My jeep won't crank, it will turn over, but not fire, any ideas? I have an automatic straight 6, 4 liter 1991. I have replaced the coil and battery, has plenty of gas, but has been sitting for a couple of years.

all 6 dead?
on all jeeps
we connect the scan tool
and crank and in many cases, over 1/2 it tells me why.
like CMP bad, CKP or spark ignitors dead.
TJ jeep it is
see the free FSM yet, posted over 300 times here.
chapter 8d pg 22
http://www.morris4x4center.com/knowledge-base/index.htm?utm_source=cj#service


my guess is the coil rail , preplexs you, as it does everyone
testing spark here is no fun.
3 coils on one pack (rail) (wasted spark system)
do you know how to test wasted spark?
must be done in pairs, or 2 plugs fail.
8w-30 page see the coil there,
see there are only 3 coils
that is defacto wasted spark systems.

so to test that, you must do all 6 at once, or 2 in pairs
there is no other ways.
are spark plugs fresh/????
did you scan it first..... ????????
if not that is hopeless

page 12 covers that in chapter 8d

questions????
1: check fuses first.?
2: does CEL lamp glow key on.
3: does ASD relay energize keyon and cranked
and hold there cranked, if not the SCAN tool tells you why not.
in every case.
4: got spark with only these wired.
1 and 6
2 and 5
3 and 4

in each case the 2 are connected, and shells grounded to engine.
and will fire in pairs, this is how it works.

best (avoiding a SHOCK)
is to insert 6 new plugs there gapped to spec.
then ground all 6 shells to the engine, metal
then crank.... is use bare copper wire to wrap all 6 daisy chained
then to a clip to metal of engine.
person 2 cranks, and you see all 6 fire, in sequence.
that is the correct way.
if the ASD is dead, then the will be no SPARK ever. or fuel.

see asd here, what it is, and how to test it.
http://jeepdied.com/


http://jeepdied.com/no-start.html


do not hold parts in hand cranking
or you light up like a June bug.

1-5-3-6-2-4 Clockwise alt="Cables order">

check all fuses first, every time, something fails EFI.
the scan tool will tell you why 90 % of time.
connect scan tool
key on
crank for 5 seconds, see scan tool show 300 RPM? about.
good, no RPM is bad sensor (Cmp or ckp)
release key , do not turn off yet
see DTCs stored, now, bingo, its telling you what is bad. OMG.
p0340/ 355? and the like? are bad CMP, bad CKP, or others get em
post em or look them up in the FSM. or at alldata.com
Theory:
the ECU creates spark
there are the 2 sensors that tell the ECU when to spark (inputs)
and the ECU DRIVER the ignition IGNOTOR, that runs the ignition coil.
1 coil or 6 coils. depends on year.
4.0L I6 Jeep engines.


did you check for spark directly at the 1 coil car or at all 6 coils for 6 cop coil cars?

cops are coil over park plug, i think your car is 1 coil, had a 99 jeep.
and this old six still had one, coil, so does this one coil make spark
to a test spark plug, Y/N
if yes, the dizzy cap is bad or wired wrong. to plugs.
I no spark here, do the DTC scans above.!!!!!
post back results.

do you hear your fuel pump kick on when you you turn the key?

You may want to check the coil also to see if it is getting fire and if not the ECM may be bad. Hope this helps

assuming its a 4.0 liter straight 6
the crank sensors go bad and the wire on them frequently get melted to the rear of the #6 exaust tube right were it attaches to cylinder head {the melted wire problem ussually happens after work done in the area of it] if its melted pull it off and see if it will start then tape it up or replace.
you could look up how to check it but they are cheap and easy to install and a new one never hurt nothing.

Check the ballast resister, should be located close to the coil

the engine is a 4.2 liter straight 6, go to the link for a diagram of the cylinder layout and firing order.

http://autorepair.about.com/library/firing_orders/bl-fo-10654.htm

It would be great if you could find the Ignition Control Module!!! From my experience on my Jeep...90 YJ 4.2 liter carb. it does not have one...Computer controlled only...

Take the distributor cap have someone crank the car and look if rotor turns, look at rotor conditions, I am sure that you have replaced it, hot wire from positive on the battery to positive on the coil, if car starts after you have a problem on the key, Is it fuel getting to the injectors? after You replaced so many things,if your rotor is not turning when You crank the engine, your timing chain must be defective or timing gear,