Fuel efficiency

[PStansberry78]

Lately, the fuel efficiency in my 93' XL has tanked. I'm looking for suggestions on where to start troubleshooting if nothing else has changed.

Paul

 

[Jason94sport]

Air filter, fuel filter, plugs, 02 sensors, clean the TB & the MAS.

 

[PStansberry78]

That's all done except for the O2 sensors and plugs. Guess I'll start there.

Thanks!

 

[Wolfie_85]

Changing the plugs was a night and day difference in my '94. More power, better gas mileage, smoother idle. Don't forget to put a little anti seize on the threads of the plugs. I used Autolite plugs, just the basic platinum ones. Don't forget the wires!

 

[Explorin'VA]

Inspect and replace brittle or torn vacuum lines

 

[PStansberry78]

Coming back around to this.

O2 sensors pulled and cleaned with brake cleaner. Doesn't seem to have made much, if any, difference. Do you think it's worth replacing them altogether if they were (are) the originals?

Plugs have been done. I'll look around for vacuum lines, but I haven't noticed any other symptoms that would make me think there's a vacuum leak.

 

[FR-425]

Do you notice a loss of power?

 

[PStansberry78]

Do you notice a loss of power?

Nothing noticeable.

 

[2stroke]

The O2's could definitely be replaced, cleaning them wont do anything. Another thing to look into is the EGR system. Are there any CEL's?

 

[PStansberry78]

OK. I ordered the O2 sensors.

No CEL. When you talk about the EGR system, do you mean specifically the EGR valve? Where are they located on this 4.0L motor?

 

[2stroke]

The EGR system is all on the drivers side of the engine. Its right above the oil dipstick. There is a tube that comes from the exhaust manifold (check it for cracks, and often they rust right out) and goes right to the valve on the plenum. I would have to check, but its recommended you change the valve every 50,000 miles or so. Most people wait until they fail. On your egr tube you have 2 rubber hoses, and both lead to the DPFE which is also a common failure part. A failed DPFE often trips a CEL. I'm not sure if a EGR valve would. The last time I had an EGR problem it came up as the DPFE and my EGR valve was always open. It caused all kinds of weird running problems.

Other causes of less than normal gas mileage that wont always trip a CEL would be things like a stuck fan clutch, leaking or dirty fuel injectors, vacuum leaks, even old tires.

 

[natenkiki2004]

Did you order Motorcraft O2 sensors? That's one sensor I'd stick with OEM (and I'm beginning to change my mind and go OEM on many others). Looking around, some thing specify that they last 100,000 miles, some 150,000 miles. We're talking 20+ year old cars, I'd change it to a new OEM unit regardless of mileage. It could still be working but it could be switching slowly.

 

[Ramblinwilly]

Ditto the use of OEM sensors. I've used non OEM sensors on a number of vehicles. It's a nightmare diagnosing problems when it's that new sensor you just bought! It does happen believe me...

 

[Ramblinwilly]

With regard to fuel economy, two components that are often overlooked are the transfer case and rear end diff. Wrestled with fuel economy on a 93 F150 awhile back. I changed the fluid in each and saw a 3MPG difference. That's significant.

Your issue doesn't appear to be fluid changes but you may want to take a peek at these. Remember these vehicles are 20+ years old. The viscosity breakdown has to be huge and the quality of grease/oil has gotten much better.

 

[natenkiki2004]

x2 on what Ramblinwilly said. The more resistance between the engine and pavement (tires, brakes, bearings, ujoints, differential, transfer case etc..), the lower your gas mileage will be. Synthetic ATF for the transfer case should be under $10, I bought a jug (4 quarts) of Valvoline Maxlife Synthetic ATF for about $16 and maybe used half. If you have a few auto parts to order, I'd recommend going to the Advance Auto Parts website and ordering with one of their frequent $50 off $125 coupons. I was able to snag quart bottles of Mobil 1 75W-90 synthetic gear oil for $7.20 each. My point is, it's really affordable to throw a good synthetic fluid in there and not have to worry about it for a long time.

 

[PStansberry78]

Did you order Motorcraft O2 sensors? That's one sensor I'd stick with OEM (and I'm beginning to change my mind and go OEM on many others). Looking around, some thing specify that they last 100,000 miles, some 150,000 miles. We're talking 20+ year old cars, I'd change it to a new OEM unit regardless of mileage. It could still be working but it could be switching slowly.

I ordered Bosch sensors, but I'll keep this in mind in the event nothing changes. At this point, there already delivered so I don't see the harm in trying.

Paul

 

[PStansberry78]

With regard to fuel economy, two components that are often overlooked are the transfer case and rear end diff. Wrestled with fuel economy on a 93 F150 awhile back. I changed the fluid in each and saw a 3MPG difference. That's significant.

Your issue doesn't appear to be fluid changes but you may want to take a peek at these. Remember these vehicles are 20+ years old. The viscosity breakdown has to be huge and the quality of grease/oil has gotten much better.

This is something I'd never considered, but it makes perfect sense. I'll get under there and take a look.

Thanks.

 

[2stroke]

You will have no problems with bosch sensors, they make a great product. Anything that meets oem specs will work, they just may not last as long as motorcraft. If you haven't been keeping up on fluid changes, that is absolutely an area you will pick up some fuel efficiency. I assume you regularly change engine oil, but change the tranny/tansfer case fluid, front and rear diff, and it wouldn't hurt to change your power steering fluid. Also something that might have been missed. If you have 4x4, make sure your hubs are unlocking.

 

[Jason94sport]

93's shouldn't have egr.....

 

[PStansberry78]

93's shouldn't have egr.....

Funny you should mention that... LOL. I was literally logging on just to check this today because I bought one, but couldn't find it on my motor.

:-/ Guess that part is going back to the store and I'll just replace the O2 sensors.