MPG drop - can't figure out why UPDATE UPDATE UPDATE

[DennisG01]

Over the last 6-8 months, my mileage has dropped from 15 city to 13 city and 13 towing to 11 towing. I don't get enough straight highway mileage without towing to tell - although about a year ago I got 21 on the highway. Maybe this also is a reason for some higher than expected EGT's. Since it started happening right around the time when the weather got colder, I originally thought it was due to extended warm-up periods/idling - but not the case as it is still the same.
Anyways, I change air and fuel filters on a regular basis (they have never been very dirty when I have changed them). I change the oil filter every 3K. I fill up the same way every time. I have tranny flushes done once a year - about 7K miles ago.
The truck runs smooth, but I do feel it is lacking power - especially with the upgrades I have done and comment others have made about how happy they are with theirs. That's another thing, with the upgrades, you would think my mileage would increase? Now, I'll admit that the first tank after the exhaust that I was heavier on the throttle than normal - but who wouldn't be? But, after the initial excitement wore off, I settled back to conservative pedal power.

Any ideas? Could it be glow plugs? I am not the original owner, but there are about 80K miles on the engine.

[ 09-22-2004, 04:11 AM: Message edited by: Dennis Galligani ]

[markrinker]

Partially plugged catalytic converter?

[tloomis]

Any smoke and what color? How many miles on the injectors? Any fuel leaks? Have you checked compression?

[Marty Lau]

Here are some thoughts, the soot trap as mentioned earlier, air filter, fuel filter. More Power suggests changing injectors every 75,000 to 100,000 miles and they do make a difference. Timing maybe your timing chain is streached. You also may try changing were you get fuel, if the place you normally fuel has gone to poor quality fuel that will make a difference.
Just a few thoughts hope it helps.

[DennisG01]

All are sound ideas, thanks - however, the dilema continues...

There is no cat to be blocked.

I have tried a few different places to fuel up, even truck stops on the turnpike. I only go to places that looks like they have a high turnover rate.

VERY little smoke - only when I don't 'roll onto the gas pedal' - grey in color and dissapears quickly.

Injectors - don't know how many miles on them - have to assume they are original.

I guess there is no way to know if timing chain is stretched unless someone actually looks at it???

By the way, I run tire pressure at 60 front, 65 rear and I check that regularly, too.

Last year's trip to Maine (when I got over 13mpg) I also had two extra people with gear and 4 mountain bikes on the roof rack - Lots of wind resistance!

on edit: before some wise guy calls me on this: only the bikes were on the roof rack - I allowed the people to stay inside. [img]tongue.gif[/img]

[tloomis]

How many miles on Engine if > 70,000 I would suspect the Injectors are due for change. As for the Glow Plugs they should only cycle at startup and you would probly notice abnormal amont of white smoke at startup. Depending on your driving habits the timing chain would also be a good check.

[catmandoo]

my sub i got about a month and a half ago has been losing mpg very slowly too,and i changed the t-chain and had the timing set and lately i have really noticed a smell of raw diesel,and the tech at the shop that set the timing also suggested inj's,which i just put in and still have about an hours worth of work to finish,but i pop tested the old ones and some of em are down around 1650,the new ones were around 2150.so they should make a big difference.

[moondoggie]

Good Day!

Since mpg is my only hobby

[DennisG01]

I have about 75K on engine - injector's are probably a good idea. I tow around 65mph - try to do the same every time I tow. I tow a 22 foot boat - also the same thing I towed last year and all the time.

[richard7]

Did you change anything on the truck when the mileage dropped, like tires (tire size or aggressive tread), or an accessory?

Was the differential oil changed, or still original? Old gear oil will get surprisignly thicker with age and drag more horsepower, especially on a 4WD.

Do you say "I love you" everyday? [img]smile.gif[/img]

[catmandoo]

speaking of gear oil,i just changed brakes all around on the sub and one axle seal was seeping a little so pulled the rear cover and man was that nasty looking ,smelling stuff.otherwise everything in there looked nice,now this weekend the front axle gets the new grease.

[kowsoc]

Is your boost pressure normal? If you loss pressure you will lose power and fuel efficiency. Wastegate solenoid and/or vacuum pump circuit may need checking.

[rjwest]

Tire size will change Odometer,

Also Northern Fuel in summer is at least 1 mpg plus
for my 1 ton, Better fuel than Virgina and south.
Ga. seems to be worst for milage,

Also I get worse mpg with Big truck stop fuel....

[fitzmeister]

I have a 99 K10 with 3.42 gears(apx 80K miles) with a similar problem (down on power,poor fuel mileage) What is the procedure for checking boost pressure?

[moondoggie]

Good Day!

fitzmeister asked,

[n3qik]

It's been said before about boost pressure low. I have been there just 2 months ago. Notice slight loss in MPG, just blow in off as my driving. Til one day I noticed no/little boost til engine warmed up. A week later had no boost. Did the normanl checks, all fine. End up cleaning Air Intake Sensor to solve my problem. This gave me my boost back an a extra mile to the gallon.

[ 09-20-2004, 03:21 PM: Message edited by: n3qik ]

[DennisG01]

Here's an update that confuses me even more:

Driving habits have stayed the same, but now the truck is back to getting right around 15 mpg city. The ONLY thing that has changed is that I have STOPPED using the Diesel Kleen (grey bottle) additive. Go figure!