I have not gotten what I would call good fuel economy ever since I replaced the head gasket in my 01.5. I spent a long time tightening up injector lines at the VP and the head after first completing the gasket replacement.

I don't see any fuel leaks to mention, but the smell of diesel is really strong, and worst of all, on a recent trip to and from Florida I got a best mpg of 17.3 mpg, which is not good at all considering the truck has 3.54 gears. I got a worst mpg of 15.9 when I was "hauling" to make time coming back.

I have seen other people mention that o-rings in the crossover tubes might be able to cause hard starting and heavy fuel smell if they are leaking.

My Cummins gasket set had these o-rings, but I didn't switch them out with the old ones.

The truck has around 201900 miles, and runs good otherwise. I am going to soon clean the IAT as some have recommended in an effort to help my fuel mileage, but I don't think I should be smelling diesel as much as I am, and I have a strong hunch there is still a leak somewhere.

Am I onto something here, or should I be looking at another problem(s)?

Thanks in advance,

Ted

 

Wash the engine to get rid of any residual fuel. With the head clean and dry, it will be easier to see fuel leaking from the lines. The o-rings on the connector tubes could leak, but you will see fuel coming out of the head connection. I wouldn't go replacing them if there isn't a leak there. Make sure to check the return line connection at the back of the head. Also check the connections in the low pressure system. You should see puddles under the truck if you are losing that much mileage and its due to a fuel leak.

 

Tate, thanks. From what you said about puddling fuel, I see something on the bottom of the engine and spots on the ground under the engine, but it is really filthy and it's hard to tell what is oil, residual coolant (replaced water pump a while back), or diesel fuel. I will clean the engine up and then check again.

It really troubles me that the mileage is like it is, especially since I now find myself commuting about 180 miles/day every other week and I am stopping at the pump more than I would like. I could have sworn that I once measured the mileage at around 20mpg. This was right after I bought the truck with around 173,000 miles on it.


As I mentioned in the original post, I just cracked 200,000 not too long back, and it seems like I have steadily been working through all the maintenance items that seem to coincide with multiples of 100k miles. I have replaced the head gasket, both batteries, and the water pump. The starter contacts need replaced and so does the in-tank fuel level sender. In fact the sender may be adding to my perception of poor fuel mileage since the fuel gauge will often read under what is actually in the tank, and periodically the level will drop to zero and the low-fuel light will come on even though I know there is plenty of diesel in the tank.

Still, the actual highway numbers (avg 17.6, low 15.5) don't seem right to me. I use the fill till it runs up the tank nozzle, drive, refill method, and I think this is pretty accurate. I wish I had the computer mileage readout like some trucks do.

I'll post back with the results of cleaning the thing up, and maybe also update with the results of my IAT cleaning.


Ted

 

Kinda odd, I didn't lose any fuel mileage when I replaced mine with a regular Cummins replacement gasket.

 

what about the return line connection on the back of the head. it could be leaking as well.

 

Thanks guys. I think I found the problem. I had bright sunlight this morning, for the first time in a while, and I saw a large leak at the #4 cylinder head injector line.

The top of the block is wet all the way behind this, and as the diesel fuel is running front to back on the engine from the #4 line while I'm moving, I can't tell if #5 and #6 are leaking or if it's all from #4.

I do believe there is enough of a leak to where it is messing with my mileage, and so I need to get it to stop.

I guess I am back to my other thought about the crossover tube seals. I have these still in the Cummins gasket set box. I hate to have to ask, but how easy/difficult is it to install these? I know I may need to remove the crossover tubes. Any advice would be much appreciated!

Thanks again,

Ted