Really strange idea of the day!!!

[jim_in_dorris]

I was talking with my son tonight, and according to him, all the new toyota's, and dodges pulse width modulate the fuel pump itself to control fuel pressure. If a 747 class ecm had a spare PWM output, is it possible to write a routine to control fuel pressure based on load and rpm? No more adjustable fuel pressure regulators. Just putting this out as a discussion item. What does everyone think. My 355 build will require #80 injectors at 20 psi or #61 injectors at 34 psi. How nice it would be if you just told the pump how much pressure to supply (like a vacuum referenced FPR except much more accurately).

[gregs78cam]

A few years back when I was working on a friends 300ZX (the one in my avatar) we learned that the fuel pump in that was controlled by a module. We ended up bypassing module control so it would put out constant pressure. I don't know if it is similar to what you thinking, but it sounds possible.

Just did a quick search, and it seems like the module runs the pump at 2 speeds depending on load. So yea it would be something to look into. And you meant '7427 right?

You would also probably have to give the PCM feedback on fuel pressure. And you would probably have to come up with another way to bypass the excess flow(like an inline restriction on return), or just dead-head the TBI.

[1project2many]

Your son's correct. The strategy today is to use a returnless fuel system which reduces vapor formation in the fuel tank with pump pressure controlled electronically. Although you could implement a non-feedback based pump control strategy you leave yourself open to problems if actual pump output doesn't match the model used for development. Better approach uses a fuel pressure sensor. Once you have fuel pressure as a variable controlled by ecm you have a lot more dynamic range for a set of injectors so larger cams and boost will become easier to tune from idle to full power.

[EagleMark]

Don't think there is extra PWM circuit on 1227747 which I believe Jim runs. But if he did a 16197427 conversion that does have a PWM circuit for the E trans which could be first part of the puzzle?

[RobertISaar]

keep in mind you wouldn't be able to directly run the pump off of the PCM, way too much current draw. you would need to setup a solid-state relay or some transistors to handle all of the load.

[jim_in_dorris]

Okay, after reading the replies, and thinking about it, I came up with the following;

Robert-- I wonder if the fuel pump relay can handle PWM

I was thinking about setting the fuel pressure regulator at a maximum pressure, then if something goes wrong, it won't go over that pressure. If I was to use say an EP377 pump which IIRC is rated at about 45 psi, I would set the regulator at 35 PSI, then build a table to drive the fuel pump. I would most likely use multiple settings like:

idle -2000 rpm 33%
2001 - 3000 rpm 66%
over 3000 100%

Then include 3 different values for flow rates depending on my injectors.

Having a closed loop feedback system would be the best route, but I am trying for a minimalist approach here at first. If that doesn't work, increase the complexity a little at a time. Also, if the FPR looks stock, it's one less thing for the smog nazis to object too.

[EagleMark]

Robert-- I wonder if the fuel pump relay can handle PWM
From what I read about this in the other $OD fan option no! On this page would be the relay you would need.

http://www.gearhead-efi.com/Fuel-Injection/showthread.php?468-Another-option-for-0D-efan-control/page3

[RobertISaar]

if you try and drive a relay via PWM, expect bad results, to say the least. those things are meant only for discrete operation, hence the suggestion of a solid-state relay or some transistors., since those don't have any actual moving parts.

[jim_in_dorris]

Just speculating at this point, I really didn't expect any other answer about the relay than what Mark and Robert replied with. So Step 1 would be to develop a circuit to run the pump. That is fairly straightforward. I guess the next step would be to investigate driving the circuit with some software. This is where I really need a test bench. I guess first I will start playing with software. Stay tuned for the next installment of "HMMM will this work?"

