Carpokes

So last summer my decade-old 044 Bosch pump started making a loud buzz/screaming sound. It happened once the car was fully warmed up, in hot weather, and was loud enough to hear with the windows rolled up and driving the car. I assumed it was failing, so ended up replacing it with the AEM '044-style' pump shown here:

https://www.aemelectronics.com/products ... -fuel-pump

All seemed fine and dandy after changing the pump. I also ran separate oversized wiring to it with a separate relay etc., since the AEM claims to pull slightly more amps than the Bosch (and even the Bosch was probably at the limit of the 'approved' amps for the factory wires).

Fast forward to last weekend when I took the car out for a rare 100 mile trip. Drove great and all was good, except by the time I got home, the AEM pump was making nearly the same screaming sound as the Bosch. It was a hot day, and temps seem related. I've been running E85 for several years, and I did change the pickup screen in the tank maybe 5-10 years ago. Fuel lines are stock, with Pauerman (-6 and -8) lines under the hood.

Seems like reports are all over the map online about how loud is 'normal' for these pumps. I don't want to keep buying new ones if they're all going to scream the same, but am wondering if the E85 or something about my car is making them get loud?

From AEM's website: 'The AEM 400lph Metric High Flow Fuel Pump is rated for use with ethanol-blended fuels, (E85/E90) and all types of gasoline, but pump life will be diminished if used with 100% ethanol fuels.'

Thoughts?

Adding a video so you can hear it. The audio doesn't do it justice, but the buzz is pretty darn loud in person....

Honestly I don't have anything to add. I only upgraded to a Bosch HVFP, and only run gasoline that is E10 or less. Is there any way to disassemble a 044 to assess wear?

Darwin wrote: Fri Jul 30, 2021 1:59 pm Honestly I don't have anything to add. I only upgraded to a Bosch HVFP, and only run gasoline that is E10 or less. Is there any way to disassemble a 044 to assess wear?

Not that I can tell, at least without ruining it.... Is the HVFP reasonably quiet? I'm not running as much boost as the old days, so might be able to get away with a smaller more civil pump...

I’ll look up flow numbers for the HV unit. I bought mine from Lindsey. To me it is very comparable to a stock unit, but maybe a tiny bit louder.

I sent you a video by e-mail. Couldn't load it onto the forum directly.

Tom,

Is the pump quiet but get noisy after driving for a while?

Does it matter if you start with a full tank of gas or with less fuel?

Are you able to measure the temp of the pump when noisy? Temp of fuel in tank? Pressure in fuel tank?

BTW in the old days, the HPFP was for a Mercedes (a 450SL IIRC).

Fuel temp and more specifically the vapor pressure at the pump is directly related to noise in the turbine-style Bosch pumps like the 044.. Especially in hot weather and/or when tank level is lower, the heat added as fuel passes through the engine bay is enough to have the pump sucking little vapor bubbles into the first pump stages. This is why Fast951 is asking about those things. Porsche (and Bosch) added some interesting higher-pressure pumps trying to solve the problem especially in early CIS cars of many makes, but they tended to be band-aids that only temporarily masked some of the symptoms. My 928 has a small in-tank pump to add just enough pressure to collapse the vapor bubbles before the primary pump. Along with a rather unique fuel cooler, it solves both the noise and vapor problems in the main pump. I have no idea how easy it might be to add a small pre-pump in the 951 tank, but if you suffer from both the suction noise and low fuel flow and pressure issues that go along with boiling fuel in the main pump inlet, it might be worth a look.

I don't know about your pump but are you running slicks?

Thanks gents. I'll do some testing this weekend, but...

Yes, from memory, it seems the pump is quiet to start and gets loud after the car is hot. I'll confirm that this weekend.

Last summer when it was happening with the 044 pump, it did happen regardless of fuel level, but 'seemed' to get louder as the gas level went down.

I have not tried to measure any temps, but would say both times I've noticed this, it's been in the dog days of summer -- so in the 90 to 100F range ambient.

Does E85 have a higher vapor pressure than E10?

When I first put the AEM pump in the 951, the screaming seemed to go away, even in hot weather. Does the fact that it is now screaming mean it's too late for this one?

I actually changed the fuel pump on my 79 450SL a few years ago and did notice how similar it was. I also remember my dad experiencing vapor lock on that car, back in the day, and I seem to remember it has a fuel cooler now. Will have to look at that... Maybe add an inline fuel cooler to the 951?