Engine/Transmission (1994 - 1998) Injectors, whats best?

[Joseph Donnelly]

I put in DD3s for my recent elk hunt. Engine started right up at zero F, ran much cleaner than with 370s. Both are good and I generally have both in my tool box to choose from. All depends on your usage and budget. Occasionally good used 370s are available and that would be the lowest cost. Pretty son I will be trying something bigger, as it is hard to get used to these little injectors

 

[Reddog1]

At the risk of being guilty of rude behavior I wonder I we are having our intelligence questioned? I tried to stay out of this, but I am so envious of 20 mpg. I typically get 17. 5 mpg. When I was stock, I was typical at 18. 5 mpg. I know my foot is heavier now.



My truck weights 6,200 lbs. I would appreciate it if someone could teach me how to drive to get 22 mpg. I would readily pay $100 for someone to teach me how to drive it and get 27. 5 mpg.



I see so many posts where someone will get 350 HP just by changing a fuel plate, that I have to be a skeptic on mpg. I hesitate to accuse anyone of anything, but this is something I personally must experience. I have dynoed my truck, and 350 hp with just a plate, yea!



I have a co-worker who gets 25 to 27 mpg, depending on what day he is telling the story. His wife is consistent with 28 mpg.



I have the 370’s with a #10 plate, with too many EGTs. I often wonder if I should have gone with smaller injectors. Turbo will be next move.





Wayne

 

[T. Baker]

I average about 21 to 22mpg in my little IH scout with the 6BT driving realistic Hwy speeds of 70 - 75 mph. I wish I could try my milage at 55 but out here in California you run a real risk of being rear ended at 55 MPH. My gearing gives me 75 MPH at 2200 RPM. I am going to be going to faster gears somtime in the near future and I expect that to help some. I wish I could figure out how to get alot better milage too. By the way I am talking flat ground even throttle setting so don't tell me to start and stop gently or coast when I can because that dosen't apply to driving down HWY 5 wich is hundreds of miles of flat constant speed driving. I do check my tire presure as well and the alignment is good. I haven't yet tried running with the tail gate down. Granted my scout doesn't have great areo dynamics but it is pretty small and weighs about 5200 LBs.

 

[Mike Ellis]

Reddog1,



I don't know how the other guys drive, but I don't take any special pains in my 3500 (5-spd with 3. 54 rear end and stock size tires). As I mentioned in my earlier post, the truck gets about the same regardless of how much I stomp it getting up to speed.



That said, one of the key items is probably the fact that I drive the posted speed limits. I usually take off in 2nd gear, don't run up to redline very often - usually shift well below 2500 (wherever it "feels" right). Every few tanks I throw in some Marvel Mystery oil, it boosts mileage a bit and truck seems to like it. Otherwise I don't do anything I can think of that would help mileage much. Still use Rotella T oil, recommended fluids in rear end and transmission. Stock airbox and all.



Truck seems to get the best mileage when I am listening to either Webb Pierce or Ozzy Osbourne, could be my imagination though

 

[Hutchew]

Never happen......

Reddog1, until you take out that power seat of yours, you will never see 20 mpg, takes up too much power. However, vssman did send me some pixie dust, but I haven't had a chance to try it out yet, will let you know if it helps.

Honestly though, What Mike Ellis and a few others have said here is about the only way. Keep your engine in the peak torque band, keep your pre-turbo egt's below 600-650, and watch your right foot. AND BEFORE anybody can question the turbo temp thing, it came straight from Mr. Cummins mouth, I think on a cross-country trip, whereas he obtained the absolute best mileage from a diesel engine by doing so. It works for me, if I concentrate on keeping EGT's low, it does make a difference.

BUT, in my fleet of company vehicles, we have 3 1997 Ford F250 Powerstroke Pickups, all three exactly the same specs, bought at the same time. The best one gets @ 17-18 mpg, the other two usually get @ 12-13. Now is it the drivers only, or are there other mysterious forces at works here? I had two of them follow me on a trip, the one that gets the best mileage, and one of the other ones. Running a consistent 80 mph, the one that gets the less still had to stop first for fuel, and we all filled up together before we left. I know there are things that will affect mpg's like plugged air filters, brakes too tight, low tire pressures, but we keep our fleet in pretty good shape, maintenance-wise. So I feel that regardless of how you drive, there are going to be some trucks that just get better mileage no matter what you do.

I am going to try that pixie dust, throw in some Marvel mystery oil, and find that old Crazy Train cassette though, just for the heck of it. LOL

 

[T. Baker]

Hutchew, It dosn't really matter how hard you concentrate on EGTs they are going to be what they are going to be to maintain a certain speed on a flat hwy in high gear.

 

[Hutchew]

That's true, to a point............

