Poor Gas Mileage

[mekelly]

Only getting about 11mpg in the city on my 1994 XLT 2WD.

It runs great, no misses, idles very smoothly, starts right up, transmission shifts great.

I recently bought it from a single owner who paid to keep it well maintained. It has 175,000 miles on it.

Here's what I've done since I purchased it:

Replaced front wheel bearings
Replaced air filter
Replaced fuel filter
Replaced spark plus
Replaced spark plug wires
Replaced water pump (radiator/heater hoses, flushed cooling system)
Replaced thermostat (Stant Superstant 195)
Replaced fan
Replaced fan clutch
Replaced power steering pump (and both hoses)
Replaced coolant temperature sender (single wire to gauge)
Replaced transmission filter (replaced transmission fluid)

To Do Shortly:

Replace coolant temperature sensor
Replace rear differential fluid
Clean MAF

There's no CEL lit up. I haven't replaced any O2 sensors.

Anything else to check / replace to try to improve gas mileage?

Again, what's throwing me is that the truck runs very smooth with no issues. Can't figure out why I am not getting better MPG!

Thanks!

 

[arco777]

Have you done a transmission band adjustment? If they are adjusted too tight, maybe.

Check for brakes dragging.

Replace O2 sensors if they are switching slowly (can test with a multimeter).

Remove and rebuild fuel injectors (this is reaching a bit).

Check for exhaust restrictions, such as catalytic converter packed up/fallen in.

 

[natenkiki2004]

Replace or test the 2-wire coolant temperature sensor (the 1-wire is strictly for the dash) and the almost identical looking 2-wire intake air temperature sensor.

 

[2stroke]

What do you get on the highway? City driving can very greatly. 11 mpg is not all that terrible for these engines.

 

[mekelly]

arco777: I haven't had the transmission bands adjusted. Will check for tire drag.

natenkiki2004: I already purchased the 2 wire coolant temperature sensor and will replace tomorrow. Will purchase an air intake temperature sensor and replace.

FR-425: What are the characteristics of 'limp mode'? Sounds like I'd notice it not running well if it was in limp mode. The ICM is relatively expensive so I'd rather not 'throw' that part at it (as opposed to $15-25 sensors) if it's not the root cause. Any simple diagnostics to check before spending $150-200?

2stroke: I haven't taken it on the highway yet so I am not sure. I have a 4WD 5.4L expedition that gets about 11-12 in the city and I thought for sure my 2WD 4L explorer would get better gas mileage than the expedition!

 

[2stroke]

Nope, these will get about the same gas mileage as a full size truck. On highway, you are probably only going to see 17-20 mpg. City 10-14 mpg is common. A very good indicator of how your engine is running is the spark plugs. What did yours look like?

 

[mekelly]

Spark plugs looked like they hadn't been changed in a while! Very worn but looked normal. No signs of oil fouling, pre detonation, overheating, etc.

 

[natenkiki2004]

For what it's worth, mine got about 11MPG when I first got it because the previous owner had removed the SPOUT connector near the EEC-IV diagnostic port. This was to combat detonation but reduces timing so your fuel economy takes a dive. Once I replaced that and did a few other things, I'm up to 14.2MPG with more back-country road driving than highway. I'd like to see it higher and there's a few things to check/replace on my list but for a 4x4 vehicle, 14 is pretty tolerable IMO.

 

[mekelly]

What's the SPOUT connector?

 

[natenkiki2004]

It's a little grey square plug that basically jumps 2 wires. Though, it may have a resistor inside.

Check this out:
http://s213.photobucket.com/user/psychopsychoticpete/media/rsz_p4030002.jpg.html

 

[mekelly]

Thanks, I'll look for that around the EEC-IV port. When you say removed it, do you mean he removed the jumper (grey square plug)?

