Ford f150 '93 stalls on start up, only sometimes tho and guzzling gas?

Question

I have a f150 1993, we've replaced dang near half the truck already we just got new spark plugs not more than a month ago, that fixed it for a tiny bit, but it continuously does it when it sits for more than... probably 5 hours or so it starts up just fine, revs up a bit then seems to drop too low, starts to sputter and stall, now if you hit the gas petal it will drop right down into the perfect idling  position, and you can start it up anytime after that and it will work just fine, also if you put it into gear when its revving up *say reverse* it will do just fine then just sputter and stall on you almost instantly with no warning at all,
 also we have duel tanks (ones a bit bigger, only by 2-3 gallons) and the smaller of the two seems to eat up 2x as much gas (we drive 30 minutes to work and back, every 2 days or so it eats up 1/4th of a tank in the front *smaller tank* every 4 days the rear tank eats up 1/4th of a tank... why is that? i know that 2-3 gallon difference doesn't account for the lost gas, and we drive the same route, and no matter how many times we test this it comes out to just about the same, the front tank *smaller* is eating up twice as much *roughly* then the back tank *bigger*

Paradise · Accepted Answer

Changing oil and Cleaning IAC will NOT solved your fuel economy issue...I do not know why the person above  said that.

Anyway, back to topic, by reading your description, it does sound like you have two non relate issue.
Before you start playing guessing game and replacing every sensors on your vehicle.....[common mistakes and very expensive]
scan for codes, do not assume you have no fault codes.
Sometimes you will have failure codes stored in computer without illuminating check engine light.
If there are codes stored in computer, do not replace sensors immediately, find out why and determine the cause....
example...intake manifold vacuum leak can cause MAP sensor and oxygen sensor codes stored in computer and on top of that a vacuum leak can cause idle quality issue.

second concern is your fuel tank situation, hook up mechanical fuel pressure guage, compare fuel pressure readings between front tank and rear tank.
Higher than OEM fuel pressure specifications can easily cause the problem you have with fuel tank.
Your front fuel pump may be putting out higher than OEM fuel pressure and this is why you're using too much fuel when using front tank.

Robert M · Answer

This is a simple, simple problem. Locate, remove, and clean your IDLE AIR CONTROL VALVE. It requires an 8mm socket wrench. CLean this valve with gum-out spray and the two exposed air ports. When you are done, find a way to clean ut the throttle body with the engine running. This will solve the problem, and improve your fuel mileage. This IAC valve is responsible for fuel mileage at low engine speeds. For even better improvement, use Mobil One 0W-30 oil in your engine. It will also improve power and fuel mileage. Good luck!

Old-guy64 · Answer

spark plugs won't fix fuel troubles, and you've got more than 1 by your descriptions. Take it to a shop and get some codes read and some diagnostics done by a pro, because everything you will read here is at best an educated guess, and not really that accurate..not being a wise guy just honest.

pedro7of9 · Answer

modern fuel injected system is under high pressure even when shut off..a pinhole can blow a lot of fuel out in short time
1 check engine lite..scan can help [but it doennt tell you what to replace]
2 shop manual..ur crazy to try working on car/truck without one..20 dollars any auto prts store...[chiltons best but haynes ok]
3  wires and cap/rotor....
4 coil[s]  sometime failact up when hot
5 are you sure tanks switch over when switched or are not wired backwards..[dont ask how i know]

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Ford f150 '93 stalls on start up, only sometimes tho and guzzling gas?

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