1994 gm td OBD1 mpgunio

[94-turbo]

Hi, I'm finally brave enough to try to begin connecting my MPGUNIO to my 1994 GMC Turbo diesel.
This engine has a computer that runs a controller (PMD.... Pump Mounted Driver) That operates a poppet valve solenoid to control the injection pump. It pulses once each time a cylinder needs fuel, it controls the length of the pulse. So with this being said, the mpgunio will see every pulse made for the engines injection not just for one cylinder, but all 8, or roughly 150hz at 2500 rpm.
Can the inj input handle that?

I used a hand held oscilloscope, I looked at the electronic controller module (PMD) and I have a square wave 2.8v that goes from 37% duty cycle at idle (800 rpm) to 50+ duty cycle at 2500 rpm (no load), I realize the mpgunio requires a 12v dropping to ground or "0v" for a duration to sense the injection time.


Do I need to use an inverter circuit to change this pulse to a ground or "0" v for the pulse duration? I see it has a 0or1 for inj pulse up or down, will this enable me to run it if it senses a pulsed 12v+ longer duty cycle upon more fuel usage rather than a 0 volt as used on your gas engines injector system?
Any info may be useful!



Also, what kind of numbers should I see when I start the engine, and numbers when I get the vehicle rolling to be sure things are working?

[94-turbo]

Update

My handheld oscilloscope has a built in adjustable square wave freq and duty oscillator, I mimicked settings I see on this sight and dialed it in for my first test bench mpg readings! I'm not yet clear on how to see distance travelled, or mph, but I will keep striving!
I can see how the duty cycle or pulse duration affects fuel usage!

Now I need to find vss on my speedo, and see what pulses are available. I was hoping someone has done a 1994 gmc Sierra truck and had pointers.
I'll keep updating! Thanks!

[94-turbo]

What do these numbers mean?
Inst tank
IM 024.75 S 060.29
TM049.46. D012.79

Inst current

IM 024.79. S066.29
CM 052.14. D005.90

Custom

MG ..... I don't know what they stand for, some I see as big tank, etc but the D & S, CE TE, MH and so forth, I don't get. I also am looking for the vss for speedo on a 1994 gmc Sierra.
Do I tap in after the buffer? Red white wire? Thanks!

[RobertISaar]

37% at 800RPM? wow, i assume fuel pressure is dependant upon RPM? if so, that would require injector flowrate compensation based on RPM.

the VSS buffer(DRAC): the signal that goes to the cluster SHOULD be a 4000PPM signal, pin C15, should be blue with a back stripe according to my diagrams.

[94-turbo]

Originally Posted by RobertISaar

37% at 800RPM? wow, i assume fuel pressure is dependant upon RPM? if so, that would require injector flowrate compensation based on RPM.

Thanks for the info! However I don't know what the quote means?
I'm not sure of many letters then numbers that increase or decrease in value mean as yet.
I'll need to figure out how distance works according to these numbers.

This was the first time my mpguino was counting by fuel injector pulses. The odometer was by oscillator. I was happy that mpg dropped by reving the engine
So I should be able to tune and fine tune the mpg.

I'm not sure why I couldn't get pulses off the blue black, I'll try again tonight.
Thanks for any and all info!

[RobertISaar]

red w/white looks like it goes to the cruise module? that could work as well, likely at 2,000 pulses per mile.

37% is a LOT of time spent injecting fuel for being at idle/such low of a load. if injector flowrate were to remain what it is at idle, then you could only inject a little less than 3X as much fuel at full output than at idle..... that doesn't seem very likely with what i remember about diesels.

[94-turbo]

1. "Custom":
| MG Instant MPG | S Instant Speed |
| GH Instant GPH | C Current MPG |
2. "Instant/Current":
| IM Instant MPG | S Instant Speed |
| CM Current MPG | D Current Miles |
3. "Instant/Tank":
| IM Instant MPG | S Instant Speed |
| TM Tank MPG | D Tank Miles |
4. "BIG Instant":
| Instant MPG |
5. "BIG Current":
| Current MPG |
6. "BIG Tank:":
| Tank MPG |
7. "Current":
| MH Current MPH | MG Current MPG |
| MI Current Miles | GA Current Gallons |
8. "Tank":
| MH Tank MPH | MG Tank MPG |
| MI Tank Miles | GA Tank Gallons |
9. "EOC mi/Idle gal":
| CE Current EOC Miles | G Current Idle Gallons |
| TE Tank EOC Miles | G Tank Idle Gallons |
10. "CPU Monitor":
| C% Max %CPU utilization | T Tank run time |
| Free Memory (bytes) |
Modifications for metric mode:
Custom screen:
MG->LK (Miles Per Gallon -> Liters per 100KM)
GH->LH (Gallons Per Hour => Litres per Hour)
Combo Screens:
IM->IL (Instant MPG -> Instant L/100KM)
CM->CL (Current MPG -> Current L/100KM)
TM->TL (Tank MPG -> Tank L/100KM)
Big number screens:
MPG->L/K (MPG -> L/100KM)
Trip screens:
MH->KH (Miles Per Hour -> KM per Hour)
MG->LK (Miles Per Gallon -> Liters per 100KM)
MI->KM (Miles -> KiloMeters)
GA-> L (Gallons -> Liters)
EOC/Idle screen:
G-> L (Gallons -> Liters)

