So a month or so ago I replaced my primary fuel pump since the one in there was making screams of death and barely hanging on. Used the Denso pump kit with strainer that comes well recommended, reused the factory harness, crimped on the new connector since the old one was a bit grungy, staggered the crimps, and did everything almost by the book. The only thing I didn't think to do was check resistance through the new crimps to make sure everything was good...

With the new pump in, everything seems good, except that the new pump still makes a noise. Much less noticeable than the old pump, but still there. One of those things you can ignore but it's still intrusive in the back of your head with cars like this. It's a bit more like a mosquito pitched whine than the dying fuel pump noise. Seems to get better as I drive longer, and seems worse when it's cold out. Also seems to change pitch slightly with engine revs - slightly louder at idle maybe, less noticeable when under load. Kind of strange. My subwoofer is out of the rear deck though since the driver was blown, so that hole is letting a bit of noise through.

Is this kind of slight mosquito noise expected, and will be quieted by blanking off the sub hole with a wood panel (something I've been meaning to do, but putting off for a while)? Am I just screwed with a defective pump that I will have to fight with having to remove the fuel tank again? The one thing I did notice was that the flat metal panel that goes on top of the area the fuel pumps sit in (can be seen in the fuel pumps guide in the forum files) was missing on mine. Would that have any effect? It seems like it's there just to prevent splashing of return line fuel...

 

I hate to ask a simple Q like this, but when did you last change the fuel filter? Have you checked your pressure on the fuel rail on the motor? Did you test your 2nd pump?

 

Fuel filter was changed at the same time that the fuel pump was. I haven't checked the fuel pressure, I tried to get a loaner tool at my local parts place and they didn't carry them. I've tested the second pump by jumping the relay and it's worked. I didn't think it would affect the primary pump at idle since it shouldn't be on then?

 

Did you try to jump the relay on the primary? If it makes the noise you're talking about it is possible it or something it's connected to came loose and it's vibrating.

 

Have you checked the holding straps that they're tight? I just want to be sure we cover anything outside the tank first.

 

Took me a while to get back to this, been caught up with other things and weather and couldn't do a proper thorough testing of the system.

I've had my subwoofer out of the car for measurement to make a baffle/adapter to put a replacement in. I stuck the sub back in today, and it seems to block enough noise to prevent the fuel pump from being heard in the cabin. Not a "fix", but the migraine inducing whine is gone, so good enough for now.

The electrical testing resulted in the following: All parts on the car itself are good (so relays, wiring harness from relays to tank, etc) are good with almost perfect conductivity. I tested resistance across the fuel pumps just out of curiousity, the fuel pump on the right side (so in my car, it has the brown/blue trace power wire going to it) tested at about .7 Ohms, while the other one tested at around .63 ish. My multimeter leads have a resistance of about .09 Ohm so that gets subtracted to get the actual resistance. I don't know what is expected, or how useful those are since there is the inline filter as well. I /think/ the higher resistance pump is the new one, but the 99 wiring diagram doesn't say which is pump 1 or 2. brown/blue trace goes to relay 1, which I think is pump 1, but I don't remember the relay numbering order.

Jumping the relays with everything connected does make noise, fuel pump 2 is slightly noisier, but uh, eh, I'll cross that bridge when I get there...

I guess my original question which got lost in my wordiness: For anyone with a good known system (ideally someone who used the same Denso pump), and who is good in hearing (able to clearly hear a 12khz range tone) - If the car is running, and you stick your head in the trunk, can you hear a fuel pump whine?

Unless I get a fuel pressure test which tells me otherwise, I'm probably putting this off until other issues are fixed...