[RobertISaar]

i'm just about to finish my 100% solid-state bench for my 16149396. :happy:

and yeah, the circuit is the easy part, getting an open loop fuel pump pressure system to work consistently is going to be the interesting part. do you happen to know if there are any spare A/D channels on the PCM you're planning on doing this with(so you can run it closed loop with a pressure sensor)? i got lucky that Ludis documented the 7727/7730/7749 type PCMs long before i knew anything about them and i actually interally modded my 9396 to add 3 extra A/D channels, though there are more that could be opened up if necessary.

[jim_in_dorris]

<quote> i'm just about to finish my 100% solid-state bench for my 16149396.<quote>

Nice. I would love that myself. I understand the problems with open loop, and will probably end up closed loop. However, I do intend to investigate open loop first before abandoning that attempt. I could probably put the pressure sensor somewhere out of sight so it would be unobtrusive.

[jim_in_dorris]

Okay, perusing 98's fan control code gives me the output for the fuel pump, now the question is: How many amps is an EP377 fuel pump? I could use the fan relays for the fuel pump.

Next question: Would an oil pressure sensor work for closing the loop on the fuel system? The one in my truck is a 1 wire, not sure if that would work or not. The range would probably work, just have to figure out what the calibration looks like. I.E. what voltage is what pressure. I think it might not work because of sensor grounding, but I could probably ground the sensor in the T adaptor.

[RobertISaar]

i actually have a similar situation with the 1 wire oil pressure sensor... what i did was grab a spare instrument cluster, powered it up on a bench, connected the oil pressure circuit to ground through various resistances(it's a 0-~80 ohm sensor) and then used my multimeter to check the voltage between the resistor and the cluster. my results? at most, i should see around 8.2 volts or so when the sensor is pegged at 80PSI. so if a run a /2 voltage divider, i can put it into the 5 volt range of the A/D circuit in the PCM, then just tap a wire into the oil pressure sensor circuit(using a high value resistor, to prevent it from skewing the gauge).

anyways, as long as you have 1 open A/D channel that is internally connected to ground via a resistor, you can do this.

[jim_in_dorris]

Okay, now I need to find an open A/D channel. One thing nobody has mentioned is the Oil Pressure Switch that is connected electrically to the fuel pump. I don't think that it would work well if it was wired in parallel to a PWM circuit.

[EagleMark]

You can remove it. It provides power when running if relay fails. If relay fails you will have long crank starts until oil pressure switch powers fuel pump IIRC. They are not used in aftermarket wiring harness and I don't use them when rewiring a harness.

[jim_in_dorris]

Actually i was aware of that because for a long time after I bought my truck the Oil Pressure Switch was disconnected and I didn't know it. I think they are just a source of another oil leak anyways, and the rebuild will not have one. I was just throwing it out there. ;) I will probably start looking at code now as it appears that the hardware is doable. ( I still don't know how may amps the fuel pump needs, but maybe by looking at the stock fuel pump relay I can get that.) I will have to re-pin for the fuel pump. I also need to look at the Key On / Engine Off fuel pump prime logic.

[RobertISaar]

key on, engine off logic that applies to almost all OBD1 applications:

first power-up, turn on pump for 2 seconds, then shut off, to build up pressure in case it has leaked down since last startup. then so long as reference pulses keep occuring, the pump will continue running. when keying off, the pump goes off as well. if the key is still in the on position and the engine quits running(stall), the pump will run for 2 seconds, then shut off.

of course, your application may be different.

[jim_in_dorris]

Well, I spent some time looking at schematics for my truck. Then I looked at the code. I may have to disable the fuel pump voltage errors, not positive yet, still thinking on that. If I repin A1 to one of the PWM outputs, I should be able to makes some code changes and all will be good. Now is time to start thinking on what parameter I should use to set output pulse width. Would RPM be sufficient? After all, HP = Tq x RPM. Or will MAP need to be part of the equation?

