So just varying the voltage. The fuel pump may actually like that better. I have been doing some reading about VFDs and a PWM voltage can induce voltage spikes of twice the running voltage.
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So just varying the voltage. The fuel pump may actually like that better. I have been doing some reading about VFDs and a PWM voltage can induce voltage spikes of twice the running voltage.
Attachment 1768
Hopefully this can be seen. It is copied out of Mitchells Repair Manual with pinouts from a 8625
Greg Thanks for looking in. The varying voltage idea has some drawbacks with SES error codes and pulse width of injectors that could actually cause me some headaches. It's not actually a PWM voltage so much as turning the fuel pump on and off really fast. I don't know about voltage spike induction, but if so, it should also occur in the soft start of the electric fan code 93 has up. Remember that what I am actually switching is ground.
Varying the voltage yes, but not to the pump. Sending a varying voltage signal to the PCM, not varying the PCM's voltage either, just a signal that the BPW code would see as voltage varying to the pump. The BPW code would in turn use the BPW Multiplier vs. Fuel Pump Voltage table to correct for this condition, which would be skewed to add or remove BPW as desired. Essentially trying to trick the PCM into doing this for you. But, I have no ideal how one would go about generating a variable voltage signal that would be relevant to the fuel needs of the engine.
Hope this makes some since.
The PWM soft start code does cause some voltage disruption.
HMMMM. Is the voltage disruption because of the draw of the current, causing voltage to drop, or is it a voltage spike? You could clamp the voltage to stop the spikes, but I'm not sure what would solve a voltage drop unless you had some kind of large cap.
Also, I think the problem of adjusting the BPW of the injectors like that is you have a max pulse width and a min pulse width you have to deal with. If you start with a high pressure system, and use the varying voltage method, you would raise the voltage, lowering the pulse width, but would run up against the minimum pulse width problem. Going the other way causes the opposite problem. The other approach to this would be a stepper motor controlled variable pressure regulator. I think Detroit uses PWM on the fuel pumps because it is more straightforward.
The disruption appearers to be a voltage drop (lights pulsate). I suspect that I may have a bad connection somewhere. Another contributing factor on my truck is that the battery is relocated to the rear with shut off switch and a big solenoid to cut the alternators power. Lots of opportunity for voltage drop. I don't think you'll have a problem with this.
I'd say your right about the min and max pulse width.
Well I've been reading and searching and came up with a bunch of infor I just cut and pasted for furthere review. HTH!
Quote:
On Celica (3S-GTE), Cressida, MR2 (3S-GTE) and Supra models,
fuel pump volume can be varied. Based on intake volume and engine RPM
signal, the ECU signals the fuel pump relay to change fuel pump speed.
If engine requires a large volume of fuel, fuel pump turns at high
speed; when a small volume of fuel is required, pump turns at a slower
speed.
The fuel pump driver module modulates the voltage to the fuel pump (FP) to achieve the proper fuel pressure. Voltage for the fuel pump is supplied by the power relay or FPDM power supply relay. (For additional information on FPDM operation, refer to PCM Outputs—Fuel Pump and PCM Inputs—FPM.)
1998 and up Ford Mustangs use PWM fuel pump
You can certainly use a PWM output to drive a solid state relay. The burden of proper operation falls on the pump controller and whether the fuel pump is designed to operate as such. The ECU "can do it", meaning provide a programmable PWM output based on RPM or load or whatever you want to the controller.
Most electric pumps are not designed to be pulse width modulated, as far as "turning them on and off". Only have the voltage varied.
http://www.power-io.com/products/hdd.htm
http://jbperf.com/pwm_converter/index.html
"Most electric pumps are not designed to be pulse width modulated, as far as "turning them on and off". Only have the voltage varied."
Funny, I was just having that exact same conversation with my son. I don't think TBI/TPI pumps were designed to work at varying voltages either. I would almost like to take an old tbi pump, and rig it up to run pulse width modulated in a test bench setup and see how it fares. Voltage spikes can be clamped with MOV's and undervoltage can be handled with large caps, but if the pump fails every 2 months, it just isn't worth it. I wonder if MTBF for tbi fuel pumps is in on/off cycles, or total run time?
what about a high/low pass filter? i can't remember which ATM, but filter the output so it's essentially a variable voltage instead of a PWM.
i may be thinking about small-signal stuff though.
That is exactly what I meant earlier. PWM causes spikes in the voltage which get worse with wire length. I have a feeling that pump life may be worse with PWM than with simply running at a lower voltage. Yes line reactors can lessen the spikes, but the PWM can still create a lot of heat in the motor. Newer systems that run PWM to the pump, may be using pump designed specifically for that purpose, they may have larger, more insulated windings.
PWM controller...
I like it, I say go for it, I'm thinkin I may build one for my water pump.
No, I just answered it awkwardly. What I meant was I don't think a tbi/tpi pump will work PW switched or voltage varied. Then you come along with a controller that is specific to fuel pumps in automotive applications. I think I'm officially confused right now, probably from lack of sleep. I'm off to bed for the night, Later.