My dad has a 97 f150 perfect condition...something has been draining the battery and we cant find it. He thought the battery was the problem so he bought a new one. Took off for the week and came back and the battery was dead. Then he went and had the alternator checked and thats fine. He went and bought new plugs and wires thinking that would help but it didnt. Everyday, i start his truck and it just sits there and spits and sputters. Anyone know how to solve this problem? The engine is a 4.2 V6

 

If you have access to a code reader or the truck can be driven to a nearby Autozone or NAPA (they will pull codes for free) - see if the computer is throwing out any codes. If the unit is giving Continuous Memory DTC's it'll help narrow down at least which system is having a problem. Some TSP's from Ford for you to try that may help find the problem or at least eliminate some common causes of rough idle;

l Start engine and let idle.

l While checking for rpm drop or engine stall, disconnect IAC valve.

l After testing, turn key off and reconnect IAC valve.

l Did rpm drop or engine stall when the IAC valve was disconnected?

If the answer is Yes the IAC check passes

Check your timing...

Check your throttle body...

When you replaced the wires did you check the distributor (even electronic ones can go bad). If your engine has the individual coil packs for each plug then I'd check those to make sure one of them isn't burned out.

As far as the battery draining goes it may or may not be related to the rough idle. If you have a short/fault in your electrical (which it sounds like you do) it could cause the truck to idle rough if it's in the same circuit as the PCM or other computer sensors (Ford computers can be very touchy) - I had a short in my 98 Taurus and it made the computer do all kinds of WEIRD stuff to the car - took 6-months to track it down.

Well I hope this gives you some ideas -

Black 97 F250 E.C. 4x4 Lariat -

 

thnks...ill let my dad know

 

if its not that..check your interior lights...sometimes theyll turn on by themselves...


on mine ill shut the door walk away...walk back out and the light will be on...ive sat and watched it do it..i think my latches are worn out..

 

sounds like a huge drain if its running the battery down overnight. turn the key off. remove battery cable. put battery cable back on. Did the cable spark? if so you probably have a drain. Remove all your fuses, yeagh you need to draw a map so you know what goes where before you pull the first fuse. let the truck set, did it drain the battery? probably not Put 3 or 4 fuses back in and see if the battery drains, if not put a few more fuses back in. keep doing this until the battery drains. once it does drain remove one of the last fuses that you put in and the next night remove another.and figure out which fuse is draining the battery. Then you will know where to start looking to fix the drain.

 

A fault with the Alternator may have ben missed.
That is the diode stack is shorted.
With this issue the alternator will still charge but reverse drain after shutdown.
.
A faster way to check for circuit problems is to make up a 12 volt lamp connection put in series with the plus battery lead as an indicator of current drain.
Choose a small lamp that will light reasonable bright from the drain.
Then as you remove one fuse at a time watch when the light goes dim or out on that fuse removal.
Check the owner manual for fuse # then chase the circuit it feeds for the issue.
I know it sounds like a hassle but if the issue is to be solved some effort has to be put forth.
Good luck.

 

Excellent idea !!!! provided the lamp can handle the amperage being drawn. Do not try to start the truck while lamp is attached. As I stated in my introduce your self section I am a electronics tech from the navy. The diode stack is called a bridge rectifier in any other application besides auto. Is diode stack its official name in autos ? A bridge rectifier turns AC electricity into Dc electricity and yes the alternator produces AC electricity. I will remeber your trick and try it the next time i run across this problem, you way is much faster than my way

 

Well, the amperage vs the lamp 'size' is only to light the lamp so a 'change' in brightness can be seen for testing . This is why a small lamp should be used not a head lamp or high wattage corner lamp.
The amperage, if referring to burn out, is not applicable.
There is only 12 volts on a 12 volt lamp max. at anytime. It will only pass enough to light it to full brilliance same as if it were placed across the battery.
.
At a starter draw attempt, the starter circuit will only look like a low resistance connection path back to the other side of the battery, same as if the lamp were directly connected to the other side of the battery causing the lamp to light to it's full brilliance.
It won't burn the lamp out nor even come close to passing enough current to run the starter. It's resistance is to high and voltage drop across it (12 volts) would leave nothing left for the PCM or rest of the circuits to operate with.
The lamp is only a troubleshooting tool.
.
I thought I should clear up for others that the lamp will not burn out at a crank attempt, as if it were a fuse. The lamp resistance is very much higher than a fuse, as the difference between the two.
To put this over the finish line, remember the lamp has low resistance cold and causes the filament to glow wherein the resistance goes up several hundred times in value to 'limit' the current flow for it's full brightness by design.
A fuse stays very low resistance and will burn open (melt) as soon at it's design temperature is exceeded as 'it' is designed to do.
Thank you for your service to our country.
Good luck.

 

Would love to see a 12 volt dome light hooked in series with the battery and battery cable and then see the truck start through it and the bulb remain undamaged. Got a video camera?

 

as bluegrass said thats not possible, your wouldnt get enough amperage through the light bulb.
to the question at hand you can also purchase a fuse buddy. you remove your fuse plug it in and it will read your draw, less back and forth checking the light bulb (that may or not burn out). correct me if im wrong others, but there is a small stand alone mini fuse for the alternator circuit located behind the high amp fuse connected to the alterantor. in my readings i have read someone had a charging issue and it came back to that mini fuse. if it were, you could check every other fuse and not find the draw. besides that there are 3 other fuse blocks. two by air filter one in the cab.... good luck

 

mavdad, you've been away from DC circuits to long.
Good luck.