Super Low MPG

[Aryeh Levy]

I bought my beautiful blue truck in February for driving around and being rediculously big:-D

My Wife's Dad has a gasser 93 k2500 and gets the same MPG as I do 12 MPG. It doesn't matter what I do really, light throttle, lead foot... Once i had 10 mpg one tank once i had 14, but now that i fill the tank all the way to the top of the filler neck, it's been 12.5 every time. I replaced the vacuum solenoid because of excess smoke, and that has been fixed, but the MPG its dead 12.4 every time. City or Highway Doesn't matter.
What gives? I'm new to this stuff, I know i should probably replace the post turbo downpipe and put mild propane injection in the airbox, but do you guys my Lockup Torque converter not locking up? I know some of you guys get 17 MPG in these trucks with this gearing. I... I want that. Also, I went to warranties 4 wheels, and they said internally lubricated parts failure for powertrain was $900 for 100,000 miles. Seems like a decent deal for this truck - what with cracked pistons, blocks, main webbings, and transmission blowouts, it seems like its a good deal.
Also I'm looking for a good 6.5 mechanic on the north side of DC - border of PG/Montgomery County.

I have to say the A/C Tech's at Fox automotive were better than the folks at precision automotive - they took $45 and didnt even jumper the cycling switch...

(they've got my baby this week because my radiator got a leak- $500 labor to put it in, my own supplied OEM radiator shipped to them $315)
$140 Coolant flush to Green.
New radiator hoses,
New Serpentine Belt
New AC Cycling Switch $300 parts/labor
$176 to diagnose everything

= My paycheck this month :-/

Any ideas how to get better mpg other than engine work?

[DA BIG ONE]

Before any mods, my burb w/4.10's had a steady 17mpg @70mph, surely your rig does not weigh much more than my 2500 Burb.

When I was a newbe with modding diesel I had the gears changed out to 3.42's and milage took a dump to about what you have now, until I learned how to calibrate the VSSB. Milage now was in the low 20's, I have big smile and love every minute of it on the highway.

First, I would look at the cat being clogged if you have one.

Second, Look at the tranny for slippage, not lockingup, or? My trans locks up in OD at just over 55mph Drive at this speed and see major milage improvments w/3.42's.

Third, Alignment.

I went to a K&N filter, 3" exhaust milage went up more. But remember I have few, if any hills to deal with day to day.

All other mods gave a little more mpg, but performance was the biggest gain.

Good luck with your truck.....

[TCombs]

I have the same problem with my 99 k 2500. Same set up,4.10 gears and about 13-14 mpg. Has been bad since pump replaced under warranty. All timing is at factory specs, and truck is stock. Truck did about 4-5 mpg better before pump. I wish I knew what timing was at before pump was replaced, as I bought it used and have no idea? :rolleyes:

[moondoggie]

Good Day!

You definitely have LOTS of room for improvement.

My 95 pickup (see my profile) has 4.10 gears, 4L80-E tranny, 4% oversize tires (VSSB calibrated to correct), & an aluminum topper. I almost never pull anything anymore, so mostly it

[Aryeh Levy]

Thanks everybody. I just paid $1100 to get a new radiator installed, new cycling switch, new serpentime belt, and coolant flush. Pricy considering I supplied my own radiator (315 @ radiator.com)

I'm leaning towards the TCC not locking up - i can't recall the rpms climbing when tapping brakes, but I'll check that.

I've got a new cat on my system, so i doubt thats the problem. I've never changed my fuel filter, so that's a likely culprit. I don't even know what filters or where they are... I've been afraid r/e the priming issue, but i read that turning the vehicle to run, putting in gear, and cranking primes well enough w/o wasing glow...

Also, i doubt my fuel injectors have been replaced ever, so between the
TCC, fuel filter, injectors is likely the source of my issue. I'd be happy with 15-19 mpg, and I really don't want my injectors clogging up and spraying, then burning a piston. The chevy tech @ the stealership said its a waste of money to test the injectors, and that my lost mpg is just something to live with. I was like uh-huh and kept my mouth shut...