T. Baker, I understand your point, I'm just saying that they (EGT's) are somewhat controllable, It depends on whether you are dead-set on maintaining a certain speed, or are willing to allow a little variance in your mph to allow more control over your EGT's. Most of the time, I can cruise 75 out on the flats @ 2100 rpm and 600*. Throw in a headwind or a few hills, and I can still run 75 mph @ 2100 rpms, but EGT's just went up to over 1000*. Downshift into 4th, rpm's go up to 2500, speed drops to 70, egt's drop to 650*. See my point?



I can peg over 1500* no problem, accelerating from say 65 to 75 in 5th gear WOT, but if I downshift into 4th, and ease up on the throttle a little, I can knock them down to 750-800*, get up to speed, then up shift.



I do think I have a huge advantage over most though, because I'm running 3. 54 gears and 35" tires. I can run 75-80 mph in 4th gear at a decent rpm, while most others can't.



http://www.f-body.org/gears/ is a fairly good gear-mph calculator if anyones interested. There is a box on the top left that already includes NV4500 & 5600 transmission gear ratios.



Dang, weren't we supposed to be talking about injectors, here? Good thread though, let's keep it going.

 

[SRehberg]

I've been reading all the posts about mileage, injectors etc. , and as a newby to this power game, will ask a dumb question(s). My '96 is bone stock, ( 3/4T 3. 54/auto/2wd) and for mileage I can't touch the 27. 5mpg that was stated, even bone empty, traveling 65mph without a headwind. The best I got was 24mpg from central Calif. to Los Angeles (approx 350mi. ) Now the questions; as stated, the engine is stock everything, and now is going to be pressed into RV trailer towing service. The stock timing from the factory is still just that, but going to Piers site, there seems to be a TSB stating it should be advanced another degree. Now the injectors; is there any advantage to changing them to the 215's, DDIII's etc. (of which I don't know the difference) for trailer pulling? Are the EGT's going to be a problem with them? I could use a little more power, but don't want to incur the problems with head gasket failures etc, or high EGT's. I know the Calif trucks are detuned from the other 49 states (lucky us) but not sure how to take the detune out.



Lots of questions, but I'm trying to learn about this great engine of ours.

 

[Hutchew]

SRehberg..........

Don't listen to us. Call Piers at Piers Diesel, tell him what you have and what you want to do, then send him all of your money.

We are all newbies compared to him, however, I would like to hear his opinion on our various opinions. LOL

 

[rnolen]

:-{} There needs to be no arguing. I would really like to know how to get even 20MPG out of my 97 with only a straight pipe on it. I think everyone wants to know how to get the most out there cummins. I agree with Hutchew on the Piers thing. They really seem to know everything. Solution is for everyone to share there secret about MPG

 

[Mike Ellis]

rnolen is right....

... we need more info on how the various folks drive to get the high mpgs. Unfortunately, the results are often so mystifying that about all you can do is scratch your head and say



I have yet to hear a coherent explanation on how my Dad's 2001 Powerstroke, auto, 2wd, F-250 crewcab short bed with everything STOCK and empty just like mine, running the SAME roads (back and forth to Houston) going the SAME speeds with the SAME driver (me) can get 20 mpg on the highway. It has an extra 1. 4 liters of displacement vs my Cummins, and an auto transmission that feels like it is slipping madly every time you take off from a stop. But it is pretty close to the same (+/- 1 mpg or so).



I have asked about this before, but nobody has an answer - other than to make the blanket claim "PSD's give worse economy than the CTD". Tain't NECESSARILY so, with the kind of variation we see in the reported numbers... . :-{}



Can't say about towing though, we use the Dodge for all the trailer work... .

 

[Gifford]

The mileage FAQ

The mileage FAQ for the TDR states the best case scenario for high MPG in a CTD is 2wd, 5 speed, 3. 54 gears. 24 MPG with conservative driving habits is within the realm of possibility.



27. 5 in a 4x4 auto is so far outside the envelope, it BEGS for further examination.

 

[dray]

Interesting thread- I'm a new Cummins driver and I've yet to see 20 MPG w/ mine. The best I've gotten is 18. 5, w/ stock tires and the 4. 10's. I do believe that there is more MPG's in my truck, I just have to find them. I think my injectors are tired and need to be changed. I also want to go to bigger tires, along w/ exhaust and air filter. I drive very conservative, trying to prolong the life of my transmission. I look forward to experimenting w/ my truck to find the best combo for power and mileage. BTW, I really like the truck and engine- can't be beat.

 

[illflem]

dray, the 4. 10 is what's keeping your mpgs down. Consider yourself lucky, 18. 5 isn't bad at all for your rear end.

 

[Sled Puller]

I like the 370's from Piers. I'm sure there is better inejctors, but these have done extremely well.



I have been getting 18 mpg, driving like an idiot. 20, if I can keep out of it. I think if I put the small 191 delivery valves back in, 21+ would be possible, easy.



I think a 2wd with 3:54 and a 5speed, mildy BOMBed could get 27 no problem. Flat highway and tailwinds CAN and DO help mileage. If you don't believe that, head for the western staes, and drive into the wind for a while, and see what your mileage does.



