Power and Mileage

**vetman** · 03-25-2002, 15:47

Being a newbie, you'll have to bear with my ignorance. I bought a Duramax upon the recommendation of a lot of people, including many on this web site. I even test drove and compared the Duramax to the 8.1-liter. They seemed comparable- so I bought the Duramax for fuel mileage reasons. I now have 1500 miles on my new truck. Don't get me wrong, the truck runs great, but I'm disappointed with the power and mileage. Keep in mind the power is O.K, but certainly will not out perform my old '95 5.7 liter (non-Vortec) gasoline V-8. As for mileage, the first tank was 18 mpg. After that, it dropped to 13-15!! What's the deal? Anyone have any suggestions? I think the next step will have to be adding a Dynomite box, just so I can get the level of performance I was expecting from the factory!

**Smorey** · 03-25-2002, 16:05

Vetman -

Kind of generic on your statements. If this is your first Turbo Diesel you will have to adjust to the way it makes power.

Gas engines are a high RPM power source. The turbo on the duramax is like a big compressor, and takes some time "spooling" up. Most people here will tell you not to pass judgement until you hook up some serious weight to it. From what I have read the 8.1 and Dmax are comparable in the power aspect, but read what some of the 8.1 owners are getting for mileage. Thge 5.7 is no where near a comparison. Remember - we are talking about hauling ability. Mileage readings will vary a lot because of fuel variables, and foaming issues when filling. There's a lot in past posts that can answer some of your questions.

There is a similar thread that you might want to read through. http://forum.62-65-dieselpage.com/cg...=3&t=002722&p=

**gun runner** · 03-25-2002, 16:06

We can cry together on this one. My truck tows really good at 70 mph loaded at 18,000 lbs. No complaints. However; in town , unloaded it's a bit of a dog.
Ordered 4" Kennedy exhaust. Hope it helps the low speed feeling.
Curious- is your call name auto related , or military?

**mackin** · 03-25-2002, 18:49

SEE SIG. for truck info.

After reading all these posts about no low end grunt I am totally amazed. Now I am not trying to rub salt in any ones wounds but.......My truck pounds the pavement from the minute I step on the go peddle. The only mods to date are drilled airbox (2001) and amsoil 2 stage filter. I can hear my turbo wine at low speeds more so when cold. I have done no software upgrades (no plans to also).I run cetane boost every tank. Haven't heard the famous pilot injection shut off noise in months. I will add some more mods but, I probably shouldn't mess up a good thing. I have never been more pleased with a vehicle that I have owned, and paid so much money for since my 1995 vette(about the same price mind you). No, I will not give my truck back for testing purposes even if the top BRASS from GM calls. I have just about 14,000 miles on the clock. With only two SELF fixed minor glitches with the Allison tranny.I got the "TICK" very mild very seldom.I got the "COLD LOPEY IDLE". Either one doesn't bother me .They both go away one when it warms up one when it feels like it. I do all my own SERVICING I'm the only one who drives it. Anyone I've taken for a ride has always said WOW!!!!!! this is a 1 TON truck and it moves. I only wish you were all as satisfied as I am. I hope you, who are having problems, get them resolved.On edit : Mileage is so debatable it isn't funny. Personally I don't watch it to much. I have gotten almost 500 miles out of a tank to a low of under 300 miles. It so depends so much on your driving style and terrain it isn't funny........
MAC

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[ 03-26-2002: Message edited by: mackin ]</p>

**mcfly** · 03-25-2002, 19:23

mackin,

What truck do you have? I have an '02 ext cab 4X4 dually and there is no way this truck will pound the pavement. My service manager told me that the software update to fix the "cold lopey idle" will actually detune the truck in first gear. He has had a few fellas complain that they would take the lopey idle to get the power back. I'm certain that I have not had any software updates to my truck so I can only assume that the General decided to go ahead and "fix" the cold lopey idle on the '02s. My truck hauls a$$, but there is NO WAY and I mean NO WAY to spin the tires, even if I load it up to 2700rpm and let off the break.
I do not really care about burnning the tires off the wheels, but I can see where some folks might mistake the inability to light them up with a lack of power.
Maybe I got a REALLY GOOD set of tires?

-Rick

**mackin** · 03-26-2002, 05:20

When I refer to "pound" as it gets its torque down to the wheels and gets its A** moving Quickly I personal do not have a lot off turbo lag . Why? I don't know. Perhaps it has a lot to do with NO software update. Frankly I'm not looking for a tire smoker.I have never spooled mine up.This is a truck after all. I guess it is a matter of interpretation .I will tell you my buddy has a 2002 D/A ext cab two wheel drive, the first day he got he spooled it up and smoked the tires no problem. I am pretty sure mine will do the same. My truck moves. Even my wife not at all mechanically challenged will even tell you it is unbelievable. I know what power is all about I know what its like to smoke tires. I owned a vette that would so easy it wasn't funny.......This is not meant to be controversial just informative.Perhaps they build them better for the Ct people they know we are so angry about paying TAXES that the want to give us more joy in ownership.Or the are afraid of us.........
MAC