There is also a setup screen that displays the first time the program is run and by pressing all three buttons at once. It walks you through the following setup variables. Use left and right buttons to select the digit you wish to change or the OK or Cancel (XX) items. Use middle button to rotate the current digit or select OK or XX if that is where the cursor is. Selecting OK will save the currently displayed value to the current variable and advance to the next variable. Selecting XX will just advance to the next variable.

Contrast - This comes up first on a brand new run and changes on the screen are immediate so if you can't see anything try pressing middle button a few times.

VSS Pulses/Mile - use this to adjust displayed speed/miles. If the speed/miles displayed on the mpguino is low then decrease this number by the percentage that it is off and vice versa for high readings. Most asian cars will be a multiple of 8204 and GM will be 10000, we are hoping users will contribute model specific data here. (Note: Later versions of the code have a setting for VSS Debounce, default is 2 mSec. With high VSS values, this needs to be set to 1 or zero)

MicroSec/Gallon - use this to adjust displayed fuel consumption. You may want to readjust this initially to get a ballpark MPG reading (after VSS Pulses/Mile is deemed accurate), then calibrate it with a couple fillups. If the mpguino displayed MPG is high or the displayed tank gallons is low at fillup then reduce MicroSec/Gallon by the percentage that the gallons are low or the displayed mpg is high. Like the vss pulses, this would benefit from user contributions about what values work for what specific cars.

Pulses/2 revs - not currently used, but a single injector on a 4 cylinder sequential system will make 1 squirt in 2 revolutions. Hope to be able to base RPM on this at some point.

Timout(microSec) - defaults to 7 minutes. If there are no injector or speed signals from the car and no buttons are pressed in that time then the display backlight turns off. When activity resumes the display will turn back on and the current trip will reset and the tank trip will be restored to the point of last activity.

Tank Gal * 1000 - not currently used, but defaults to 13300 or 13.3 gallons.

Injector DelayuS - Represents the mechanical delay of the injector in microseconds. Advanced topic.

[94-turbo]

Well I ball parked my units distance tonight, I plan on going on a 20 hour round trip this weekend, I'll be setting it up with a gps. I should be able to get it close.
I will add my setting to the boards here. So far. I can see a difference in tru fuel economy, compaired to what I would estimate at a given time!
What will changing the inj vss timing do? Will it buffer any signal bounce? How do I tell if it is happening?

[94-turbo]

I travelled through Alberta Canada and have some interesting results.
My first test was keeping the truck @ 90kmh for 250 km and then comparing the results.
My calc results was 19 mpg (using truck odo.)
MPGUINO tank 20.1mpg, without setting anything but mph
Instant was 22.1 mpg level over a few minutes
Current was 22.0 mpg

My next test was @ 100 kmh
Instant jumped up to 25mpg
Current to 22.5 mpg
Tank to 22.5 mpg

Next was to 110kmh
Instant jumped to 26-27 mpg
Current to 24.5 mpg
Tank 24.5 mpg

Unfortunately there were many hills, valleys, trailer pulling, idling so results were not apples to apples....

This calculation jumped to 21.6mpg (truck odo)
I then used gps to record distance, MPGUINO was within 1km in 100km, speed was near spot on, truck odo off 10%!
Now my MPGUINO is within 1.5 mpg! Without setting up injection us from day 1!
The interesting thing is, the faster I drive, the better mileage! Within limits of course!

[94-turbo]

My 1994 gm 6.5 td with OBD1 computer uses an electronicly controlled vacuum operated waste gate to regulate boost.

I've read that opening the waste gate while cruising where the turbo is not needed can improve mpg! The turbo is actually a bottleneck causing back pressure and poor economy.

I built a turbo master that uses a spring to regulate boost pressure, and is manually adjustable. but that system closes the waste gate until exhaust pressure overtakes spring pressure, and creates back pressure during cruising, likely destroying fuel economy.

I reinstalled the original system and I am thinking of building an electronic circuit that can have a 3 way toggle switch for economy, power. And normal . For economy the switch opens the waste gate until needed, possibly with a throttle activated switch to resume ecm control above 1/2 throttle, and for power, an electronic manual control for boost like the turbo master had-non ecm control. I'd be using the vacuum - electronic solenoid but under my control for boost.

Anyone try opening the waste gate to increase economy?