Back to stock injectors for a short time

[AH64ID]

What calibration were you on? You have a post that said 15.5%, but I just want to verify.

[Mopar1973Man]

15.5%

[AH64ID]

So if you drove round trip to Lewiston and got 17.2 with the scan gauge on a 15.5% calibration the SGII thinks you burned 13.5 gallons. That's at 115.5% of the fuel it received from the 100% baseline, the 100% baseline would have been 11.7 gallons, and to bring it to 109.2% would have been 12.7 gallons for a net mpg of 18.2 mpgs. Think about how you calibrate the scan gauge, if you were to go from 15.5% to 9.2% it takes the left arrow decreasing the fuel burned for the tank, thus increasing the mpgs, not decreasing them. The ECM was in a higher load category based on less fuel per injection from the smaller injectors. This means, on any truck, that the ECM thinks you are burning more fuel than you actually are and the OBDII/Overhead indications go down. It's also the same with larger injectors. With 400K miles on the RV275's we won't know until you calibrate the SGII if they were worn enough to flow more fuel than the new ones or not; however, lets assume they were still +40 and the new ones are +50. If you run the SGII on the 15.5% setting with the new ones you are actually getting worse mileage than the SGII is telling you because for every gallon of fuel the ECM tells the SGII you are burning the injectors are actually flowing more fuel. Anything else is just a guess. My point is that you got better mileage with the stock sticks than the SGII told you, but the stock sticks still appear to be worse in the mileage department than the RV275's by a few points. Additionally until you calibrate the new injectors with the SGII you don't know if your mileage is going up or down, despite any increase in the SGII readings.I'm not trying to beat a dead horse, I just see this confused by a lot of people on many forums and want to make sure anyone reading it sees what actually occurs inside the ECM as you adjust fueling with injectors. This is something I deal with when tuning other peoples trucks with UDC when they have aftermarket injectors. The HPCR ECM is a lot more complicated but the base computations and operation is the same in terms of how they report fuel usage to the OBDII and overhead.

[Mopar1973Man]

Maybe your right. I was tried when I posted last night. I start thinking about Mom's truck and it extreme high offset I think you might be right too. Ahh... What the hell. We'll find out when I fill up.

[bry1216]

9.2% <- 15.5% -> 22.5% So the 9.2% would of gone down in MPG's. Lower the offset the lower the MPG numbers. Higher the offset the higher the MPG numbers.

I have no idea what this scan gauge or the calculations are about. I will loan you a Garmin GPS and you can fill the tank till you see diesel and calculate with simple division. Maybe I am just old fashion, but there is no second guessing.

[Mopar1973Man]

I have no idea what this scan gauge or the calculations are about. I will loan you a Garmin GPS and you can fill the tank till you see diesel and calculate with simple division. Maybe I am just old fashion, but there is no second guessing.

I've got a Garmin as well but Garmin will not tell you a instant MPG on the fly on after everything is said and done. Which with my life I can't do that because one day I might be towing trailers and the next day climbing around the forestry roads fighting fires who knows. With the ScanGauge II I can use a single day as a test bench and measure out MPG's as a single day instead of a full tank. ScanGauge figures on... Speed (MPH) / Flow (GPH) = MPG So if you can calibrate you speed with the Garmin which I know my odometer is off but the ScanGauge II is dead on. The calibrate your flow or consumption of fuel rate then you can see real time MPG's numbers. So now I'm not stuck having to drive conservatively the entire tank, doing all my towing with the gasser, etc. I can test bench on a single day and set have good numbers to report. But what AH64ID is after is the fact the fuel system has change which I admit it has too. But the changes are so very small I doubt the 10HP change (Rv275's +40 to +50 HP) is going to change offset a huge amount. Even the fuel gauge is pointing that the numbers have to close. Even worse case I would say maybe the number is 1 MPG off.

http-~~-//www.youtube.com/watch?v=SRQdoPs_tLo

Also give me a break the injectors have only been in the truck a little over 48 hours... Geez!

[dripley]

I have no idea what this scan gauge or the calculations are about. I will loan you a Garmin GPS and you can fill the tank till you see diesel and calculate with simple division. Maybe I am just old fashion, but there is no second guessing.

