Still trying to figure out intermittent fuel pump noise.
I’ve renewed entire fuel system, and have newish Bosch 69536 pump. It’s definitely not related to tank pressure. Fuel filter is new, surge screen is clean, no kinks in hoses.
It seems I can make the noise decrease by increasing fuel pressure.
At idle in Park at 900rpm, I have 17 inHg vacuum. Fuel pressure at rail is 28psi. If I disconnect and plug vacuum to outlet FPR, fuel pressure jumps to 36psi, and fuel pump noise goes away. Both FPR’s are new.
I’ve got a Walbro fuel pump I’m thinking of swapping to see if there’s a difference.
Is this Bosch pump just noisy when it’s fuel pressure is being knocked down?
Do you have an added filter before the pump? My pump gurgles somewhat more with an additional filter before it (between the sump and it). I suspect this is because it does not appreciate having to “suck” as it really is mostly meant to push.
The intermittent nature depiction sounds very familiar to me though. Some days my pump is very noisy and others it’s silent. I have tried to isolate conditions ie. low fuel, hot fuel, etc. but really haven’t come up with much.
My car has its original fuel pump btw. I’m just living with the occasional gurgle and figuring the pump is past due to be replaced anyhow even if it’s being worn out a bit faster now sometimes.
No, I am just using the screen filter in the surge tank.
About a month ago, i emptied the tank using the pump. With no restriction of pressure on the outlet side, it was super quiet. It made the noise before I used it to pump out tank, so this isn’t what caused it.
Does the ECU adjust voltage to pump? Or is it 12V on = full capacity?
Dunno much about the XJS fuel plumbing configuration, but in my XJ there is an Air Bleeder, after the Pump and before the Fuel Filter.
It’s a hex cylinder thing with three hose connections, in - out and air purge that goes back to the return line. It also incorporates a one-way check valve.
The rubber in the check valve gets hard and it can make noise, from inside the cabin can be mistaken as Fuel Pump noise.
In my case it was so irritating that I removed the check valve and put an external one.
Noise gone!
You mentioned no kinks in the hoses, and that’s good, but are the under body pipes in good shape?
Over the years, on various cars, I’ve cured some odd noises by just slightly modifying the hoses and pipes. A larger or smaller radius bend, typically. But sometimes any change to slightly alter the way the liquid flows will create or eliminate noise. It takes some experimenting.
I call it ‘fluid harmonics’ but I’m no scientist or engineer…not that anyone would inadvertently mistake me for one, I’m sure
Anyhow, the manner in which the gasoline moves before and after the pump can change the sound of the pump.
