I just got done with a near 300 mile trip and calculated 14 mpgs, I knew I was getting bad gas mileage but this is just ridiculous! I recently posted about new gear ratio and smaller tires, is that whats killing my mpgs? I have 4:11's with 37"s and a custom front bumper that probably weighs a deuce.50 or so. Any tricks you guys know of? Special tuning with the pump? Am I shifting at the wrong time? Any help is appreciated guys thanks!

 

Get it down out of the wind, and slow down to have less wind.

 

Do you have injectors or a plate? I was wondering on the need for the HX40. But either way, without mods, your mileage shouldn't be that bad. I would be wondering about things such as timing and fuel pressure.

 

37s use fuel to get rollin. Try increasing tire pressure a little. Ride will suffer a bit. Over 55, lift is like an aerodynmic brick.

 

No plate that Im aware of and no injectors, if it has them something is seriously wrong cause shes a dog off the start! Its just the turbo the guy had in it when I bought it, I do have a hx35 that he gave me as well, do you think that would help?

 

Did he give you the down pipe for the HX-35?? I tested a HX-40 on my truck and it also was a dog...Found out later that it was overheated bad and bearings where burned...

It doesn't take long to swap in your HX-35..With problems like this its better to troubleshoot by going back to stock form..

 

You are lucky to be getting what you are with all the stuff you have done.

 

Sounds like it had some of those items before it was sold. Changing to the HX35 would help in the ******* dept., but the mileage won't be affected that much. The high smoke sounds like the AFC has been modded or gutted and all that fuel and a that larger turbo will make the truck very sluggish. There used to be an adapter that you could use from your HX35 to the HX40 downpipe, but I can't seem to find it anymore.

 

You don't mention anything about AIR intake?

 

Low rpms help a lot with efficiency, but not if the turbo won't spool at low rpm, and I'm gonna guess that hx40 has some real trouble making boost at low rpm.

Also the tires not only cost some efficiency, but they also make your speedometer, and thus your odometer, lie to you. This makes you think you are going slower, and not as far, which makes your efficiency look worse than it is.

Having said that, I'd guess that if you can get that hx35 in there your efficiency will improve. I'm not a big 12v guy, so I could be wrong, but if at low rpm your hx40 isn't delivering enough air, your efficiency will suffer where the efficiency sweet spot normally would be. EGT's probably aren't happy either.

I believe it is possible to put the hx40 compressor wheel on the hx35, but don't know much about it.

 

Im not to edumucated on turbos but I have the hx40w, is what he said. The turbo for a tractor not a truck, when Im on it it'll do 30 psi, ill take it for a spin tomorrow and get the specifics of if it spools in low end good or not, I just started a 10 pm - 6 am shift this week so my mind isnt too clear right now. No my intake is stock, it just seems when Im in low rpms its dumpin a whole lotta fuel but not goin no where. And as for the smoke its more of a medium haze then smoke. I had browns diesel in riverdale ca do a clutch and some other stuff for me and he said he thinks theres pump mods from the smoke so i guess ill jus have to get in there and see. Ill post tomorrow after the drive.

 

If all you are getting out of it with your level of fueling is 30 psi I would guess the hx35 would perform better across the board. Smaller turbo is easier to spool up and the hx35 is good to 35 psi before choke point.

It's "normal" to smoke upon acceleration, but if it continues to smoke, the turbo is not keeping up. I'm guessing that a smaller turbo would develop enough air at low rpm to clean up that haze which is wasted fuel, and give you WAY more seat of the pants power. Maybe more power overall. To get 35 psi out of the hx35 you need to put on a boost elbow though.

Couldn't hurt to make sure there are no preturbo exhaust leaks or boost leaks as these can cause similar problems even with a smaller turbo. And weigh personal experience with the 12v/hx40 heavier than anything I say, as I'm just going on generalizations of turbodiesel function.

 

i replied on your other post- i put 35"s on and went from 23 to 22 mpg @ 65mph so im not sure what the problem is. granted my truck is stock except for 4" straight pipe. i dont even get lower than 16-17 mpg riding it hard in town. and yes the bigger tires mess ur calculations. with 35"s my truck runs 10 mph faster than the speedo shows at 60mph, so odometer will b out as well. timing is supposed to help too, but i havent done that yet so cant comment on that. if your constantly smoking black your burning too much fuel....add more air or decrease fuel as per power needs

 

My '92 has 3.55s and is on 35" rubber and a 4" lift. Gets 18-20mpg all day long.

My '97 4wd 3500 auto w/4.10s got 16-18mpg after I BOMBed it.

My '99 3500 5spd w/4.10s gets 16.

All the trucks can get this running 70mph.

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Do you ever pull a trailer? If not, it helps burn the the crap out. When my mileage goes down lower than normal, I always get it back after pull a load. Usually over 8k and best on the interstate up to speed. Keeps the EGTs up to clean things up.

Never saw a mileage change on the '97. I imagine most that do gain mileage, had slipped timing or wasn't to spec from the beginning.

As asked earlier, what other fueling mods do you have? Without any, the 40 is a waste. Though, I did gain mileage with mine before the injectors got here. Though, I still had the stock 215 rubber at the time and the engine was running faster than yours is with the 37s.

Running the HX40 with or without injectors WILL cause excessive smoke. PERIOD. Been there, done that. It is plenty bad with stock injectors because the engine has trouble lighting the turbo as good as it can the HX35.

 

14mpg seems pretty reasonable for the truck, as it is described.