Worse mileage after tuneup?!

[jbhebert]

Since my '94 Ex was rather neglected by its previous owners, I decided to do a tuneup a little over a week ago. I put new spark plugs and wires (Motorcraft platinums gapped to .054" and Bosch wires), new Bosch OEM O2 sensors (still have the bruises from plugging them in), a new fuel filter and a new air filter in. I had recently changed the oil, so I did do so again at this time. I had been averaging about 17.5 MPG in my commute (about 50/50 city highway by time, 30/70 by mileage). The truck is a 4x4 with 3.30 or 3.50 gears (don't recall which). I was hoping to see an improvement, especially when I pulled out the rusty Autolite plugs and found one of the O2 sensors was so loose I could remove it by hand. However, when all was said and done, I have actually seen a decrease in economy by about 1 MPG. I commute 150 miles a day, so it's easy to establish data points rather quickly. I have filled the tank 4 times since, and have been averaging almost exactly 16.5 MPG. I am going to the same gas stations and my driving style has not changed. I will say that the motor is running smoother and seemsa little peppier, but I want better fuel economy darn it.

Any thoughts on what I might have messed up? The only other thing I've noticed is that the truck has always run at the bottom of the temperature gauge. I put in a "high temp" thermostat a while back that is rated for 198 deg. and it didn't make much of a difference. I'm wondering if the truck is running too cool and therefor not burning efficiently.

Thanks,

 

[410Fortune]

Running too cool would point to your new thermostat, a bad fan clutch (spinning all the time = poor MPG) or a faulty temp sensor.
The factory gage is not exactly accurate.

You did re-set the PCM after the tune up yes?
Did you clean the MAS, TB, and IAC as well?

I would guess in time you will get your 1 MPG back and then some.
Also if you are looking for better MPG pump up your tires closer to the max PSI

 

[Positive Vibes]

One thing you might want to do is clean your MAF if you havent done so.

 

[jbhebert]

Running too cool would point to your new thermostat, a bad fan clutch (spinning all the time = poor MPG) or a faulty temp sensor.
The factory gage is not exactly accurate.

You did re-set the PCM after the tune up yes?
Did you clean the MAS, TB, and IAC as well?

I would guess in time you will get your 1 MPG back and then some.
Also if you are looking for better MPG pump up your tires closer to the max PSI

The old thermostat did the same; I was hoping the second thermostat would run a little hotter. The fan seems fine but it's hard to say. I would guess the sender or gauge.

I disconnected the battery and pumped the brakes to drain the capacitors. Is there another way to reset the PCM? I didn't clean the sensors, but they wouldn't have changed from before the tuneup.

I run 35 to 37 PSI when I do a lot of highway.

Thanks,

 

[jbhebert]

One thing you might want to do is clean your MAF if you havent done so.

I have not, and probably will this weekend, but it would have been a pre-existing condition that I don't think would cause a sudden loss after the tuneup.

Thanks,

 

[walterd140]

How long did you disconnect the battery? Whenever I need to reset my computer, I usually pull it for 15 - 30 minutes.

Also, If you want to clean the MAF, let me know & I'll loan you my tools so you don't have to try to find them, seeing how your just up the road (Outside Springfield here). You will need a torx 20 star hex wrench. But it has to be a secure one (they have a hole in the middle). Got mine in a kit from Autozone for $10. A few q-tips & contact spray will get that clean in about 20 minutes.
The wife says if we are loaning tools, you have to bring a candle from Yankee
Where do you work that you drive 150 a day? NH?
Walter

 

[410Fortune]

a small screwdriver and hammer will take care of those security pins, then you can use a regular t bit

 

[jbhebert]

How long did you disconnect the battery? Whenever I need to reset my computer, I usually pull it for 15 - 30 minutes.

Also, If you want to clean the MAF, let me know & I'll loan you my tools so you don't have to try to find them, seeing how your just up the road (Outside Springfield here). You will need a torx 20 star hex wrench. But it has to be a secure one (they have a hole in the middle). Got mine in a kit from Autozone for $10. A few q-tips & contact spray will get that clean in about 20 minutes.
The wife says if we are loaning tools, you have to bring a candle from Yankee
Where do you work that you drive 150 a day? NH?
Walter

The cable was disconnected the entire time of the tuneup, so several hours. I find that stepping on the brake so the brake light drains the capacitors works well in other Ford products, so I assume the Ex is the same.

I have the tools; I was just too lazy after battling the O2 sensors to do it. This weekend, after I finish rebuilding the transfer case in the GMC.

I wouldn't go near YC with a 10' candle.

I work outside of Boston. The Ex isn't my normal commute vehicle, but it has had to serve that purpose for about a month while I fixed yet another vehicle in the fleet.

Thanks,

 

[jbhebert]

a small screwdriver and hammer will take care of those security pins, then you can use a regular t bit

That works, too.

A long time ago I took all my torx bits and machined holes in them so I wouldn't get delayed by a stupid safety screw.

 

[jbhebert]

Thermostat Seems OK

Last night when I got home I checked the temperature of the thermostat housing with my instant read and got 189.7 deg. F., so it appears that the thermostat is OK and my gauge is just reading low. I guess the problem is not temperature rated.

I have put an additional 500 miles or so on the truck with no improvement seen so far.

 

[Positive Vibes]

I didn't go back and read everything but have you tried running some injector cleaner. The stuff you add to the gas???