How much would a competent diesel shop (reccomendations just north of Washington, DC Please!) charge to test my injectors to see how worn they are, change Both? fuel filters, and i don't even know what to ask for r/e the tcc...

thanks everybody

lots of love!

[markrinker]

My experience is the heavier rear end used in 3500 series trucks will cost you mileage, regardless if you run single or dual rear wheels. Set the 3500 series brake drum next to a 1500 series truck. Lots of extra mass to spin! Add to that 4 rims and 4 skins to spin and you're talking LOTS of unsprung weight to move around.

The best mileage I have coaxed out of any of my three 3500 series trucks is 12. That was unloaded, no trailer, but still with a heavy foot - which I cannot seem to contain...

As for $1100 for the services you mentioned, you believe you were GROSSLY overcharged for labor.

I hope they de-bugged your tranny cooler and A/C condensor, walked your dogs and folded your laundry for that!

[Aryeh Levy]

When i'm going 65 Mph, the rpm is around 22-2300
when i take my foot off the skinny pedal for a second, the rpm drop to 14-1600

That's a sign of my tcc not locking up aint it? need advice how to proceed on getting tc to lock up.

Did all the 1998 3500 6.5 silverados come with lockup torque converters? Is it possible this

[rjschoolcraft]

The 2200 or so RPM at 65 sounds about right for a locked converter. When you let off the pedal, factory programming unlocks the converter immediately.

The best way (if Moondoggie's suggestion is inconclusive) to know for sure is to have someone ride along with a Tech II and tell you if the converter clutch engages.

Next best is to set the shift selector in 3 (direct) and accelerate up to about 60 mph. You should feel the 1-2 shift, the 2-3 shift and then the TCC engagement (which can feel like a 3-4 shift, but you've locked 4th out). If you feel the third "shift" with the selector in 3, your TCC is locking up. Move the selector on up to OD (4th) and ensure that the actual 3-4 shift occurs.

[MTTwister]

Aryeh Levy - on the '96 an d up - the fuel pump will run during the glow cycle. You should be able to hear it pumping under the drivers side. this will let you prime the fuel filter without the Pre'96 "hassles".
You do hear the fuel pump during the glow cycle, don't you?

EDIt - excuse me! Lift Pump. If it was a fuel pump it would only cost 1/2 as much. smile.gif

[HANK1948]

My 96 CC dually w/4:11's gets 13-14 never gotten better I have read in past post that this seems normal so I have never tried to worry about it considering it weights 8360!

[Diesel Dan]

Brake drums on the 2500/3500 are pretty much the same size. Dually drum slightly heavier due to more offset for the rim.

My TCC doesn't unlock when just tapping the brake. This was confirmed with a scanner, brake switch is functioning normally. The TCC will drop off when the accelerator pedal is released. The OBDII will pick up converter slippage fairly fast, mine did.

Fuel mileage isn't the greatest on my '00 either. It is around 15mpg with a SRW and flush mount fiberglass topper. Didn't really change with new injection pump, then new motor(AMG block) and injectors. According to the scanner TDC offset is -0.7* and is VERY loud when cold, the Cummins is much quieter. Installed 3" downpipe and mandrel bent crossover, stock exhaust for now.

Haven't checked mileage too much lately. Truck has sat alot since new motor installed. Probably 5K miles since Oct. Been driving the wheels off the dodge :D .

[Aryeh Levy]

Well if everything's working fine and i get 12 mpg, i might as well get more power.

i'm thinking of taking my compuer w/o my truck (missing the golden HD badge, cuz its a L56) to the dealer and asking them to flash the eprom to the newest '2000 3500 L65 HD program, 210 vs 195 hp :D if i'm goin to get 12 mpg i might as well get those extra horsies, right? Any advice about how to get them to do this?