**vetman** · 03-26-2002, 08:02

As gun runner asked, the name vetman is auto related. I've been restoring and racing Corvettes for 20 years. Believe me when I say I know what 600 lb. ft. of stump pulling torque feels like, and this Duramax is not it! Now again, so as not to upset anyone, it is a good running truck. I do understand the difference between a turbo diesel and a high-revving big block. My problem is I don't think mine runs the way the '01 model did that I test drove. My biggest problem? Running unloaded at 70 mph the truck has adequate power and acceleration. However, come up on a moderately steep hill, ascend 2/3 of the way to the top and then decide you want more power. I can put my foot to the floor, and nothing.... no acceleration, no downshift out of overdrive... essentially NO POWER!!! Sure, push in the tow/haul button, and it will accelerate some, but not even close to a carbureted gasoline big block. Am I expecting too much? I have towed some small loads with the truck (6500-700 lbs), and observe much the same behavior. Unfortunately, I don't know much about diesel engines or injection systems, so don't know where to look for a problem. Help!?

**7mmSTW** · 03-26-2002, 15:29

Just wondering if this could be related to the topic I posted yesterday about Mass Airflow sensors and Mileage. I am trying to figure out if a problem with the MAF sensor could cause low MPG's and Low or Sporatic power. Any opinions or ideas?

**mackin** · 03-26-2002, 19:10

Vetman,

Why your truck is not downshifting I couldn't tell you. Was the cruise on? There was an issue about shift business in cruise or not holding and downshifting a lot that was fixed with a PCM update. Mine does not have yours probably does being a 2002 . I can tell you that this is the first truck that I got a friggen speeding ticket going up hill in NO LIE 67 in a 35 >>>>>>>>>>
These trucks must have the turbo spooled up producing boost to give that seat off the pants rush. In my opinion WOT does no good unless you are at maximum boost. So lugging along in overdrive and you mash the peddle if you don't get a response that's the nature of a turbo charged diesel. In addition on launching this torque monster is defuled so as not to over strain the drivetrain. So again a mash to the carpet makes no sense. I believe maximum HP & Torque is 2800 rpm. If you haven't done it, at a stop light when it turns green give it about 1/2 to 3/4 throttle and hold it there. You will notice once the turbo lag is gone (which it you can shorten with some simple mods) and it spools up @ 2800 rpms does it not run thru the gears and PULL REAL HARD without giving it any more throttle?
In my opinion out of all the TURBO DIESEL I have owned and driven this one stock out runs them all. To compare them to gassers in any way can't be done IMHO. They are a completely different apples to oranges. Gassers are high revers diesels not but in saying that you got to have it in the MAX boost range to unleash its power or it is lack luster. Once you figure that out it is a whole lot of fun just like I'm having.
For a couple simple TURBO LAG breakers may I suggest:
Get rid off that paper air cleaner element. I run a AMSOIL 2 Stage filter cleanable reusable @ about $47 bucks there are others. Why your doing that drill some holes in your stock joke of a GM airbox. First in the bottom to let the water out that collects in the bottom half. Then in the bottom half, in the front. Let some cooler air in. Some have made theirs into Swiss cheese I choose to drill 2" holes in the front only. Then go for a low restrictive bigger (4") exhaust, I haven't yet but will. I will tell you I definitely felt the difference in airbox mods. It is breathing and spooling up definitely faster. It is your option to do this if you chose to. I speak only for myself. Do a search here you will see other members have done the same.... Good luck on that downshifting problem hope you get it resolved......
MAC

**tmg115** · 03-26-2002, 20:10

well my truck will hit the pavment hard. this thing has tons of power. it is all stock and runs like a mother... i average 15mpg in town and 20 on the hight way. this thing will out run my 5.7 vortec suburban. and comes close to our 99 F250 V10. but when i get my banks exhaust and duramaximizer power chip i will be smoking that V10.

**mackin** · 03-26-2002, 20:20

tmg115 ,

THAT IS WHAT I'M SAYING.......

I do have airbox mods thats a must........
I got some plans of my own.........
WE must of got the two good ones they built....
Or we figured out how to get that power released......
WANT TO RUN IT>>>>LOL
MAC

**gun runner** · 03-26-2002, 20:39

vetman- I just knew you were vette related,such as I. 69'A/P 82'S/G & 95'street. We have higher expectations of our day-ly drivers. Little brown truck delivered the 4" Kennedy today. Hope to have it on in 24 hrs.
My best G-tech was 17.60 @ 78 mph. We'll see how the exhaust compares.

**preaver** · 03-26-2002, 21:11

Guys I think there may be something wrong with your trucks, cause my dad has a March 2001 Duramax, with no changes, not even software updates. To make a long story short while he was on vacation me and my cousin raced my dads truck against my cousins singe wheel F-350 Crew cab, and against his friends 98 454 chevy crew cab dually. This was not a strick 1/4 mile, it was until the 96 MPH govern, but against the 454 it continued to pull away until about 80, at that point it was about 5 truck lengths, and then by 96 it was down to about 4-4.5 lengths, and against the Ford it was about 6 lengths by the end and never quit gaining. I am not saying this to start a war, just as a comparison if you say yours won't run with your old 5.7. Off the line without spooling it up my dads will just barely spin the tires for a second, and after that it just takes off. If you spool it up it will easily smoke the tires. I would say that if your trucks are performing this poorly there is definetly something wrong. Just my opinion though.

