Fuel Guzzler

[Rodd]

I have been having problems with my fuel economy for a while now. My ffm manager had a leak and was fixed 400 miles ago and it is still dry. I am starting to run out of things to check. Even though it isn't leaking fuel it is still getting 10-11 mpg after 339 miles of driving.

The poor fuel economy started a couple years ago after I replaced the IP with a rebuilt one. I went from 14 mpg to 10 mpg. Here is what I have done:

-Added racor 10 micron pre filter
-Feed the beast
-New o rings in the ffm
-Synthetic Rotella
-rebuilt injectors about 20k miles ago
-turbo master (I have been increasing boost to see if it helps but it doesn't)
-Treadwrights 265/75r16's (same size as last set)
-my f intake does have slight oil coming from around one corner where it is probably leaking but I don't think that would affect the economy. My turbo gauge appears normal.

What am I missing? I have done other things but I don't think they will affect the fuel economy.

 

[buddy]

Did you replace the IP yourself? Did you happen to use a scanner to reset and verify the timing? I would also check the warm idle fuel rate, to see if the IP was calibrated when rebuilt. It should be about 8mm3 fuel rate at idle.

You are probably getting slightly better than what your recording if using the odometer as the basis. They commonly are off, and those tires a little larger than stock so it wont be totally accurate from that. Maybe you have verified the odometer with GPS or mile markers on the highway as a gauge of the odometer?

However it is still low, you are having some issues. The oil is not a concern, unless it was a lot to suggest you have low compression which could cause poor mileage. Is there much blowby?

Typically increasing boost will reduce economy after some point. I would set the TM to 2-3psi when you are cruising at whatever speed you normally run at.

An aftermarket PCM reprogram like Heath's increases timing quite a bit and can net you some more MPG. Or you could request that from Kojo progamming as well.

 

[Rodd]

Did you replace the IP yourself? Did you happen to use a scanner to reset and verify the timing? I would also check the warm idle fuel rate, to see if the IP was calibrated when rebuilt. It should be about 8mm3 fuel rate at idle.

You are probably getting slightly better than what your recording if using the odometer as the basis. They commonly are off, and those tires a little larger than stock so it wont be totally accurate from that. Maybe you have verified the odometer with GPS or mile markers on the highway as a gauge of the odometer?

However it is still low, you are having some issues. The oil is not a concern, unless it was a lot to suggest you have low compression which could cause poor mileage. Is there much blowby?

Typically increasing boost will reduce economy after some point. I would set the TM to 2-3psi when you are cruising at whatever speed you normally run at.

An aftermarket PCM reprogram like Heath's increases timing quite a bit and can net you some more MPG. Or you could request that from Kojo progamming as well.

I set the timing myself. It was at -1.06 when I first did it and then again about 6 months later when I checked it again but that was a few years ago. I will check the warm idle fuel rate like you suggested. I have been planning on getting a PCM tune but I don't want to do that until I get the economy figured out.

I haven't figured the odometer w/ a mile marker but the speed o is spot on w/ my gps.

 

[Rodd]

Before the IP swap I had the timing set at -1.94

 

[buddy]

What temperature does the truck normally run at? If its not 190-200F you might want to pull the T-stats and check them in water or put new 195 T-stats in.

You might want to take the belt off and see if the alternator spins freely, and vacuum pump minimal resistance if its still there.

 

[ak diesel driver]

my odometer and my speedometer don't reconcile with each other.245s read too fast on both 265s make my speedo right but not my odo

 

[Paveltolz]

With my tires I'm spot on with speed and GPS. Miles driven, Odometer reads 6% low.

 

[Rodd]

I just took the truck out for a test drive for about 20 minutes w/ my autoenginuity connected and here is what I saw:

The water temp start was at 127 (it was sitting for about 20 min. before I started) peaked at 184 and when I got done it was at 176 idling for a couple minutes before I shut her down.

The warm idle was 10 mm3 when I started and 10 mm3 when I finished.

I am wondering if my stats are bad as Buddy suggested because every few months I get a code saying coolant temp is too low for normal vehicle operation.

What are your thoughts?

 

[schiker]

Probably bad stat(s). I had the SES light come on with code for insuffcient ECT for normal operation due to stuck open stat.