In the vein of MPG, a good gearing would be 3.42 or 3.08's even... my friend also said that an axle swap would be much easier, and much cheaper(can be done without a pain in the butt shim job on the differential. for the rear, sure i can see that... but how hard would something simple like that be on the front - the IFS has to make my beautiful plan harder, huh?

if i get a junkyard 3.42 rear axle and front differential, they basically bolt up right? How would i do it easy? this would be much easier for me than shimming etc. and much cheaper imo - anybody do this?

also i've been thinking of a 20 lb propane cylinder set to fog through around 1-3 psi or so - preturbo this should get the combustion temp high enough to increase efficiency.

I've been noticing a little particulate matter in the night - the headlights behind me get dimmer. i don't really notice it in the day, but maybe my boost should be higher (8-10 lbs) I guess i'd need a turbo master to set it steady there, and also a boost gauge...

I just want to fully burn the fuel and eliminate the particulates.

For the propane, i've seen this: http://www.rv.net/forums/index.cfm/fuseaction/thread/CFB/1/Tid/198668/DoOnePage/es.cfm

[Aryeh Levy]

Oh yeah and i did have a friend crank the engine to activate glow cycle in drive - neutral safety prevented cranking, but when i loosened the bleed on top of filter, fuel shot up 5" so i think it works just fine :D

I didn't feel any shift from TC lockup, so i guess i'll have to have a tech somehow ride with me to see if it locks up.

I get about 12.8 MPG every tank, with 6 cetane boost level of power service in the tank.

I've got a MY 98, so it was built 7/1997. It should have the high flow water pump, and the 20.2 pistons, right? I think this means that if i turn the boost up to 9 lbs it should be the same strain of 8 lbs with the old model pistons

[DA BIG ONE]

Originally posted by Aryeh Levy:


... but how hard would something simple like that be on the front - the IFS has to make my beautiful plan harder, huh?

if i get a junkyard 3.42 rear axle and front differential, they basically bolt up right? How would i do it easy? this would be much easier for me than shimming etc. and much cheaper imo - anybody do this?

There are 2 versions of the GM IFS 4wd, yours would be the HD version

Find a 3.42 for heavy duty 14 bolt IFS in the bone yard? Very doubtful, because 4 wd 2500/3500 series did not have a 3.42 option w/6.5td engine, you have to find, then order the gears for a 14 bolt IFS, and 3.42 is highest you can go with that carrier (4.10/3.42 spread)!

I think you still have the 14 bolt rear on that 3500, so 3.42 would be easy to get.

"Make sure to identify your gear ratio, if I remember right the carrier changes for anything over 4.10:1, if that was even an option?"

[JohnC]

I wasn't paying close attention, but all dualies are L65.

I have the 3.42 rear axle you need...

[Aryeh Levy]

Eh?

I've got the EGR tuna can... and duallies. I think my RPO's say L56... I only have the 3500, not 3500 HD...

Isn't that a L56 Option?
For the front end IFS diff gear. a 3.42, would that be difficult to bolt in and out with a simple u-joint swap? How difficult would it be to do?

[Aryeh Levy]

I asked the dealer to flash my 3500 to 3500 HD 2000 programming - they said it was a "modification" and they wouldn't do it unless i bought a new computer - company policy. I think the 2000 3500 HD computer (PCM) is compatible with my 1998 3500, right? It's 15 more HP, and i think with 8-9 turbo master boost (will get soon) thats where i'll be happy with my truck. - more fuel, more boost, steady boost should smoke about same and be perfect to drive.

Anybody know where or how i can get the stock higher HP rating computer on the cheap? Do other dealers do that, or is it emissions legality issues?

Worst case scenario, junkyarding for 3500 HD computer would work, right? :cool: Please i want to know this - I drive this thing, and its just a squeak anemic for me. ;)


Also my coolant was double flushed by dealer to green. Now the coolant isn't pressurized.. I squeeze upper radiator hose, overflow tank rises appropriate ammount. There's plenty of flow, i feel the pulsing back when i pinch it like that... it's running 188 deg f according to computer. Is that too low to get pressure?

