black2000xj

this just started about 3 days ago

jeep will turn over, fire up then die.

when you try to re-start it again it cranks and cranks but wont fire

when you give it gas when its cranking it will fire then die

after 3-4 tries it will fire on its own and idle at 300 rpms before slowly idleing at 600-700 where it normally is?

I was told the fuel pump was bad 5-6 months ago when it did this so i had a brand new one put in.

Could it be the fuel pump again or is it some form of a sensor

oh, also when it does idle, the rpms bounce from 500ish to 800ish

the tach just bounces up and down....something to do with this issue?

Kalali

Get the battery load tested.

lukes_ranger

^this^

RTorrez1

Have you verified the fuel pressure at the fuel rail with a mechanical pressure gauge? Do you recall what brand of fuel pump you installed last time?

black2000xj

its in my jeep and the jeep is at the shop

i bought the one with the warranty thank goodness

i dont rememeber what brand it was.

battery is just going on its 3rd year...should be more than fine...

black2000xj

could it be a crankshaft position sensor?

quick search on google led me to that...

Cherokeekid4x4

Mines got a similar problem... If you hold your foot on the gas will it start and stay running?

black2000xj

yes

Cherokeekid4x4

Mine does the same thing. My friend suggested a leaky fuel injector. Which would cause it to flood. Makes sense I just haven't checked yet.

black2000xj

i read a crankshaft position sensor is more than likely causing it

my is so on and off

It did it all weekend to the point where i didnt dare drive it and be left stranded.....so i got it to the shop last night

they said its starts and runs great (of course it does when its there)

all my symptoms i had are they same for a bad crank sensor

black2000xj

update
I dropped of my jeep at the shop, of course it works great when its there, so they started running some test
after testing everything yesterday, from fuel pressure in the rail, to spark, to cps, tps, etc...


their only thought is my battery is showing some signs of wear

now its only 3 years old, so maybe. The tech said that b/c my jeep sits for 4 days out of 7, they battery is not holding a good charge and thats what causing my jeep to do this. He explained how the cps and tps would act up b/c they "loose memory"?

Basically my jeep forgets how to idle, which is why i have to give it gas to get it to run

Im calling a big load of b.s. on this, but they couldnt find a thing wrong with my jeep

Does this sound like the actual problem? anybody else have this?

lukes_ranger

I think its possible. Because you're not running it every day, the battery doesn't stay at it's full charge. In other words the generator can't keep it charged up.

CCKen

When cranking the engine, does the voltmeter on the dash show it holding at 12 volts or does it drop down to around 9 volts? A weak battery will drop off while cranking.

Some batteries are only good for around 3 years. A load test on the battery at a store/shop would tell you if your battery is any good.

Try cleaning the IAC pintle and the orifice in the TB where the pintle seats. Sometimes it's best to remove the TB to a work bench and remove all sensors and give the TB a complete cleaning with carb & throttle body cleaner. If you do this replace the TB using a new gasket.

black2000xj

well when cranking its just below 12...the wierd part....one night pulling into my garage im waiting for the door to open, the volt meter dropped to like 3-4, almost killed the jeep and then came back to normal

I had the throttle body cleaned with all the sensors about 5 months ago when the new fuel pump went in

What I will do is leave my jeep on the battery tender from now on until i get back from my trip and get a new battery....

you guys dont think the crank position sensor could do this?

CCKen

Good idea on the new battery.

The voltage dropping below 9 volts is like disconnecting the battery ground cable. The PCM will lose its memory momentarily and have to relearn your idle settings. The PCM is basically nonfunctional below 9 volts.

At this point I wouldn't be concerned about the crank sensor.

I didn't see it mentioned, but have you inspected/cleaned all your engine bay grounds and positive lead connections in the engine bay?