It is suppose to reach 160F within a certain amount of time after starting. Then it must reach 170F for timing to adjust to normal from cold advance.

Depends on local temps PMD or FSD location and overall build strategy as to what stat temp to run. 180F should be minium stat and can go up to 205F stat with most running either 180F or 195F. 180F is a bit cool but ok for warmer climates. 195F should yield better performance and efficiency. Then again 180F will give you just a tad more time at a heavy load before ECT rises to engage fan and take away 10-15 hp off the crank when it could have helped you crest a hill. That is a bit of arguement as to which is best for you and where you tow. I see you are from CA so I doubt 180F would help with western hills but around here with rolling small hills it could buy just enough to crest a hill.

But reguardless of stat temp I'd change the stats even with 180F stats and sporadic mid 20'S F start up I never get a SES light/code (with good stat(s)).

 

[Rodd]

Buddy,

Is there a way to change the warm idle mm3?

 

[buddy]

Buddy,

Is there a way to change the warm idle mm3?

Yes, it is just like an optic bump, or unbump for Optical Sensor. Sometimes a rebuilder might replace the OS or other components and not calibrate its actual output to commanded fuel rate.

Did you check it out on the scanner? And rerun TDCO learn to see if its still accurate?

 

[Rodd]

Yes, it is just like an optic bump, or unbump for Optical Sensor. Sometimes a rebuilder might replace the OS or other components and not calibrate its actual output to commanded fuel rate.

Did you check it out on the scanner? And rerun TDCO learn to see if its still accurate?

The tdco is -1.06 and the warm idle is 10 mm3. I was talking to Wyatt and his is 6 mm3

 

[buddy]

10mm3 is alright. Its not actually more necessarily, just saying more.

Did you try to rerun the TDCO learn, because it wont change unless you initiate the scan, even if it has slipped or gotten messed up somehow.

 

[Rodd]

I'll run TDCO again when my wife gets home from school and see what it says.

 

[WarWagon]

Check the fan clutch for locked up bearings. Start it up, hit 2000 RPM for 2 min. Shut it off. The fan clutch should be freewheeling assuming the engine was cold
Alignment?
Brakes binding/stuck? Including calipers or parking brake cables frozen.
Plugged K&N? (I hate those filters!)

Fuel leaks... Sample the engine oil and look for fuel.
Look under the IP for leaks.
Check return lines and injectors for leaks.
The exhaust manifold will evaporate diesel return line leaks on the turbo side...

 

[Rodd]

10mm3 is alright. Its not actually more necessarily, just saying more.

Did you try to rerun the TDCO learn, because it wont change unless you initiate the scan, even if it has slipped or gotten messed up somehow.

I did a TDCO relearn and it increased from -1.06 to -.97. I think if I rev up the rpms while doing the tdco it will increase it a bit.

 

[buddy]

Well thats really close, the IP hasnt moved at all and that value is fine.

 

[Rodd]

Just checked my first tank since adding 195 stats and I increased my fuel economy a whopping 1 mpg. I am stumped.

 

[buddy]

Warwagon had a valid point about the fan clutch. You might try running around with no fan and clutch for a while and see if it will get too warm. If you run all highway it wont need a fan, whereas in traffic and around town might need the fan. Getting the clutch on and off is not really hard if you just leave the upper shroud off I suppose.

The quality of some injectors isnt that great, like a lot of parts you can buy today. Poor atomization could account for a couple MPG.

Do you notice the torque converter lockup? What speed and RPM are you normally driving?

 

[Rodd]

Warwagon had a valid point about the fan clutch. You might try running around with no fan and clutch for a while and see if it will get too warm. If you run all highway it wont need a fan, whereas in traffic and around town might need the fan. Getting the clutch on and off is not really hard if you just leave the upper shroud off I suppose.

The quality of some injectors isnt that great, like a lot of parts you can buy today. Poor atomization could account for a couple MPG.

Do you notice the torque converter lockup? What speed and RPM are you normally driving?

Is the fan and the clutch one piece? When I replaced my water pump the fan screwed right off. Is that all I need to do? I'm not sure when the torque converter locks up. How do I tell? When I drive I try and keep the rpm's as low as possible except when I'm getting on the freeway or in a hurry. My wife drives it most of the time. I know when I was getting 14mpg's I wasn't ***** footing it.