Alright I am working through the process of creating a true instant MPG meter.   

 

 

In theory, I love that word, we should be able to know how much fuel is being burned.   We know commanded duration, we know speed, we know rpms.  

 

Below is the rough draft #1 for my testing, I am not concerned about it being %100 accurate. 

Quote

 

building the equation

 

A 4 stroke 6 cylinder engine should have 3 power strokes per rev, so power strokes, or injections, per minute will be RPM * 3. 

 

Mph to MPM would be MPH / 60 = miles per minute

 

we need to get stroke converted into gallons. 3785410 mm3 = 1 gallon

 

The last thing we need is a MM3 of fuel per stroke in the vp44.  

 

After a good bit of reading I have come to the vp44, in stock form, producing 125mm3 of fuel per stroke max.  

 

Now we throw some fuzzy math at it and say that duration % is linear to stroke. 

 

 

If we plug that equation into excel and input duration, rpm, and mph into it we get output mpg's that match, considering fuzzy math, a vp44 truck.  

 

IE: stock, 55 mph, %20-%25 duration 1460 rpm = ~22-24 mpg in a perfect world.   

 

 

So my Question is when it comes to injectors in the VP44 system.  If the vp44 can produce 125mm3 of fuel per stroke in stock form, what happens when you increase injector size?  Does having larger injectors mean the vp44 will produce more fuel, IE 200 mm3 of fuel?    Or is the 125mm3 the vp44 is spec'd to produce a constant unrelated to the injectors?  

 

@jlbayes @mopar1973man @carbur8tr and anyone else that has an input.

Yeah that makes sense. This is unrelated, but what would happen if you commanded a fix value for canbus fuel? Would the truck idle like crap?

Yea,  idle fueling needs to be dynamic.   it would idle good in a perfect situtation, but that never exists

 

 

5 minutes ago, Me78569 said:

oh I get you.  No the idle state fuel is not stable enough long term to base a calculation on.  I see a 200 or so bounce in canbus fuel at idle.

 

I see a flow rate from 0.2 to 1.0 GPH fuel flow or 5% to 18% engine load depending on what is running on the truck and the coolant temperature. So idle fuel usage is very dynamic...

2 minutes ago, Mopar1973Man said:

 

I see a flow rate from 0.2 to 1.0 GPH fuel flow or 5% to 18% engine load depending on what is running on the truck and the coolant temperature. So idle fuel usage is very dynamic...

 

Balls. So there isn't really a way to compare without a doubt how much fuel one truck uses compared to another with different injector nozzles.

Nope,   I will publish at general % offset per injector size once I get it figured out.  Still working on the Gallon used trip meter,  that's gonna take time to figure out if I have it close enough.

I sat in the truck and started playing with different things to load the engine. Turn on the A/C on high fan can put nearly a 20 HP load on the truck increasing idle fuel flow at least 0.5 GPH. Stack on the 200w worth of lights and my HID's I can tip 1.0 GPH fuel flow at idle. Then engine temperature will vary the fuel commanded to keep the idle at 800 RPM's. 

 

Then if you want to toss high idle 3 CYL and exhaust brake you can push upwards of 9.0 GPH idling at 1,200 RPM's. 

 

Too many things to vary idle fuel flow...

1 minute ago, Me78569 said:

Nope,   I will publish at general % offset per injector size once I get it figured out.  Still working on the Gallon used trip meter,  that's gonna take time to figure out if I have it close enough.

 

Yeah just a manual adjustment would be fine with some guess and check.

 

That's the trouble with an open loop fueling system.

1 minute ago, Mopar1973Man said:

I sat in the truck and started playing with different things to load the engine. Turn on the A/C on high fan can put nearly a 20 HP load on the truck increasing idle fuel flow at least 0.5 GPH. Stack on the 200w worth of lights and my HID's I can tip 1.0 GPH fuel flow at idle. Then engine temperature will vary the fuel commanded to keep the idle at 800 RPM's. 

 

Then if you want to toss high idle 3 CYL and exhaust brake you can push upwards of 9.0 GPH idling at 1,200 RPM's. 

 

Too many things to vary idle fuel flow...

 

Ok, now find me a way to load the truck up to 25% on jack stands so I can do some tuning, lol.

I know the ScanGauge II and Dash Command both use a fillup routine to calculate offset amounts. 

That's prob what will happen.  You will set your offset to %100, then burn a tank of fuel and compare how much fuel you used on the screen vs at the pump and calculate from there.

This is cool, I like this.

On 9/16/2017 at 10:20 AM, Me78569 said:

That's prob what will happen.  You will set your offset to %100, then burn a tank of fuel and compare how much fuel you used on the screen vs at the pump and calculate from there.

 

Missing a step... On ScanGauge & Dash Command when you do the fillup process it will display what fuel you burn and then you change the offset to match the gallons pumped. It automagically does the math for you so no calculations required. Now just hit done and everything is calibrated. 

that's not something that would be programmed into the box under the hood.  I could go through the work to do that, but it owuld require 3 more data items to push across the bluetooth.   Each of those would need to be coded in and then set to be used somehow.    

 

The easier solution would be to put it in the app itself, but for the beta testing of this manual calcs are required.  UI interfacing code needs to be left up to the app and not the box under the hood.

I like it. I'm skeptical, but I like it.

I wonder how bad different timing will throw it off?

Say you calibrate everything for cruising empty, then hook a big trailer up. Could the timing difference make that big of a change in MPG vs what it's calibrated at?

The MPG info is directly related to the canbus fueling amount.  Doesn't matter what timing is doing canbus fuel will always be 1:1.  Timing will adjust how much canbus fuel is used, but won't change the relationship to mpg

Just now, Me78569 said:

The MPG info is directly related to the canbus fueling amount.  Doesn't matter what timing is doing canbus fuel will always be 1:1.  Timing will adjust how much canbus fuel is used, but won't change the relationship to mpg

So you're saying the efficiency will be seen in the amount of fuel injected regardless of timing - Hmm. If you get this setup well it could really help with tuning timing for MPG purposes.

the relationship of fuel burned is static compared canbus regardless to the timing command   As you get better mpg, related to timing changes, the canbus message will drop,  but is still related to the canbus 1:1

 

 

I have the instant mpg working well, now I am workign on a gallons burned calc.  

I think the only uncontrollable source of error would be related to pump health and injector health. A wearing injector could change the amount of fuel actually being injected. Same with a weak pump. However, these things don't change overnight, and that's why you'll have the offset % adjustment. Any truck should be able to be offset to be close.

One thing I am curious about is if the relationship between fuel into the engine vs the fuel return out of the back of the head.  

 

Is that a 1:1 relationship between the duration command and how much actually gets injected?  in theory it should be because the injectors are not smart enough to control flow.  I would guess that the bigger the injector the less fuel is pushed out hte back of the head at a given duration.

 

I am guessing, wildly, that this is where that 125mm^3 of fuel comes from.  The injectors are passing that amount but the remaining ~350 mm^3 of fuel the vp can supply is pushed out the back of the head.

Time to get a flow meter and measure the return. And find someone with a bench you can measure nozzle flow on. Orrrrr talk to a certain builder as he has flowed a few nozzles.

What is return out of the head is the pressure bleed off after the injection occurred. So if your injectors are set to 310 bar as that cylinder injector bleeds pressure past the pintle its sent down the return rail. It should be a very small amount of fuel. There is way more fuel returned from the VP44 than the back of the head. 

 

The few times I've been to a fuel injection shop to bench test injectors there has always been very very little fuel weep from the return port. As for exactly how much in ratio vs injected to the cylinder I don't know.