 

[natenkiki2004]

Yes, the grey square plug. It's a common thing that a lot of people do with these EEC-IV engines due to detonation. However, it doesn't solve the problem, only masks it. I use premium ethanol-free gas in my Explorer and experienced pinging only once, at the top of a really long climb I decided to do in D, up past 3500RPM. I have a couple running issues that need sorting and it probably wouldn't hurt to run some Seafoam in and clean things out but that's a whole other story.

 

[Watchman]

Is the spout connector something you can get at an auto parts store ?

 

[mekelly]

I removed the old coolant temperature sensor and the air temperature sensor. I then took OHM readings of the old and new coolant temperature sensor at different temps (see results below) and an OHM reading of the old and new air temperature sensor at ambient air temp.

Readings for the coolant sensor were taken at 3 different temperatures. I filled a cup with ice water and let it stabilize, took one with water right out of the tap, and heated water in the microwave and let it stabilize. Submerged the 'sensor' part of the sensor and recorded the ohm readings once they stopped changing.

Coolant temperature Sensor Readings:

Water Temp - 30F
New Sensor - 90.1
Old Sensor - 87.4

Water Temp - 50F
New Sensor - 54.6
Old Sensor - 55.5

Water Temp - 180F
New Sensor - 2.9
Old Sensor - 3.4

Definitely a difference in readings although the old sensor seemed like it was still working pretty well. Going to replace it anyway.

Air Temperature Sensor:

Ambient Air Temp - 53F
New Sensor - 43.5
Old Sensor - 47.5

About a 10% difference. Don't think it's that material but the old sensor was pretty oil fouled. I included 2 pictures below:

Side View - https://www.dropbox.com/s/zqf7whxwfdxg8gi/Side View.jpg?dl=0
Top View - https://www.dropbox.com/s/v529ejifuhdeym4/Top View.jpg?dl=0

Is this normal (I am sure it's original to the car) or should I be concerned?

Replacing this sensor as well.

 

[mekelly]

On the SPOUT connector: I found this connector with duct tape over it next to the EEC-IV connector. It has a metal jumper connecting the pins. Best I could tell with the OHM meter, there was continuity between the two pins.

What is the connector for?

It had a green and grey/red wire connected to the harness. Here are 2 pictures:

https://www.dropbox.com/s/gshkjex0d3bwiyz/Top View of Jumper.jpg?dl=0
https://www.dropbox.com/s/c7s0j21awvq3rpf/Side View of Jumper.jpg?dl=0

 

[Watchman]

Concerning your coolant temp sensor - I replaced mine with aftermarket from Advance. The issue I found is that these inexpensive coolant sensors do not register on you dash gage accurately. They were skewed to the cold side. I finally spent $30 on a motorcraft and now it registers in the normal range, like it used to.
Concerning the AIT sensor, my original looked just like yours, so I did replace it. I did use Advance this time because the Motorcraft was way more. I noticed no difference in MPG. I'm having the same MPG issue you are having. I've also checked blocked CAT, replaced O2 sensors with Motorcraft, cleaned injectors, checked FPR. I believe if you let these trucks sit they lose their fuel efficiency. I used to get 20-22 avg, not just highway and this was with over 250K miles on it. It would only go down sometimes in winter to 18 and I believe that was due to winter fuels - same thing happens to my 2011 Corolla now. I now get 15-18 MPG on the Hwy. If you find the solution to MPG you will find a lot of folks here sitting up and listening. My belief is that it must have something due to the timing or fuel delivery issues. You can throw a lot of money on parts and still not improve your MPG. So, it makes sense to test them (as people have stated here) to qualify your purchase.

 

[natenkiki2004]

I'd try to bend that sensor prong to the center on the IAT sensor, or just replace it. It's supposed to measure the air temp, not the engine temp, which it will do if it's touching the metal housing.

You cannot get a SPOUT connector at an auto parts store, your best bet is a junkyard (they're expensive on eBay). What I don't know is if there's a diode or resistor in the SPOUT connector itself. There was a similar connector on my AC system and it got so hot that it crumbled and there was a diode inside. But I think that was an aftermarket job so who knows what's actually inside the OEM SPOUT connector. I ran mine jumped like that briefly, not long enough to notice any MPG differences but enough to know I didn't fry anything

 

[2stroke]

If I'm not mistaken, that connector is supposed to have a fuse plugged into it. Not a regular one, but a kind of end plug in one. If it blew, its very possible some meat head just jumped it and called it good. I can check for you, but I'm pretty sure that's what that is based on the picture. I could be wrong.

