Engine/Transmission (1994 - 1998) fuel consumption whoes....

[Rawbrown]

Yes, this is my first post in 2 years of membership. I like to exhaust the search features of this forum to the best of my ability.
so here is my story...
96' 12v, 4x4 extracab, longbed. 47re rebuilt by me. previous owner took it to banks and had them build it up with the powerpack setup. He was happy, I wasn't... found the afc arm diving under the fuel plate. That fixed alot of problems and triggered the demis of the transmission. Its also running an amsoil bypass filtration setup.
So when I first got it, it wasn't uncommon for me to achieve 600 miles to a tank. then things slowly began to go downhill from there.
things I have done. Timing was the latest thing I had done last week with no significant improvement. Air filters, fuel filters... fuel screen... overflow valve... dropped the tank and cleaned it out... replaced some of the fuel lines.

I see no leaks on the ground from fuel. It doesn't matter if I run petroleum diesel, BioDiesel, WVO or a blend of any of them.
More importantly, the truck runs great. it fuels thru 3000rpm pleanty hard, on cold mornings here in Socal below 40, it starts right up as in less than a second, so that eliminates an airleak in the fuel lines. It does smoke a little for a minute or so but I think thats only because right now I am running 50/50 petrol/WVO.
Off the line foot to the floor I get about 2 seconds of turbo lag or about that much time of smoke out the pipe, then it cleans up and hauls axle.
I'd be alot quicker to change the lift pump if fuel delivery felt like a problem but if I leave the TC unlocked and stand on the stupid pedal from a stop, my egt's will hit 1250 with 32psi of boost. I do notice that I used be able to get 34 psi of boost.
I find no leaks from the turbo to the intercooler to the intake.
what else can I check. 10-11 mpg sux balls.

Ryan Brown
Rawbrown - Offroad drivetrain, suspension and protection
760-505-9924

 

[EKlem]

It sounds like you have gone through the obvious stuff.

Have you done any changes to tires, suspension or anything else which might affect windage(racks etc)? The biggest factor in highway mileage is wind resistance.

Have you been driving differently? The driver makes a big difference. You don't say whether 10-11mpg is in city traffic or on highways or how you use your truck. If you drive in bad city traffic, that is about right but it is definitely low for the highway.

If you care convinced that it is an engine problem and not a driveline problem, then you need to get more information by putting some gauges in if you don't have them. You will need egt, boost, and fuel pressure gauges.

Since you are running unheated(that is correct right?) wvo, that can lead to some problems which could cause lower mileage. You could have coked injectors, you could have enlarged your injector holes, or you could have gummed something up in your pump. Gauges would help a lot with the diagnosis if it indeed a fuel related issue.

 

[MMcCallie]

Looks like you do already have a pyrometer and boost gauge. Fuel pressure gauge would let you know if it is low. You didn't describe any problems of hesitations or any other engine health issues. EKlem's suggestion is good, you might have your injectors pop tested. Are they stock and how many miles are on them? Maybe you can find someone who'd let you try a different set, or maybe go ahead and invest in some DDP Stage IIs for better mileage.

As you probably know, biofuels can have some negative tendencies, including increased NOx production. You also take a chance with you fuel pump and injectors. I used to run 100% soy bean oil when I lived near enough a dealer in Colorado. To solve the problem of NOx, and to keep my engine cleaner, I use water/methanol injection. I also have an electric fuel heater that wraps around my fuel filter and have needed it even for #2. But you're not seeing near the cold my truck has been through like -42 F wind chill -56 F.

If you haven't tried any additives, definitely try Power Service and I've been running Red Line recently as well. My truck gets about 10 mpg when all of my driving is short trips under 5 miles and 5 minutes a few times a day, stop and go under 30 mph, in the snow, and my truck weighs 10,000 lbs.

Have you tried any other types of air intakes? Have you checked your turbo for shaft play? Did that Banks kit include any exhaust modifications? Have you checked to see if you have a catalytic converter that is plugged or a muffler that is causing restriction? Any brakes that need servicing? You didn't mention whether your truck is 2x4 or 4x4. Also with your transmission, is it possibly your torque converter is locked but clutches are slipping?

 

[BDaugherty]

From what you described, look at the injectors first. Either have then rebuilt to stock or take advantage of this opportunity to add some DDP nozzles.