Pseudo code for RPM base would probably look something like this:

If (RPM lt 2000) then
Injector constant = (61# at 15 psi)
fuel pump DC = 33%
else
If (RPM gt 3000) then
Injector constant = (61# at 34 psi)
fuel pump DC = 100%
else
Injector constant = (61# at 23 psi)
fuel pump DC = 66%
endif
endif

I still need to look at fuel pump relay to see what amp value is. The way I drive, 85 % of the time my RPM's will be below 2000. (in OD at 55 I am doing 1875 + -)

[RobertISaar]

RPM alone is a bad idea, since the fuel flow required at 1600RPM at 30kPa is vastly different that 1600RPM at 85kPa.

i'm not fluent with the later truck cals, but is there any kind of airflow calculation? if so, base pump DC off of estimated airflow would be my route, maybe with a target AFR value modifying DC, and that would allow you to create a "fuel flow required" value based off airflow and the amount of fuel compared to amount of air.

[EagleMark]

i'm not fluent with the later truck cals, but is there any kind of airflow calculation? Speed/Density would be the air flow...

[RobertISaar]

right mark, but some of the speed-density stuff doesn't make an actual airflow value that makes much sense(WAY off of scale), or makes a seriously fudged number (RPM multiplied by MAP, no VE component involved).

[EagleMark]

Some things are based on airflow, more in later P4 PCM which I think he is going to need to get a PWM AD circut, I'm not sure the 1227747 C3 is going to have anything available? But I agree the numbers would not be real accurate like MAF...

[jim_in_dorris]

Mark, this would be $0D code on an 8625 so that isn't a problem

HP = TQ (ft-lbs) x RPM/5252 from fullsizechevy gives my 400 x 1600/5252 or around 122 hp. 61 # injectors can feed that fine at 15 psi. Remember that I still use VE tables for fueling, Changing the pressure by PWM the fuel pump is just like having an electrically controlled fuel pressure regulator. I am thinking that the VE tables should be fairly stable if I change the injector constant to reflect the differing pressures.

and Robert, yes 1600 RPM at 30 map requires different fueling that 1600 at 85 map, but again, the VE tables should take care of that.
Here again, I could be way off base because of something I don't know.

[jim_in_dorris]

After playing a little more, I would adjust the RPM points to 2600 RPM ~ 200 HP and 3800 RPM ~ 290 hp. Below 2600 RPM DC would be 33% , from 2600 RPM to 3800 RPM would be 66% DC and 100% above 3800 RPM to my max HP of 350hp at 5000 RPM.

Obviously, if somebody else does this, it will have to be modified to what their engine parameters are.

[EagleMark]

This is a very cool project you have going on! :thumbsup:

Seems the relay and PWM and even setting are in order. Are you sure the oil pressure switch is going to give you readings you need? I wish I had one here, I just looked for one to test... what do newer cars use for this switch? It could be a cheap JY Part? Or is it built into newer fuel pumps?

[jim_in_dorris]

Well, the soft start on the electric fans were sort of an inspiration. I am not sure if the oil pressure sensor has the range I need, but it sure would be cheap. Robert used a spare instrument cluster to measure resistance, and it does look doable. I also looked at the fuel pump relay, and the connector might need to be changed from stock. These are modifications I would really like to try the parts and code on a test bench first, so that may end up being a priority soon. I am mainly doing research right now because I know when I do my 355 build ( I start tearing down the block as soon as it gets warmer outside) I will need more fuel to feed it.

[93V8S10]

I was reading this and though of the L497E BPW Multiplier vs. Fuel Pump Voltage table. Would this be affected? Or could it be used to your advantage? Maybe if you could get a adjustable voltage signal to the PCM, change that section of code to use your new voltage input, adjust table to get more/less fuel. Just a though, maybe not a good one.

[jim_in_dorris]

Nice of you to drop in, 93. I looked at the schematics and some code, and I think I have to check that carefully. I don't think a PWM output would work well as an A/D input. It might however be isolated. If you are grounding the relay with PWM, would it affect the input voltage on the relay? or just how long the relay is turned on? The way the relay works (I think) is Ign switch pwr is actually 12V reference from 2 pins on the ECM connector (I don't have the wiring diagram in front of me right now) and pin A2 supplies the gnd. I would be switching the gnd rapidly, not sure if that affects the voltage. I am glad you brought this up though, those are the kind of gotcha's I want to avoid.