I, like you, have been calculating mine the same as you forever. though not as technical as the scan gauge my mileage has remained fairly consistent over the years and is about all i need. But alas i broke down and bought one to look a other parameters with the engine and it is pretty neat what you can see with it. It also serves a code reader and you can clear them as well. I still have not calibrated it for the fuel mileage function. I guess I will one day just because it does it. Though filling at at the same pump every time is near impossible for me. Nothing wrong with being old fashioned. It still works and serve us well.

[CSM]

So if you drove round trip to Lewiston and got 17.2 with the scan gauge on a 15.5% calibration the SGII thinks you burned 13.5 gallons. That's at 115.5% of the fuel it received from the 100% baseline, the 100% baseline would have been 11.7 gallons, and to bring it to 109.2% would have been 12.7 gallons for a net mpg of 18.2 mpgs. Think about how you calibrate the scan gauge, if you were to go from 15.5% to 9.2% it takes the left arrow decreasing the fuel burned for the tank, thus increasing the mpgs, not decreasing them. The ECM was in a higher load category based on less fuel per injection from the smaller injectors. This means, on any truck, that the ECM thinks you are burning more fuel than you actually are and the OBDII/Overhead indications go down. It's also the same with larger injectors. With 400K miles on the RV275's we won't know until you calibrate the SGII if they were worn enough to flow more fuel than the new ones or not; however, lets assume they were still +40 and the new ones are +50. If you run the SGII on the 15.5% setting with the new ones you are actually getting worse mileage than the SGII is telling you because for every gallon of fuel the ECM tells the SGII you are burning the injectors are actually flowing more fuel. Anything else is just a guess. My point is that you got better mileage with the stock sticks than the SGII told you, but the stock sticks still appear to be worse in the mileage department than the RV275's by a few points. Additionally until you calibrate the new injectors with the SGII you don't know if your mileage is going up or down, despite any increase in the SGII readings. I'm not trying to beat a dead horse, I just see this confused by a lot of people on many forums and want to make sure anyone reading it sees what actually occurs inside the ECM as you adjust fueling with injectors. This is something I deal with when tuning other peoples trucks with UDC when they have aftermarket injectors. The HPCR ECM is a lot more complicated but the base computations and operation is the same in terms of how they report fuel usage to the OBDII and overhead.

So injectors meter fuel? I thought on poppet injectors they provided a pressure drop across the nozzle appropriate for the fuel volume and popped at a consistent pressure? I thought the VP44 is where the actual metering happened. I know your truck, as a common rail, meters with injectors... but help me out here.

[bry1216]

I, like you, have been calculating mine the same as you forever. though not as technical as the scan gauge my mileage has remained fairly consistent over the years and is about all i need. But alas i broke down and bought one to look a other parameters with the engine and it is pretty neat what you can see with it. It also serves a code reader and you can clear them as well. I still have not calibrated it for the fuel mileage function. I guess I will one day just because it does it. Though filling at at the same pump every time is near impossible for me. Nothing wrong with being old fashioned. It still works and serve us well.

Thanks for the video and the explanation. For me, I usually take 3-4 trips a year from Boise, ID to Hamilton, MT and fill up at the same stations. It is 340 miles and usually run 2 mph over speed limit. MPG is 18.5 with a leer shell, extended cab, automatic, LT245/75/16 and 3.55 gears (stock from factory). What would be the "mpg" benefit of changing stock injectors to +40 or +50 (Bosch RV275 if available)?

[dripley]

Thanks for the video and the explanation. For me, I usually take 3-4 trips a year from Boise, ID to Hamilton, MT and fill up at the same stations. It is 340 miles and usually run 2 mph over speed limit. MPG is 18.5 with a leer shell, extended cab, automatic, LT245/75/16 and 3.55 gears (stock from factory). What would be the "mpg" benefit of changing stock injectors to +40 or +50 (Bosch RV275 if available)?

I dont know the technical info nor would I even try give to you. I will leave that to the more knowledgeable. My understanding is more fuel delivered in a in a more efficient spray pattern allowing the fuel to burn better. This gives you more power and lets you use a lighter foot to cruise down the highway. And more fun when when you want to use the power. I saw about 1 mpg better with the RV's. went from the 18's to the 19's as long as I behaved my self. That is with the truck at 7500# and cruising around 70mph. I have seen the 20's on a few tanks.

[Mopar1973Man]

What would be the "mpg" benefit of changing stock injectors to +40 or +50 (Bosch RV275 if available)?