 

[Rawbrown]

ok a little more. I wasn't to worried about the FP because there is no hesitations and it fuels hard through 3000rpms if I let it. I do believe that there is a fuel heater just above the fuel screen? Its not cold enough to warrent that. even on the coldest mornings with straight BioD the truck would start right up with no problems. I'm not running straight WVO but its blended 50/50 with petrol D. Fuel choice has no impact. I did run a BHAF for a short time but performance suffered and I went back to the K&N that I've been running before that.
Cat has been opened up and it has Banks exhaust. As well as us gear exh brake. turbo is good and tight. I did find that my (gag... ) EGR had a bad diaphram which fixed a vacuum problem. I did turn the star wheel a bit tighter to see what it did. And I spent some time today going through a bunch of the lines and stuff.
I do have a pretty respectable 3. 5" of grey matter stuffed between my ears so keep that in mind. I have a clue.
It doesn't matter if its city or highway. My commute to work as a tow truck driver is about 10 miles up the freeway. my house is a mile from the freeway and work is 1/4 mile from it. doesn't matter if I baby it or drive it hard. It still sucks. There are no signs of anything leaking around the engine out of the ordinary.
I do see one suggestion for the injectors. That might be the way to go.
could I simply pop an injector out and do a visual. or is it better to pull them all and send them in for a rebuild.
While yes, I am a tow truck driver and my job is recession proof (I'm a rotation driver for the local sherriff, PD, CHP, Border patrol and we handle all the evidence tows for the CHP... So as long as there are DUI's and accidents going on, I'm getting paid)...
I just don't have the kind of money to throw and a set of DDP. I'll be looking for someones good used. would probably be an improvement over what I have now.

 

[hsmith]

Did not see if you mentioned mileage on your truck and if it still is the stock injectors. I have DDP's in mine and am satisfied. Have a set of PDR 215's I removed with real low mileage I will make you a deal on if you are interested. Just don't know if that will solve your problem though.

 

[Rawbrown]

sorry,
120k... dismal, I know...

 

[Missouri Mule]

Could someone be stealing your fuel? A locking fuell cap will deter some people of doing it. ( Of course there are ways to open the locking fuel cap but then you will know for sure. )

 

[Rawbrown]

I have a private driveway with video surveilance on it... But since I work nights as a tow truck driver. I lock my truck in the towyard... plus, I have a bed setup in the back of my truck in which I sleep half the night in.
plus I can watch the needle go down as a driver literally...

 

[hsmith]

That's pretty low mileage for our year models. Injectors should not be the problem, but I'm no expert. My mileage towing is around 12 and empty around town 18.
I have no suggestions except good luck. There has to be an answer.

 

[EKlem]

Rawbrown,

What is your cruising EGT and boost at 65mph on the highway?

Unless I missed, you also didn't say whether you had a lift or different tires, those make a huge difference.

There are many opinions on what running any percentage of unheated wvo will do to you but if your problem is engine related, I suspect that it could well be related to this. Even mixed 50/50 with diesel or kerosene, it puts a lot more wear on your fuel system components unless it is heated. It also has the tendency to settle out it your fuel tank so the percentage getting to the engine is not the same.

It sounds like you are going to need to do some more testing. Fuel pressure is where I would start, then move to stuff like sending out your injectors to be pop tested. Good luck.

 

[Rawbrown]

265-75-16 with a camper shell. I've had those tires for the past year and have watched my economy drop since I put those tires on.
I can cruise down the hwy at 65 on flat ground 600º egt at about 4-5 psi of boost.

 

[EKlem]

If the camper has a lot of windage, that would be a large factor in mileage but you should have seen a drop once and then it shouldn't change. Your boost and egt numbers sound pretty good and hint that you don't have a problem like bad brake drag. Somehow, you are either loosing the fuel or pushing it very inefficiently through your engine without getting things hot. My own guess is that a review of your fuel system is in order.

 

[Rawbrown]

no difference with or without the camper shell...
I'm leaning torwards the injectors.

 

[San Felipe Bob]

Fuel pressure

I say check your fuel pressure closely.

You need alot of pressure to properly atomize the fuel at part throttle / low rpms.

WFO will just dump the fuel in. So it's probably not a good gauge?

That's why we get terrible milage with big 370 injectors if we are always "in" the throttle.

When is the last time you cleaned the fuel filter and heater screen and checked the Overflow valve?

I have over 200,000 miles on my 370's.

I still get 14 to 15 mpg So Cal freeway driving. (I don't baby it).

I'm close to 8,500 lbs with my tools and camper.



Let us know what you find.



SFB

 

[Rawbrown]

fuel screen, filter, heater about a month and a half ago. with no improvment.

 

[Missouri Mule]

Going from a 245 to 265 (taller) with out changing the speedo gear will cause a small difference in mileage/speed.



What type of tires are you running: Highway, Offroad... ?

 

[PRohr]

If you changed tire size then the odometer is going to be off and your numbers won't be right.

 

[JoeMartin]

Here's a quick suggestion, i've got a 94 12V that I love to death that went thru this metmorphasis about 2 months ago, It seemed like someone drilled a hole in the fuel tank, anyways try this on for size and see if it helps. After talking to someone who races these things and has one that he tows a trailer with and still gets 24mpg i listened to what he had to say. I started running 2qts used motor oil ( yea the stuff you drain out of that very same truck your driving) to a tank of fuel, I know it sounds a little crazy but I'll tell you it really does work, My mileage is right back up and the truck runs fine and even starts with no heater @-10 degrees. What was explained to me is the oil raises the btu or burn rate of the fuel which in turn raises the cyl temp . . I'm no rocket scientist but I can tell you what it did for me. .



joe.

 

[LVJUNIOR]

rawbrown,

did you ever get anywhere with your fuel mileage problems?