Got a problem I can't figure out

I have a 99 ranger auto 4.0 4x4 so here is my problem it started last week and I'm out of ideas I don't want to start replacing parts and that not be the problem so I'm hoping someone else has had the problem ok so . It will not start it will crank and crank and crank I've got spark and fuel . Now here is the part that I can't figure out if I hook up my battery charger and turn it on to boost it will start up and run fine like nothing is wrong had the battery checked and it's good had the alt checked and it's good any ideas . This is my only transportation and I'm not ready to get rid of it . Thank you everyone in advance

I would say loose bad battery cable/terminal.

You need a volt meter.

Key off
Test battery voltage at battery, 12.3 to 12.8v is OK, under 12.2v is failing battery

Now test battery voltage using engine, put black volt meter probe on alternators case.
Put Red probe on alternators "B+" terminal, on the back of alternator has large wire on it.
Should read exactly the same as battery voltage.

Now you are going to do a AMP test for the battery and cable
Hook volt meter up to battery again
Watch voltage while someone tries to start the engine.
If it drops under 10volts battery doesn't have enough AMPS, battery is "good" just not good for your truck

Could be starter motor is going out and pulling too many AMPS, so battery may be "good" for your truck, or battery cable to starter motor is failing, heating up and drawing too many AMPS, feel it after starting, but that can be cable or starter motor.
Also feel the Battery Ground cable, if it is heating up then it may be the problem.
AMPS have to pass from one battery post to the other.
If positive cable can pass 200AMPS but negative cable can only pass 70AMPS then 70 AMPS is the limit, positive can't send 200AMPS to starter because negative cable won't let it.
And visa versa

Reason it works when you give it extra AMPS is because battery doesn't have enough AMPS on is own, so that can be battery, battery cables, or starter motor

Seems pretty obvious that if it works when the battery is eliminated... The battery is not good. Run a tester battery at O'Reilly and see if that is the issue. If it works on their battery, get a new one.

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Positive the battery is good . After you get it to start it will run great but as soon as you shut it off and try to start it back up is will run for a sec then die and cough back through the intake . It ran fine never had any problems until it got cold

Weather extremes are hard on batteries. If your battery is weak, a cold snap will kill it. A few weeks ago the 4 year old battery in my Grand Caravan wouldn't crank the engine at 20 degrees at 5 am. At noon it was 45 and the battery started the van. Time to replace it.

AfterShock said:

Positive the battery is good . After you get it to start it will run great but as soon as you shut it off and try to start it back up is will run for a sec then die and cough back through the intake . It ran fine never had any problems until it got cold

Click to expand...

As Slammin Sam said, temperature effects batteries.
Car battery's use a chemical reaction to store energy, in warm temps this chemical reaction can occur quickly and release full battery AMPS when using starter motor.
As temperature drops the chemical reaction slows down, so available AMPS also goes down, the starter motor also needs more AMPS to turn colder engine, so double whammy.

After engine starts battery is not used at all, the alternator provides all vehicle power.
The Battery's only purpose is to start the engine.
Battery voltage is 12.5volts, approx.
When engine is running vehicle voltage is 13.5 to 14.5 volts so higher than battery voltage, this keeps battery charged for next time you need to start engine, but also shows you that the Battery is not used at all to power any vehicle systems while engine is running.
A 12volt battery simply can not show the 14volts you see while engine is running.
The fact the engine runs fine when started means problem occurs only when starter motor is used.

Point being, the battery can be good, brand new in fact, but the description of your problem points to a lack of AMPS when trying to start engine.
Starter motor for a V6 can draw 100amps, when you pull that many AMPS from a 12volt battery the voltage will drop, usually down to about 10volts, but this is still enough voltage for a good strong spark.

Starter motor is turning the engine but voltage is dropping to low in fuel/spark system for it to work, when you release the key(starter motor off) voltage pops back up to 12volts and you get a good spark which you feel as engine starting for a second and then back firing before dying.
i.e. when starter motor is on and if voltage drops under 9 volts the spark is very very weak, and cold engine needs strong spark to ignite fuel.
When you release the key voltage pops back up to 12volts and spark gets strong so fuel ignites, and engine seems like it wants to start but can't, it fires and then can back fire, because of the extra fuel from cranking engine with weak spark.
Adding "battery charger" gets the cranking voltage back up above 10volts and engine starts

So you need to test voltage in the system to find out why the AMPS are limited.
Starter motor pulling too many amps
Failing battery cables, corroded connections on cable ends
Battery with limited CCA(cold cranking amps)

If engine didn't start with "battery charger" connected then you would look at fuel or spark issue, but because it does then best course of action is checking electrical system during starting

Here's 2 cents. I don't trust the digital battery testers. You need to use the old style with the big resistor that can really put a load on the battery.

What I think is going on is either the starter has issues or you have a bad ground. Crank the motor for a minute or have somebody else crank and feel the ground wires. Your looking for hot wires. Take a jumper cable and go from battery ground right to the starter. You can do the same for the positive side. You could put a jumper cable from ground to the motor.

In Oct 2014 I purchased a Brand new 2014 Wrangler Rubicon. In December 2015 the Battery went tits up as in the wife backed it into the garage after work I went out to run to the store and the Battery was totally dead. Well I pulled the battery went and grabbed a brand new AGM and thru into it. so just because it tested fine does not mean the Battery is good. You would think the battery in a 13 month old new vehicle would be good, it is garage kept.