Really strange idea of the day!!!

[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!

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.