Dropping MPG - Diesel Forum

ford_x_3 · 04-12-2003, 08:43 AM

MPG's seem to be dropping with every new tank full.I haven't changed
a thing in my driving characteristics.I never get into the pedal at all.Takes me a good mile to get to highway speed.
I'm down to 13.2 now in mixed driving but mostly highway at 60-65mph.I drive total of 45 miles a day back and forth to work of which probably 7-8 of them are local rest is highway.
Don't know enough about diesels to know if it doesn't sound right but it seems like it's making more noise than it used to.
I haven't done any of the fuel mods.
Any advise?Anybody know a dealer in Northern Jersey that really knows these diesels?The local dealer by me only has one guy and they really don't sell a whole lot of trucks.

jjtproperty · 04-12-2003, 08:57 AM

Are you checking it by hand or using your overhead console. When new with no mods 13-14 MPG is all mine would register on the overhead console. Never checked it by hand.

ford_x_3 · 04-12-2003, 05:23 PM

Doing it both ways.Believe it or not my overhead seems to be pretty accurate. [img]/ubbthreads/images/graemlins/shocked.gif[/img]
Just tanked up again and reset overhead.Got on highway and topped out at 65mph and the overhead reads 16-17mpg and she runs much quieter.
How far down the tank does the intank mod actually take its effect?Anybody know?I've purposefully been filling the tank at the halfway point hoping this would get me out of dropping the tank.If it's only a quarter way down I might as well drop the thing I guess.

CHPMustang · 04-12-2003, 06:25 PM

Steve,sounds like you could open up the intake and exhaust,that should get your mileage up some.

Doing the in-tank I'd try and get it down as much as possible(quarter or less)

I had a quarter tank so I brought a few clean 5 gallon buckets to pump out the tank dry,that helped tremendously on dropping and handling the tank.

BILL

dmftoy1 · 04-12-2003, 07:36 PM

The intank mod shouldn't really give you much of an improvement unless you're less than 1/2 tank. Most of the estimates I've seen say that it's around 1/4 tank that the mixing chamber "duck bill" valve (is that the right term?) can leak air.

How many miles do you have on your X? If your near 10k and haven't done it already I'd try changing the air and fuel filters. I'd also do the pre-pump mod if you haven't already.

Just my .02

Regards,
Dave

ford_x_3 · 04-13-2003, 08:25 AM

I've got 7,500 miles now.Changed out the air filter last week was figuring on doing the fuel filter at 10k but think you're right might as well do it now 'specially since the air filter was as dirty as it was.
There must be something else besides the quick connect lines and the in-tank mod with the mixing chamber that also causes these problems.Not that I won't do them,I will, but there's got to be something besides unless I'm missing something.
1.) I would think that the quick connect problem should be a constant problem.
2.)If the fix to the pump is that far down in the tank why am I hearing and seeing such a radical change between full and half full?
Is anything done besides the mixing chamber when you do the intank mod that is higher up in the tank that could be the cause of this?
Sorry 'bout questioning this,guess it's the diagnostician in me trying to get a better idea of what the problem is.

CHP,I do plan on a more open air flow but first want to get the bugs out.

dmftoy1 · 04-14-2003, 07:12 AM

Well I can only answer on the quick connect part. If you take them off you will see how easily they could leak air. I was amazed at how "unpositive" the lock seemed to me. I think it probably varies by truck though. You might try PM'ing Shamuex2000, I think he's done the tank mod on his X, or at least had it apart to examine it in detail. I've removed the QC on my tank also, but I didn't do the tank mod as there were no good kits when I dropped my tank. If I ever drop it again I will probably do it.

Regards,
Dave

shamuex2000 · 04-14-2003, 08:53 AM

ford_X_3, after reading your first post, I was thinking that you might have an injector going bad given the noise and mpg loss. Since the re-fuel made it run better/quieter, you might have either gotten bad fuel, or you just happen to be getting non-winterized fuel and warm weather while in the middle of your trouble diagnosis. With regard to the "duck bill" in the fuel pick up, I believe the duck bill is the outlet for the fuel return to the tank.(someone correct me if I'm wrong) The auxiliary fuel pick-up is a poppet type valve on the side of the pick-up, which opens by suction inside the pick-up assembly in the event that the strainer gets restricted. If this valve is leaking, then it will bleed air into the pick-up. The manual states that the tank must be above 1/4 in order for this auxiliary valve to be able to draw fuel in the event that the strainer gets restricted. But, I know that the tank of my EX doesn't have any internal baffles, so given fuel slosh, it could probably still bleed air unless the tank is over 1/2 full. With colder weather, my ex seems to run a little quieter when the fuel level is lower, which I believe is due to the heated fuel return from the engine having a better chance to heat the fuel in the tank. Do you have any other symptoms?

ford_x_3 · 04-14-2003, 11:55 AM

I don't think it's a bad tankfull because it's been like this for more than the last 4 tankfulls that I've been trying to pay closer attention to.
Not sure about the blend I'm getting even though it still states on the pump winterized.I've even tried fuel from 3 different stations.No change.

shamuex2000 · 04-14-2003, 04:23 PM

Winterized fuel will cause a drop in MPG since it has lower BTU value.
How old is your fuel filter? How's your engine oil? Oil foaming problems could also cause this, but it wouldn't depend on the fuel tank level. After a highway-speed run, check your dipstick for bubbles/oil foam. This is probably one of the first things the dealer might ask about and test for. Otherwise, is the idle smooth? Dale

ford_x_3 · 04-15-2003, 10:01 AM

Idle seems smooth,will change fuel filter this weekend(7,500 miles on truck,still original)3 oil changes so far with Rotella and doesn't seem to have lost much at all between 2nd and 3rd change.Drained water seperator 2 weeks ago,no water.Replaced air filter week and a half ago.
Have now put on 130 miles since refilling Sat.Gauge is hovering just over 3/4 full.Overhead is saying I'm down to 15.2-.4 now from the 16.3-16.7 I was getting when it was full and starting to get noisy again on acceleration.
Will check foaming tonight on my way home.

ford_x_3 · 04-16-2003, 10:38 AM

No foam.

dmftoy1 · 04-16-2003, 10:43 AM

what's your tire inflation? Is it possible that someone "de-flated" your tires at an oil change?

shamuex2000 · 04-17-2003, 08:40 AM

Still might be an injector, but with these limited symptoms the dealer might not be able to find anything wrong using the contribution test. Some injectors suffer from internal galling when they fail. You might want to try using a fuel lubricity additive and see if that makes a difference. There's even a possibility of an issue with your thermostat causing your engine to run cooler which will also drop the mpg.

BadAndy · 04-21-2003, 02:04 PM

I've been watching this thread closely. I just turned 10,000 on the odom. I have exactly the same symptoms. My mileage has been dropping constantly since early December. I was getting mid 12s at best around town and lately not even able to break out of the 13s on the highway. Before I was getting almost 19 on the highway and 16 and some change around town. All numbers were calculated by hand and matched the computer exactly!

I took a small trip last Thursday and filled up while I was out of town. My mileage JUMPED to 17.5 on the highway and 16 around town. I'm talking immediately! Winter fuel? Does it have that much of an impact? Or did something finally give way?

Weird!

-Andy