[DA BIG ONE]

Originally posted by Aryeh Levy:
Eh?
For the front end IFS diff gear. a 3.42, would that be difficult to bolt in and out with a simple u-joint swap? How difficult would it be to do? Your IFS has a split case (HD 14 bolt unit), best left to those who have the know how for ring and pinion change out and setup. But, If you are good at mech tinkering, a shop manual will go far to show change out and setup.

[DmaxMaverick]

Originally posted by Aryeh Levy:
Eh?

I've got the EGR tuna can... and duallies. I think my RPO's say L56... I only have the 3500, not 3500 HD...

Isn't that a L56 Option?
For the front end IFS diff gear. a 3.42, would that be difficult to bolt in and out with a simple u-joint swap? How difficult would it be to do? That "tuna can" is your CDR. Not the EGR. EGR is under the air cleaner lid. The CDR (Crankcase Depression Regulator) is the Diesel version of a PCV, and is on the valve cover.

If you truck is OEM, and a 2500HD (8600 GVWR) or higher, it is an L65. If not, someone screwed up along the way. The L65 PCM doesn't have accomodations for EGR.

The diff....
Swapping the U-joints won't change anything. The R&P has to be swapped. 3.42 is pretty tall if any moderate to heavy towing is planned. Increasing tire size and light towing may give you fits with that ratio.

[Aryeh Levy]

CDR Huh... Cool.

So basically the only way to change gearing up front is to open up the diff case and swap ring and piton?
Sux...
i'll just get tall tires
lik 285s or something

I bought the truck for being able to drive across broken terran and take massive jolts to the suspension (3500 is stronger)
Not to tow... i'll probably be driving in 4lo anyway during those situations...

So having a 1998 3500 non HD
I've got 195 HP
Can i get the 210 programming from a dealer or anybody else? Who does that?

I'm not too interested in paying $500 bucks for a custom PCM from the vendors . i spent $500 on a pcm cooler and pmd when it breaks and i'm basicaly broke...

Can the 3500 non HD be flashed to the HD programming successfully w/o longevity issues/compatiblity?

[rjschoolcraft]

As has been said repeatedly, if it's a 3500, it's an HD. Your engine should not have egr unless someone swapped it into the truck. The 215 hp rating never made it to production.

[DmaxMaverick]

RJ

A 3500 is not necessarily an HD. The "pick up" is a 3500. The 3500HD is a chassis/cab, used for tow trucks, dumps, etc, and have a GVWR if 15K.

I think what you're meaning is the 3500 is an L65, rather than an L56.

[rjschoolcraft]

Yes, I was referring to the engine. More specifically the program for the PCM. The L65 is referred to as an HD engine/program and the L56 is referred to as an LD engine/program. I can see how my statement could be misinterpreted, but I was not referring to the different truck chassis as you pointed out.

[DmaxMaverick]

I hear ya.
I don't think he was seeing that.


Aryeh Levy

If you were thinking of spending the cash for an upgraded GM PCM, you can have a lot more for the same money with the aftermarkets. If you want +20 HP, you can have that with the simpler stuff. Search the posts and spend however fast you want to go.

[Aryeh Levy]

I thought the 3500 HD chassis cabs didn't have a tuna can on em...

All 3500 6.5s with factory programming have 190 hp?????
there's no stock program that's got otherwise?

That's sad...

a #9 Stanadyne resistor probably will give me what i'm looking for, i've got one... but i was wondering if the trucks had more fuel at low end and more boost...

also
do the custom pcm's have custom boost levels and TC lockup points set as you direct? I'd like my TC to lockup around 1500 in 3 and 4.

I'll probably go with propane injection and a turbo master instead if i want the extra horsies - I'm not looking for anything special out of the engine, but i'd like a little moe mpg and a little more power - propane does that right? i'm thinking of fogging the air intake post air filter with low propane psi - maybe 1-3 psi - not enough for real amounts of knock...

[JohnC]

There are only 2 Diesel engine options for pickups, L56 and L65. Each has its own unique engine management programming. Look at the 8th position in your VIN number. It will be "F" which means you have the L65. (Also look at the option list in the glovebox for "L65".) L56 was only on chassis below 8600 lbs GVW and is indicated by an "S" in the 8th position.