[RobertISaar]

the ignition voltage signal is created by a voltage divider (to bring it in range of the 5 volt A/D system, a 33.2 and 8.06 to make a 25.5 volt range), and after that it's fed into the A/D converter.

that's how it's done on a 7727/7730 type PCM anyways.

[93V8S10]

I don't think a PWM output would work well as an A/D input.
No, I was just throwing that out as a possible alternative to the PWM system.

Actually, I think your on the right track with this.

[gregs78cam]

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.

[jim_in_dorris]

1768
Hopefully this can be seen. It is copied out of Mitchells Repair Manual with pinouts from a 8625

[jim_in_dorris]

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.

[93V8S10]

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.

[jim_in_dorris]

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.

[jim_in_dorris]

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.

[93V8S10]

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.

[EagleMark]

Well I've been reading and searching and came up with a bunch of infor I just cut and pasted for furthere review. HTH!


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

[jim_in_dorris]

"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?

[RobertISaar]

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.

[gregs78cam]

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.

[EagleMark]

"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?I think you read that backwards?

[EagleMark]

PWM controller...

[gregs78cam]

I like it, I say go for it, I'm thinkin I may build one for my water pump.

[jim_in_dorris]

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.

[1project2many]

I wonder if MTBF for tbi fuel pumps (http://shop.ebay.com/i.html?_nkw=fuel+pumps) is in on/off cycles, or total run time?
On/off cycles are minimal for most pumps compared to the total number of hours of operation. And start/stop cycles do little to cause wear to the pump. Consistently, pumps fail when the copper contacts on the armature wear through. IME the MTBF is directly related to the amount of fuel pumped vs the amount of run time. IOW running the pump dry or with low fuel level will take it out of service much faster than ensuring fuel is available to cool and lubricate the armature and the brush/armature interface. I have also noticed that almost all manufacturers except GM tend to have large intervals between failures. I have Ford and Dodge vehicles with 300k miles which have never received pumps, while most of the GM's have used as many as four pumps in the same time.

MSD?? or maybe Holley? has a pump control module which steps up voltage to the fuel pump to create higher than stock pressure and volume. I've worked with vehicles using this system although ultimately I always try to remove it and use proper tuning to make the engine run correctly. There are quite a few stories around about these modules causing premature pump failure but I haven't left one in place long enough to know.

Brushed DC motor controllers aren't new, of course. There are quite a few guys using PWM controllers on brushed motors in Power Wheels type vehicles (yes, the kids toy). Soft starts as well as variable speed control are usually the goals here. These motors usually get abused once Dad is done "fixing up" the toy and if they burned out quickly after modifications I'd be willing to bet there would be a lot of discussion on the forums.

You know, there is another option that might cause less worry and effort. The vacuum regulator is a very nice analog pressure control device. Why not PWM the signal to the regulator? This allows you to use the stock fuel system without worry about purging the vapors which will inevetably form, or purging air after a filter change or extended storage, or worry about deadheading the pump. A small vacuum pump and reservoir could ensure a constant supply of vacuum. An EGR control solenoid already designed to PWM a vacuum signal would be a perfect match for the control system, and the existing EGR control code and ecm output could be repurposed for the FPR. And really, the system could even be connected to pressure rather than vacuum, which would allow increases in pressure above base regulator settings vs reductions below max. Just a thought.

[JeepsAndGuns]

You know, there is another option that might cause less worry and effort. The vacuum regulator is a very nice analog pressure control device. Why not PWM the signal to the regulator? This allows you to use the stock fuel system without worry about purging the vapors which will inevetably form, or purging air after a filter change or extended storage, or worry about deadheading the pump. A small vacuum pump and reservoir could ensure a constant supply of vacuum. An EGR control solenoid already designed to PWM a vacuum signal would be a perfect match for the control system, and the existing EGR control code and ecm output could be repurposed for the FPR. And really, the system could even be connected to pressure rather than vacuum, which would allow increases in pressure above base regulator settings vs reductions below max. Just a thought.

