proudpapa97

Hello Everyone,
I was just wondering if anyone else is noticing a very large drop in their gas mileage with the ultra low sulfer diesel? I recently filled up, and averaged 12.54 MPG around town with a 2WD regular cab, stock, and driven very easy.

Over the last 6 months or so, I have noticed about 14-16 MPG around town, and a bit better on the highway. Any ideas?? or is this common with the ultra low sulfer diesel? My truck is well maintained etc. I am pretty disappointed at this point as now, I am not getting to much better mileage than a gas motor.
Thanks,
97 3/4 ton Standard Cab, all stock 207K miles

mwlu711

use diesel instead of gas.

Tate

Hows the smoke and power with it? Have you looked at your timing?

96_12V

At most - 1mpg drop, but that's been since june of 1996 when Illinois and Wisconsin first started getting ulsd. I average 18.5+, keep track of every tank, but have a 5-speed regular cab, otherwise nearly the same rig as yours. I also have stock tires - have you installed taller tires? They will affect speedo reading & indicated mileage as well.

patdaly

Check your fuel pressure.

I saw a huge drop just before winter hit and now have the ticking pump syndrome.

Too cold for me to mess with it right now, but I am pretty sure that is where my mileage went.

I went from a consistent 15-17 in town to 12-13.

chariotdriver

What is the ticking pump syndrome. How fast/frequency of the ticks? thanks

kawi600

Keep an eye on your fuel pressure, even with the older mechanical pumped 12v's. It should be something like 25psi or higher at idle and 30-35psi at 2k rpm no load (I -think-). You can get the plumbing to install a fuel pressure gauge from vulcan performance.
Once you can measure pressure, check to see if you have air leaks or a tired pump. could be as simple as a bad relief valve on the back of the pump.
If the injector pump or injectors are going bad you might want to listen for a loping idle or look for excessive soot in the exhaust and oil. Poor combustion from poor fuel atomization can make a lot of soot that gets washed into the oil.
Im doing my pump and injectors soon Ill make a post if this does what Im hoping it will. Right now im seeing 13mpg with a modded pump and stock injectors. the oil turns black and thick like paint almost immediately even if Im easy on the throttle. I run a bypass filter too.. you should see what that comes out looking like. Ugh!

Dartmouth 12V

There are some people that are reporting worse mileage with ULSD but it really doesn't seem to be making a considerable difference. There are several factors that can contribute to burning more fuel.

Increased rolling resistance- Have you changed tires to a more aggressive or wider tread? Also, going to larger diameter tires will really hurt your mileage in town and can go either way on the highway depending on the size. Are any of your bearings bad? Are your brakes dragging? The quick and dirty way to check brakes and bearings is to put your hand on the hub after a driving for a while and see whether it is hot. If one or more hubs are much warmer, something is wrong.

Windage- It is pretty rare for people to change this unless they put a lift or different size tires on.

Drivetrain efficiency- Your engine or transmission may not be working right. The common problems with the engine is fuel delivery. If you have an air leak or your timing is off, your mileage will go down. If you have an auto tranny that is slipping, that will cost you some mileage.

You- Driving style is real important. Accelerating hard is not an efficient way of driving. Also, on the highway the slower you go, the better mileage you get. A lot of people complain about mileage but they still drive 80mph. The resistance is proportional to the square of your velocity so slowing down makes a ton of difference.

BigErksG2

do you smell a fuel leak anywhere? check the fuel return line if you do... very common.

xzaq103

ticking pump syndrome? Please explain what this is. Every now and then I hear a ticking sound coming from the lift pump area. But I also heard it on my 97.

Chirs

patdaly

Ticking pump syndrome is exactly what it says, the lift pump ticks. Supposedly it is because the return spring breaks and the follower doesn't follow the cam fully anymore.

I need to get mine changed, but it has been too bloody cold for me to mess with it, and I also want to get my fuel pressure gauge in to make sure that is it.

Mine is most noticeable when it is colder out.

xzaq103

Same here the colder it is the louder the tick How do you fix it wand why is it bad? Low fuel pressure?

Chris

proudpapa97

Thank You all for the response. The truck is totally stock, the tires are the ones that I have been running all along, I have changed the fuel filter regularly in the 25K miles that I have had the truck.

I definately hear a ticking in my lifter or injector pump but, I have heard that all along as well.

My driving style is REALLY easy on the truck, when I am on the highway I rarely take it above 70, and in the city I drive it super easy.

I do notice some soot build up on the side of the truck and the bumper but, I don't really wash it all that much to be honest.

I am hoping that it is nothing to big or pricey to deal with!! My tranny could be sliping I think as it seems to be searching for a point to shift under easy acceloration.

It is good to see that other people aren't seeing much of a drop with the new ULSD, that gives me some encouragement that I can get it all dialed back in.

My bigges problem is that I don't know how to work on it so when I take it into the shop I am at their mercy and it usually is quite pricey.

Thanks again for all of your guys help.
Regards,
Steve

patdaly

The problem is it could be either the overflow valve or the lift pump. Both are either worn out return springs or broken return springs.

It causes low fuel pressure, and once you have a fuel pressure gauge, you can crimp off the return line to see if the fuel pressure jumps, if it does, the pump is fine, and the overflow valve is the likely culprit. This all assumes you have a known good filter and pre-filter.

patdaly

Steve, even though you don't know much about the trucks, you should get a factory service manual, perhaps join a DTR chapter near you, and ask questions right here, there is more combined Cummins know how here than you could find in all the diesel shops in Arizona........

I have not had much luck with trusting my truck to the shops....... They seem to want to replace a bunch of expensive stuff to see if it fixes it.

So, get your FSM, ask the questions, and dive in man, the waters just fine.