[rjschoolcraft]

96 and earlier L65 models had 190 hp and 385 lb-ft at the crank. Somewhere mid 96 or 97, the rating went to 195 hp and 430 lb-ft. The 215 hp, 430 lb-ft rating never made it to production.

The after market programs do all sorts of things. Yours requires an ecm reflash, but the 94 and 95's have a removeable prom. The Electronic Power Project (http://www.thedieselpage.com/members/features/schoolcraft.htm) article shows what one aftermarket chip can do. About mid-way through that article, you'll find dyno charts and tabulated data.

Propane will increase power and mpg, but you have to figure the cost of the propane in your mileage calculations. Propane kits are much more expensive than computer programs. Furthermore, no power mods are recommended unless you have boost and egt gages.

An intercooler is an absolute must for significant power increase.

[Aryeh Levy]

http://www.rv.net/forums/index.cfm/fuseaction/thread/CFB/1/Tid/198668/DoOnePage/es.cfm

Should run under $300

[Aryeh Levy]

Alright,

I was driving around and around 40-50 mpg, there was a small drop in rpm ~100-200 or so...

Soooo TC locks up.

Guess from what I'm hearing, my 12MPG is average/fine for this truck. Can't think of anything that doesn't work well. Only mods less than $200/1mpg will be worth it to me...

Thinking that the propane system at light flow (regulated .5-1.5 psi) should boost ecomony ~1-2mpg w/o increasing power too much.

Also looking to increase boost level to 8psi mechanical turbo-master - plug vacuum pump line. should decrease pumping losses +~1/2Mpg?

Fiberglass/hard tonneau cover ~1-2mpg?

[moondoggie]

Good Day!

To figure out when a modification will pay for itself, put this in your spreadsheet program (do NOT input the quotes

[Aryeh Levy]

I think the figure i heard was $1000 for 1 mpg is a 120,000 mile payback
I'm just really interested in range more than anything...

[Govt issue]

Would the Timing chain being worn retard the cam timing enough to push the peek Tq up a few hundred rpm . Then the engine would get the same gas milliage a 75 as it would at 60. If the cam produced peek tq at 1800 then anything over that will be wasted fuel. May be some one needs to take a problem truck and chart the difference.
Maybe we need to change the timing chain every 80000 Miles. Or switch to gears. Any thoughts.

[DA BIG ONE]

Originally posted by Govt issue:
Would the Timing chain being worn retard the cam timing enough to push the peek Tq up a few hundred rpm . Then the engine would get the same gas milliage a 75 as it would at 60. If the cam produced peek tq at 1800 then anything over that will be wasted fuel. May be some one needs to take a problem truck and chart the difference.
Maybe we need to change the timing chain every 80000 Miles. Or switch to gears. Any thoughts. Gears make more sense, my next project w/waterpump!

[moondoggie]

Good Day!

[i]

[Aryeh Levy]

Timing chain: I've got the 1998, i thought the timing chain didn't need adjustment due to the electronic PCM and Injection Pump...

DO i need to adjust something for peak torque?
Also
i just heard that the 1998 had a MAF sensor instead of the previous MAP sensor.

So is the consensus that purely b/c of weight of 3500 and duallies i get low mpg?

also, I'm thinking of swapping in a cummins 4bt when this motor poops if it ever does. Anybody got a good write up of that? I want to be prepared for it if it happens, i know it wouldn't be easy, so i'd want to be able to spring on the necessary stuff...

I've got a k&n, and my friend said the K&N oil clogs up MAF sensors, but not MAF sensors...

What's up? Anybody know well the specs for 1998?

Also What's the max boost until the computer gets angry, using turbo master?

And how $ and where can i get an electronic boost fooler that uses the stock system to get boost upwards of that limit w/o angering the pcm?