I've been reading this thread with a little intrest. I think you might be onto something there. Find a vac refrenced pressure regulator and re use/re purpose a part of the bin thats already there. Use the egr solenoid to controll the vac to the regulator. Very interesting.

[EagleMark]

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.Surely was not trying to confuse you! :thumbsup:

Just trying to gain some insight to a worthy project. If I knew the answer I would tell!

The fuel pump is a DC motor, it will take varied voltage just like an RC car motor will. But switching it on off repeatedly to get the effect is what will kill it. I think that is where the controller comes in. Seems it's part of the cars and diesel trucks I have found with same system. The one above is for home made. There is a link above that to jbperf that has one cheap, they make other things for megasquirt like the JimStim.

[jim_in_dorris]

Mark, did you read the PWM controller pdf you posted? It seems to indicate that PWM controlled DC motors will last longer than voltage controlled DC motors. That circuit was specifically designed to control a fuel pump in a boosted application. The article even claims that most DC motor manufacturers recommend PWM control rather than voltage control.

I'm still trying to get my head around this problem. I also need to keep in mind that I can run 2 80# 454 injectors off a simple vacuum referenced pressure regulator and be done with it. I just worry about big injectors even at low pressures having trouble at the bottom end where I don't need as much fuel.

[gregs78cam]

I'm still trying to get my head around this problem. I also need to keep in mind that I can run 2 80# 454 injectors off a simple vacuum referenced pressure regulator and be done with it. I just worry about big injectors even at low pressures having trouble at the bottom end where I don't need as much fuel.

I do like this thread's whole idea, but......
What engine is this going on again? I have 4 61lb injectors feeding my 383 and @13psi, I can idle it at around 15:1. I could even swap one pair to 45lb injectors and still have plenty at the top end.

[EagleMark]

Mark, did you read the PWM controller pdf you posted? It seems to indicate that PWM controlled DC motors will last longer than voltage controlled DC motors. That circuit was specifically designed to control a fuel pump in a boosted application. The article even claims that most DC motor manufacturers recommend PWM control rather than voltage control.

I'm still trying to get my head around this problem. I also need to keep in mind that I can run 2 80# 454 injectors off a simple vacuum referenced pressure regulator and be done with it. I just worry about big injectors even at low pressures having trouble at the bottom end where I don't need as much fuel.Yes I have and a bunch more, like you I am still trying to get the entire concept in order.

Back to your engine, 400 HP can be done and tuned with BB injectors at around 15PSI without vacuum referenced regulater...

But I don't want to kill a sweet idea! If/when this works a VE table would be a fairly straight line?

[jim_in_dorris]

Mark
Using the formula's from the sticky on getting enough fuel from the "Performance" forum on fullsizechevy, I need 103#/hr to feed 350hp. with an 80# injector (rated I think at 13psi) i need 22psi to feed the beast. If I wasn't in California (home of the Smog Nazi's) I would have an easy time feeding this engine using an mpfi system or 4 bbl TBI.

I still like this approach, and can get a take-out vortech fuel pump (not delivering enough pressure) to use as a test mule to see what happens, then build the PWM circuit and actually test the pump to see how it handles it.

[EagleMark]

Mark
Using the formula's from the sticky on getting enough fuel from the "Performance" forum on fullsizechevy, I need 103#/hr to feed 350hp. with an 80# injector (rated I think at 13psi) i need 22psi to feed the beast. If I wasn't in California (home of the Smog Nazi's) I would have an easy time feeding this engine using an mpfi system or 4 bbl TBI.The injector sizing spreadsheet I have gives 80# 15PSI BSFC .5 90% injector duty cycle 309 HP. But that is at 108 BPW. Stock BPW is 135 I beleive, I ended up at 130. The Injector sizing calulater I have is not set to adjust BPW... it's the numbers I used for 398 HP motor on Dyno so it worked with WideBand showing 12.7 to 1 AFR from 4000 to 6200 RPM.

