My Milage Is Killing Me

[imsweetdaddy]

2002 GMC 3500 C/C Dually I AM GETTING 12-13MPG at 70mph on the HIGHWAY and 10mpg in town. My father has a 2001 Chevy I dentical truck and gets 15-16mpg on highway. What the heck is wrong with my truck??? I have not seen anyone anwhere get suck poor milage as me! ! ! Truck is hard to start 8-10 second range, but if I put a new filter on it it cranks just fine. But after one tank of fuel run through it, it's back to the same hard to start. SOMEONE PLEASE HELP WITH SUGGESTIONS!!! ImSweetDaddy@aol.com I need some help because the 3 dealers around here say it's the injectors, already replaced 2 times. 140k and at 190k. I have 232k now, and that's only 40k on the injectors. This surely can't be the problem. I am diesel illiterate, but I am learning fast. Could my lift pump be weak, but if it is then why is it using more fuel, if it's starving? Truck has no smoke out off tail pipe, ever! Very clean burn, no blow by, uses about 1/2 a quart of oil over about 6500 miles. PLEASE REPLY AND GIVE ME SOME SUGGESTIONS>>> I NEED THE HELP>>> WALLET IS GETTING LIGHT FROM SPENDING IT ON DIESEL! ! ! !

[Mark Rinker]

Look for restriction in the intake tract. Clean air filter? Clean MAFS?

I would also be very suspicious of the catalytic converter being plugged - especially with the high miles on your truck.

Keep a close eye on your dipstick. If it starts 'making oil' you are probably suffering from injector problems again...

[conway]

Just to keep you from going down the wrong trail, your truck does not have a fuel pump.

[silverback]

Mark Rinker, I didn't think the 02 had a catalytic converter. My 04 doesn't. Also, conway, maybe he has an after market lift pump (but my 04 doesn't). Imsweetdaddy, have you checked the other basics like adequate tire pressure? I pretty much stick to 66 MPH and get 16 to 18 MPG. Kick it down a notch.
-KL

[letsgo]

He said lift pump, the fuel pump puts out 23,000psi,
CA. have CATALYTIC CONV.
A simple test for checking a blocked cat. conv. is to put truck in park while running and instantly slam your foot to the floor (DONT LET RPM EXCEED 3000 RPM) if blocked you will be lucky if the RPM exceeds 1500 RPM if it instantly reaches 3000RPM cat.conv. should be OK.
I DROVE FOR A YEAR with low power, trying to find my problem.

good luck drive safe

[Jake99Z71]

Start with having your CP3 pump checked to make sure you are making good pressure. If it's weak mileage will drop and truck will start hard. Have you ever had the rail pressure sensor replaced? If not replace it. If you don't have an aftermarket lift pump yet get a Kennedy single with his Mega at tank filter kit. You need extra fuel filtration.

[imsweetdaddy]

Mark Rinker, Yes I have a clean air filter and clean MAFS, and I have no cat. No I am glad to say I am not making any oil either. If you have any more suggestions I am open to all of them! Thanks for your input!!!
Conway, Thanks for your input!!!
Silverback, Thanks for your input!!!
Letsgo, Thanks for your input!!!
Jake99Z71, Will do, I'll have it checked at my dealer, I have an appointment set up for this week on tuesday. The dealers around here suck and I know the mechanics like to fill up there pockets so I am trying to get suggestions so when they tell me something needs to be done I have a little knowledge and don't have to do anything that doesn't need to be done!

THANKS AGIN EVERYONE WHO HAS REPLIED!!! I APPRECIATE THE INFO KEEP IT COMING SO I CAN GET BACK ON TRACK!!!!

[utsi]

You could have youre tank foul of dirt. This engins/injectors aint happy for dirt. They need clean diesel to work. I would have cleaned my tank if I have that issue.

[imsweetdaddy]

INJECTORS>>> FOUR are supposedly bleeding down, and I have a high fuel return rate, Is what the dealership told me. So I have ordered the injectors. Found a new set for $1400..... least expensive I could find, but what sold me was the $1200 core charge. And if the core is bad but part of it can be used I still get credit minus the part. Every other place I checked wanted $2400 core charge, that is just crazy, can buy new ones for that! Anyhow thanks to everyone for the input. Will let ya know in a week or two when I get the injectors in and see if that fixes my problem. :D

[Kennedy]

Replacing only 4 on an engine with injector grief history will likely come back to haunt you. A set of 8 injectors should be appprox $2400 with $800 core and no risk (at this time) of losing your deposit.

[imsweetdaddy]

Haven't got my injectors in yet but they are ordered, $1400 best deal I could find, for all 8. Will keep ya updated, when I get them in and truck rolling again. I turned my PowerPup all the way up and I dont have a problem starting it anymore, but my milage is killing me. Later.

[c5dura]

I have a '02 3500 w/ 60K on it, and I have never gotten more than 13mpg. I've yet to get 400 miles out of a full tank running empty on the highway @ 73 mph.

I just don't think a 4x4 3500 crew cab long bed @ 8000# is going to do much better than 13 mpg...

[rob from bc canada]

OK, I think you should do better than that.

Everybody complains about the 05 LLY's, and here is what I get:

4x4 3500 SRW as below - relatively empty, except for a Box-mounted toolbox, and some junk, four freeway trips of about 140 km = 90 mi each at steady 110 kmh = 70 mph, and a few local 15 km 10 mi trips including a few steep hills, total 750 km = 470 miles on the tank filled to the top took 96 litres = 25.26 US Gal = 18.6 US Mpg.

When I filled up to the top, the computer showed the range at 999 km = 624 miles. The MPG's on the DIC are always about 1 to 1.5 mpg higher.

With a big basement style camper and lots of junk on it, total weight 10,650 lbs, winding hilly highway across Vancouver Island to Long Beach, 327 KM = 204 Mi at speeds varying from 30 to 60 mph, 2 overnights, several stops between, I squeezed in 61 litres = 16 Gals on the way back, for an average of 12.75 US MPG.

[Black95TD]

One last 2 cts That issue of the truck starting well when you replace the filter and then back to normal after one tank raises the question of fuel quality. Does your father buy fuel at the same station? Have you looked at the fuel? Did you cut open a fuel filter to see whats up?

I'v had some BAAAAD loads of fuel!

[silverback]

I just read an article (http://www.azcentral.com/business/articles/0731nitrogen-tires31-ON.html) that says filling your tires with Nitrogen can increase your milage by 1 to 1.5 miles per gallon. It also said some Costco (tire?) stores can do this. It is not free but it doesn't sound real expenise considering the price of diesel. I'm going to check it out.
-KL

[imsweetdaddy]

Got my injectors in, put them in the truck, and now my milage is WORSE! Now I am only getting about 10-11 MPG. Have no problem starting truck now, cranks right up. Now what the heck??? Truck has plenty of power, but no milage at all. 10 MPG just plain stinks!!!! HELP ! ! ! ? ? ?

[David Proske]

I assume you have checked to make sure there are no leaks...as in fuel in oil? Does the truck smoke at idle? exhaust smell like raw fuel?