M1009 Getting bad gas mileage

[rickyman32]

Hello everyone,

I have a 1984 M1009. It has been running great, but now it's not doing so good. I drove it from Houston to Corpus Christi, it's about a 4 hour / 220 mile drive. I filled up the tank and I didn't even make it all the way without having to stop for gas. Also I couldn't even get over 70 MPH and the engine was running at about 220 degrees. I had a full size mattress and a bed spread tied to the top, so I'm hoping that the extra wind resitence is what was causing it to run so bad, but it shouldn't have that much of an affect on a 6.2 diesel.

When I first got the trunk, it had a blow head gasket, I replaced it and then the transmission went. I had ammaco rebuild it. After that the truck ran great. I got about 18Mpg lots of horsepower. Never got hot. I towed a ford ranger from Alabama to Texas with no problem. I think I was getting about 15mpg while towing it which is awesome. I have changed every filter and fluid.

I now live in Corpus Christi and when I drive it around town it runs at 190 degress which sounds about right. I can get it over 70 mph but I'm not sure how long I can. I'm not too sure about the gas milage. I'm going to fill it up and find out what I'm getting. So maybe the extra wind resitence was causing it but I don't think it is. Any ideas of what could be causing this?

 

[2deuce]

Tire pressure?, fuel leak? but if the air was getting up under the mattress thats like dragging an anchor, add a headwind and you may not make 70.

 

[rickyman32]

I'm sure it's not something simple like tire pressure. I'll get back to you on my mpg while driving in the city.

 

[12vctd]

1 or more dirty injector's or possible faulty injectors, injection pump timing off. Are there any new leaks or any fuel leaks? I also agree with 2 duece the matress was probably one heck of a drag.

 

[rickyman32]

No fule leaks. I'll give the injections a good look at. How does the timing on a diesel get off?

 

[12vctd]

The timing gets off by wear on the timing chain and stretch can cause the timing to be off. Also pumps can wear and this can affect the timing.

 

[dilvoy]

Is the back of your truck spotted with unburnt fuel?

 

[ragedracer]

Bumping this thread, cause I have a similar issue.

My M1009 went from ~20mpg to 11.5mpg over the last 3 tanks. Nothing has changed otherwise. I replaced the fuel and air filters and no change.

Any suggestions on where to look next?

 

[Scarecrow1]

Yes the drag created from the mattres could have been the culpret . The drag created is massive .Have you tryed to calculate the milage since , with no drag ???

 

[gillean]

Is the back of your truck spotted with unburnt fuel?

the back of my truck is spotted with unburnt fuel. I'm actually not sure if it's fuel, i always thought it was oil from my tcase leak. now that i think about it though, it goes away after a couple days whereas if it was oil it would probably stick for awhile. I guess I better start looking for my fuel leak