It also helps to have an accurate speedometer, and make sure you fill with same grade diesel each time, and fill the same.

 

[Reddog1]

Jburnes – I hope we are giving you a little info on the injectors. I did not see gauges in your post. You gota have gauges, especially EGT.





Mike Ellis – You posted that you wouldn’t be surprised that 25-mpg figures are possible. Are you surprised with 27. 5 highway/20 in town? I believe the MPG you have experienced is realistic. Ozzy Osbourne? Now, your post are suspect!



Hutchew – I am impressed that you noticed my power seat, you are the first to mention it. I use it only when on the Dyno, that’s how I get 821 HP. Used to get 821, now only 814. I thought pixie dust was the mystery in Marvel mystery oil? :-laf



Rnolen – Good post. If I make a statement, I don’t think someone should hesitate to ask me to qualify the statement. This is especially true if they want to have the same result. Unfortunately, our words appear harsh, but I bet if we were at a Coffee Shop, even Gifford would not appear to have rude behavior. LOL







So far, my experience has been to add a #10 plate, 370 Marine Injectors and a 3GSK and start fighting EGTs. I have not checked my timing as yet, but will soon (Santa brought timing kit).



I think with a plate or 370s (not both) you probably would not have EGT problems. I ran with plate only for about three weeks. I was afraid of my 140,000-mile transmission, so they were easy miles. I don’t recall an EGT problem. I installed the 370s and headed for DTT. I been smoking and ducking EGT’s ever since.



During the first six months I owned my truck (new to me), I went from Sacramento to LA This is well over 500 miles, flat, 65 to 70 MPH, with and without a tail wind, bets MPG was 19. 5. The truck (6,200 lbs. ) was stock-auto, with 3:54 gears and a US Gear under drive. I tried in under and over. I got 17 to 17. 5 in under. I think under drive is equal to 4:10. I might add, seldom did I exceed 1800 to 2000 RPM.



TDR has over 14,000 members. So many of us can tell others how much HP you can get, and how to achieve it, and prove the HP on the Dyno. Yet, I have not found a post where someone says, “my truck was getting 18 MPG. I made the following mods and now get 24 MPG”. I want to see how it is done. Respectfully, the mileage claimed by some, would be easier to believe.





Wayne

 

[dray]

Hey illflem - do you agree that bigger tires and air filter/exhaust would be worth the effort, along w/ new injectors, to increase mileage some?

 

[LSMITH]

If you want to mod to increase fuel economy there are a few things you can do, like timing and cams and pistons, or even compression ratio. To have any prayer of getting better fuel economy from upgrades you must change the volumetric efficiency of the engine, PERIOD. Injectors and plates and on and on, these things will NOT change the volumetric efficiency provided they work properly in your engine. Set your timing, pray for the cash for a cam. Other than that it is the loose nut behind the wheel that is THE factor in fuel economy.



Also remember that each truck is different. I have known a guy with a truck that was a copy of mine but with a long bed as the only difference, his NEVER got over 14 MPG. It ran good, had no problems that anyone could find either. His just sucked the fuel. Mine will get 21 easily on winter fuel and over 23 easily in the summer. How is the difference explained? PFM maybe, I really don't know. I average 20 highway/16 town with winter fuel running 285 tires and a big grillguard with somewhere around 350 rwhp on tap, I do it without trying too.



One thing I see over and over is guys with poorer mileage saying they never step on it, never go over 2000 RPM and so on. That will kill my economy. If you need to accelerate GET ON IT, get up to speed and then cruise. Time at cruise is important, lumbering up to speed is just sucking fuel. Grandpa it around and economy will suffer in my experience. Drive it aggressively then just CRUISE, works for me.

 

[Koa Man]

OK, I'll be completely honest and I get an average of 10. 5 to 12 mpg with my truck. Of course I am usually running a GCVW of 16 to 20K most of the time, not driving for economy and lots of hills where I live. The 5 ft. high headboard on my truck doesn't help either.

 

[illflem]

I've found that cruising over 2000 rpms and the fuel economy goes down the tubes fast. With 285 tires that's 75 mph on my rig, plenty fast for me. Like LS said don't grandpa it up to cruising speed, step on it.



Power upgrades will increase your mpgs because they allow you to stay in a higher gear on hills and with loads thus keeping the rpms down.



Adjusting your timing up to 16. 5 will also increase mpgs. If your timing has never been adjusted it can be much lower than the 13. 5 factory recommendation, mpgs will suffer.

My feeling is the lack of consistency in the factory timing is what leads to the wide variability in mpgs in similar trucks that we see.



Keeping a steady throttle also increases your mpgs, the cruise control doesn't keep a steady throttle at all and your mileage will suffer. The cruise in our trucks is much too sensitive. I found out accidentally I could gain 1-2 mpgs in cruise by restricting the vacuum line to the cruise servo under the battery. I did this by cutting the line and inserting a tubing coupler full of glue with a pin sized hole though it. Cruise is slower to respond but the throttle stays steady.