I did a manual calculation for the fuel mileage and am getting 12.5 MPG. Does this sound right? I was hoping for something in the neighborhood of 15 but I may be unrealistic.

On another note, the truck is not coming up to temperature as it should. It appears to be running colder (about 1/4 of the way to hot) and it's difficult to start when warmed up. Cold starts are easy but warm starts give me issues including stalling.

SubFord suggested a bad ECT sensor. However, would the rough idle be caused by an engine that's not warming up to proper temps? Would the computer be sending too much fuel to the engine and causing my poor fuel mileage and rough warm starts? I was thinking the thermostat could be staying open. Any thoughts?

 

I have a 95 supercab with the exact same symptoms.. getting around 11 mpg, but i'm running 35" tires, neve really warms all the way, about 1/4... and it hates to start warm, but fires right up when cold.. i'm stuck, please let me know if you find any solutions

 

I've got a 91 with the 5 liter auto, my avg. mpg is around 15 city, 17-18 hwy and I'm running a 160F thermostat simply because my old one failed and I darn near overheated it if it wasn't for the thermostat housing gasket hissing at me and warning me. My temp needle never really goes above the first line on the gauge and I don't really have any heat, but I wouldn't think a running a bit cooler would really affect your mileage that much. If you were running at around 130F or so, then I could see a significant drop. As far as the hard starting when cold issue, I haven't been around Fords very long, so I'm not sure if they run cold start injectors, but if they do, then that might be going bad. Also check your air filter, throttle body, etc. One other thing it could be is your catalytic converters, they might be plugged up. Just a couple of thoughts.

 

i have a 93 with the 5.0 4r70w automatic and factory 3.55 gears 4x4. last weekend i drove 480 miles home and i was getting 23mpg going 55mph. 14mpg at 80mph in the mountains. 13 around town. with a cai and bigger cam and a fairly heavy foot.

with my old bone stock motor i was getting 9mpg around town and close to 18 on the highway with a worn out motor.

 

what do you mean by cai?

 

Cold Air Intake

 

No issue on the cold start, only the warm starts. It's also missing under acceleration. At low RPM's on a climb it pops like it's trying to backfire under the hood. It's hard to describe. I'm not sure about the catalytic converters. Is there a way to test or inspect it for the clogging issue?

The plugs, cap and rotor are all new. I set the timing and pulled off the upper intake manifold and scrubbed it out and the throttle body is clean.

It's still running cold, especially today with temps in the low 40's.

Let me know what you think. I might try switching out the thermostat tomorrow.

The truck has 175,000 miles on it.

 

if you were to have a bad ect then it'll tell the computer that its not warmed up and it'll keep sending more fuel to the cylinders until it does warm up. it could be causing the miss and a fuel milage drop and starting problems. the same deal would be with the thermostat. if the computer isnt getting the correct temperature readings then it'll give you lower fuel mileage and a miss because it'll be running rich and a starting problem because the fuel injectors will be droping to much fuel into the cylinders on startup.

 

With a vacuum gauge, there are two easy tests you can run to determine if your exhaust is restricted (cats clogged).

First test:
1) Attach vacuum gauge to manifold vacuum source.
2) Observe vacuum at idle.
3) Snap throttle to WOT and release, while watching the gauge.

The vacuum gauge should drop to almost zero when you hit WOT. When the throttle snaps closed immediately after, the vacuum should read 4" to 6" higher than what it did at idle. It should then settle back at the same reading it was at idle before the WOT snap. This whole exchange should go from idle reading to idle reading in 2-3 seconds, tops. If it takes longer for the gauge to return to the same idle reading, your exhaust is restricted. The longer it takes, the worse the restriction.

Second test:
1) Attach vacuum gauge to manifold vacuum source.
2) Warm up engine.
3) Observe vacuum at idle.
4) Leave engine idling for 10 minutes. Do not touch anything on the truck during this time. In fact, go inside and fix some coffee.
5) After 10 minutes, observe the vacuum.

If the vacuum is the same or higher, you don't have any resctrictions. If the vacuum gauge has dropped, you do have a restriction. The more it drops, the greater the restriction. If it drops 1" or more, you have a serious restriction. 2" or more and you might as well have the exhaust welded shut.

 

I'll check the cats using the vacuum test and switch out the thermostat. I think Matt's Ford might be on to something............

This truck has one cat and it's part of the y pipe coming from the manifolds. Is there a way to clean out the cat? I would think replacing the y pipe and cat is an expensive proposition. Not to mention it's never been touched before and I'm sure bolts and nuts are more liable to snap than back off the threads.

 

take the cat off, knock out the guts with a prybar and a hammer, and reinstall the empty shell as a resonator to eliminate the raspy noise people complain about by not running cats.

 

Try a Mr. Gasket performance thermostat. It reaches op.temp.(enters closed loop function) in about 1/2 the time. Their $3 more but but by reducing time spent in warm up (wild guess 13:1 air fuel ratio) with closed loop(not guess 14.7:1) you'll end up recouping the total cost plus.

 

New thermostat and new ECT sensor. I'll do another manual calculation and report back. The new thermostat did not correct the hard start after warm up. However, I'll have to drive it tomorrow and see what the ECT did for it.

 

maybe a dumb question, but whats ECT stand for?

 

engine coolant temp sensor.