Mileage after sitting for a while

PatM

Original poster
Member
Jan 27, 2012
25
I just bought a 4.2L LTZ a week ago and it had been sitting for an unknown amount of time. Initially I was getting 18.4 L/100KM but each day it drops a bit and now, after a week, its at about 16.2 L/100 KM and appears to still be slowly dropping.

The vehicle did have work done on it which I assume meant disconnecting the battery and losing the control module memory. Could the initial high consumption and slow improvement simply be a case of the control's re-learning?

I immediately installed a new air filter. The old one was only slightly gray but the pleats were all wavy which means they'd been wet (probably condensation) and the paper was probably mudded and plugged. I have a set of iridiam plugs ready (the 0.50 gap for the 2003, not the 0.43 for the later models) but I've been waiting to see if the consumption will drop to around 13L/KM I think I should be getting (15KM city, 10KM highway - twice a day!) and a light foot.

Should I just pull the trigger on new plugs (127K kilometers on the odometer) or wait for the consumption to drop more? Anything else in the realm of simple fixes for a vehicle that's been sitting for up to six months?

I have thought of the gas being skunky but there was only 1/8th tank when I got it and I filled it immedietly so it shouldn't affect consumption very much.

Just lovin' this truck!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Use Delco 41-103 iridiums that come pre-gapped. All years use the pre-gapped plugs now which are 42 or 43 thousandths IIRC.
 

mwking

Member
Dec 7, 2011
9
Your fuel consumption seems on the high side, but not necessarily out of line. If you manage to get 13L/100km consistantly in mixed driving you will be doing really good from my experience. You can probably expect the average to improve another 1.5-2L/100km if you pay attention to the display and drive accordingly. There is a big difference between the mileage you will get out on the highway at a steady reasonable speed and what you will get in town. Add in increased consumption during warm up, even if you start up and drive away nice and easy right away. These trucks are big and heavy and it takes a lot of fuel to get them moving. A little around town driving and some short trips can bring the average down really fast. For anyone wondering 18.4L/100Km is about 13 miles to the U.S. gallon and 16.2L/100Km is about 14.5, and 13L/100Km is about 18.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
:tiphat: Welcome:tiphat:

In case you haven't
heard:
http://gmtnation.com/f5/welcome-gmtnation-com-heres-story-226/



If it sat for 6 months with only an 1/8 of a tank, you may have some sludge pumped into the injectors and fouled plugs.

Also, what year is your truck? (Please fill out your TB info.)

As Roadie stated, the plugs come pre-gapped. If you change the gap, be very careful. The Iridium is brittle and can be chipped.
 

PatM

Original poster
Member
Jan 27, 2012
25
Yeah I already knew not to try and gap irridium plugs -they're brittle and as likely to snap as bend.

My Haynes manual says 50s for the 2003 and the local crappy tire store lists 50s and 43s. I downloaded an owners manual for the 2003 and it says 42s. I guess I'll echange the 50s and not rely on Haynes for this kind of data any more.

Got my ride info filled but I had to switch to IE to do it. In firefox the edit boxes only work once (e.g. year) and none of the others will open.

Maybe I'll grab some of that Seafoam everyone is talking about and give the engine a cleanout.

EDIT:

I was just reading the I6 spec sticky and it too lists 0.050 gap for 2002-2004... So which is it really? I'd tend to go by the owner's manual at 0.042 but there must be some reason for the discrepencies..
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
PatM said:
...Haynes manual ... local crappy tire store ....
Neither of whom are trustworthy sources, as you discovered. I think our sticky might be outdated as well. The issue is that DELCO changed their recommendations as time went on. And that new data didn't make it back into already-printed manuals like Haynes, and possibly the data bases used by the tire store. We know even today, that parts stores have wrong data for the serpentine belt length. Pretty certain that .042" Delco 41-103 are suitable and optimum for all I6 engines.
 

Forum Statistics

Threads
23,438
Posts
639,266
Members
18,655
Latest member
Jaywebb25

Members Online