Electric Fuel Pump Fix for my 87 DL

[azdave]

I've had a spell of bad electric fuel pumps in the short time I've had my 87 DL SPFI and unfortunately, it also applies to some of my other classic cars as well so it's not an isolated issue with just one car. They just aren't making quality pumps these days, especially in the pressure ranges that are close to our needs. I found a pump that I trust so far but it puts out way more pressure than I need, which in my opinion, just makes the pumps loud for no good reason and wears them out even faster. I really hate to hear the pumps whining, especially when I have the turn signal blinking and the pump noise jumps up and down with each activation of the bulbs. I was not ready to pioneer an in-tank pump installation so I looked for a better way to skin this cat.

My solution? I first installed a simple, fixed voltage 12-volt regulator so that the voltage swings were gone and the whining noise at least stayed steady, That was step one. The next step was a pulse width modulator (aka, DC motor speed controller) so I could dial down the pump power by using the duty-cycle setting while still feeding it 12 volts. The end result has been great. I now have a pump that I can barely hear with no more rising and falling pump whine when idling in a turn lane. Bonus feature is that the pump should last much longer as it's no longer trying to put out 50-60 PSI when I only need about 30 PSI for the regulator to maintain a steady 22 PSI at all engine speeds. Anyone else doing anything like this or am I the only nut case here? 

 

 

[Numbchux]

Most cars in the last 20-30 years do that from the factory, using a controller to vary pump duty. And actually take it further, to vary it based on engine load. I'm in the middle of swapping a 1994 Lexus 4.0 V8 into my 4Runner, and in one of my test runs, I pulled the return hose out of my fuel bucket, and it was just a dribble coming out, even at idle. This helps fight overheating of the fuel, and probably reduced wear on the fuel filters, as it cuts down on the volume of fuel going through them.

When I worked at AutoZone, the fuel pump companies said (grain of salt....but it makes sense) that the vast majority of fuel pump warranty claims were caused by debris, which is why you should always replace the prefilter when replacing a pump. I don't believe such a thing exists on the EA Subarus, so it might be worth putting an inline filter between the tank and pump.

The nice thing about the inline filter design on the EAs, is that you can get one anywhere. I've used ones for Ford trucks, and several other things. Can't get a $40 fuel pump for anything I drive, now.

[GeneralDisorder]

Seems like a herculean effort for an EA82. The Bosch Ford F150 lift pumps have always worked fine for that application and I've never been able to hear them when mounted in the stock location with rubber vibration dampening. 🤷‍♂️

Sounds like a fun experiment though. We do crazy stuff like that at the shop. Next week we are going to experiment with Nitrous Spool on a 2020 STi. 🙂

GD

Edited November 10, 2022 by GeneralDisorder

[Steptoe's photos]

i hope you can submit a wiring diagram or photos. Sounds very clever.

[azdave]

15 hours ago, Numbchux said:

Most cars in the last 20-30 years do that from the factory, using a controller to vary pump duty. And actually take it further, to vary it based on engine load. 

Yup. I know I've not invented something unique here. I'm just applying it here to hopefully get some better reliability and less noise.

Filter before the pump? Certainly. I installed one of those when I installed the first new pump. The tank appeared quite clean inside when I originally drained it but no harm adding a pre-filter just in case. After the first few pumps failed (including one from an F-150 application) I began to wonder if the tank pickup tube feeding the pump was clogged (such as from sediment in the tank). I temporarily installed a low-range vacuum gauge on a T-fitting at the inlet to the pump so I could see if the pump was being starved of fuel and maybe that was causing them to become loud and fail. That was not the issue. I even cut open the first fuel filter after about 100 miles to inspect the pleats and found very little junk so I'm certainly getting plenty of clean fuel to the pump.

12 hours ago, GeneralDisorder said:

Seems like a herculean effort for an EA82. The Bosch Ford F150 lift pumps have always worked fine for that application and I've never been able to hear them when mounted in the stock location with rubber vibration dampening. 🤷‍♂️

I find great satisfaction in repairing old things, especially somewhat forgotten vehicles. We also have a 1987 Mazda B2000 and five 1965-66 Corvairs in our family fleet that all get regular use so not really something out of the ordinary for me to keep these on the road. Since I'm using cheap, off the shelf parts from Amazon and love to do electronics it's a fun project but certainly not something a normal mechanic would do, especially with a customer's car. 

 

8 hours ago, Steptoe's photos said:

i hope you can submit a wiring diagram or photos. Sounds very clever.

I might do a quick block diagram to show the basics. If you've ever needed to control the speed of a small DC motor then you'll have done this all before. Here's a link to a video that shows pretty much what I did with the PWM controller.