The timing is not adjustable (within reason) as far as I know. Your fuel system can certainly be compromised by sitting. With the ethanol in fuel up to 15% sometimes, gas can begin breaking down in as little as 30 days. If you ever want to store a vehicle for extended periods, make sure it has non oxygenated gas, and a fuel stabilizer helps.

One thing that is very bad about the 4.0 is the fuel injectors are susceptible to all kinds of problems. I have not had one that hasn't had injector problems. If you really want to improve mileage, cleaning or replacing the injectors would be your best bet. You still are not going to see over 14 in city traffic, and I have never seen a 4.0 OHV ever get a 22 mpg average. Maybe a 2x4 5 speed can see it once in a blue moon, but for an average that is very rare. My current daily driver is a 1994 Mazda B4000 (4.0 OHV) 4x4 5 speed. These are lighter than explorers, and mine has a 3.27:1 differentials (better gas mileage than 3.73's), and I still only average 19 mpg. I've only seen 20 once, and there was a tail wind. Good luck, but I wouldn't expect much.

 

[Watchman]

I bought this 93 Sport 4WD with auto trans brand new in CA. It has CA emissions with EGR. In those days CA fuels had a state mandated additive which actually enhanced mileage. I am not exaggerating when I could cross the Central Valley on long trips of 250+ miles and get 25 MPG easily, and this included driving 50-75 miles in 4WD in the Sierras. Of course speed limit was 55 in those days. My problem is that this vehicle went from a daily use avg 20-80 miles a day for 18+ yrs, and now for the last 3+ years, to being parked and only used 10-15 miles per month, and sometimes sitting for 3-4 weeks. I'm not giving up on it. These are great vehicles and that 4.0 is a solid engine. It now has 322,000 miles on it. I believe with the great amount of knowledge and experience by all the above commentators and others on this forum that there's no reason not to hang on to the 1st gen Ex. Sorry for the long windiness. And thank you Nate and 2stroke for the info.

 

[2stroke]

25 mpg is practically unheard of. I would definitely hang on to that one. My very first car of my own was a 1994 ford explorer 4x4 auto that was in my family since it had about 30,000 miles. I ended up with it, because it was just a spare vehicle with a few problems. I fixed it up, and drove it a long ways. It was pretty consistent at 18 mpg on the highway. That was at 55-60 mph with cruise control on. I never saw 20 mpg. Around town, it got around 14 mpg, but I never lived in a city, and I have a light foot. The other 4.0 in our family is a 2000 explorer, and that gets about 17 mpg highway, but it has a little issue. Somewhere along the line Ford changed the heater controls to vacuum actuated instead of the manual link that first gen's have. Somewhere in the dash the system develops a leak and causes all kinds of problems. The worst part is that Ford still puts these into vehicles. We have had a couple other trucks with the 4.0. Anyway, I'm getting off topic. Gas Mileage drop (from normal) is a good indication of a problem, but poor gas mileage to begin with is nothing to be worried about. Your spark plugs would have been black if it was running rich. One thing I wanted to note about winter driving. The reason your gas mileage drops during winter is because your engine has to put in more gas to compensate for the denser air. Since your engine is still sucking the same volume of air, you are getting "more" are because it is denser. I don't know what air/fuel ratio explorers run, but just to throw a number out there 13:1. Now in winter with the same amount of gas being injected it falls to 13.5:1 (I'm just throwing numbers out as an example), so the engine adds more fuel to compensate. Thats why you use more gas the colder it gets. Technically people should have richened up their carb's on cars years ago, but nobody did. This is true of all engines, and its why I can't believe you never see adjustable carbs on anything anymore.