tank blocking the in tank filter to clog making the pump work harder.
08-15-2018, 10:07 PM
#13
RL Technical Advisor
Several things shorten the life of fuel pumps:
1) Running out of fuel
2) Dirt, water, rust
3) Poor electrical connections that make the pump draw too much current
4) Poor quality parts (usually aftermarket but not always)
1) Running out of fuel
2) Dirt, water, rust
3) Poor electrical connections that make the pump draw too much current
4) Poor quality parts (usually aftermarket but not always)
08-17-2018, 06:44 PM
#14
Rennlist Member
Thread Starter
Thanks for the replies all
the soob pump is in the tank unlike our cars so when I replaced it I was able to peek inside the tank and was impressed by how clean it was. No sediment and the tank walls were shiney golden (is that chromate finish?)
ive never run out of gas but I do run it down below 1/4 before filling up every other week or so
it depressing to think that the dealer replacement parts aren't manufacturer quality but there no other choice.
i still think there may be something aged in the fuel pressure regulator so I think I'm going to replace as part of an experiment. The soob FPR isn't too expensive unlike ours ($700+ With fuel rail)
if I let the return pipe fill a gas bottle for a minute at idle, replace the FPR and repeat I'll get a measure of relative flow rates
if there the same then I'll schedule a new pump for 2023
the soob pump is in the tank unlike our cars so when I replaced it I was able to peek inside the tank and was impressed by how clean it was. No sediment and the tank walls were shiney golden (is that chromate finish?)
ive never run out of gas but I do run it down below 1/4 before filling up every other week or so
it depressing to think that the dealer replacement parts aren't manufacturer quality but there no other choice.
i still think there may be something aged in the fuel pressure regulator so I think I'm going to replace as part of an experiment. The soob FPR isn't too expensive unlike ours ($700+ With fuel rail)
if I let the return pipe fill a gas bottle for a minute at idle, replace the FPR and repeat I'll get a measure of relative flow rates
if there the same then I'll schedule a new pump for 2023
10-06-2018, 08:43 PM
#15
Rennlist Member
Thread Starter
In my 50 year experience with things mechanical and automotive, I've found that component replacements generally only have a life of 50-70% of the original component. So, if an original component lasted 10 years, you should be happy if the replacement lasts 5-7 years. This isn't true for every replacement component, but you'd be surprised how accurate it is for most. Two fuel pumps in 250K miles is actually pretty excellent.
so i idled the warm engine for 1 min with recycled gas from old FPR into a gas bottle, put the new FPR in and repeated. They both dispensed the same amount of gas per unit time. I estimate about 0.66 gallon per minute or 36 galls/hr or more than 10 times peak consumption.
all makes perfect sense now of course. There is only one flow impedance that will result in a particular back pressure for a particular pump. If the FPR gets the pressure right then the flow rate must also be right.
bit like a shunt regulator (for the EEs)