sudden drop in fuel miles question
#11
03-03-2010, 09:28 PM
Not saying this is your problem, but I have a W900L Daycab, Cat C-15, my mileage started dropping off the charts and done everything I knew to do. The computer still showed getting 5.5 mpg but according to everything else it was showing 4.0 to 4.3 mpg. Changed all filters, had air to air checked, did overhead, ran dyno and checked for turbo boost, fuel pressure, drained my tanks thought might be getting water in them real bad, done more stuff to it and spent over 2,000.00 and still nothing.
Well one day it showed up when I took a trip and I knew how far the mileage was and found out the odemeter was stuck. It did not affect the speedomter part but the mileage it did. Took it out and blowed it out with air, (was gonna get a new one, but whew $500.00 for that, I figured I didn't need it that bad) but anyway after I blew it out with air real good it has worked great. Not saying it is your problem, but after all I spent and then found it to be the problem was a real funny thing except for my billfold was alot lighter. I would get the cat people to run the computer on it and see what the mpg is showing and any codes it may have (you can check for codes as well) On mine I turn the cruise off and hold down the resume button and then it will start lighting up, 5 blinks and pause 5 blinks more means nothing is wrong. The computer might be able to show when the fuel mileage started to drop, and unless it has been cleared it will show what the fuel mileage was from way back. 
#12
03-06-2010, 05:57 PM
Thanks Papa Rick i just got it back from cat on mon.The transfer pump was going bad no fuel pressure .They did an overhead even though i had one done about 90,000 miles ago.I was told all the valves were to tight on the motor. Only put about 1000 miles on it since getting it back and i got around 5.5 mpg 1st tank and its running stronger so will see what happens.
- installed an extrude honed manifold for 130 CFM extra air flow (must provide 0.2 MPG gain) - changed from 3.73 to 3.42 axle rears - installed a rolling tarp on my dropdeck trailer. My Wilson is pretty low and now with the tarp I didn't think it should give me worse fuel mileage than a dry van. I got 6 MPG consistently at 59 MPH 1370 with 3.73 ratio pulling a dry van with 45,000 lbs. Now, I pulls a similar looking rolling tarp dropdeck and at 62 MPH 1330 RPM with 3.42 (same load) I did ... 5.5! This was going from Ontario Canada to Missouri. On the way back, I had 4,200 lb load (!) and driving the same 62 MPH I got 5.9 MPG. Something is amiss.... The truck does feel sluggish but I'm governed at 65 so I can't even go past 1380 RPM. Also, I checked it while bobtailing this morning and at 1300 RPM the speed changes very little if I push on the throttle. In other gears and other RPMs it's okay (quick response) but for some reason in top gear (13 speed), the fuel pedal feels like it's not connected to the engine  I should probably go to CAT and have them put a body with a laptop in and ride around. I suspect a fuel pump or something like that. The truck is a 2004, C15 ACERT, with 440,000 miles, 3.42 axles, 295 low pro tires, 13 speed tranny, and as I mentioned it does 65 MPH at 1,385 RPM. Any comments would be welcome.
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#13
04-28-2010, 11:45 PM
My problem with poor fuel mileage was completely solved after I re-installed my full-roof deflector on top of the truck's sleeper. Turns out the Nose Cone was a waste of money
Who knew ...
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#14
06-27-2010, 11:04 PM
Bad Fuel Economy on 2005 Volvo w/ 535 ISX Cummins
I have a 2005 Volvo 780 with the 535 ISX Cummins engine. The truck does pull good but my fuel economy is bad, its between 4.8 to 5.2 mpg. Anybody have any idea that will help me out? Thank you.
#17
07-18-2010, 04:51 PM
Holy cow! Your "normal" MPG is low. My '01 Volvo 660 w/ 465 HP Volvo engine gets between 6.1 MPG (@ 80,000 lbs.) and 9.0 MPG (MT trailer) to 10.3+ MPG bobtailing.
#18
08-23-2012, 11:02 PM
Same thing is happening to my truck.
Thanks Papa Rick i just got it back from cat on mon.The transfer pump was going bad no fuel pressure .They did an overhead even though i had one done about 90,000 miles ago.I was told all the valves were to tight on the motor. Only put about 1000 miles on it since getting it back and i got around 5.5 mpg 1st tank and its running stronger so will see what happens.
I have checked the charge air cooler, I also checked all the clamps on the turbo and the clamps and boots on the hoses leading to the charge air cooler, all seems fine. What say you all?
#19
08-24-2012, 04:45 PM
You have described my problem to a T. I have an 06 Pete 379 with a C15 Cat. Recently my fuel mileage has dropped down to around 2 MPG, my boost gauge has trouble getting much over 25 where in times gone by 40 PSI was no problem. My pyrometer seems to run a little hotter than usual. The truck seems to run fine, I mean, no smoke, no unusual noises or anything, it just doesn't feel right for some reason. I can't put my finger on it, but it seems a little sluggish. I have a fuel pressure gauge, but I think its broken, the needle moves but it just bounces up and down on the zero. My fuel filter restriction is in the green, my air filter restriction is in the green as well.
I have checked the charge air cooler, I also checked all the clamps on the turbo and the clamps and boots on the hoses leading to the charge air cooler, all seems fine. What say you all?
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