[jim_in_dorris]

Well, I think I know the "fly in the ointment". If I am thinking clearly, the problem is going to be at the injector end of things. I think the injectors would not work properly. Let me try to explain. At idle, the pump would cycle on once delivering 34 psi to the injector (remember that the regulator caps it at 34 psi) followed by 2 off pulses. Depending on the pulse width of the pump, the injectors could see 34 psi dribbling off to nothing, all the way to opening with no fuel and spiking at 34 psi. PWM of pumps may work for modern systems designed to deal with a dead-head system, but I think that this is the deal breaker. Guess I need to learn more about vacuum referenced regulators. Mark, How did that 398 hp motor idle with the 80# injectors set at 15 psi with a bpw of 130?

[EagleMark]

Fine of course! I tuned it! :rockon:

It takes a little work which is easy with Emulater, things like raising idle RPM, idle timing, making min air adjustments so there's still a little IAC control, while engine gets to temp while watching a vacuum gauge, then rinse and repeat when warmed up. IIRC this one ended at 850 RPM and 14-15 inches of vacuum and under 10 IAC counts. Started with not being able to idle and vacuum of around 10-11 with a screw driver tip in stop screw to raise idle so I could work on tune.

From there it's tune as usual.

[EagleMark]

Well, I think I know the "fly in the ointment". If I am thinking clearly, the problem is going to be at the injector end of things. I think the injectors would not work properly. Let me try to explain. At idle, the pump would cycle on once delivering 34 psi to the injector (remember that the regulator caps it at 34 psi) followed by 2 off pulses. Depending on the pulse width of the pump, the injectors could see 34 psi dribbling off to nothing, all the way to opening with no fuel and spiking at 34 psi. PWM of pumps may work for modern systems designed to deal with a dead-head system, but I think that this is the deal breaker. Guess I need to learn more about vacuum referenced regulators.I think that is the purpose of the module between the PWM regulater and fuel pump, to keep a steady voltage? It's be nice to test one...

[gregs78cam]

Well, I think I know the "fly in the ointment". If I am thinking clearly, the problem is going to be at the injector end of things. I think the injectors would not work properly. Let me try to explain. At idle, the pump would cycle on once delivering 34 psi to the injector (remember that the regulator caps it at 34 psi) followed by 2 off pulses. Depending on the pulse width of the pump, the injectors could see 34 psi dribbling off to nothing, all the way to opening with no fuel and spiking at 34 psi. PWM of pumps may work for modern systems designed to deal with a dead-head system, but I think that this is the deal breaker. Guess I need to learn more about vacuum referenced regulators. Mark, How did that 398 hp motor idle with the 80# injectors set at 15 psi with a bpw of 130?

Actually the on-off action is so fast that the only thing you would notice would be the pump would run slower, there won't be any pulsing of the fuel pressure at the injectors, your fuel lines and hoses will act somewhat like an accumaulator, and buffer any high frequency pulsing in the pressure.

[jim_in_dorris]

It may still be possible to figure out a variable voltage driver to do the trick, just trick the ECM into not seeing the voltage changes. Just have to figure out what pump voltage = what pressure.

[EagleMark]

There's acually 2 kinds of pumps as well. The vane drive the Carter makes does not pulsate like whatever kind the AC/Delco part is...

[RobertISaar]

It may still be possible to figure out a variable voltage driver to do the trick, just trick the ECM into not seeing the voltage changes. Just have to figure out what pump voltage = what pressure.

resulting pressure will be considerably modified by the flow of the injectors.

and as long as the cycle is fast enough (64Hz or higher should be plenty, i would think), then the injectors would never know the difference.