Help! Sudden extreme fuel consumption

[Blue Rebel]

Hey guys, this problem is on my 93 F350 7.3 N/A. Ive been getting poor (14-15mpg) fuel economy since last fall, but i attributed that to winter blend fuel. But now this last fill up ive only put on 64 miles, and ive used over 1/2 a tank of fuel!!! There are no leaks on the ground, the oil level has not risen, its not bypassing to the other tank, and its not smoking excessively. ***?!?!? Anybody have any ideas where i could look next? At this rate im gonna have to start driving my 89 f250 every day, cuz the 7mpg it gets is better than this!!!

 

[truckermark]

Hey guys, this problem is on my 93 F350 7.3 N/A. Ive been getting poor (14-15mpg) fuel economy since last fall, but i attributed that to winter blend fuel. But now this last fill up ive only put on 64 miles, and ive used over 1/2 a tank of fuel!!! There are no leaks on the ground, the oil level has not risen, its not bypassing to the other tank, and its not smoking excessively. ***?!?!? Anybody have any ideas where i could look next? At this rate im gonna have to start driving my 89 f250 every day, cuz the 7mpg it gets is better than this!!!

Some helpful hints would be idle. how does it idle rough or smooth. and when you put load on it what type of smoke is there. And is start up differant then when it warms up? also check your air intake and what exuast are you running?

 

[Blue Rebel]

It idles the same as it always has, sitting here listening to it seems to be fairly smooth. I dont have a tach so i cant tell you what rpm tho.
When i load it (full throttle) i do get some smoke out the tailpipe, but not billows.
When cold it does need to crank for roughly 5-10 seconds, when warm starts right up.
As i sit here i am noticing a little bit of blue smoke out the tailpipe as its idling, but i honestly couldnt tell you if thats a new symptom or not.

 

[89Laredo]

Might just be a screwed up sender.

And 14-15 is far from bad mileage, actually pretty decent.

 

[truckermark]

It idles the same as it always has, sitting here listening to it seems to be fairly smooth. I dont have a tach so i cant tell you what rpm tho.
When i load it (full throttle) i do get some smoke out the tailpipe, but not billows.
When cold it does need to crank for roughly 5-10 seconds, when warm starts right up.
As i sit here i am noticing a little bit of blue smoke out the tailpipe as its idling, but i honestly couldnt tell you if thats a new symptom or not.

what type of smoke come out the tailpipe at full load? ad as for the blue smoke. are you putting any additives in your tank such as wmo or tranny fluid or anything along those lines? if not then it could be worn rings. how many miles are on it? might wana look into a compression test. also hows your air cleaner look. if the cdr valve is failing it may cause excess oil to get in your air cleaner with restricts air there for using more fuel. and the oil running down your intake may cuase blue smoke. if it were me i would remove the air cleaner housing bolt and see if there is oil on it. if there is i would clean my cdr valve and try a new air filter and see if that fixes your problem

 

[Blue Rebel]

Black smoke at full throttle, I dont really load it down much
And i have no idea how many miles are on it. the gauge cluster has been replaced, its out of a gasser. Only hint i have is someone at some time wrote what i believe to be oil change intervals in the door jamb, and the highest number there is 191583. Ive put 10k on it since i bought it, so i believe its got at least 200k on it.
Would an air restriction cause this poor of fuel economy? I wouldnt think that was possible

 

[truckermark]

Yes..in fact it is right in the boook..i just double checked..and a resticted air supply will cuase ecesseive unburnt fuel (a.k.a) poor fuel mpg's. Like i said check your air cleaner..and if it is full of oil check and clean your cdr.. the easy way to see if your cdr is bad is remove the air cleaner lid bolt and look at the bottom for oil

 

[Blue Rebel]

I wish i had the book lol Ill check the CDR tomorrow, replace the fuel filter and air filter also, Its been about 10k since the last time they were changed

 

[fuzzy1626]

Do you have dual tanks? If so, make sure your not sending fuel from the return system back to the other tank instead of the tank your pulling from.

 

[Blue Rebel]

Yup already checked that, good there.

 

[truckermark]

to mee its sounding more and more like a clogged air filter maybe cuased bu the cdr. check thoise please and lets us know. thanks! best of luck and god bless

 

[Blue Rebel]

Yup, intake is all sorts of oily, cdr def is not doing its job. I removed it, and its soaking in parts solvent right now. Ive got a new air filter on order, that wont be in until the end of the week. Picked up a new fuel filter as well, i think im just gonna siphon out the rest of this fuel, and refill from a known good station.

In other news, just for chits and giggles i started it up w/ no air cleaner or CDR on it, and just sitting in the shop i can tell the trucks breathing better. BUT now its also constantly smoking grey....

 

[truckermark]

Yup, intake is all sorts of oily, cdr def is not doing its job. I removed it, and its soaking in parts solvent right now. Ive got a new air filter on order, that wont be in until the end of the week. Picked up a new fuel filter as well, i think im just gonna siphon out the rest of this fuel, and refill from a known good station.

In other news, just for chits and giggles i started it up w/ no air cleaner or CDR on it, and just sitting in the shop i can tell the trucks breathing better. BUT now its also constantly smoking grey....

hmmm. the grey smoke could be from disturbed crankcase pressure with no cdr. i geuss the only way to tell is to put the cdr on and new aircleaner and give her a try! best of luck and god bles. please post your results.

 

[mjs2011]

I'm not an expert here, but I do know that a cdr has a diaphragm in it. Parts cleaner is probably not a good thing for the cdr. You may want to look into a new one.

 

[Black dawg]

if the cdr is hooked up, these engines will always have oil in the intake.

What mpg is it getting now? The suggestion on fuel being returned to the other tank is a good one, how did you prove this was not the case.