Car guys, why would replacing a battery fix a crank but no start?

[Slacker]

2000 crown Vic, random no start while cranking fine, come back later and fires right up.

I resisted changing the six year old battery because it cranked just fine, but a couple times when jumper cables were used it started, this is when my son was driving it, I wouldn't have tried jumping it since it was cranking and I wrote it off as coincidence that it started with cables.

So finally I gave in and replaced the battery, it cranks faster than with the old one, still seems to me to crank too long, but since we put in the new battery it hasn't failed to start.

 

[LTC8K6]

The new battery is able to maintain a higher voltage to the ignition system while cranking?

You may also have questionable plugs/coils/wires and the higher voltage helps with those?

 

[DaTT]

Sounds like crank position sensor. It doesn't know which plug to fire when, so it guesses. Eventually it guesses right and fires up.

 

[Slacker]

The new battery is able to maintain a higher voltage to the ignition system while cranking?

You may also have questionable plugs/coils/wires and the higher voltage helps with those?

The more I think about it, I need to take a good look at the coil wires and crank sensor harness for damage.

Sounds like crank position sensor. It doesn't know which plug to fire when, so it guesses. Eventually it guesses right and fires up.

Crank sensor was my first guess, replaced it about three weeks ago, seemed to fix it for a week or so but this has been so random I can't say that replacing the crank sensor did anything.

 

[DaTT]

Crank sensor was my first guess, replaced it about three weeks ago, seemed to fix it for a week or so but this has been so random I can't say that replacing the crank sensor did anything.

Did you buy a generic unit? It is possible that it's bad. No engine codes? Come to think of it, a crank sensor will sometimes throw a code.

 

[Meghan54]

Did you buy a generic unit? It is possible that it's bad. No engine codes? Come to think of it, a crank sensor will sometimes throw a code.

I've noticed over the years that some brands of vehicles do better with OEM replacement parts vs. "generic" parts, esp. in the electric/ignition systems, i.e. sensors, coils, sp. plug wires, etc.

 

[tortillasoup]

if crank sensor isn't bad, cam sensor could be bad as well. Could have dirty/broken wires or grounds that need cleaning up/inspecting. A vehicle of that vintage probably has some very dirty grounds.

 

[Evadman]

Check the battery voltage while cranking. If it stays over 10v, then the problem isn't the battery.

 

[slag]

is it worse the colder it gets?

 

[Slacker]

Doesn't seem to be related to cold, still no problem since replacing the battery.

 

[monkeydelmagico]

I've noticed over the years that some brands of vehicles do better with OEM replacement parts vs. "generic" parts, esp. in the electric/ignition systems, i.e. sensors, coils, sp. plug wires, etc.

It's a crown vic. It will run with parts crafted out of tin foil by a two year old. I would generally agree if the brand was Honda but not so much with this ford brick house 2v 4.6

Yes a battery replacement could help by having lower voltage drop and steady amperage during cold crank.

 

[Thegonagle]

Simple: Weak battery = not enough voltage to ignition, fuel pump, and/or ECM while cranking.

Agree that old plugs and wires could be helped by higher voltage, and I'd also hypothesize that the fuel pump could be on its way out, so it could also be helped along by higher voltage.

 

[thomsbrain]

Dead distributor? If the engine is cranking, you either don't have fuel or you don't have spark.

 

[Slacker]

Dead distributor? If the engine is cranking, you either don't have fuel or you don't have spark.

Its electronic, so no distributor.

And it runs fine after it starts so I don't think it is a fuel issue.

It also starts fine with the new battery so it looks like an electrical resistance problem that the new battery overcame for now.

 

[Zargon]

check the battery cables

I played this game with a 93 grand Cherokee

kept stranding me

check Voltage, looked low

replaced the alternator, still would randomly not start ~75 'OEM reman' from auto zone)

replaced the starter and solenoid(one package couldn't buy separate ~45 bucks) still would randomly not start

warranty'd the battery to interstate (~$25 fee) still would not start atleast once a week

would always JUMP OK

went to check some conections so I pulled the battery cables off and the ground cable came apart in my hand, it was rusted to death from the inside out it turns out

30 bucks in cables and it never happened again for the next year I owned it, after I already had ~150 in it in other parts

of course it started first crank even in 10F temps after that

the PO had already done plugs and wires(bought it from a friend of mine, sold it back to him 2 years later) so I didn't check that

 

[SpatiallyAware]

Definitely check the terminals, as well as the ground connections.