Electronic PPR

[Bitsyncmaster]

I have been thinking about this idea for a long time. This is not something anyone needs but trying to convince myself to try it.

The major gain I think would be your gas would stay cooler. Most engine guys know cooler gas and cooler air will give your engine more power. I think most of our gas heating in the tank is due to the recirculated gas from the returned fuel. The fuel pump also adds heat from the electrical power it uses. I also found the normal PPR pressure does change with voltage change at the fuel pump. So the normal PPR is affected by the amount of returned fuel. Of course it would reduce electrical loading of the car system.

I would keep the original PPR working, just shim it to a few PSI above 75 PSI. A pressure sensor would be installed in the CSV hose to read primary pressure. An electronic unit would be installed in the circuit driving the fuel pump which would pulse width modulate the fuel pump power according to the pressure sensor.

Displaying fuel pump power could also warn you before your fuel pump will fail due to low pump output.

I will probably never get around to doing this. It just keeps me thinking.

[jackb]

I think its impressive as hell that you *can* do this, both imagine and do.

[Bitsyncmaster]

Well I threw together a simple electronic circuit to switch the fuel pump on and off with the software set for 50 PSI just for testing. Now waiting on the sensor and some banjo fittings to make up a new cold start hose with the pressure sender.

I really want to see how solid it holds the set pressure. I don't think I will need to PWM it but the fast switching is really doing the same thing. If it works it will be interesting to see what adjusting PPR pressure will do to my mixture setting and other things. Nice to not need to change shims, just turn a pot to tweak the PPR pressure.

[Bitsyncmaster]

More thought about switching full power on and off to the fuel pump. It will all depend on the delays of the sensor and the fuel pump response. Any delay would create overshoot and under shoot. Kind of like the problems with the lambda and idle ECU. To correct that you need to use slower acting fuel pump power (constant PWM) so you can slowly control power under software control.

I don't think the fuel accumulator will help. My testing of rest pressure makes me believe the fuel accumulator is fully charged at 42 PSI.

[Bitsyncmaster]

Got my banjo fittings. Got the electronic pressure sender tapped into the CSV hose. Got my mechanical pressure gauge tapped into the FV line. Just running a rest pressure test to see if anything is leaking.

By the way, NPT fittings definitely need a sealer. Without had bad leaks. Used my Permatex #2 and seems to be leak free.

One thing to note. Primary pressure is 71 PSI running pump just on battery. I get 75 PSI running pump with 14.5 volt charger in cig lighter. So if you adjust PPR shims, do it with a charger attached (so you get normal engine run voltage).

I will start playing with my electronic PPR tomorrow.

I was thinking of getting the fuel hose clamps that you crimp with clamp pliers. Has anyone used these to replace the normal screw type fuel injector clamps? I don't like the long screw sticking out of the clamp.

[Bitsyncmaster]

Well the basic on off to the fuel pump resulted in a very fast deviation of 5 or 6 PSI. I changed the software to use PWM at 60 hz. That resulted (with some time delays) of about 1 PSI slower deviation. So the time for the fuel pump to change pressure and the time for the pressure sensor delay is going to be a problem. My guess is the pressure sensor has more delay then I expected. The delays will probably make it not work responding to quick throttle changes.

It does hold the setting and if it's below the stock PPR setting would eliminate returned fuel from the PPR. I think I'm going to set my electronic PPR to a few PSI below the stock PPR and see how the engine runs.

[Bitsyncmaster]

I ran a test to see how much overpowered the fuel pump is. Right now it looks like my fuel pump is not that much overpowered.

This test is on a cold engine not running so the WUR is letting some fuel bypass to the return line. A warmed up engine would have less bypassed fuel to the return line.

With 10 volts driving the fuel pump at the RPM relay, I get 62 PSI primary pressure.
11 volts I get 68 PSI.
12 volts I get 71 PSI.
13 volts I get 74 PSI. This is where my PPR will start limiting.

So my idea to PWM the fuel pump does not look like I'm going to gain much of anything.

It may be different fuel pumps would work with more fuel flow. I seem to remember testing the original stock pump and it would work down to 7 volts but I don't remember how I tested that.

Later today I will test primary pressure on a hot running engine. I'm interested to see if it dips when I punch the throttle. I never thought of testing that before.

[Bitsyncmaster]

With my mechanical fuel pressure gauge T'ed into the FV hose I get a very rapid jitter of the primary pressure of -1 to +1 PSI centered around 75 PSI. I'm guessing that is caused by the FV running. Don't see much drop in PSI when I punch the gas. Just a little if opened rapidly enough.

I will move the gauge to the CSV and see if that has that 2 PSI jitter.

[Bitsyncmaster]

Running engine with mechanical gauge on CSV port shows very little jitter. Maybe a half pound at first but it stopped after engine warmed up.

By the way my electronic sensor never showed that jitter, so I do think it has slow response. Never got a data sheet with it.

FYI: The CSV port shows 79 PSI with my engine running. My car has 14.5 volts running at idle. The FV port showed 75 PSI with the jitter running. I guess I should get a thinner shim for my PPR.

[Aaron Cake]

Years ago I used a product like this on an RX-7. I forget what it was called but something like "boost a pump". Took a boost/vacuum reference and drove the pump harder during boost to increase fueling in a very crude way (by essentially overpowering the stock FPR).

When I looked inside it, there was a boost converter. I am terrified to think what it bumped the voltage level to in order to get so much more output from the pump. Sounds like you need a similar design if the stock pump isn't going to put out the required pressure at 14V. Bonus is that you can control pump speed entirely through the converter without the need to PWM the pump itself. Since you only need control over a narrow range.