Engine/Transmission (1998.5 - 2002) MPG Dive

[jRagains]

The truck seems to be running fine, have always kept up on maintenance, etc, but lately it's dropped 3-4 mpg both loaded and unloaded. It's got almost 150K on it. It's got the same setup that is in my signature. Diesel shop has no answers for me. Anyone out there have any idea why the mileage has dropped off so bad?

 

[HSpiering]

Did you change tires??

 

[HBarlow]

Many owners report that winter fuel will reduce fuel mileage.

Winter winds will also cause a reduction in fuel economy.

Sometimes impressions are incorrect. Its difficult to accurately determine true mpg and identify a decline without careful documentation and testing under controlled conditions because subtle changes in wind, direction of travel, and load can have an effect and be unnoticed.

 

[NIsaacs]

I would jack up all 4 wheels and spin the tires by hand. You might have one or more brakes dragging, calipers or parking brake cable sticking.



Nick

 

[jRagains]

Tires are the same size, but different make. This actually started last summer and I used to have great mileage both winter and summer. I'll try jacking it up and checking the tire rotations - that'll be easy enough. I fat-fingered the mileage - it's actually close to 190K.

 

[mwilson]

Are you fueling up at the same station??? If so, try a different brand.



They haven't snuck a Bio-Blend or something into Colorado, have they???



Sometimes it can be that simple, huge difference up here in Diesel quality between Irving Oil and Mobil for example...



Worth a try...



Mike.

 

[Vaughn MacKenzie]

When VP44 injection pumps start getting tired the timing piston has difficulty advancing as much as it should which results in poorer mileage. If that's the case it throws code 216, you might scan for codes. According to Blue Chip Diesel's website weak lift pump pressure can contribute to this too VP44 Diagnostic

I have read a few times of fuel economy gradually deteriorating then ultimately the injection pump gives out, then when it's replaced fuel economy returns.

 

[NIsaacs]

How about tire air pressure? I like 65/70 front and 60 rear for empty driving. This is with stock 265/75RX16 10 ply/load range E. They ride a little rough, but the fuel milage is worth it.



Nick

 

[HBarlow]

When VP44 injection pumps start getting tired the timing piston has difficulty advancing as much as it should which results in poorer mileage. If that's the case it throws code 216, you might scan for codes. According to Blue Chip Diesel's website weak lift pump pressure can contribute to this too VP44 Diagnostic

I have read a few times of fuel economy gradually deteriorating then ultimately the injection pump gives out, then when it's replaced fuel economy returns.

That is good information. It's a good starting point to consider.

 

[jRagains]

Thanks for all the tips. Well... No codes, no wheel drag, PSI @ 65 front, 55 rear, FASS filter was replaced last fall, I use Stanydyne fuel treatment most of the time. I haven't tried fueling up somewhere different yet - will do that in the next week or two.



Don't know if this would be related to the MPG or not but this past fall I took it to the shop because of a long crank time and Edge was reading 0 fuel pressure. It would finally kick over with FP @ 13-14. This would happen if I didn't start it often but then it would do it even over night. (After it starts, the FP stays at about 13-14 and full throttle may go down to 7-8. ) I was still on my original batteries so the shop replaced them. Still had long crank time. They found the rubber fuel line to the FASS was dry rotted and replaced that. Worked fine for a couple of weeks but if it sits for a week or so, it does the same thing. They made a comment that it may be the Edge. I keep it on level 1 and always have (after I played with it right after getting it installed ), but in all appearances, seems to be working just fine.



Would EGTs at 1100ish to 1300ish for 5-10 minutes or so at a time damage something that would cause a drop in fuel efficiency? I pull doubles quite often - a 28' fifth wheel with either an 18' pontoon boat or 19' open bow for 200 miles or so. Mostly flat but with a few long climbs.

 

[HBarlow]

No, 1100* to 1300* won't hurt anything.

I ran my old '01 HO/six speed for 325k miles letting it climb grades at 1300* on the pyro gauge.

 

[ESwartzer]

It might be running rich!

I had a sensor go out on me but can't remember if it was the IAT or MAP that finally gave me a code. My mileage had dropped by several mpg with no codes until mid vacation on the oregon coast when it finally showed. I tried cleaning first but ended up replacing the sensor and mileage went back up to where it belonged.

Hope that helps ES

 

[WaltHess]

Could the fuel filter be losing some of the prime requiring the long startup?

 

[jRagains]

That's a good question. How would I be able to tell?

 

[ESwartzer]

Again, check your IAT and MAP sensors. If they are really crudded up they will kill your fuel mileage. Its best to start with the least expensive fix anyway, and cleaning them only costs some carburetor cleaner and a little time.

 

[Vaughn MacKenzie]

No, 1100* to 1300* won't hurt anything.



I ran my old '01 HO/six speed for 325k miles letting it climb grades at 1300* on the pyro gauge.

1100 is OK, 1300 is flirting with danger for sure. I have read of two cases of piston damage on a 24-valve occuring climbing a grade at 1200-1250F sustained. You are at the mercy of your gauge when you get that high, as in you hope it's accurate From the early days it was always preached to limit the pyro on 12 & 24-valves to 1200F, and even 1200 is iffy. They can't take as much heat as a common rail.

 

[BDW]

Can we assume it not as simple as a dirty air filter?

 

[jRagains]

Don't think so - I just had it replaced at my last oil change.

 

[MARK JAQUITH]

I have a 2001. 5 3500 HO 6spd quad cab lb drw -I have found that as my IAS gets dirty I start to lose mpg--pull the sensor out-clean-test if you use a mulitmeter--it has always helped mine--



Mark

2001. 5 HO QC 3500 LB 6SP 4x4 DRW orig VP-44 275 inj 233550 miles

 

[jRagains]

Thanks for that info - I'll be taking it in next week and get that checked out. Sure would be nice to get my MPG back!