Drop in Fuel Mileage

[53 F100]

Got another one for you all,

On my current vacation trip, I notice my mileage has drop from my normal 25 MPG on the highway to 16. In the past I asked the Dealer about doing a tune up and the usual answer I get is there is nothing to tune up. they say most you can do is change the plugs and they said you do not have to do that often.

I have used fuel injector cleaner at least once a yr and I am good about changing the oil. Do you think changing the plugs will help or is there something else that can be done. I do not want to take in for servicing and have them do all kind of diags to tell me they can not find anything.

Any thought would be appreciated, I am use to working older cars with distributors and points.

TIA

Greg

[LeSabre97mint]

Greg

How many miles on your 99? Do you notice any difference in the way the engine starts? Drives? Accel? Any check engine light? You may be due for O2 sensors.

Post back with what you can answer.


Regards

Dan

[12Ounce]

Make sure the air intake filter and the fuel filter (got me on a vacation trip) are in good shape.

You may be in the early phases of the isolater bolt failure. If you've never done this replacement ... you may be due.

[road_rascal]

25 mpg on the highway?!?! The most I have ever been able to squeeze out of my '01 on 95% highway miles doing 65mph is 20.5 mpg. What's your year/ engine?

[zombie13]

Originally Posted by road_rascal

25 mpg on the highway?!?! The most I have ever been able to squeeze out of my '01 on 95% highway miles doing 65mph is 20.5 mpg. What's your year/ engine?

Wow. I bought my '02 with 95k miles and the following week went on a trip where I got at least 23mpg. All I did to it was get an oil change.

Z.

[53 F100]

I have 95K miles on the van and I have replaced the air filter and ran fuel injector clean in a full tank recently. Most of the mileage on the Van is highway driving. I tend to get between 23 and 25 on the highway depending on the terrain, and in the trip it was all flat so it was a surprise to see 16 MPG.

I have the 3.6L engine with the towing package so I have the engine and trany coolers. Up to this point it has run great. I have notice it does take a little longer to start on cold morning.

Thanks for any help

Greg

[joeuser742]

You should do or have done that TSB for the P171/P174 codes. It sounds like your EGR ports are clogged. Oil gets past the PCV, gets into the intake, and over time clogs the EGR ports. Or another thing that happens is the vaccum hose cracks and get the same codes. If your engine light is not coming on yet, it will soon.

[wiswind]

16MPG is low.
20+ is normal.
Of course if you do much full throttle accelleration, it will kill your fuel economy.

Other things that can cause fuel economy problems in addition to what others have already mentioned would be .....

Dragging brakes (does not take much of a drag) or warped rotor(s), which causes dragging also.

How new are the spark plugs?, and if new, are they the correct ones?

Battery being weak, causing the alternator to spend a lot of time charging, which is a load on the engine.
Beyond 5 years is pushing it for battery life.
The Autozone Duralast has been highly recommended and is pretty cheap.
Also check and clean battery connections.

Does the CEL come on for a few seconds when you start the car?
It should come on, and then go off.
If it does not come on, the lamp could be burned out....and you would not know if there is a code that would cause it to come on.

Check the brake pressure switch on the bottom of the master cylinder.
If it is even slightly damp, replace it.
This is a known high failure item......and one of the things that I read that it does (in addition to shutting down the cruise control) is to prevent the transmission torque converter from "locking up", which certainly would impact fuel economy.

Is the intake manifold runner control (IMRC) system working correctly?
If the runners are stuck open, it could cause lower fuel economy.
I have read about nylon clips breaking, causing the actuators to still work....but not be actually connected to the runners.
My '96 has springs that return the runners to the open position when the actuators are not pulling them closed.
I read on this forum that some of the newer ones do not have the springs.
If yours are not connected to the actuators....as I mentioned, you could temporarily prop them CLOSED, which would give you better fuel economy.
It would reduce your full throttle power, but most of us would not be bothered by this with the price of gasoline so high.
The only time that they are normally open when the engine is running is when the engine is above 2900 RPMs. They open to give you more power.
They are closed below 2900 RPMs to give you better fuel economy
The actuators would still move, and the sensor is part of the actuator, so in theory, the PCM would think that the IMRC is working, and not light up the CEL.

[Headbolt]

Originally Posted by 53 F100

I have the 3.6L engine ........
Greg

Are you sure about the engine size (3.6L)? I thought the 3.8L and 3.0L were the only engines offered. I've got the 3.8L in my '99 and the best I've ever gotten was 20.8 MPG. Usually get in the 15-16 MPG. The 20.8 MPG was achieved when we were out in west Texas and New Mexico last year. Would sure like to see that 25MPG you're talking about.

[garync1]

The first time the fuel mpg dropped I did the isolator bolt fix, went back to 27 mpg
A few weeks ago the mpg droped again. At 93,000 I thought I would go ahead with the spark plug changed. Used autolight double plat.they look just like the motorcraft plat. When I took them out they looked really good ecept the gap was at 67 it needed to be at 52-56 so the had some burn on them. MPG went back up..after the change.

[98er]

Is the engine getting up to temp? If your thermostat is stuck open, she may not go closed loop and will burn rich. I'm guessing that is true on the Windstar as it is on the Taurus.

I had a friend with a 3.0 that had a similar problem, except that the mileage was more like 12. It turned out to be a defective engine coolant temp sensor (not the one for the dash gauge).

Both nice and cheap parts.
Marc/Atlanta

BTW, my 98 gets about 25 on the highway as well.