**JrTuner** · 03-26-2002, 21:16

My DMax runs well but sometimes it feels sluggish to me but I am use to driving a Grand National everyday so it isn't a fair comparison. Nor would I compare it to my 225 RWHP turbocharged Hayabusa. That thing is just plain insane, and honestly, useless to ride on the street. The truck is what it is. A 6800 lb. vehicle that gets out of its own way fast. I too good a speeding ticket not even realizing I was speeding. It sounds to me that something is obviously wrong with your truck. You admitted that you don't know much about diesels, so have somebody who does look at it. If you don't have a boost gauge your truck could be not making any boost, a defected wastegate actuator. Anything is possible, remember as sophisticated as these trucks are they are still made by humans. I don't expect my truck to run like my GN, to do that would be asking it to do an impossible task. But than again it can out tow by GN, and I wouldn't ask my GN to do that.

**Brucec** · 03-26-2002, 21:19

Well I also have a 2001 and have done nothing to my truck not even air box, runs good no problems. Love it just started towing my 35 foot Cedar Creek fifth wheel around 12 to 13,000 pounds. truck handles the weight ok , I am very pleased at how good it takes the 5th wheel. I have no plans to touch my dmax because it is under warranty and I have an old sayingif it runs good let it alone.

**vetman** · 03-27-2002, 08:02

Thanks (everyone)for all the comments. Mackin- I did buy the Amsoil air filter, and am now starting to wonder if I'm having the MAF sensor problem. I double checked for excess oil on the filter at installation, but haven't looked since. Still, the most frustrating problem is the downshift issue. I've been trying to get my hands on a shop manual from Helm, but they tell me they're out of stock. Maybe a trip to the dealer is in order....

Gun Runner -good to find another 'vette man who appreciates the real "seat of the pants" power I'm talking about! Most of what I've built lately are street cars, but nevertheless, some will scare the sh*t out of you when you put your foot to the floor.

**Zapper** · 03-27-2002, 15:57

Mackin, this pilot injection shut off noise you are speaking of , is it a sound somewhat like a valve floating at around 3000rpm? I have a sound at this range when I'm on it. I was wondering if it was the wastegate. I don't know much about diesels myself but am learning. I have built my share of muscle car small blocks over the years from 283's to 383 strokers and in the quarter these motors in camaros or Novas or whatever would would destroy my CC D/A but heck they should, they better anyway. My truck for 7000lbs hauls a--!! I have had more fun in my daily commutes in this vehichle than any other. If I want to humiliate a peestroker off the line I'll spool her up a bit light the tires and run away, sometimes I will let them get out of the hole and let the turbo spool normally and do a blow by. For some reason it seems every truck no matter the brand or moter want to challenge my D/A. Couldn't be me. My wife of 25 years who in her day could bang a Muncie with the best of them and loves horsepower is just as impressed as myself. I can attest to the difference the holes in the air box made , really unbeleivable and that's all I have done. I guess I'm a little of a Scrooge but I have a hard time replacing a perfectly good exhaust system but am getting ready to order the Amsoil. As I said in another post I'm in love with her (the truck) and it normally takes me at least a year for that kind of a committment.
P.S. Don't forget to plug the air box sensor back in after service (or drilling) it sets off the SES and runs like crap until you plug it back in.

**mackin** · 03-27-2002, 17:28

Zapper

Welcome.......

Pilot injection is a little extra shot of diesel fuel that keeps our trucks quiet A better explanation here C/PASTE ---------->http://www.duramaxdiesel.com/02_bosch/sub03.htm
It does shut off at a certain rpm .
I rarely, I guess here mine shut off, very seldom as I stated above haven't heard it in months. A louder diesel clatter is what you here when it stops. I guess you can call it a what you explained it as. a big loose sloppy gasser .LOL
MAC

[ 03-27-2002: Message edited by: mackin ]</p>

**mackin** · 03-27-2002, 17:46

vetman ,

Ran a little test for you today. All right I did it for my own enjoyment. LOL
At the base off a 1 mile pretty steep grade not real good at determining you know 7% 8% but steep enough so you couldn't see the crest. Hit the base running 70 mph (in overdrive no cruise) about 1/2 way up I eased the go peddle down fairly quickly (no wot) and it downshifted and 90 mph came up REAL fast had to let up before I reached the top ......Man I luv this thing GM calls a truck. This is one 2001 that will not get software updates if I can help it....You should go to the dealer and see if they can correct it. You never did tell me if you had the cruise on with no downshift out of overdrive?
MAC

**vetman** · 03-28-2002, 07:57

Mackin,

No, the cruise is NOT on. I have never had the performance you describe. Half way up the hill I put the hammer down, and the truck will not accelerate AT ALL! I'm lucky even to maintain present speed. I'm not impressed!

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