Terrible Gas Mileage

Im really glad you started this thread! I just went thru my first full tank in my truck. (Bought it a few weeks ago). I got 173 miles to a TANK of shell premium!! Damn! At this rate it would have been cheaper to keep my duramax! Im gonna follow all the steps listed here to see what i can work out. Good luck with your search!

Lastlaugh, Have started any of the suggestions to help improve your MPG? Mine is getting close to twice as much as I was getting before. Keep us updated!
 
Sorry for delayed reply...
Ok. So your pic is pretty small but it looks like some vacuum lines are wrong. The one line you've got connecting the EGR Vacuum Modulator to the EGR Valve is incorrect.

Look at mine:
y7yvymym.jpg
bagusude.jpg


And here's the schematic from the hood:
ze8emunu.jpg
 
Sorry for delayed reply...
Ok. So your pic is pretty small but it looks like some vacuum lines are wrong. The one line you've got connecting the EGR Vacuum Modulator to the EGR Valve is incorrect.

Look at mine:
y7yvymym.jpg
bagusude.jpg


And here's the schematic from the hood:
ze8emunu.jpg

Nice catch Scalded Dawg, Its early/late here but will definitely check those out. From what I can tell the pics of yours lead to the ones that were open and I plugged them with hose and screw. Man brother you have been a tremendously helpful. Thank you.

I am saving up for a saweet paint job this summer, and some major under carriage restoration. not shocks...I replaced those when I put the original Yoko Tires on.

Hopefully after setting the vacuum lines correctly it will start quickly after some adjustments around the throttle body and resetting idle speed and timing. My mileage has improved a lot all ready and I think it will het better.
Thanks Again, Rob:lock1:
 
Thanks to everybody's input on this. I really appreciate all the help all have given me. I definitely have improved my gas mileage.

Having said that I am experiencing a hard to start engine. Before making all the changes this engine would start up within 5-10 seconds. Now it takes 45 or more seconds to start and I have to press on the gas pedal.

I need to order a replacement Dashpot on the throttle body along with the adjusting screw and the nut that screws on and locks it down.
The Dealer wants over seventy five bucks for this. If anybody knows where I can get these hard to find parts I would appreciate the information.

Again thanks to all. This forum ROCK'S:rockon:
 
I don't know if they have them, but rockauto.com is always a great place to look. They seem to be an aggregate of a lot of places, so often you find great prices because someone somewhere is clearing out something.

And it's searchable, so if you have an accurate name, even if you don't know what category it would be in, you can probably find it.
 
Scalded_Dawg Can you tell me if the upper vacuum lines on your very 1st picture, are they following the schematic. I see 4 vacuum lines above the 3.0 emblem not including the one on the far left pointing straight back. Do they follow the schematic? Can you tell me which vacuum line hooks to that diaphragm? Thanks Bro.
 
apa7ymun.jpg
mubyze4e.jpg


Here's what I got.... The line going to the diaphragm is the lower elbow back side of throttle housing.
The diagram is hard to read right there, almost looks like those two lines are one from the upper back elbow with a "T".

y8epyjyq.jpg


Mine appears to be all stock hoses but no telling if that is actually correct. There's been a lot of mechanics in there over the last 19 years.
 
huh that is odd, The one that points straight back show to have a plug on it. I am going to have to study a little more....Scalded_Dawg what kind of GPM do you get?
 
huh that is odd, The one that points straight back show to have a plug on it. I am going to have to study a little more....Scalded_Dawg what kind of GPM do you get?

Yeah that port is not even on the diagram either...

Crappy MPGs...
I bought it back in Sept last year... Had a bad #6 cylinder, needed full rebuild to include new block and crank. I've put about 700 miles on the new engine, pretty much all city driving, short stretches of highway; engine runs really good. Best I've gotten so far is 12MPG. (Hence why I started watching your thread. lol!)

HOWEVER...
I may have found a big source of my problems last night while prepping for my lift... Front passenger side brake drags horribly; can't even spin the tire half a revolution. Driver's side only slightly better....

Looks like I'm doing a full brake rebuild now.... I could probably just repair it but I don't want to be back in there again, so I'll do it all at once. Probably do the wheel bearings too... Good times!
 

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