Yeah my 4.10 geared m5od 4wd 1988 F150 on 31x 10.5s gets a solid 10 mpg and will tear a house down. When I have a working rear axel any way. With a 3 inch sraight pipe with 3inch cat. And electric fan and 5.0throttle body.

 

AHHHHH now THAT makes sense. Good to know ...now ill be able get some money back. Thanks for the reply. I'm not sure how to reset ECU other than just cutting power to it .. which i did do by removing negative battery cable while while replacing the sensor.

A vacuum leak would make sense... by the way its running (FLAT as hell with no pickup and **** poor MPG) ..that was my next move. Have never done it before, From what I've read spraying carb cleaner all around hose fittings and intake manifold is the best way???

Also, any idea what that hose is i posted in the pic? Your help is greatly appreciated!

 

Check your timing, also yes spray carb cleaner or propane. Check the 2 vac canisters to see if they are rotted out too. Yea removing power for about 30 seconds or so will reset the ecu

 

I have had two F150s 4x2 with the 300 and 5 speed. One had the 3.55 and the other had 3.08. Gas mileage was about the same. The big problem was the stupid high ratios of first and especially reverse in the Mazda gear box. The 3.08 allowed a pretty high cruise speed. BTW both trucks broke 200k with the original eng and trans,
I keep a log of my gas mileage and in mixed driviing I get 16.5 to 17.5 Mpg
Best ever was 20 Mpg at 60 Mph, the worst was 15 Mpg during a week of snow storms.
Steady 60 Mph 20 Mpg,
Steady 70 Mph 18.5 Mpg (3.08) 18 Mpg (3.55)
Steady 75 Mph 18.0 Mpg (3.08) 17 Mpg (3.55)
The 3,55 truck was a 94 RC SB 4000 lbs
The 3.08 truck was a 95 Sc SB 4400 lbs.
Not the fastest trucks but incredible torque.
Both trucks had the timing bump to 12 Deg BTDC, .050 gap on the copper core plugs, and low resistance wires. 20" vacuum at idle and no codes.
YMMV
rikard

 

I verified timing is set at 12, no vacuum canister rot, no apparent leaks after spraying carb cleaner, still no codes.

I did notice that a couple weird things:

1) my gas mileage is getting worse: when i first bought the truck i initially hit the 13 range with a tank of gas if i was doing more hwy driving. that slowly dropped to the 12 range and then to the 11-11.5 range ...then lest week i hit my lowest mark with 10.6.

2) there are a couple loose wires floating around in my engine compartment that have connectors on the end but no place to plug them into. One is coming out of the same wiring harness as the IAC valve and the other seems to be running out of the same harness as the fuel injectors. I cant imagine dangling wires in your engine compartment is a normal thing. Any one recognize these? or can anyone verify why they're there or why they're not plugged in? Here's a couple pics:





3) My engine runs extremely cool (not even above the first white line cool) so after reading some threads on FTE some guys are saying that the fan clutch may be stuck and the fan is running full time. I noticed my fan starts running as soon as i start the engine on a cold morning. Is that a sure sign?

 

It could be that your fan clutch is locked up.
Would you say that there is the definate "roar" of the fan being engaged when starting it up on a cool morning or is it just free spinning at about the same rpm as the engine (there's a huge difference between the two) ??

Also, when you checked the timing did you remove the spout connector, set your timing from the passenger side of the engine (this is VERY important), then replace/reinstall the spout connector ??????
Did your truck ever have a spout connector ???

The other extra connectors you found were likely for a different year engine sensor(s)/option your year didn't have ie.... Ford may have used an 88' harness in your 92' or a 5.0 or 5.8 harness in your 4.9.

"Winter blend" fuel could be a reason for your most recent MPG drop.........if you live in an area that gets "winter blend" fuel.

The most concerning thing about your truck is the poor driving performance AND poor fuel economy.
You're about 30-50% off on your MPGs.

Sumpthins' not right.

Bob

 

As far the harness goes that make sense. And yes I have a SPOUT connector but i didn't remove while checking the timing. I DID check the timing form the passengers side though.

As far as the fan goes... I cant tell.. it looks like its spinning pretty damn good. I have never really heard it "roar" because I don't think my engine ever gets hot enough for the fan to kick in. Is there any other way to tell. If the clutch was locked up would i be able to spin the fan with my hand with the engine off? Would it spin freely?

 

Try re-timing the engine with the spout connector removed.
The spout connector, when removed, disables the EEC from advancing and retarding your timing.
Once you adjust the "base timing"(spout connector removed),turn off the engine and snap the spout connector back in its connector. The EEC will now adjust it's "real time" timing based off the new "base timing".

I'm not 100% positive on this, but you may have to drive the truck around for 10-20 minutes in order for the computer to re-learn what it now "sees" from all of the sensors.

If I were a good, fast, typist I would give you a multitude of scenarios/problems that would be/could be associated with having incorrect "base timing".

Your fuel mileage and driving performance would be in those scenarios.......

And, I applaud you for attempting to time your truck from the passenger side of the motor.
Lot's of people have missed that one completely..........good job.

Re-adjust the base timing on your truck and see if some of the other problems were associated with the timing being "off".

As far as the fan.......I'd think if it were "locked up" you wouldn't be able to turn it by hand with the engine off.....sounds logical, that's what I'd try !!!

As far as the running temprature on the guage goes.......could be a multitude of things.
Sending unit could be corroded and no longer giving correct output readings, poor ground(s), cluster pin corrosion, pinched wire, thermostat stuck in the open position, the list goes on and on.

I'd say you're best off starting with re-adjusting the timing and go from there....

Let us know what the outcome is !!!

Bob