I'd expect oil to be ~$100-$200/barrel within 10 years worst case scenario "IF AND ONLY IF MAXIMUM OUTPUT IS ALREADY REACHED" (I don't want to start a thread bout' oil arguments, so thats the premise) b/c of china's massive increases in demand, and worldwide maximum output, combined with the water injection the middle east does, which increases production, but results in rapid declines to zero when easily available oil is used.

So i'd say $5-10/gallon diesel within 10 years is possible, unless some other cheap source of oil can be found: biodiesel will rise in price accordingly due to supply/demand.

Therefore, small mpg increases could save $... but i dunno, all i know is the max oil output / year as far as i heard was in 2000

[Aryeh Levy]

Also, does the Gear vendors Aux transmission tell your VSSB the final gearing? You're basically swapping in and out of different effective gear ratios without telling the odometer that you're doing so. You could test it by always putting your gear vendors in OD and gearing your VSSB to the right ratio, 3.08 you say, and then running 2 or three tanks of diesel to the overflow tube (to be precise, diesel's real foamy you know), then calcularing MPG. Unless the Gear vendors does the gear stepping before the transmission (output shaft ??) speed sensor, this would be necessary to determine real MPG gains.

If you did that and found the gains purported for apx. 3.08 gearing, then i'd be on board for one of those... especially if i end up with a cummins 12 valve4bt in my chevy when my 6.5 blows up... Get like 20-30 mpg i'd hope with that combo

[DA BIG ONE]

3.08's & mpg?

I went from 4.10's by changing out ring & pinion frt/back to 3.42's using stock sized tires, cost about $1,600. dollars US. Drives good, hardly notice gear change because of power mods. 65 mph seems to be sweet spot for best mpg at close to average highway speeds. However, just over 55mph at lower rpms gives much better mpg gains, providing you are on flat roads, throw in hills and any would be gains become losses!

Installing 33" tires to above will bring overall ratio to 3.09 allowing higher speeds @ that magic 1,800 rpms, but a question comes to mind.

Since I have done all the performance mods the engine output has changed, so the 1,800 rpm window may verywell be 1,600 rpms, or 2,000 rpms, maybe higher, or? This rpm data is not published by those selling the aftermarket mods, just a ball park figure of hp/tq gains to expect.

So, some pulls on a good dyno would be in order to see where hp/tq changes end up in rpm window! It would be nice to see if anyone has done such research already, and if they could share it with us?

[moondoggie]

Good Day!

From VERY limited-capacity memory, the VSSB on my 95 pickup has speed one sensor input, which comes from the output shaft on transfer case, which is behind the tranny. After installing my GV, there is an additional output shaft sensor which goes into the GV. This provides the input to a 2nd VSSB that comes with the GV; it

[Aryeh Levy]

I just got my Stanadyne fuel filter from Diesel Injection Group http://www.dieselpage.com/
$20 after shipping.

Tried to remove old filter.

Ow.

Used a rock and a screwdriver to tangentally apply force to one side of that black nut.

Got it going.

Old filter:

Tar Black.

Eww.

On the bonus, i bought this truck in february:

Went to dealership, said that IP was replaced in november.

They must've replaced the filter then...
right?


Guys Replace your Fuel Filters Regularly. I've heard 10,000 miles isn't too soon.

[rjschoolcraft]

Originally posted by DA BIG ONE:
Since I have done all the performance mods the engine output has changed, so the 1,800 rpm window may verywell be 1,600 rpms, or 2,000 rpms, maybe higher, or? This rpm data is not published by those selling the aftermarket mods, just a ball park figure of hp/tq gains to expect.

So, some pulls on a good dyno would be in order to see where hp/tq changes end up in rpm window! It would be nice to see if anyone has done such research already, and if they could share it with us? Look here (http://www.thedieselpage.com/members/features/schoolcraft.htm) or here (http://www.schoolcraftpowertrain.com/index_files/Page414.htm). The torque peak for the engine as tested in June of 2004 was about 2000 rpm. However, as shown in the data, the modded torque curve is very flat and holds near the peak till about 2700 rpm...