<TABLE cellSpacing=2 cellPadding=3 border=0><TBODY><TR><TD vAlign=top align=left>BARO </TD><TD vAlign=top align=left>Barometric Pressure Sensor
Strategy input; PCM uses this to adjust fuel quantity and injection timing for optimum running and minimum smoke, also glow plug on time to aid starting at higher altitudes; 5 volts in, @ 4.6 volts/14.7 psi at sea level, decreasing as altitude increases. </TD></TR></TBODY></TABLE>

So in theory if you could get the sensor to read 4.6 volts all the time would it deliver maximum fuel??? because at higher altitudes there would be less air, which shouldnt be a factor for a turboed engine, it should deliver less fuel, to prevent excessive smoke, or is it the other way around, at a lower voltage it will deliver more fuel, any one tried it??? what where the results.

Might have something to try when I get home from CO.


Diesel Rod

 

DR, I will be watching your post here dude, not sure what the voltage does on this but I can find out if someone doesn't already know. I have drove my 95 MY truck to Colorado several times and each time I always seen 4-5 MPG better fuel mileage up there and know it was from the ECM leaning out the motor to keep the PSD running good.

I think long as we watch the EGT's while leaning the motor out we could use a manual adjustment for the voltage to this sensor for when we wanted better mileage or even when we wanted all the fuel we could get at other times LOL...Good post started here and hope it gets the info we all can use...

 

i agree, good post... i would love to have a dial that could adjust for power or fuel ecomony...!

 

As a flight instructor, I taught students to lean out the mixture as altitude increased. We're talking bout the small single-engine pistons here. If the density altitude was above 3500' at ground level we would lean it before takeoff and adjust as we climbed. The factor was EGT, optimum lean was at 25 degrees F below peak temp. If it was too lean it would run too hot and fry the engine or shock cool it in the decent and crack the block. Believe me, this DOES happen! If you have an EGT hooked up you could stop the flow of current or reduce it and see what the EGT reads. Don't know that I would want to mess with it on the PSD, too much money to replace a 7.3 they don't make anymore.

 

steve_250's post reminded me of what we used to do with the old snowmobiles. in the days before oil injection was standard on the 2-stroke machines, we used to experiment with fuel-to-oil mix ratios.. if you were gonna be on trails all day, going slow... you could lean it out. problem was, if you got out on a lake and opened it up, you cooked your motor, so what we did was put a thumbscrew on the main jet... (this was back when you could richen or lean out your fuel mix while you rode), and we could lean it out for the trails or richen it for lake speeds... this helped keep the machine from fouling spark plugs, but it also increased fuel mileage for trail riding... man that was a long time ago... i must be gettin' old...!

i also have to say... i would want to be really careful about egt's if i did this.. saving a little fuel doesn't offsett the cost of a rebuild...

 

mine was better in louisiana than it is here in Colorado? not sure why?!?!?!

 

I'm not sure about this but I think I'm right. Someone let me know if I'm wrong.

Very few sensors generate a voltage. The o2 and thermocouples come to mind. Many sensors recieve a voltage from the PCM, and the voltage is changed by the sensor because the sensor has a variable resistance. The voltage returned to the PCM is an effect of the resistance of the sensor. You could use a variable resistance (potentiometer) to get the voltage that you desire to conduct your experiment.
Based on your info regarding the values at sea level you could even overfuel if you went over 4.6 volts.
I must be honest when I say that I'm glad this experiment is happening on someone else's truck though.

 

well it's a great concept.... but i'm thinking that it maxes out at 4.6 volts... it says it's getting that at sea level, which would be at it's highest setting is at 4.6 volts... Just a thought...

-Robb

 

The problem for you 99.5+ folks is that is when the Baro. sensor became internal to the PCM.

Should be some fun experimenting for you 99 and earlier bunch. You might be able to just unplug the thing, a baro sensor fault will result in an out of range signal to the PCM, and it (the PCM) will assume a default value of 14.5 PSI.

 

Hey cookie... any idea on where i would find the baro on my 97? thanks... (also congrats on 3,000 - 1 posts!!!)

 

bodabdan- thats exactly what I was thinking, a speed pot to change the voltage to the PCM on the fly, see what it does, leans it out, or richens it up, have to whatch the pyro for sure.

Cookie, we are all waiting, do it, do it, do it.


Robbgt, its up under the dash somehwere, I thought it was on the inside of the cab, near the brake rod in the firewall. I had a pic, will have to dig it out. I am heading to Colorado tomorrow at 8am so I wont be able to play with it untill I get back prolly tuesday so.... If anyone else tries it before me, please post the results. I will prolly have access to a computer while out there, so I can check in.


Diesel Rod

 

Yeah, it's way up under your dash. There should be a wiring harness running straight up above your brake pedal....follow it up to the sensor.

 

HAHA!! no way dude! I'm not even thnking abut disassembling the PCM....unless somebody is going to donate a spare

 

thanks Cookie. and glad to have been a part of the big 3K


Diesel Rod

 

Thanks. Only took four years.