Most have seen a improvement over the stock injectors. But your improvement is based on driving habits.

usually run 2 mph over speed limit.

So more than likely you gains will be near nothing. I'm typically 5-10 under the speed limit (55-60 MPH) so my gains are going to be greater. For every 10 MPH over 55 MPH your wind drag doubles by 65 its 4 times then by 75 MPH its 8 times. Speed is a huge factor to MPG's.

My understanding is more fuel delivered in a in a more efficient spray pattern allowing the fuel to burn better.

Larger holes in the nozzle means that the same amount of fuel can be sprayed in the cylinder faster or in a shorter burst compared to stock. So this gives the illusion of having advanced timing.

[dripley]

i knew the more knowledgeable would do better job than I on that explanation. Thanks Mike.

[diesel4life]

Regardless of whether your driving 10 mph over or 10 mph under the speed limit you will still see a benefit in mpg's, as long as your driving habits remain the same. I just took my first road trip on my new RV275's and pulling a trailer weighing approximately 6k pounds and a 1000 lbs in the bed (figuring conservatively) I still averaged 15.3 Mpg hand calculated as of my last fill up. I have yet to fill the truck up and check my final numbers since I've been home (the truck has also sat since I got home) but I'm confident my numbers will improve slightly because my last fill up was in West Virginia where the speed limit is 70 and I was pulling many steep Grades. Once we crossed into Ohio the terrain is considerably flatter and the speed limit drops. I did this same trip last year and while I have yet to dig out my records I keep of all my road trips I remember being somewhere in the low 14's mpg overall. Again same load same destination and same speeds so the injectors have definitely made an improvement in mileage not to mention some of the steep 7 and 8% grades I previously had to drop out of OD and run in 3rd to prevent egt's from climbing. This year I pulled everyone of them in OD and never saw any higher than 1100 degrees for a very short time. For the most part temps hung right around the 1000 degree mark on the steep grades. They compliment my Smarty very well and I'm very happy with the performance of them, well worth the money IMO.My buddy drove his 2500chevy with a 6.0 And at every fill up I hung right with him in gallons filled. I consistently within a gallon or two every fill up. His truck was empty other than a little cargo in the bed. Needless to say he is not very impressed with his brand new 30k dollar truck!

[bry1216]

i knew the more knowledgeable would do better job than I on that explanation. Thanks Mike.

Hey Dave, If you are into reading about VP44 fuel system and repairs, open this link and print it or save it. http://m.bluechipdiesel.com/site/vp44diagnostichelp.html

[dripley]

Hey Dave, If you are into reading about VP44 fuel system and repairs, open this link and print it or save it. http://m.bluechipdiesel.com/site/vp44diagnostichelp.html

I have had a blue chip pump on my truck for 65k and near 3 years. Spoke with Chip many times before I found this site. He tried to help me with my ECM problem. It crapped out the day before I was going to install the pump(VP). I spoke to him at length about who builds his pumps when Mike was putting the sticky together about pump builders. He does have a wealth of knowledge. The retention of said info is what I have a problem with. Appreciate the link.

[Mopar1973Man]

Refer to: http://forum.mopar1973man.com/threads/7821-Screaming-Beavers I know my ScanGauge isn't exactly right on the money but even with the 2 trips of firewood hauling I did I still pulled a nice 16.5 MPG. What is quite amazing is my pyrometer temperatures are roughly 50-100*F cooler than the RV275's and even my boost pressure is lower. Even with all the weight from the wood it was like 600*F worth of pyro and 5 PSI of boost at 55 MPH. I really do want to hitch up the RV next...

[CTcummins24V]

It's looking like rv275s are becoming obsolete

[Mopar1973Man]

It's looking like rv275s are becoming obsolete

I wouldn't say that. It just my Rv275's were already well used when I got them so its not exactly a fair challenge. But still in all both gave good power and performance. Just the new +50's are more efficient than the wore 275's. The other reason I went up was assuming that a custom injector would net slightly better gain than a factory Bosch injector. I think I'm right on that... Time will tell.

[Texas CTD]

It'd be cool to eventually test with +75 HP injectors, and then bump up to some +90 or +100, just to see how they perform, MPG wise.

[Mopar1973Man]

Personally I think they would be too hot to use at least for me. Just running around loaded with firewood and getting a heavy foot I can tip the 1,200*F in exhaust temperatures. This why I'm looking at the RV as the next test. Load it up!